A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods.
Most barges are not self-propelled and need to be moved by tugboats towing or towboats
pushing them. Barges on canals (towed by draft animals on an adjacent towpath) contended
with the railway in the early industrial revolution but were outcompeted in the carriage of
high value items due to the higher speed, falling costs, and route flexibility of rail
transport. Barges are still used today for low value bulk items, as the cost of hauling
goods by barge is very low. Barges are also used for very heavy or bulky items; a typical
barge measures 195 feet by 35 feet (59.4 meters by 10.6 meters), and can carry up to 1500
tons of cargo.
Self propelled barges may be used as such when traveling downstream or upstream in placid
waters and operated as an unpowered barge with the assistance of a tugboat when traveling
upstream in faster waters.
Types of barges:
* Barracks barge (living quarters)
* Company barge
* Dry bulk cargo barge (coal, rock, grain, etc.)
* Jackup barge, mainly used inshore for a stationary stable platform for civils diving
or drilling operations.
* Lighter
* Liquid cargo barge (fresh water, finished petroleum products)
* Pleasure barge- providing a floating bedroom, dance floor, or viewing platform
* Railcar barge (with tracks and using special loading/offloading facilities such as a
barge slip)
* Royal barge (ceremonial)
* Row barge
* Sand barge
* Severn trow
* Vehicular barge, often used to transport vehicles to natural shorelines such as
beaches
* Ware barge
* West country barge
On the UK canal system, the term barge is used to describe a boat wider than a narrowboat.
The people who move barges are often known as lightermen.
In the U.S. deckhands perform the labor and are supervised by a leadman and or the mate. The
Captain and Pilot steer the towboat. The towboat pushes one or more barges that are held
together with rigging and is called collectively the tow. The crew live aboard the towboat
as it travels along the inland river system and or the intracoastal waterways. These
towboats travel between ports and are also called line haul boats.
Poles are used on barges to fend off the barge as it nears other vessels or a wharf, often
called pike poles, and on shallow canals for example in the UK long punt poles are used to
manoeuvre or propel the barge.
[edit]
Etymology
Barge is attested from 1300, from Old French barge, from Vulgar Latin barga. The word
originally could refer to any small boat, the modern meaning arose around 1480. Bark "small
ship" is attested from 1420, from Old French barque, from Vulgar Latin barca (400 AD). The
more precise meaning "three-masted ship" arose in the 17th century, and often takes the
French spelling for disambiguation.
Both are probably derived from a Latin *barica, from Greek baris "Egyptian boat", ultimately
from m Coptic bari "small boat."
By extension, the term "embark" literally means to board the kind of boat called a "barque".
The long poles used to manoeuvre or propel a barge have given rise to the saying, "I
wouldn't touch that (subject/thing) with a barge pole." This is a variation on the phrase "I
wouldn't touch that with a (insert length) pole." It appears that the association with barge
poles came after the phrase was in use. Modern useage uses a ten foot pole, but the earliest
instances in print involve a forty foot pole[1], which is improbably long for operating a
barge.
Weigh bridge
A Weigh bridge is a device for weighing loads carried by road or rail wagons. It is a very heavy duty weighing scale which can weigh the vehicle both empty and when loaded and thus calculate the load carried by the vehicle. In earlier versions the bridge is installed over a rectangular pit that contains levers that ultimately connect to a balance mechanism. The most complex portion of this type is the arrangement of levers underneath the weigh bridge since the response of the scale must be independent of the distribution of the load. Modern devices use multiple strain gauges that connect to electronic equipment to totalize the sensor inputs. In either type of semi-permanant scale the weight readings are typically recorded in a nearby hut or office.
For many uses (such as at police over the road truck weigh stations or temporary road intercepts) weigh bridges have been largely supplanted by simple and thin electronic weigh cells, over which a vehicle is slowly driven. A computer records the output of the cell and accumulates the total vehicle weight. By weighing the force of each axle it can be assured that the vehicle is within statutory limits, which typically will impose a total vehicle weight, a maximum weight within an axle span limit and an individual axle limit. The former two limits ensure the safety of bridges while the latter protects the road surface.
For many uses (such as at police over the road truck weigh stations or temporary road intercepts) weigh bridges have been largely supplanted by simple and thin electronic weigh cells, over which a vehicle is slowly driven. A computer records the output of the cell and accumulates the total vehicle weight. By weighing the force of each axle it can be assured that the vehicle is within statutory limits, which typically will impose a total vehicle weight, a maximum weight within an axle span limit and an individual axle limit. The former two limits ensure the safety of bridges while the latter protects the road surface.
Helicopter
A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors.
Helicopters are classified as rotary-wing aircraft to distinguish them from conventional
fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and
pteron (wing). The first single-rotor, fully-controllable helicopter to enter large
full-scale production was made by Igor Sikorsky in 1942.
Compared to conventional fixed-wing aircraft, helicopters are much more complex, more
expensive to buy and operate, and are more limited in speed, range, and payload. The
compensating advantage is maneuverability: helicopters can hover in place, reverse, and
above all take off and land vertically. Subject only to refueling facilities and
load/altitude limitations, a helicopter can travel to any location, and land anywhere with
enough space (approximately twice the area of the rotor disk).
Compared to other vertical lift aircraft like tiltrotors (V-22 Osprey for example) and
vectored thrust airplanes (AV-8 Harrier for example), helicopters are very efficient,
carrying more than twice the payload, consuming less fuel in hover and costing considerably
less to buy and operate. However these other configurations have a much higher cruise speed
than a helicopter (270 km/h for a helicopter, 460 km/h for a tiltrotor, 900+ km/h for a
vectored thrust airplane).
Generating lift
In conventional aircraft, the wing profile (called airfoil) is designed to deflect air
efficiently downward. This downward deflection causes an opposite lifting force on the wing
(described by Newton's third law) and a lower pressure on the upper surface, higher pressure
on the lower surface. This pressure difference integrated over the airfoil area causes a net
lift. However, the more the lift of the airfoil, the more drag that is caused (induced drag
by creating wingtip vortices). A helicopter makes use of the same principle, except that
instead of moving the entire aircraft, only the wings themselves are moved in a circular
motion. The helicopter's rotor can simply be regarded as rotating wings, from where the
military name of "rotary wing aircraft" originates.
Conventional layout
There are several possible layouts for arranging a helicopter's rotors. The most common
design is the Sikorsky-layout, which is used by approximately 95% of all helicopters
manufactured. Turning the rotor generates lift but it also applies a reverse torque to the
vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor if
no counter-acting force was applied. At low speeds, the most common way to counteract this
torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a
tail rotor. This rotor creates thrust which is in the opposite direction from the torque
generated by the main rotor. When the thrust from the tail rotor is sufficient to cancel out
the torque from the main rotor, the helicopter will not rotate around the main rotor shaft.
The world's largest and smallest series-produced helicopters follow this Sikorsky layout.
The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight
of 1300 lb (590 kg). Almost all civilian helicopters have the main rotor and tail rotor
system.
Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an
X-shape, which is supposed to reduce the noise levels for military use (e.g. AH-64 Apache).
The primary reason is to make the arrangement of the pitch controls simpler. If the tail
rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The
fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox
to turn the fan. It is less efficient but the advantages are that less noise is generated,
it is safer for people that may walk near it and there is less chance of the blades being
damaged by objects because it is shrouded, unlike the traditional tail rotor.
The amount of power required to prevent a helicopter from spinning is significant. A tail
rotor typically uses about 5 to 6% of the engine's power, and this power does not help the
helicopter produce lift or forward motion. To reduce this waste during cruise, the vertical
stabilizer is often angled to produce a force which helps counter the main rotor torque. At
high speeds, it is possible for the vertical stabilizer to counteract the entire torque,
leaving more power available for forward flight. This is commonly known as slip-streaming
and can make hovering turns difficult on windy days. Another reason for the angled vertical
stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case
of the tail rotor failure or damage.
Many military helicopters, especially attack types, have short wings called stub wings to
add lift during forward motion. They are also used as external mounts for weapons. In
extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow
down from the rotors, making the helicopter all but unable to hover.
Alternative layouts
There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor.
Such Coaxial rotor designs use two main rotors which turn in opposite directions, or
contra-rotate, so that the torques from each rotor cancel each other out. These methods
introduce even more mechanical complexity to the design and are usually relegated to
specialized helicopter types.
The co-axial design, where rotors are mounted on top of each other at the top of the
fuselage and share a common main axle complex, was first built by Theodore von Karman and
Asbóth Oszkár in 1918 and later became the hallmark of soviet Kamov design bureau (see for
example the Kamov Ka-50 "Hokum"). Co-axial helicopters in flight are highly resistant to
side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing
system. Another example is the Kamov Ka-26, a successful crop duster aircraft. See Coaxial
rotor.
The slightly different system of intermeshing rotors, also called a synchropter, which was
developed in Nazi Germany for a small anti-submarine warfare helicopter, the Flettner Fl 282
Kolibri, features two main rotors on separate, obliquely mounted axles. The counter-rotating
rotors are on top of the fuselage, close to each other. During the Cold War the American
Kaman company started to produce similar helicopters for USAF firefighting purposes. Kamans
have high stability and powerful lifting capability. The latest Kaman K-Max model is a
dedicated sky crane design, used for construction works.
In the flying-wagon or tandem rotor system (sometimes called "flying banana" for the
peculiar shape of early U.S. examples), the two main rotors are located at the front and
rear extremity of a long, boxy fuselage that resembles a railway wagon. A prime example is
the Boeing CH-47 Chinook, that can carry 14 tons of payload. Wagon helicopters are practical
for military logistical purposes, because entry and unloading is easy via the unobstructed
front and rear ramps. The rotors and turbines are located very high on top of the fuselage,
making them less sensitive to damage and dirt. The main drawback of a tandem rotor is
limited agility in air and the need for a highly trained crew, as the large main rotors have
long outreach beyond the fuselage and may easily hit nearby obstacles. In 2001, while on
live TV, a South Korean Army CH-47 Chinook crashed into a bridge for this reason.
A helicopter built by Juan de la Cierva had three main rotors. These were placed at the
corners of an equilateral triangle and all turned the same direction.
In the cross system, the rotary wing aircraft resembles a traditional fixed-wing airplane,
with the two main rotors mounted at the extremities of its wings. Such helicopters are rare,
because structural integrity of the wings is difficult to maintain against the amplified
resonance of far off-board rotor-turbine units. The 1930s German FW-61 helicopter was built
to such design. The world's largest ever helicopter, the Soviet Mil-V-12 prototype, was a
cross of two Mil Mi-6 turbine-rotor units built onto a modified Antonov cargo plane. The
U.S. V-22 Osprey tilting rotorcraft is similar, although its nacelles can be rotated, and
shares some of the inherent technical problems of a cross system.
A recent development in helicopter technology is the NOTAR system, which stands for N'O'
TAil Rotor. The NOTAR eliminates the tail rotor by conducting high-velocity air through the
tail boom, using the Coandă effect to produce forces to counter the torque. NOTARs adjust
thrust by opening and closing a sliding circular cover near the end of the tail boom. The
NOTAR system was developed in the United States and is used exclusively by McDonnell Douglas
Helicopters.
The most unusual design is the roto-rocket principle, where the single main rotor draws
power not from the shaft, but from its own wingtip jet nozzles, which are either pressurized
from a fuselage-mounted gas turbine or have their own pulsejet combustion chambers. Although
this method is simple and eliminates precession, development of such helicopters ceased
because their extreme noise levels preclude both military and civilian use.
[edit]
Controlling flight
Useful flight requires that an aircraft be controlled in all three dimensions (see flight
dynamics). In a fixed-wing aircraft, this is easy: small movable surfaces are adjusted to
change the aircraft's shape so that the air rushing past pushes it in the desired direction.
In a helicopter, however, there is often not enough speed for this method to be practical.
For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch
of the tail rotor alters the sideways thrust produced. Dual-rotor helicopters have a
differential between the two rotor transmissions that can be adjusted by an electric or
hydraulic motor to transmit differential torque and thus turn the helicopter. Yaw controls
are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing
aircraft's rudder pedals.
For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the
main rotor blades is altered or cycled during the rotation creating a differential of lift
at different points of the rotary wing. More lift at the rear of the rotary wing will cause
the aircraft to pitch forward, an increase on the left will cause a roll to the right and so
on.
Helicopters maneuver with three flight controls besides the pedals. The collective pitch
control lever controls the collective pitch, or angle of attack, of the helicopter blades
altogether, that is, equally throughout the 360 degree plane-of-rotation of the main rotor
system. When the angle of attack is increased, the blade produces more lift. The collective
control is usually a lever at the pilot's left side. Simultaneously increasing the
collective and adding power with the throttle causes a helicopter to rise.
The throttle controls the absolute power produced by the engine that is connected to the
rotor by a transmission. The throttle control is a twist grip on the collective control. RPM
control is critical to proper operation for several reasons. Helicopter rotors are designed
to operate at a specific RPM. However, for each weight and speed there would be an ideal RPM
(design-rpm). In practice, a single (higher) RPM is used in order to minimize resonance
design requirements and add a safety margin to rotor stall RPM. Usually only in autorotation
are different RPMs used to increase rotor efficiency, which can be crucial in the case of an
emergency without engine power.
If the RPM becomes too low, the rotor blades stall. This suddenly increases drag and slows
the rotor down further. The centrifugal forces are then not able to straighten the rotor
blades any more, excessive coning ("tuliping") develops and a catastrophic accident is
certain.
If the RPM is too high, damage to the main rotor hub, power transmission and engine from
excessive forces could result. In general, RPM must be maintained within a tight tolerance,
usually a few percent. In many piston-powered helicopters, the pilot must manage the engine
and rotor RPM. The pilot manipulates the throttle to maintain rotor RPM and therefore
regulates the effect of drag on the rotor system. Turbine engined helicopters, and some
piston helicopters, use a servo-feedback loop, otherwise known as a governor, in their
engine controls to maintain rotor RPM and relieves the pilot of routine responsibility for
that task.
The cyclic changes the pitch of the blades cyclically, that is, during the rotation of the
blades around each complete circle (2 pi radians). This causes the lift to vary across the
plane of the rotor disk. This variation in lift causes the rotor disk to tilt and the
helicopter to move during hover flight or change attitude in forward flight. The cyclic is
similar to a joystick and is usually positioned in front of the pilot. The cyclic controls
the angle of the stationary section of the swashplate, which in turn controls the angle of
the rotating section of the swashplate. The rotating section rotates with the rotor and is
connected to blade pitch horns through pitch links, one link for each blade. When the
swashplate is not tilted, the blades are all at the collective angle. When it is tilted, the
links give a pitch-up at some azimuthal angle and a pitch-down at the opposite angle, hence
creating a sinusoidal variation in blade angle of attack. This causes the helicopter to tilt
in the same direction as the cyclic. If the pilot pushes the cyclic forward, then the rotor
disc tilts forward, and the rotor produces a thrust in the forward direction.
As a helicopter moves forward, the rotor blades on one side move at rotor tip speed plus the
aircraft speed and is called the advancing blade. As the blade swings to the other side of
the helicopter, it moves at rotor tip speed minus aircraft speed and is called the
retreating blade. To compensate for the added lift on the advancing blade and the decreased
lift on the retreating blade, the angle of attack of the blades is regulated as the blade
spins around the helicopter. The angle of attack is increased on the retreating blade to
produce more lift, compensating for the slower airspeed over the blade. And the angle of
attack is decreased on the advancing blade to produce less lift, compensating for the faster
airspeed over the blade.
If the angle of attack of any wing, including rotor blades, is too high, the airflow above
the wing separates causing instant loss of lift and increase in drag. This condition is
called aerodynamic stall. On a helicopter, this can happen in any of four ways.
1. As helicopter speed increases, airflow over the advancing blades approaches the speed
of sound and generates shock waves that disrupt the airflow over the blade causing loss of
lift.
2. As helicopter speeds increase, the retreating blade experiences lower relative
airspeeds and the controls compensate with higher angle of attack. With a low enough
relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. This
is called retreating blade stall. See dissymetry of lift for a fuller treatment of cases 1
and 2 together in a single analysis.
3. Any low rotor RPM flight condition accompanied by increasing collective pitch
application will cause aerodynamic stall.
4. Unique to helicopters is the vortex ring state (also known as settling with power)
which is when a helicopter in a hover or descent comes into contact with its own down wash
causing immense turbulence and loss of lift.
Helicopters are powered aircraft but they can still fly without power by using the momentum
in the rotors and using downward motion to force air through the rotors. The main rotor acts
like a "windmill" and turns. This technique is known as autorotation. A transmission
connects the main rotor to the tail rotor so that all flight controls are available after
engine failure. Autorotation can allow a pilot to make an emergency landing if the engine
failure occurs while the helicopter is traveling high enough or fast enough. (see
Height-velocity diagram).
Helicopters are classified as rotary-wing aircraft to distinguish them from conventional
fixed-wing aircraft. The word helicopter is derived from the Greek words helix (spiral) and
pteron (wing). The first single-rotor, fully-controllable helicopter to enter large
full-scale production was made by Igor Sikorsky in 1942.
Compared to conventional fixed-wing aircraft, helicopters are much more complex, more
expensive to buy and operate, and are more limited in speed, range, and payload. The
compensating advantage is maneuverability: helicopters can hover in place, reverse, and
above all take off and land vertically. Subject only to refueling facilities and
load/altitude limitations, a helicopter can travel to any location, and land anywhere with
enough space (approximately twice the area of the rotor disk).
Compared to other vertical lift aircraft like tiltrotors (V-22 Osprey for example) and
vectored thrust airplanes (AV-8 Harrier for example), helicopters are very efficient,
carrying more than twice the payload, consuming less fuel in hover and costing considerably
less to buy and operate. However these other configurations have a much higher cruise speed
than a helicopter (270 km/h for a helicopter, 460 km/h for a tiltrotor, 900+ km/h for a
vectored thrust airplane).
Generating lift
In conventional aircraft, the wing profile (called airfoil) is designed to deflect air
efficiently downward. This downward deflection causes an opposite lifting force on the wing
(described by Newton's third law) and a lower pressure on the upper surface, higher pressure
on the lower surface. This pressure difference integrated over the airfoil area causes a net
lift. However, the more the lift of the airfoil, the more drag that is caused (induced drag
by creating wingtip vortices). A helicopter makes use of the same principle, except that
instead of moving the entire aircraft, only the wings themselves are moved in a circular
motion. The helicopter's rotor can simply be regarded as rotating wings, from where the
military name of "rotary wing aircraft" originates.
Conventional layout
There are several possible layouts for arranging a helicopter's rotors. The most common
design is the Sikorsky-layout, which is used by approximately 95% of all helicopters
manufactured. Turning the rotor generates lift but it also applies a reverse torque to the
vehicle, which would spin the helicopter fuselage in the opposite direction to the rotor if
no counter-acting force was applied. At low speeds, the most common way to counteract this
torque is to have a smaller vertical propeller mounted at the rear of the aircraft called a
tail rotor. This rotor creates thrust which is in the opposite direction from the torque
generated by the main rotor. When the thrust from the tail rotor is sufficient to cancel out
the torque from the main rotor, the helicopter will not rotate around the main rotor shaft.
The world's largest and smallest series-produced helicopters follow this Sikorsky layout.
The Mil Mi-26 can lift 27 metric tons, the Robinson R22 has a crew of two and a gross weight
of 1300 lb (590 kg). Almost all civilian helicopters have the main rotor and tail rotor
system.
Sometimes the blades of a tail rotor are not separated by the same angle, but laid out in an
X-shape, which is supposed to reduce the noise levels for military use (e.g. AH-64 Apache).
The primary reason is to make the arrangement of the pitch controls simpler. If the tail
rotor is shrouded (i.e., a fan embedded in the vertical tail) it is called a fenestron. The
fenestron rotor system on the model EC120 helicopter uses a shaft driven system and gearbox
to turn the fan. It is less efficient but the advantages are that less noise is generated,
it is safer for people that may walk near it and there is less chance of the blades being
damaged by objects because it is shrouded, unlike the traditional tail rotor.
The amount of power required to prevent a helicopter from spinning is significant. A tail
rotor typically uses about 5 to 6% of the engine's power, and this power does not help the
helicopter produce lift or forward motion. To reduce this waste during cruise, the vertical
stabilizer is often angled to produce a force which helps counter the main rotor torque. At
high speeds, it is possible for the vertical stabilizer to counteract the entire torque,
leaving more power available for forward flight. This is commonly known as slip-streaming
and can make hovering turns difficult on windy days. Another reason for the angled vertical
stabilizer is to make it possible to stage a successful high-speed, run-on landing, in case
of the tail rotor failure or damage.
Many military helicopters, especially attack types, have short wings called stub wings to
add lift during forward motion. They are also used as external mounts for weapons. In
extreme cases, such as that of the Mil Mi-24, the wings are large enough to obstruct airflow
down from the rotors, making the helicopter all but unable to hover.
Alternative layouts
There are alternatives to Sikorsky's layout, which save the weight of a tail boom and rotor.
Such Coaxial rotor designs use two main rotors which turn in opposite directions, or
contra-rotate, so that the torques from each rotor cancel each other out. These methods
introduce even more mechanical complexity to the design and are usually relegated to
specialized helicopter types.
The co-axial design, where rotors are mounted on top of each other at the top of the
fuselage and share a common main axle complex, was first built by Theodore von Karman and
Asbóth Oszkár in 1918 and later became the hallmark of soviet Kamov design bureau (see for
example the Kamov Ka-50 "Hokum"). Co-axial helicopters in flight are highly resistant to
side-winds, which makes them suitable for shipboard use, even without a rope-pulley landing
system. Another example is the Kamov Ka-26, a successful crop duster aircraft. See Coaxial
rotor.
The slightly different system of intermeshing rotors, also called a synchropter, which was
developed in Nazi Germany for a small anti-submarine warfare helicopter, the Flettner Fl 282
Kolibri, features two main rotors on separate, obliquely mounted axles. The counter-rotating
rotors are on top of the fuselage, close to each other. During the Cold War the American
Kaman company started to produce similar helicopters for USAF firefighting purposes. Kamans
have high stability and powerful lifting capability. The latest Kaman K-Max model is a
dedicated sky crane design, used for construction works.
In the flying-wagon or tandem rotor system (sometimes called "flying banana" for the
peculiar shape of early U.S. examples), the two main rotors are located at the front and
rear extremity of a long, boxy fuselage that resembles a railway wagon. A prime example is
the Boeing CH-47 Chinook, that can carry 14 tons of payload. Wagon helicopters are practical
for military logistical purposes, because entry and unloading is easy via the unobstructed
front and rear ramps. The rotors and turbines are located very high on top of the fuselage,
making them less sensitive to damage and dirt. The main drawback of a tandem rotor is
limited agility in air and the need for a highly trained crew, as the large main rotors have
long outreach beyond the fuselage and may easily hit nearby obstacles. In 2001, while on
live TV, a South Korean Army CH-47 Chinook crashed into a bridge for this reason.
A helicopter built by Juan de la Cierva had three main rotors. These were placed at the
corners of an equilateral triangle and all turned the same direction.
In the cross system, the rotary wing aircraft resembles a traditional fixed-wing airplane,
with the two main rotors mounted at the extremities of its wings. Such helicopters are rare,
because structural integrity of the wings is difficult to maintain against the amplified
resonance of far off-board rotor-turbine units. The 1930s German FW-61 helicopter was built
to such design. The world's largest ever helicopter, the Soviet Mil-V-12 prototype, was a
cross of two Mil Mi-6 turbine-rotor units built onto a modified Antonov cargo plane. The
U.S. V-22 Osprey tilting rotorcraft is similar, although its nacelles can be rotated, and
shares some of the inherent technical problems of a cross system.
A recent development in helicopter technology is the NOTAR system, which stands for N'O'
TAil Rotor. The NOTAR eliminates the tail rotor by conducting high-velocity air through the
tail boom, using the Coandă effect to produce forces to counter the torque. NOTARs adjust
thrust by opening and closing a sliding circular cover near the end of the tail boom. The
NOTAR system was developed in the United States and is used exclusively by McDonnell Douglas
Helicopters.
The most unusual design is the roto-rocket principle, where the single main rotor draws
power not from the shaft, but from its own wingtip jet nozzles, which are either pressurized
from a fuselage-mounted gas turbine or have their own pulsejet combustion chambers. Although
this method is simple and eliminates precession, development of such helicopters ceased
because their extreme noise levels preclude both military and civilian use.
[edit]
Controlling flight
Useful flight requires that an aircraft be controlled in all three dimensions (see flight
dynamics). In a fixed-wing aircraft, this is easy: small movable surfaces are adjusted to
change the aircraft's shape so that the air rushing past pushes it in the desired direction.
In a helicopter, however, there is often not enough speed for this method to be practical.
For rotation about the vertical axis (yaw) the anti-torque system is used. Varying the pitch
of the tail rotor alters the sideways thrust produced. Dual-rotor helicopters have a
differential between the two rotor transmissions that can be adjusted by an electric or
hydraulic motor to transmit differential torque and thus turn the helicopter. Yaw controls
are usually operated with anti-torque pedals, on the floor in the same place as a fixed-wing
aircraft's rudder pedals.
For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the
main rotor blades is altered or cycled during the rotation creating a differential of lift
at different points of the rotary wing. More lift at the rear of the rotary wing will cause
the aircraft to pitch forward, an increase on the left will cause a roll to the right and so
on.
Helicopters maneuver with three flight controls besides the pedals. The collective pitch
control lever controls the collective pitch, or angle of attack, of the helicopter blades
altogether, that is, equally throughout the 360 degree plane-of-rotation of the main rotor
system. When the angle of attack is increased, the blade produces more lift. The collective
control is usually a lever at the pilot's left side. Simultaneously increasing the
collective and adding power with the throttle causes a helicopter to rise.
The throttle controls the absolute power produced by the engine that is connected to the
rotor by a transmission. The throttle control is a twist grip on the collective control. RPM
control is critical to proper operation for several reasons. Helicopter rotors are designed
to operate at a specific RPM. However, for each weight and speed there would be an ideal RPM
(design-rpm). In practice, a single (higher) RPM is used in order to minimize resonance
design requirements and add a safety margin to rotor stall RPM. Usually only in autorotation
are different RPMs used to increase rotor efficiency, which can be crucial in the case of an
emergency without engine power.
If the RPM becomes too low, the rotor blades stall. This suddenly increases drag and slows
the rotor down further. The centrifugal forces are then not able to straighten the rotor
blades any more, excessive coning ("tuliping") develops and a catastrophic accident is
certain.
If the RPM is too high, damage to the main rotor hub, power transmission and engine from
excessive forces could result. In general, RPM must be maintained within a tight tolerance,
usually a few percent. In many piston-powered helicopters, the pilot must manage the engine
and rotor RPM. The pilot manipulates the throttle to maintain rotor RPM and therefore
regulates the effect of drag on the rotor system. Turbine engined helicopters, and some
piston helicopters, use a servo-feedback loop, otherwise known as a governor, in their
engine controls to maintain rotor RPM and relieves the pilot of routine responsibility for
that task.
The cyclic changes the pitch of the blades cyclically, that is, during the rotation of the
blades around each complete circle (2 pi radians). This causes the lift to vary across the
plane of the rotor disk. This variation in lift causes the rotor disk to tilt and the
helicopter to move during hover flight or change attitude in forward flight. The cyclic is
similar to a joystick and is usually positioned in front of the pilot. The cyclic controls
the angle of the stationary section of the swashplate, which in turn controls the angle of
the rotating section of the swashplate. The rotating section rotates with the rotor and is
connected to blade pitch horns through pitch links, one link for each blade. When the
swashplate is not tilted, the blades are all at the collective angle. When it is tilted, the
links give a pitch-up at some azimuthal angle and a pitch-down at the opposite angle, hence
creating a sinusoidal variation in blade angle of attack. This causes the helicopter to tilt
in the same direction as the cyclic. If the pilot pushes the cyclic forward, then the rotor
disc tilts forward, and the rotor produces a thrust in the forward direction.
As a helicopter moves forward, the rotor blades on one side move at rotor tip speed plus the
aircraft speed and is called the advancing blade. As the blade swings to the other side of
the helicopter, it moves at rotor tip speed minus aircraft speed and is called the
retreating blade. To compensate for the added lift on the advancing blade and the decreased
lift on the retreating blade, the angle of attack of the blades is regulated as the blade
spins around the helicopter. The angle of attack is increased on the retreating blade to
produce more lift, compensating for the slower airspeed over the blade. And the angle of
attack is decreased on the advancing blade to produce less lift, compensating for the faster
airspeed over the blade.
If the angle of attack of any wing, including rotor blades, is too high, the airflow above
the wing separates causing instant loss of lift and increase in drag. This condition is
called aerodynamic stall. On a helicopter, this can happen in any of four ways.
1. As helicopter speed increases, airflow over the advancing blades approaches the speed
of sound and generates shock waves that disrupt the airflow over the blade causing loss of
lift.
2. As helicopter speeds increase, the retreating blade experiences lower relative
airspeeds and the controls compensate with higher angle of attack. With a low enough
relative airspeed and a high enough angle of attack, aerodynamic stall is inevitable. This
is called retreating blade stall. See dissymetry of lift for a fuller treatment of cases 1
and 2 together in a single analysis.
3. Any low rotor RPM flight condition accompanied by increasing collective pitch
application will cause aerodynamic stall.
4. Unique to helicopters is the vortex ring state (also known as settling with power)
which is when a helicopter in a hover or descent comes into contact with its own down wash
causing immense turbulence and loss of lift.
Helicopters are powered aircraft but they can still fly without power by using the momentum
in the rotors and using downward motion to force air through the rotors. The main rotor acts
like a "windmill" and turns. This technique is known as autorotation. A transmission
connects the main rotor to the tail rotor so that all flight controls are available after
engine failure. Autorotation can allow a pilot to make an emergency landing if the engine
failure occurs while the helicopter is traveling high enough or fast enough. (see
Height-velocity diagram).
Ships
A ship is a large, sea-going watercraft, usually with multiple decks. A ship usually has
sufficient size to carry its own boats, such as lifeboats, dinghies, or runabouts. A rule of
thumb saying (though it doesn't always apply) goes: "a boat can fit on a ship, but a ship
can't fit on a boat". Often local law and regulation will define the exact size (or the
number of masts) which a boat requires to become a ship. (Note that one refers to submarines
as "boats", because early submarines were small enough to be carried aboard a ship in
transit to distant waters.) Compare vessel.
During the age of sail, ship signified a ship-rigged vessel, that is, one with three or more
masts, usually three, all square-rigged. Such a vessel would normally have one fore and aft
sail on her aftermost mast which was usually the mizzen. Almost invariably she would also
have a bowsprit but this was not part of the definition. The same economic pressures which
increased sizes to the point of carrying four or five masts, also introduced the fore and
aft rig to larger vessels, so few ship-rigged vessels were built with more than three masts.
The five-masted Preussen was the outstanding example, but the big German ships and barques
were built partly for prestige reasons.
Nautical means related to sailors, particularly customs and practices at sea. Naval is the
adjective pertaining to ships, though in common usage it has come to be more particularly
associated with the noun 'navy'.
Measuring ships
One can measure ships in terms of overall length, length of the waterline, beam (breadth),
depth (distance between the crown of the weather deck and the top of the keelson), draft
(distance between the highest waterline and the bottom of the ship) and tonnage. A number of
different tonnage definitions exist; most measure volume rather than weight, and are used
when describing merchant ships for the purpose of tolls, taxation, etc.
In Britain until the Merchant Shipping Act of 1876, ship-owners could load their vessels
until their decks were almost awash, resulting in a dangerously unstable condition.
Additionally, anyone who signed onto such a ship for a voyage and, upon realizing the
danger, chose to leave the ship, could end up in jail.
Samuel Plimsoll, a member of Parliament, realised the problem and engaged some engineers to
derive a fairly simple formula to determine the position of a line on the side of any
specific ship's hull which, when it reached the surface of the water during loading of
cargo, meant the ship had reached its maximum safe loading level. To this day, that mark,
called the "Plimsoll Mark", exists on ships' sides, and consists of a circle with a
horizontal line through the center. Because different types of water, (summer, fresh,
tropical fresh, winter north Atlantic) have different densities, subsequent regulations
required painting a group of lines forward of the Plimsoll mark to indicate the safe depth
(or freeboard above the surface) to which a specific ship could load in water of various
densities. Hence the "ladder" of lines seen forward of the Plimsoll mark to this day.
[edit]
Propulsion
[edit]
Pre-mechanisation
Until the application of the steam engine to ships in the early 19th century, oars propelled
galleys or the wind propelled sailing ships. Before mechanisation, merchant ships always
used sail, but as long as naval warfare depended on ships closing to ram or to fight
hand-to-hand, galleys dominated in marine conflicts because of their maneuverability and
speed. The Greek navies that fought in the Peloponnesian War used triremes, as did the
Romans contesting the Battle of Actium. The use of large numbers of cannon from the 16th
century meant that maneuverability took second place to broadside weight; this led to the
dominance of the sail-powered warship.
[edit]
Steam propulsion
The development of the steamship became a complex process, the first commercial success
accruing to Robert Fulton's North River Steamboat (often called Clermont) in the US in 1807,
followed in Europe by the 45-foot Comet of 1812. Steam propulsion progressed considerably
over the rest of the 19th century. Notable developments included the condenser, which
reduced the requirement for fresh water, and the multiple expansion engine, which improved
efficiency. As the means of transmitting the engine's power, the paddle wheel gave way to
the more efficient screw propeller. The marine steam turbine developed by Sir Charles
Algernon Parsons, brought the power to weight ratio down. He had achieved publicity by
demonstrating it unofficially in the 100-foot Turbinia at the Spithead naval review in 1897.
This facilitated a generation of high-speed liners in the first half of the 20th century and
rendered the reciprocating steam engine out of date, in warships.
Most new ships since around 1960 have been built with diesel engines. Rising fuel costs have
almost lead to the demise of the steam turbine, with many ships being re-engined to improve
fuel efficiency. One high profile example was the 1968 built Queen Elizabeth 2 which had her
turbines replaced with a diesel-electric propulsion plant in 1986. The last major passenger
ship built with steam turbines was the Fairsky, launched in 1984. Some specialised merchant
ships have also been built with steam turbines since then, notably Liquified Natural Gas
(LNG) and coal carriers where part of the cargo has been used as fuel for the boilers.
[edit]
LNG Carriers
LNG carriers in particular have remained a stronghold for steam , and new ships continue to
be built with steam turbines in this high growth area of shipping. This is because the
Natural Gas is stored in a liquid state in cryogenic vessels onboard these ships. A small
amount of "boil off" of gas is required to maintain the pressure and temperature inside the
vessels to within operating limits. The "boil off" gas provides the fuel for the ship's
boilers, which provide steam for the turbines- the simplest method of dealing with the gas.
Technology to operate internal combustion engines (modified marine two stroke diesel
engines) on this gas has improved however, so these engines are beginning to appear in LNG
carriers; with their greater thermal efficiency, less gas is burnt. Also, developements have
been made in the process of re-liquifying "boil off" gas, enabling it to be returned to the
cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the
marine grade fuel oil burnt in conventional diesel engines, so the re-liquification process
is starting to be used on diesel engine propelled LNG carriers. Another factor driving the
switch from turbines to diesel engines for LNG carriers is the shortage of steam turbine
qualified sea going engineers. With the lack of turbine powered ships in other shipping
sectors, and the rapid increase in size of the worldwide LNG fleet, not enough have been
trained to meet the demand. It may be that the days of the last stronghold for steam turbine
propulsion systems are numbered, despite all but sixteen of the orders for new LNG carriers
at the end of 2004 being for steam turbine propelled ships. [1]
[edit]
Diesel propulsion
The marine diesel engine first came into use around 1912: either the Vulcanus or the
Selandia (depending upon who you talk to) first deployed it. It soon offered even greater
efficiency than the steam turbine but for many years had an inferior power-to-space ratio.
About this period too, heavy fuel oil came into more general use and began to replace coal
as the fuel of choice in steamships. Its great advantages were the convenience, the
reduction in manning owing to the removal of the need for trimmers and stokers, and the
reduction in space required for fuel bunkers. Diesel engines today are broadly classified
according to their operating cycle (two-stroke or four-stroke), their construction
(crosshead, trunk, or opposed piston) and their speed (slow speed, medium speed or high
speed). Most modern larger merchant ships use either slow speed, two stroke, crosshead
engines, or medium speed, four stroke, trunk engines. Some smaller vessels may operate high
speed diesel engines. The operating ranges of the differant speed types are as follows;
* Slow speed- any engine with a maximum operating speed up to 300 revs/minute, although
most large 2 stroke slow speed diesel engines operate below 120 revs/minute. Some very long
stroke engines have a maximum speed of around 80 revs/minute. The largest, most powerful
engines in the world are slow speed, two stroke, crosshead diesels.
* Medium speed- any engine with a maximum operating speed in the range 300- 900 revs/
minute. Many modern 4 stroke medium speed diesel engines have a maximum operating speed of
around 500 rpm.
* High speed- any engine with a maximum operating speed above 900 revs/ minute
As modern ships' propellers are at their most efficient at the operating speed of most slow
speed diesel engines, ships with these engines do not generally require gearboxes. Usually
such propulsion systems consist of either one or two propeller shafts each with its own
direct drive engine. Ships propelled by medium or high speed diesel engines may have one or
two (sometimes more) propellers, commonly with one or more engines driving each propeller
shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine
will most likely drive through a clutch, allowing engines not being used to be disconnected
from the gearbox while others continue to operate. This arrangement allows maintenance to be
carried out while under way at sea. Diesel electric is another propulsion system that has
been around for a long time, but is becoming more common. By having the engines drive
alternators, which supply electricity to motors driving the propellers, gearboxes and
clutches can be dispensed with and greater flexibility gained in the positioning of the
engines, while still providing the step down in speed required for a medium speed engine to
efficiently drive a ships propeller.
The size of the differant types of engines is an important factor in selecting what will be
installed in a new ship. Slow speed two stroke engines are much taller, but the foot print
required- length and width- is smaller than that required for four stroke medium speed
diesel engines. As space higher up in passenger ships and ferries is at a premium, these
ships tend to use multiple medium speed engines resulting in a longer, lower engine room
than that required for two stroke diesel engines. Multiple engine installations also gives
greater redundancy in the event of mechanical failure of one or more engines and greater
efficiency over a wider range of operating conditions.
[edit]
Other propulsion systems
Many warships built since the 1960s have used gas turbines for propulsion, as have a few
passenger ships. Most recently, the Queen Mary 2 has had gas turbines installed in addition
to diesel engines. Due to their poor thermal efficiency, it is common for ships using them
to have diesel engines for cruising with gas turbines reserved for when higher speeds are
required. Some warships and a few modern cruise ships have also utilised steam turbines to
improve the efficiency of gas turbines in a combined cycle. In such a combined cycle, where
waste heat from a gas turbine is used to create steam for driving a steam turbine, thermal
efficiency can be the same or slightly greater than that of diesel engines. However, the
grade of fuel required for gas turbines is much more expensive than that required for diesel
engines so running costs are higher.
A few ships have used nuclear reactors, but this is not a separate form of propulsion; the
reactor heats steam to drive the turbines. Nonetheless, it has caused concerns about safety
and waste disposal. It has become usual only in large aircraft carriers and in submarines,
where the ability to run submerged for long periods holds obvious advantage. In such
long-endurance vessels, the resulting saving in bunkerage is an important consideration.
[edit]
General terminology
Ships may occur collectively as fleets, squadrons or flotillas. Convoys of ships commonly
occur.
A collection of ships for military purposes may compose a navy or a task force.
In the past, people counting or grouping disparate types of ship may refer to the individual
vessels as bottoms, but this generally refers only to merchant vessels. Groups of sailing
ships could constitute, say, a fleet of 40 sail. Groups of submarines (particularly German
U-boats in the 1940s) hunt in wolf packs.
[edit]
Shipboard terminology
See also: Glossary of nautical terms. The complexity of ships, particularly of sailing
ships, led to the development of a rich and various vocabulary. Many of the following terms
link to more detailed discussions of nautical terminology.
* Amidships - toward the middle of the vessel.
* Bow - strictly, one of the two curved structures where the hull broadens out from the
stem (the pointed end). The bows is a term for the head of the vessel or front of the ship.
Compare prow, a more poetical term for the ship's head.
* Stern - the after end of the ship.
* Aft - towards the stern when the relationship is within the ship.
* Astern beyond the stern where the relationship is outside the vessel.
* Starboard - the side of the ship which lies to the right when an observer within the
ship faces forward.
* Port - the side of the ship which lies to the left when an observer within the ship
faces forward. (A mnemonic to distinguish port and starboard notes that left and port both
have four letters. Another incorporates the navigation light: Is there any red port left?)
* (Navigation) Bridge - A structure above the weather deck, extending the full width of
the vessel, which houses a command centre, itself called by association, the bridge. A
bridge usually extends a little beyond the ship's side to enable observation of boats
alongside, or the proximity of a dock or lock gate; these projections are called bridge
wings. In big vessels, a docking bridge used to be found aft. (See Lord, Walter. A Night to
Remember (1976) p.96). It enabled an officer to observe docking manoeuvres before giving
orders. RMS Titanic had one but they have been superseded by Closed-circuit television
cameras.
* Bulkheads - internal "walls" in a ship. Bulkheads are the vertical equivalent of
decks. They have a structural function as well as dividing spaces. They serve to prevent
collapse of the hull under stress, to maintain stability, in the event of flooding, and to
contain fire. Many bulkheads feature watertight doors which, in the case of certain types of
ships, the crew may close remotely. An internal "wall" that is not load-bearing is usually
referred to as a "partition". It is to a bulkhead as a flat is to a deck.
* Cabin - an enclosed room on a deck or flat.
* Capstan - a winch with a vertical axis.
* Coaming - Raised edges of hatches in decks for keeping water and articles free on the
deck from falling into the hold.
* Decks - the structures forming the approximately horizontal surfaces in the ship's
general structure. Unlike flats, they are a structural part of the ship.
* Deck Head - The under-side of the deck above. Sometimes panelled over to hide the pipe
work. This panelling, like that lining the bottom and sides of the holds, is the ceiling.
* Draft - The vertical distance from the current waterline to the lowest point of the
ship or in the part of the ship under consideration.
* Figurehead - symbolic image at the head of a traditional sailing ship or early
steamer.
* Forecastle - a partial deck, above the upper deck and at the head of the vessel;
traditionally the sailors' living quarters.
* Freeboard - The vertical distance from the current waterline to the highest continuous
watertight deck. This usually varies from one part to another.
* Galley - the kitchen of the ship
* Gunwale - Formerly a fabricated band placed for strengthening around the ship at the
main or upper deck level to accommodate the stresses imposed by the use of artillery. In
later use it is the angle between the ship’s side and upper deck. It remained as a
structural member, in wooden boats where it was mounted inboard of the sheer strake
regardless of the need for gunnery.
* Bulwark - the extension of the ship's side above the level of the weather deck.
* Hold - In earlier use, below the orlop deck, the lower part of the interior of a
ship's hull, especially when considered as storage space, as for cargo. In later merchant
vessels it extended up through the decks to the underside of the weather deck.
* Hull - the shell and framework of the basic flotation-oriented part of a ship
* Keel - the central structural basis of the hull
* Kelson - the timber immediately above the keel of a wooden ship.
* Mast - a spar (in a ship, a very heavy one stepped in the keelson) formerly designed
for the support of one or more sails. In modern ships, it is a steel or aluminium
fabrication which carries navigation lights, radar antennae etc.
* Prow - a poetical alternative term for bows.
* Scupper - a drainage waterway at the edge of a deck, is drained by a pipe or, on the
weather deck, a small opening in the bulwarks, leading overboard. It is called a scupper
which is distinct from larger openings with hinged covers on the bulwarks, designed for
relieving the ship of large quantities of water in a seaway. These are called freeing ports
or wash ports..
* Windlass - A winch mechanism, usually with a horizontal axis. used where mechanical
advantage greater than that obtainable by block and tackle was needed.
* Weather deck - whichever deck is that exposed to the weather – usually either the main
deck or, in larger vessels, the upper deck.
sufficient size to carry its own boats, such as lifeboats, dinghies, or runabouts. A rule of
thumb saying (though it doesn't always apply) goes: "a boat can fit on a ship, but a ship
can't fit on a boat". Often local law and regulation will define the exact size (or the
number of masts) which a boat requires to become a ship. (Note that one refers to submarines
as "boats", because early submarines were small enough to be carried aboard a ship in
transit to distant waters.) Compare vessel.
During the age of sail, ship signified a ship-rigged vessel, that is, one with three or more
masts, usually three, all square-rigged. Such a vessel would normally have one fore and aft
sail on her aftermost mast which was usually the mizzen. Almost invariably she would also
have a bowsprit but this was not part of the definition. The same economic pressures which
increased sizes to the point of carrying four or five masts, also introduced the fore and
aft rig to larger vessels, so few ship-rigged vessels were built with more than three masts.
The five-masted Preussen was the outstanding example, but the big German ships and barques
were built partly for prestige reasons.
Nautical means related to sailors, particularly customs and practices at sea. Naval is the
adjective pertaining to ships, though in common usage it has come to be more particularly
associated with the noun 'navy'.
Measuring ships
One can measure ships in terms of overall length, length of the waterline, beam (breadth),
depth (distance between the crown of the weather deck and the top of the keelson), draft
(distance between the highest waterline and the bottom of the ship) and tonnage. A number of
different tonnage definitions exist; most measure volume rather than weight, and are used
when describing merchant ships for the purpose of tolls, taxation, etc.
In Britain until the Merchant Shipping Act of 1876, ship-owners could load their vessels
until their decks were almost awash, resulting in a dangerously unstable condition.
Additionally, anyone who signed onto such a ship for a voyage and, upon realizing the
danger, chose to leave the ship, could end up in jail.
Samuel Plimsoll, a member of Parliament, realised the problem and engaged some engineers to
derive a fairly simple formula to determine the position of a line on the side of any
specific ship's hull which, when it reached the surface of the water during loading of
cargo, meant the ship had reached its maximum safe loading level. To this day, that mark,
called the "Plimsoll Mark", exists on ships' sides, and consists of a circle with a
horizontal line through the center. Because different types of water, (summer, fresh,
tropical fresh, winter north Atlantic) have different densities, subsequent regulations
required painting a group of lines forward of the Plimsoll mark to indicate the safe depth
(or freeboard above the surface) to which a specific ship could load in water of various
densities. Hence the "ladder" of lines seen forward of the Plimsoll mark to this day.
[edit]
Propulsion
[edit]
Pre-mechanisation
Until the application of the steam engine to ships in the early 19th century, oars propelled
galleys or the wind propelled sailing ships. Before mechanisation, merchant ships always
used sail, but as long as naval warfare depended on ships closing to ram or to fight
hand-to-hand, galleys dominated in marine conflicts because of their maneuverability and
speed. The Greek navies that fought in the Peloponnesian War used triremes, as did the
Romans contesting the Battle of Actium. The use of large numbers of cannon from the 16th
century meant that maneuverability took second place to broadside weight; this led to the
dominance of the sail-powered warship.
[edit]
Steam propulsion
The development of the steamship became a complex process, the first commercial success
accruing to Robert Fulton's North River Steamboat (often called Clermont) in the US in 1807,
followed in Europe by the 45-foot Comet of 1812. Steam propulsion progressed considerably
over the rest of the 19th century. Notable developments included the condenser, which
reduced the requirement for fresh water, and the multiple expansion engine, which improved
efficiency. As the means of transmitting the engine's power, the paddle wheel gave way to
the more efficient screw propeller. The marine steam turbine developed by Sir Charles
Algernon Parsons, brought the power to weight ratio down. He had achieved publicity by
demonstrating it unofficially in the 100-foot Turbinia at the Spithead naval review in 1897.
This facilitated a generation of high-speed liners in the first half of the 20th century and
rendered the reciprocating steam engine out of date, in warships.
Most new ships since around 1960 have been built with diesel engines. Rising fuel costs have
almost lead to the demise of the steam turbine, with many ships being re-engined to improve
fuel efficiency. One high profile example was the 1968 built Queen Elizabeth 2 which had her
turbines replaced with a diesel-electric propulsion plant in 1986. The last major passenger
ship built with steam turbines was the Fairsky, launched in 1984. Some specialised merchant
ships have also been built with steam turbines since then, notably Liquified Natural Gas
(LNG) and coal carriers where part of the cargo has been used as fuel for the boilers.
[edit]
LNG Carriers
LNG carriers in particular have remained a stronghold for steam , and new ships continue to
be built with steam turbines in this high growth area of shipping. This is because the
Natural Gas is stored in a liquid state in cryogenic vessels onboard these ships. A small
amount of "boil off" of gas is required to maintain the pressure and temperature inside the
vessels to within operating limits. The "boil off" gas provides the fuel for the ship's
boilers, which provide steam for the turbines- the simplest method of dealing with the gas.
Technology to operate internal combustion engines (modified marine two stroke diesel
engines) on this gas has improved however, so these engines are beginning to appear in LNG
carriers; with their greater thermal efficiency, less gas is burnt. Also, developements have
been made in the process of re-liquifying "boil off" gas, enabling it to be returned to the
cryogenic tanks. The financial returns on LNG are potentially greater than the cost of the
marine grade fuel oil burnt in conventional diesel engines, so the re-liquification process
is starting to be used on diesel engine propelled LNG carriers. Another factor driving the
switch from turbines to diesel engines for LNG carriers is the shortage of steam turbine
qualified sea going engineers. With the lack of turbine powered ships in other shipping
sectors, and the rapid increase in size of the worldwide LNG fleet, not enough have been
trained to meet the demand. It may be that the days of the last stronghold for steam turbine
propulsion systems are numbered, despite all but sixteen of the orders for new LNG carriers
at the end of 2004 being for steam turbine propelled ships. [1]
[edit]
Diesel propulsion
The marine diesel engine first came into use around 1912: either the Vulcanus or the
Selandia (depending upon who you talk to) first deployed it. It soon offered even greater
efficiency than the steam turbine but for many years had an inferior power-to-space ratio.
About this period too, heavy fuel oil came into more general use and began to replace coal
as the fuel of choice in steamships. Its great advantages were the convenience, the
reduction in manning owing to the removal of the need for trimmers and stokers, and the
reduction in space required for fuel bunkers. Diesel engines today are broadly classified
according to their operating cycle (two-stroke or four-stroke), their construction
(crosshead, trunk, or opposed piston) and their speed (slow speed, medium speed or high
speed). Most modern larger merchant ships use either slow speed, two stroke, crosshead
engines, or medium speed, four stroke, trunk engines. Some smaller vessels may operate high
speed diesel engines. The operating ranges of the differant speed types are as follows;
* Slow speed- any engine with a maximum operating speed up to 300 revs/minute, although
most large 2 stroke slow speed diesel engines operate below 120 revs/minute. Some very long
stroke engines have a maximum speed of around 80 revs/minute. The largest, most powerful
engines in the world are slow speed, two stroke, crosshead diesels.
* Medium speed- any engine with a maximum operating speed in the range 300- 900 revs/
minute. Many modern 4 stroke medium speed diesel engines have a maximum operating speed of
around 500 rpm.
* High speed- any engine with a maximum operating speed above 900 revs/ minute
As modern ships' propellers are at their most efficient at the operating speed of most slow
speed diesel engines, ships with these engines do not generally require gearboxes. Usually
such propulsion systems consist of either one or two propeller shafts each with its own
direct drive engine. Ships propelled by medium or high speed diesel engines may have one or
two (sometimes more) propellers, commonly with one or more engines driving each propeller
shaft through a gearbox. Where more than one engine is geared to a single shaft, each engine
will most likely drive through a clutch, allowing engines not being used to be disconnected
from the gearbox while others continue to operate. This arrangement allows maintenance to be
carried out while under way at sea. Diesel electric is another propulsion system that has
been around for a long time, but is becoming more common. By having the engines drive
alternators, which supply electricity to motors driving the propellers, gearboxes and
clutches can be dispensed with and greater flexibility gained in the positioning of the
engines, while still providing the step down in speed required for a medium speed engine to
efficiently drive a ships propeller.
The size of the differant types of engines is an important factor in selecting what will be
installed in a new ship. Slow speed two stroke engines are much taller, but the foot print
required- length and width- is smaller than that required for four stroke medium speed
diesel engines. As space higher up in passenger ships and ferries is at a premium, these
ships tend to use multiple medium speed engines resulting in a longer, lower engine room
than that required for two stroke diesel engines. Multiple engine installations also gives
greater redundancy in the event of mechanical failure of one or more engines and greater
efficiency over a wider range of operating conditions.
[edit]
Other propulsion systems
Many warships built since the 1960s have used gas turbines for propulsion, as have a few
passenger ships. Most recently, the Queen Mary 2 has had gas turbines installed in addition
to diesel engines. Due to their poor thermal efficiency, it is common for ships using them
to have diesel engines for cruising with gas turbines reserved for when higher speeds are
required. Some warships and a few modern cruise ships have also utilised steam turbines to
improve the efficiency of gas turbines in a combined cycle. In such a combined cycle, where
waste heat from a gas turbine is used to create steam for driving a steam turbine, thermal
efficiency can be the same or slightly greater than that of diesel engines. However, the
grade of fuel required for gas turbines is much more expensive than that required for diesel
engines so running costs are higher.
A few ships have used nuclear reactors, but this is not a separate form of propulsion; the
reactor heats steam to drive the turbines. Nonetheless, it has caused concerns about safety
and waste disposal. It has become usual only in large aircraft carriers and in submarines,
where the ability to run submerged for long periods holds obvious advantage. In such
long-endurance vessels, the resulting saving in bunkerage is an important consideration.
[edit]
General terminology
Ships may occur collectively as fleets, squadrons or flotillas. Convoys of ships commonly
occur.
A collection of ships for military purposes may compose a navy or a task force.
In the past, people counting or grouping disparate types of ship may refer to the individual
vessels as bottoms, but this generally refers only to merchant vessels. Groups of sailing
ships could constitute, say, a fleet of 40 sail. Groups of submarines (particularly German
U-boats in the 1940s) hunt in wolf packs.
[edit]
Shipboard terminology
See also: Glossary of nautical terms. The complexity of ships, particularly of sailing
ships, led to the development of a rich and various vocabulary. Many of the following terms
link to more detailed discussions of nautical terminology.
* Amidships - toward the middle of the vessel.
* Bow - strictly, one of the two curved structures where the hull broadens out from the
stem (the pointed end). The bows is a term for the head of the vessel or front of the ship.
Compare prow, a more poetical term for the ship's head.
* Stern - the after end of the ship.
* Aft - towards the stern when the relationship is within the ship.
* Astern beyond the stern where the relationship is outside the vessel.
* Starboard - the side of the ship which lies to the right when an observer within the
ship faces forward.
* Port - the side of the ship which lies to the left when an observer within the ship
faces forward. (A mnemonic to distinguish port and starboard notes that left and port both
have four letters. Another incorporates the navigation light: Is there any red port left?)
* (Navigation) Bridge - A structure above the weather deck, extending the full width of
the vessel, which houses a command centre, itself called by association, the bridge. A
bridge usually extends a little beyond the ship's side to enable observation of boats
alongside, or the proximity of a dock or lock gate; these projections are called bridge
wings. In big vessels, a docking bridge used to be found aft. (See Lord, Walter. A Night to
Remember (1976) p.96). It enabled an officer to observe docking manoeuvres before giving
orders. RMS Titanic had one but they have been superseded by Closed-circuit television
cameras.
* Bulkheads - internal "walls" in a ship. Bulkheads are the vertical equivalent of
decks. They have a structural function as well as dividing spaces. They serve to prevent
collapse of the hull under stress, to maintain stability, in the event of flooding, and to
contain fire. Many bulkheads feature watertight doors which, in the case of certain types of
ships, the crew may close remotely. An internal "wall" that is not load-bearing is usually
referred to as a "partition". It is to a bulkhead as a flat is to a deck.
* Cabin - an enclosed room on a deck or flat.
* Capstan - a winch with a vertical axis.
* Coaming - Raised edges of hatches in decks for keeping water and articles free on the
deck from falling into the hold.
* Decks - the structures forming the approximately horizontal surfaces in the ship's
general structure. Unlike flats, they are a structural part of the ship.
* Deck Head - The under-side of the deck above. Sometimes panelled over to hide the pipe
work. This panelling, like that lining the bottom and sides of the holds, is the ceiling.
* Draft - The vertical distance from the current waterline to the lowest point of the
ship or in the part of the ship under consideration.
* Figurehead - symbolic image at the head of a traditional sailing ship or early
steamer.
* Forecastle - a partial deck, above the upper deck and at the head of the vessel;
traditionally the sailors' living quarters.
* Freeboard - The vertical distance from the current waterline to the highest continuous
watertight deck. This usually varies from one part to another.
* Galley - the kitchen of the ship
* Gunwale - Formerly a fabricated band placed for strengthening around the ship at the
main or upper deck level to accommodate the stresses imposed by the use of artillery. In
later use it is the angle between the ship’s side and upper deck. It remained as a
structural member, in wooden boats where it was mounted inboard of the sheer strake
regardless of the need for gunnery.
* Bulwark - the extension of the ship's side above the level of the weather deck.
* Hold - In earlier use, below the orlop deck, the lower part of the interior of a
ship's hull, especially when considered as storage space, as for cargo. In later merchant
vessels it extended up through the decks to the underside of the weather deck.
* Hull - the shell and framework of the basic flotation-oriented part of a ship
* Keel - the central structural basis of the hull
* Kelson - the timber immediately above the keel of a wooden ship.
* Mast - a spar (in a ship, a very heavy one stepped in the keelson) formerly designed
for the support of one or more sails. In modern ships, it is a steel or aluminium
fabrication which carries navigation lights, radar antennae etc.
* Prow - a poetical alternative term for bows.
* Scupper - a drainage waterway at the edge of a deck, is drained by a pipe or, on the
weather deck, a small opening in the bulwarks, leading overboard. It is called a scupper
which is distinct from larger openings with hinged covers on the bulwarks, designed for
relieving the ship of large quantities of water in a seaway. These are called freeing ports
or wash ports..
* Windlass - A winch mechanism, usually with a horizontal axis. used where mechanical
advantage greater than that obtainable by block and tackle was needed.
* Weather deck - whichever deck is that exposed to the weather – usually either the main
deck or, in larger vessels, the upper deck.
All-terrain vehicle
The term "all-terrain vehicle" is used in a general sense to describe any of a number of
small open motorised buggies and tricycles designed for off-road use. However, the American
National Standards Institute (ANSI) defines an ATV as a vehicle that travels on low pressure
tires, with a seat that is straddled by the operator, and with handlebars for steering
control. By the ANSI definition, it is intended for use by a single operator. The 4-wheeled
versions are most commonly called "quads," "four-wheelers" or "ATVs" in the United States
and Canada, and "quad bikes" or "quad cycles" in other English-speaking countries. Models
with 3 wheels are typically known as ATCs (though this is a Honda trademark) and
"three-wheelers," and less commonly "all-terrain cycles" and "trikes." 6- and 8-wheel models
exist for specialized applications. The rider sits on these models just like on a
motorcycle, but the extra wheels make them more stable at slow speeds. ATVs can also be
considered Off Highway Vehicles (OHV) or Off Road Vehicles (ORV), along with motorcycles,
Jeeps and other off-road capable machines.
Engine sizes of ATVs currently for sale in the United States (as of 2006) range from 50cc to
800cc. They range in price from about $2000 to nearly $8000.
Safety Issues
Since the expiration of the consent decrees between the major manufacturers and CPSC in
April of 1998, the manufacturers have entered into "voluntary action plans" that mimic the
previously mandatory consent decrees. However, despite the move from 3-wheel to 4-wheel
models and the action plans, some deaths and injuries still occur. Statistics released by
CPSC show that in 2004, there were an estimated 136,100 injuries associated with ATVs
treated in US hospital emergency rooms -- more than double the number of injuries treated in
the last year of the consent decrees. In 2003, the latest year for which estimates are
available, 740 people died in ATV-associated incidents.
The action plans in place with CPSC cover only certain manufacturers of ATVs. Other
manufacturers that have entered the market since the expiration of the consent decrees are
not covered by the action plans and so are not bound by the rules governing things such as
labelling and safe marketing practices, and what ages a distributor may recommend a
particular sized ATV for. These manufacturers and distributors, most of whom originate from
Asia and Italy, are completely exempt of government oversight.
Focus has shifted since the consent decrees ended to attention to machine size balanced with
rider age. Many states have enacted legislation specifically governing the usage of ATVs on
state run land categorized by age ranges and engine displacements - in line with the consent
decrees. ATVs are mandated to be labelled from the manufacturer that the use of machines
greater than 90cc by riders under the age of 16 is prohibited. Critics point out that
blanket policies concerning age are not sufficient and often use as example that early teen
male children are physically larger and stronger than many adult women riders. Some
localities have either banned minors (typically those under 16 years of age) from using ATVs
or are considering such legislation. Advocates of ATVs argue that starting younger improves
safety. They recommend that children can develop the necessary expertise by starting as
young as 6 years of age instead of waiting until age 16. The U.S. Consumer Product Safety
Commission approved the sale of sub-50cc ATVs for use by youngsters as young as age 6.
In 1988, the All-terrain Vehicle Safety Institute (ASI) was formed to provide training and
education for ATV riders. The cost of attending the training is minimal and is free for
purchasers of new machines. Successful completion of training such as provided here is in
many states a minimum requirement for minor-age children to be granted permission to ride on
state lands.
[edit]
EPA Concerns
[edit]
Emissions
Due to the lack of emission controlling hardware and software, for year 2000 all
recreational spark ignited (SI) non-road vehicles (of which ATVs are a subset) contributed
8% of HC, .16% of NOx, 5% of CO and .8% of PM emissions for the entire non-road EPA family.
The entire range of non-road emissions accounted for 49% of engine produced emissions of all
types. (Source: EPA 1) While recreational SI vehicles (of which ATVs are a subset) produce
an aggregate of <4% of all HC emissions in the US, based on the relatively small population
of ATVs (<1.2M) and small annual usage (<350 hrs), EPA emission regulations now include such
engines starting with model year 2006. (source: EPA 2)
[edit]
Fuel Economy
The EPA estimates that each ATV consumes less than 59 gallons of fuel per year and obtains
between 40 and 50 mpg, making them not likely to fall under future fuel economy regulations.
(Ibid. EPA 1)
[edit]
Land Usage
Some ATV riders cross privately owned property in rural areas and travel overland where
their use is explicitly limitied to trails. Further, environmentalists criticize ATV riders
for excessive use in areas they consider biologically sensitive, especially wetlands and
sand dunes. While the deep treads on some ATV tires are effective for navigating rocky,
muddy, and root covered terrain, these treads also dig channels that may drain boggy areas,
increase sedimentation in streams at crossings and damage groomed snowmobile trails. Studies
have also shown that ATVs may help in the spread of invasive species such as knapweed. While
there is much scientific evidence regarding the impact of ATVs, its credibility often comes
under great scrutiny from ATV users who believe them to be overtly biased against ATVs.
To address these land usage concerns, well funded ATV advocacy groups have been organized to
purchase property and/or obtain permission of landowners, build and maintain trails suitable
for ATV riding and educate ATV riders about responsible riding. Many states have also formed
separate governing bodies that license ATVs separately than other ORVs. The monies from
these registrations are used to secure trails to ride and perform grooming and maintenance.
Unfortunately, the image of the great majority of responsible riders is often tainted by the
actions of some who ride off designated trails, on private land without permission, and
under the influence of alcohol or drugs. Additionally, self regulation has proven
particularly difficult considering that the main public complaint against ATVs is excessive
noise. Although the majority of ATVs comply with noise regulations, there are those whose
intentional violation can disturb the activities of other recreational users for miles
across open landscapes. Tampering with an ATVs exhaust silencer and spark arrestor is
illegal on all federal lands and most state lands, however enforcement is spotty. It is also
possible to install aftermarket exhaust systems that do not have silencers and spark
arrestors.
Fellow outdoor recreationists who have expressed concern about irresponsible ATV use are
snowmobile users who resent improper use of exclusive snowmobile trails, ATV trail riders
whose trails have been damaged by improper use and hunters whose game has been driven off by
those riding during prime hunting times.
Nationally, the US Forest Service considers managed ATV use to be a legitmate activity in
national forests, yet it also lists their unregulated use as one of the four greatest
threats to long term forest management. The US Forest Service recently released a national
travel management plan designed to minimize the negative environmental impacts of ATVs while
providing a safe, sustainable and enjoyable opportunity for ATV users.
small open motorised buggies and tricycles designed for off-road use. However, the American
National Standards Institute (ANSI) defines an ATV as a vehicle that travels on low pressure
tires, with a seat that is straddled by the operator, and with handlebars for steering
control. By the ANSI definition, it is intended for use by a single operator. The 4-wheeled
versions are most commonly called "quads," "four-wheelers" or "ATVs" in the United States
and Canada, and "quad bikes" or "quad cycles" in other English-speaking countries. Models
with 3 wheels are typically known as ATCs (though this is a Honda trademark) and
"three-wheelers," and less commonly "all-terrain cycles" and "trikes." 6- and 8-wheel models
exist for specialized applications. The rider sits on these models just like on a
motorcycle, but the extra wheels make them more stable at slow speeds. ATVs can also be
considered Off Highway Vehicles (OHV) or Off Road Vehicles (ORV), along with motorcycles,
Jeeps and other off-road capable machines.
Engine sizes of ATVs currently for sale in the United States (as of 2006) range from 50cc to
800cc. They range in price from about $2000 to nearly $8000.
Safety Issues
Since the expiration of the consent decrees between the major manufacturers and CPSC in
April of 1998, the manufacturers have entered into "voluntary action plans" that mimic the
previously mandatory consent decrees. However, despite the move from 3-wheel to 4-wheel
models and the action plans, some deaths and injuries still occur. Statistics released by
CPSC show that in 2004, there were an estimated 136,100 injuries associated with ATVs
treated in US hospital emergency rooms -- more than double the number of injuries treated in
the last year of the consent decrees. In 2003, the latest year for which estimates are
available, 740 people died in ATV-associated incidents.
The action plans in place with CPSC cover only certain manufacturers of ATVs. Other
manufacturers that have entered the market since the expiration of the consent decrees are
not covered by the action plans and so are not bound by the rules governing things such as
labelling and safe marketing practices, and what ages a distributor may recommend a
particular sized ATV for. These manufacturers and distributors, most of whom originate from
Asia and Italy, are completely exempt of government oversight.
Focus has shifted since the consent decrees ended to attention to machine size balanced with
rider age. Many states have enacted legislation specifically governing the usage of ATVs on
state run land categorized by age ranges and engine displacements - in line with the consent
decrees. ATVs are mandated to be labelled from the manufacturer that the use of machines
greater than 90cc by riders under the age of 16 is prohibited. Critics point out that
blanket policies concerning age are not sufficient and often use as example that early teen
male children are physically larger and stronger than many adult women riders. Some
localities have either banned minors (typically those under 16 years of age) from using ATVs
or are considering such legislation. Advocates of ATVs argue that starting younger improves
safety. They recommend that children can develop the necessary expertise by starting as
young as 6 years of age instead of waiting until age 16. The U.S. Consumer Product Safety
Commission approved the sale of sub-50cc ATVs for use by youngsters as young as age 6.
In 1988, the All-terrain Vehicle Safety Institute (ASI) was formed to provide training and
education for ATV riders. The cost of attending the training is minimal and is free for
purchasers of new machines. Successful completion of training such as provided here is in
many states a minimum requirement for minor-age children to be granted permission to ride on
state lands.
[edit]
EPA Concerns
[edit]
Emissions
Due to the lack of emission controlling hardware and software, for year 2000 all
recreational spark ignited (SI) non-road vehicles (of which ATVs are a subset) contributed
8% of HC, .16% of NOx, 5% of CO and .8% of PM emissions for the entire non-road EPA family.
The entire range of non-road emissions accounted for 49% of engine produced emissions of all
types. (Source: EPA 1) While recreational SI vehicles (of which ATVs are a subset) produce
an aggregate of <4% of all HC emissions in the US, based on the relatively small population
of ATVs (<1.2M) and small annual usage (<350 hrs), EPA emission regulations now include such
engines starting with model year 2006. (source: EPA 2)
[edit]
Fuel Economy
The EPA estimates that each ATV consumes less than 59 gallons of fuel per year and obtains
between 40 and 50 mpg, making them not likely to fall under future fuel economy regulations.
(Ibid. EPA 1)
[edit]
Land Usage
Some ATV riders cross privately owned property in rural areas and travel overland where
their use is explicitly limitied to trails. Further, environmentalists criticize ATV riders
for excessive use in areas they consider biologically sensitive, especially wetlands and
sand dunes. While the deep treads on some ATV tires are effective for navigating rocky,
muddy, and root covered terrain, these treads also dig channels that may drain boggy areas,
increase sedimentation in streams at crossings and damage groomed snowmobile trails. Studies
have also shown that ATVs may help in the spread of invasive species such as knapweed. While
there is much scientific evidence regarding the impact of ATVs, its credibility often comes
under great scrutiny from ATV users who believe them to be overtly biased against ATVs.
To address these land usage concerns, well funded ATV advocacy groups have been organized to
purchase property and/or obtain permission of landowners, build and maintain trails suitable
for ATV riding and educate ATV riders about responsible riding. Many states have also formed
separate governing bodies that license ATVs separately than other ORVs. The monies from
these registrations are used to secure trails to ride and perform grooming and maintenance.
Unfortunately, the image of the great majority of responsible riders is often tainted by the
actions of some who ride off designated trails, on private land without permission, and
under the influence of alcohol or drugs. Additionally, self regulation has proven
particularly difficult considering that the main public complaint against ATVs is excessive
noise. Although the majority of ATVs comply with noise regulations, there are those whose
intentional violation can disturb the activities of other recreational users for miles
across open landscapes. Tampering with an ATVs exhaust silencer and spark arrestor is
illegal on all federal lands and most state lands, however enforcement is spotty. It is also
possible to install aftermarket exhaust systems that do not have silencers and spark
arrestors.
Fellow outdoor recreationists who have expressed concern about irresponsible ATV use are
snowmobile users who resent improper use of exclusive snowmobile trails, ATV trail riders
whose trails have been damaged by improper use and hunters whose game has been driven off by
those riding during prime hunting times.
Nationally, the US Forest Service considers managed ATV use to be a legitmate activity in
national forests, yet it also lists their unregulated use as one of the four greatest
threats to long term forest management. The US Forest Service recently released a national
travel management plan designed to minimize the negative environmental impacts of ATVs while
providing a safe, sustainable and enjoyable opportunity for ATV users.
SUV
A sport utility vehicle, or SUV, is a type of passenger vehicle which combines the
load-hauling and versatility of a pickup truck with the passenger-carrying space of a van or
station wagon. Most SUVs are designed with a roughly square cross-section, an engine
compartment, a combined passenger and cargo compartment, and no dedicated trunk. Most
mid-size and full-size SUVs have 5 or more seats, and a cargo area directly behind the last
row of seats. Mini SUVs, such as the Jeep Wrangler, may have fewer seats.
It is known in some countries as an off-roader or four wheel drive, often abbreviated to 4WD
or 4x4, and pronounced "four-by-four". More recently, SUVs designed primarily for driving on
roads have grown in popularity. A new category, the crossover SUV uses car components for
lighter weight and better fuel economy.
Design characteristics
SUVs were traditionally derived from light truck platforms, but several SUVs and crossover
SUVs are based on platforms of unibody construction.[1].
SUVs typically have high seating and most can be equipped with four wheel drive, providing
an advantage in low traction environments. The design also allows for a large engine
compartment, which allows for a wide variety of engine choices, both gasoline and diesel.
Popularity
SUVs became popular in the United States, Canada, and Australia in the 1990s and early 2000s
for a variety of reasons. Buyers became drawn to their large cabins, higher ride height, and
perceived safety when in the market for a new vehicle. Additionally, most full-size SUVs
have far greater towing capacities than conventional cars, allowing owners to tow RVs,
trailers, and boats with relative ease, adding to the utilitarian image.
A large growth in SUV popularity and sales is due to advertisement targeted towards women.
Women constitute more than half of SUV drivers, and SUVs are the most popular vehicle choice
of women in the United States. [citation needed]
In Australia, a unique situation resulted in the growth in popularity of SUVs. There, SUVs
have a much lower import duty compared with cars. This means a typical SUV has a significant
price advantage over a similarly-equipped, imported sedan. However, in recent years, the
import duty has been lowered for cars as well, and is currently at 10% (compared with 5% for
SUVs).
A common reason for SUV popularity cited by owners was their perceived safety advantage in a
collision with regular cars. For instance, the higher profile allows for better visability
and anticipation of danger. The enhanced weight helped reduce the risk of injury by a third
in children under the age of 16, though the roll-over fatality risk is much higher in SUVs
than cars negating the advantage.[citation needed] Some of their success could also be
attributed to their "utilitarian" image. In the late 1990s and early 2000s, vehicle
manufacturers sold SUVs very effectively, with per-vehicle profits substantially higher than
other automobiles. Historically, their simpler designs often made the vehicles cheaper to
make than comparably-priced cars.
In the mid 2000s, however, their popularity has waned, due to higher gasoline
prices[citation needed], rollover accident fatalities[citation needed] and higher relative
pollution.[citation needed] As of the spring of 2006, some of the larger SUVs now require
over 100USD per fillup, making thier everyday use more cost-prohibitive.[citation needed]
Current model SUVs (crossovers) take into account that 98% of SUV owners never
offroad[citation needed]. As such, SUVs now have lower ground clearance and suspension
designed primarily for paved road usage.
[edit]
SUVs in remote areas
SUVs are often used in places such as the Australian Outback, Africa, the Middle East,
Alaska, Northern Canada and most of Asia, which have limited paved roads and require the
vehicle to have all-terrain handling, increased range, and storage capacity. The low
availablity of spare parts and the need to carry out repairs quickly allow model vehicles
with the bare minimum of electric and hydraulic systems to predominate. Typical examples are
the Land Rover, the Toyota Land Cruiser and the Lada Niva.
SUVs targeted for use in civilization have traditionally originated from their more rugged
all-terrain counterparts. For example the Hummer H1 is derived from the HMMWV, originally
developed for the US Armed Forces.
[edit]
Other names
Outside of North America and India, these vehicles are known simply as four-wheel-drives,
often abbreviated to "4WD" or "4x4". They are classified as cars in countries such as the UK
where the U.S. distinction between cars and 'light trucks' is not used. In Australia, the
automotive industry and press have recently adopted the term SUV in place of four wheel
drive in the description of vehicles and market segments. "Utility" or "ute" refers to an
automobile with a flatbed rear or pick-up, typically seating two passengers and is often
used by tradesmen, and is typically not a 4WD vehicle.
[edit]
SUVs in recreation and motorsport
SUVs are also used to explore off-road places otherwise unreachable by vehicle or for the
sheer enjoyment of the driving. In Australia, China, Europe, South Africa and the U.S. at
least, many 4WD clubs have been formed for this purpose. Modified SUVs also take part in
races, most famously in the Paris-Dakar Rally, and the Australian Safari.
With the increasing urbanisation of the world, SUVs are also becoming more of a requirement
for those seeking unmodified landscapes and isolation, especially in nations with large
wilderness areas through which a viable road network could not be maintained without
excessive costs. Of course, roads are rarely constructed with scenic purposes foremost in
mind, instead trying to utilise the shortest and most economical length in order to reach a
specific destination and in many cases this means many natural features of interest are
inaccessible to cars. To travel with the absence of this infrastructure (which often leads
to settlements being built) serves to add to the appeal of SUV ownership due to a sense of
independence this invokes in many people, an ability to appreciate natural landscapes upon
their own terms.
The recreation value of SUVs also brings with it a pro environmentalist agenda which is
often overlooked in debates over their overall merits. By allowing owners to go off road,
SUVs promote a greater value being applied to wilderness areas, an attachment difficult to
gain through reading or simply seeing things on television. SUV clubs often promote this
ideal and a commercial manifestation of this can be seen in the number of tourism operators
dependent on SUVs for their activities, Australia being a strong example. Sensible off road
driving can promote a greater physical connection between people and the pristine
environment, something which has decreased with ever growing urban areas
Fuel economy
The recent popularity of SUVs is one reason the U.S. population consumes more gasoline than
in previous years. SUVs are as a class much less fuel efficient than comparable passenger
vehicles. The main reason is that SUVs are classified by the U.S. government as light
trucks, and thus are subject to the less strict light truck standard under the Corporate
Average Fuel Economy (CAFE) regulations. The CAFE requirement for light trucks is an average
of 20.7 mpg (US), versus 27.5 mpg (US) for passenger cars (8.6 and 11.4 km/L, respectively).
As there is little incentive to change the design, SUVs have numerous fuel-inefficient
features. The high profile of SUVs increases wind resistance. Heavier suspensions and larger
engines increase vehicle weight. Some SUVs also often come with tires designed for off-road
traction rather than low rolling resistance.
The low fuel economy is caused by
* high parasitic masses (compared to the average load) causing high energy demand in
transitional operation (in the cities) {P_{accel}= m_{vehicle} \cdot a \cdot v } where P
stands for power, mvehicle for the vehicle mass, a for acceleration and v for the vehicle
velocity.
* high cross-sectional area causing very high drag losses especially when driven at high
speed {P_{drag}= A_{cross} \cdot cw_{vehicle} \cdot \frac {v_{air}^3 \rho_{air}} {2} } where
P stands for the power, Across for the cross-sectional area of the vehicle, ρair for the
density of the air and vair for the relative velocity of the air (incl. wind)
* high rolling resistance due to all-terrain tires (even worse if low pressure is needed
offroad) and high vehicle mass driving the rolling resistance {P_{roll}= \mu_{roll} \cdot
m_{vehicle} \cdot v } where μroll stands for the rolling resistance factor and mvehicle for
the vehicle mass.
Average data for vehicle types sold in the U.S.A. (source theautochannel.com):
load-hauling and versatility of a pickup truck with the passenger-carrying space of a van or
station wagon. Most SUVs are designed with a roughly square cross-section, an engine
compartment, a combined passenger and cargo compartment, and no dedicated trunk. Most
mid-size and full-size SUVs have 5 or more seats, and a cargo area directly behind the last
row of seats. Mini SUVs, such as the Jeep Wrangler, may have fewer seats.
It is known in some countries as an off-roader or four wheel drive, often abbreviated to 4WD
or 4x4, and pronounced "four-by-four". More recently, SUVs designed primarily for driving on
roads have grown in popularity. A new category, the crossover SUV uses car components for
lighter weight and better fuel economy.
Design characteristics
SUVs were traditionally derived from light truck platforms, but several SUVs and crossover
SUVs are based on platforms of unibody construction.[1].
SUVs typically have high seating and most can be equipped with four wheel drive, providing
an advantage in low traction environments. The design also allows for a large engine
compartment, which allows for a wide variety of engine choices, both gasoline and diesel.
Popularity
SUVs became popular in the United States, Canada, and Australia in the 1990s and early 2000s
for a variety of reasons. Buyers became drawn to their large cabins, higher ride height, and
perceived safety when in the market for a new vehicle. Additionally, most full-size SUVs
have far greater towing capacities than conventional cars, allowing owners to tow RVs,
trailers, and boats with relative ease, adding to the utilitarian image.
A large growth in SUV popularity and sales is due to advertisement targeted towards women.
Women constitute more than half of SUV drivers, and SUVs are the most popular vehicle choice
of women in the United States. [citation needed]
In Australia, a unique situation resulted in the growth in popularity of SUVs. There, SUVs
have a much lower import duty compared with cars. This means a typical SUV has a significant
price advantage over a similarly-equipped, imported sedan. However, in recent years, the
import duty has been lowered for cars as well, and is currently at 10% (compared with 5% for
SUVs).
A common reason for SUV popularity cited by owners was their perceived safety advantage in a
collision with regular cars. For instance, the higher profile allows for better visability
and anticipation of danger. The enhanced weight helped reduce the risk of injury by a third
in children under the age of 16, though the roll-over fatality risk is much higher in SUVs
than cars negating the advantage.[citation needed] Some of their success could also be
attributed to their "utilitarian" image. In the late 1990s and early 2000s, vehicle
manufacturers sold SUVs very effectively, with per-vehicle profits substantially higher than
other automobiles. Historically, their simpler designs often made the vehicles cheaper to
make than comparably-priced cars.
In the mid 2000s, however, their popularity has waned, due to higher gasoline
prices[citation needed], rollover accident fatalities[citation needed] and higher relative
pollution.[citation needed] As of the spring of 2006, some of the larger SUVs now require
over 100USD per fillup, making thier everyday use more cost-prohibitive.[citation needed]
Current model SUVs (crossovers) take into account that 98% of SUV owners never
offroad[citation needed]. As such, SUVs now have lower ground clearance and suspension
designed primarily for paved road usage.
[edit]
SUVs in remote areas
SUVs are often used in places such as the Australian Outback, Africa, the Middle East,
Alaska, Northern Canada and most of Asia, which have limited paved roads and require the
vehicle to have all-terrain handling, increased range, and storage capacity. The low
availablity of spare parts and the need to carry out repairs quickly allow model vehicles
with the bare minimum of electric and hydraulic systems to predominate. Typical examples are
the Land Rover, the Toyota Land Cruiser and the Lada Niva.
SUVs targeted for use in civilization have traditionally originated from their more rugged
all-terrain counterparts. For example the Hummer H1 is derived from the HMMWV, originally
developed for the US Armed Forces.
[edit]
Other names
Outside of North America and India, these vehicles are known simply as four-wheel-drives,
often abbreviated to "4WD" or "4x4". They are classified as cars in countries such as the UK
where the U.S. distinction between cars and 'light trucks' is not used. In Australia, the
automotive industry and press have recently adopted the term SUV in place of four wheel
drive in the description of vehicles and market segments. "Utility" or "ute" refers to an
automobile with a flatbed rear or pick-up, typically seating two passengers and is often
used by tradesmen, and is typically not a 4WD vehicle.
[edit]
SUVs in recreation and motorsport
SUVs are also used to explore off-road places otherwise unreachable by vehicle or for the
sheer enjoyment of the driving. In Australia, China, Europe, South Africa and the U.S. at
least, many 4WD clubs have been formed for this purpose. Modified SUVs also take part in
races, most famously in the Paris-Dakar Rally, and the Australian Safari.
With the increasing urbanisation of the world, SUVs are also becoming more of a requirement
for those seeking unmodified landscapes and isolation, especially in nations with large
wilderness areas through which a viable road network could not be maintained without
excessive costs. Of course, roads are rarely constructed with scenic purposes foremost in
mind, instead trying to utilise the shortest and most economical length in order to reach a
specific destination and in many cases this means many natural features of interest are
inaccessible to cars. To travel with the absence of this infrastructure (which often leads
to settlements being built) serves to add to the appeal of SUV ownership due to a sense of
independence this invokes in many people, an ability to appreciate natural landscapes upon
their own terms.
The recreation value of SUVs also brings with it a pro environmentalist agenda which is
often overlooked in debates over their overall merits. By allowing owners to go off road,
SUVs promote a greater value being applied to wilderness areas, an attachment difficult to
gain through reading or simply seeing things on television. SUV clubs often promote this
ideal and a commercial manifestation of this can be seen in the number of tourism operators
dependent on SUVs for their activities, Australia being a strong example. Sensible off road
driving can promote a greater physical connection between people and the pristine
environment, something which has decreased with ever growing urban areas
Fuel economy
The recent popularity of SUVs is one reason the U.S. population consumes more gasoline than
in previous years. SUVs are as a class much less fuel efficient than comparable passenger
vehicles. The main reason is that SUVs are classified by the U.S. government as light
trucks, and thus are subject to the less strict light truck standard under the Corporate
Average Fuel Economy (CAFE) regulations. The CAFE requirement for light trucks is an average
of 20.7 mpg (US), versus 27.5 mpg (US) for passenger cars (8.6 and 11.4 km/L, respectively).
As there is little incentive to change the design, SUVs have numerous fuel-inefficient
features. The high profile of SUVs increases wind resistance. Heavier suspensions and larger
engines increase vehicle weight. Some SUVs also often come with tires designed for off-road
traction rather than low rolling resistance.
The low fuel economy is caused by
* high parasitic masses (compared to the average load) causing high energy demand in
transitional operation (in the cities) {P_{accel}= m_{vehicle} \cdot a \cdot v } where P
stands for power, mvehicle for the vehicle mass, a for acceleration and v for the vehicle
velocity.
* high cross-sectional area causing very high drag losses especially when driven at high
speed {P_{drag}= A_{cross} \cdot cw_{vehicle} \cdot \frac {v_{air}^3 \rho_{air}} {2} } where
P stands for the power, Across for the cross-sectional area of the vehicle, ρair for the
density of the air and vair for the relative velocity of the air (incl. wind)
* high rolling resistance due to all-terrain tires (even worse if low pressure is needed
offroad) and high vehicle mass driving the rolling resistance {P_{roll}= \mu_{roll} \cdot
m_{vehicle} \cdot v } where μroll stands for the rolling resistance factor and mvehicle for
the vehicle mass.
Average data for vehicle types sold in the U.S.A. (source theautochannel.com):
Hovercraft
A hovercraft, or air-cushion vehicle (ACV), is a vehicle or craft that can be supported by a
cushion of air ejected downwards against a surface close below it, and can in principle
travel over any relatively smooth surface, such as gently sloping land, water, or marshland,
while having no substantial contact with it.
The first recorded design for a vehicle which could be termed a Hovercraft was in 1716 by
Emanuel Swedenborg, a Swedish designer, philosopher and theologian. His man-powered air
cushion platform resembled an upside-down boat with a cockpit in the center and manually
operated oar-like scoops to push air under the vehicle on each downward stroke. No vehicle
was ever built, no doubt because it was realised that human effort could not have generated
enough lift.
In the mid-1870s, the British engineer Sir John Isaac Thornycroft built a number of ground
effect machine test models based on his idea of using air between the hull of a boat and the
water to reduce drag. Although he filed a number of patents involving air-lubricated hulls
in 1877, no practical applications were found. Over the years, various other people had
tried various methods of using air to reduce the drag on ships.
Early development of the modern "hovercraft" began with a design of American inventor
Charles J. Fletcher, who designed his "Glidemobile" while in the United States Navy during
World War II. The design worked on the principle of trapping a constant airflow against a
uniform surface (either the ground or water), providing anywhere from ten inches to two feet
of lift to free it from the surface, and control of the craft would be achieved by the
measured release of air. Shortly after being tested on Beezer's Pond in Fletcher's hometown
of Sparta Township, New Jersey, the design was immediately appropriated by the United States
Department of Defense and classified, denying Fletcher the opportunity to patent his
creation. Fletcher's claim as the original inventor was substantiated during the case of
British Hovercraft Ltd v. United States, in which the British corporation which maintained
the rights to Sir Christopher Cockerell's patent unsuccessfully sought to win $104,000,000
in lost royalties.
Col. Melville W. Beardsley (1913-1998), an American inventor and aeronautical engineer,
along with Dr. W. Bertelsen worked on developing early ACV's in the USA.
In 1952 the British inventor Christopher Cockerell designed a vehicle based on his
'hovercraft principle'. He was knighted for his services to engineering in 1969. Sir
Christopher invented the word 'Hovercraft' to describe his invention.
Cockerell used simple experiments involving a vacuum cleaner motor and two cylindrical cans.
He proved the workable principle of a vehicle suspended on a cushion of air blown out under
pressure, making the vehicle easily mobile over most surfaces. The supporting air cushion
would enable it to operate over soft mud, water, and marshes and swamps as well as on firm
ground.
The British aircraft manufacturer Saunders Roe which had aeronautical expertise developed
the first practical man-carrying hovercraft, the SR-N1, which carried out several test
programmes in 1959 to 1961 (the first public demonstration in 1959), including a
cross-channel run. The SR-N1 was powered by one (piston) engine, driven by expelled air, and
could carry little more than its own weight and two men,and did not have any skirt at first
trials. It was found that the craft's lift was improved by the addition of a 'skirt' of
flexible fabric or rubber around the hovering surface, to contain the air. The skirt was an
independent invention made by a Royal Navy officer who worked with Sir Christopher to
develop the idea further.
The first true passenger-carrying hovercraft was the Vickers VA-3, which in the summer of
1961 carried passengers regularly along the North Wales Coast from Wallasey to Rhyl. It was
powered by two turboprop aero-engines and driven by propellers. During the 1960s Saunders
Roe developed several larger designs which could carry passengers, including the SR-N2,
which operated across the Solent in 1962 and later the SR-N6, which operated across the
Solent from Southsea to Ryde on the Isle of Wight for many years. Operations commenced on
24th July 1965 using the SR-N6 which carried just 38 passengers. Two modern 98 seat AP1-88
hovercraft now ply this route, and over 20 million passengers have used the service as of
2004.
Bell licenced and sold the SRN-5 as the Bell SK-5. There were deployed on trial to the
Vietnam War by the Navy as PACV patrol craft in the Mekong Delta where their mobility and
speed was unique. Advanced AACVs were developed with automated turrets and slab sides, but
use was eventually abandoned. Experience led to the proposed Bell SK-10 which was the basis
for the LCAC now deployed.
As well as Saunders Roe and Vickers (which combined in 1966 to form the British Hovercraft
Corporation), other commercial craft were developed during the 1960s in the UK by
Cushioncraft (part of the Britten-Norman Group) and Hovermarine (the latter being 'sidewall'
type hovercraft, where the sides of the hull projected down into the water to trap the
cushion of air).
In the late 1960s and early 1970s, Jean Bertin developed a hovercraft train dubbed the
Aérotrain in France. His I-80 prototype established the world speed record for overland air
cushion vehicles with a mean speed of 417.6 km/h (260 mp/h) and a top speed of 430 km/h (267
mp/h).
By 1970 the largest British hovercraft were in service, the Mountbatten class SR-N4 model,
each powered by four Rolls-Royce Proteus engines, regularly carrying cars and passengers
across the English Channel from Dover or Ramsgate to Calais. This service ceased in 2000
after years of competition with traditional ferries, catamarans, and the opening of the
Channel tunnel.
In 1998, the US Postal Service began using the British built Hoverwork AP.1-88 to haul mail,
freight, and passengers from Bethel, Alaska to and from eight small villages along the
Kuskokwim River. Bethel is far removed from the Alaska road system, thus making the
hovercraft an attractive alternative to the air based delivery methods used prior to
introduction of the hovercraft service. Hovercraft service is suspended for several weeks
each year while the river is beginning to freeze to minimize damage to the river ice
surface. The hovercraft is perfectly able to operate during the freeze-up period, however,
it could potentially break the ice creating hazards for the villagers using their
snowmobiles for transportation along the river during the early winter.
The commercial success of hovercraft suffered from rapid rises in fuel prices during the
late 1960s and 1970s following conflict in the Middle East. Alternative over-water vehicles
such as wave-piercing catamarans (marketed as the Seacat in Britain) use less fuel and can
perform most of the hovercraft's marine tasks. Although developed elsewhere in the world for
both civil and military purposes, except for the Solent Ryde to Southsea crossing,
hovercraft disappeared from the coastline of Britain until a range of Griffon Hovercraft
were bought by the Royal National Lifeboat Institution.
There are an increasing number of small homebuilt and kit-built hovercraft used for fun and
racing purposes, mainly on inland lakes and rivers but also in marshy areas and in some
estuaries.
Hovercraft typically have two (or more) separate engines (some craft, such as the SR-N6,
have one engine with a drive split through a gearbox). One engine drives the fan (aka the
impeller) which is responsible for lifting the vehicle by forcing air under the craft. One
or more additional engines are used to provide thrust in order to propel the craft in the
desired direction. Some hovercraft utilise ducting to allow one engine to perform both tasks
by directing some of the air to the skirt, the rest of the air passing out of the back to
push the craft forward.
cushion of air ejected downwards against a surface close below it, and can in principle
travel over any relatively smooth surface, such as gently sloping land, water, or marshland,
while having no substantial contact with it.
The first recorded design for a vehicle which could be termed a Hovercraft was in 1716 by
Emanuel Swedenborg, a Swedish designer, philosopher and theologian. His man-powered air
cushion platform resembled an upside-down boat with a cockpit in the center and manually
operated oar-like scoops to push air under the vehicle on each downward stroke. No vehicle
was ever built, no doubt because it was realised that human effort could not have generated
enough lift.
In the mid-1870s, the British engineer Sir John Isaac Thornycroft built a number of ground
effect machine test models based on his idea of using air between the hull of a boat and the
water to reduce drag. Although he filed a number of patents involving air-lubricated hulls
in 1877, no practical applications were found. Over the years, various other people had
tried various methods of using air to reduce the drag on ships.
Early development of the modern "hovercraft" began with a design of American inventor
Charles J. Fletcher, who designed his "Glidemobile" while in the United States Navy during
World War II. The design worked on the principle of trapping a constant airflow against a
uniform surface (either the ground or water), providing anywhere from ten inches to two feet
of lift to free it from the surface, and control of the craft would be achieved by the
measured release of air. Shortly after being tested on Beezer's Pond in Fletcher's hometown
of Sparta Township, New Jersey, the design was immediately appropriated by the United States
Department of Defense and classified, denying Fletcher the opportunity to patent his
creation. Fletcher's claim as the original inventor was substantiated during the case of
British Hovercraft Ltd v. United States, in which the British corporation which maintained
the rights to Sir Christopher Cockerell's patent unsuccessfully sought to win $104,000,000
in lost royalties.
Col. Melville W. Beardsley (1913-1998), an American inventor and aeronautical engineer,
along with Dr. W. Bertelsen worked on developing early ACV's in the USA.
In 1952 the British inventor Christopher Cockerell designed a vehicle based on his
'hovercraft principle'. He was knighted for his services to engineering in 1969. Sir
Christopher invented the word 'Hovercraft' to describe his invention.
Cockerell used simple experiments involving a vacuum cleaner motor and two cylindrical cans.
He proved the workable principle of a vehicle suspended on a cushion of air blown out under
pressure, making the vehicle easily mobile over most surfaces. The supporting air cushion
would enable it to operate over soft mud, water, and marshes and swamps as well as on firm
ground.
The British aircraft manufacturer Saunders Roe which had aeronautical expertise developed
the first practical man-carrying hovercraft, the SR-N1, which carried out several test
programmes in 1959 to 1961 (the first public demonstration in 1959), including a
cross-channel run. The SR-N1 was powered by one (piston) engine, driven by expelled air, and
could carry little more than its own weight and two men,and did not have any skirt at first
trials. It was found that the craft's lift was improved by the addition of a 'skirt' of
flexible fabric or rubber around the hovering surface, to contain the air. The skirt was an
independent invention made by a Royal Navy officer who worked with Sir Christopher to
develop the idea further.
The first true passenger-carrying hovercraft was the Vickers VA-3, which in the summer of
1961 carried passengers regularly along the North Wales Coast from Wallasey to Rhyl. It was
powered by two turboprop aero-engines and driven by propellers. During the 1960s Saunders
Roe developed several larger designs which could carry passengers, including the SR-N2,
which operated across the Solent in 1962 and later the SR-N6, which operated across the
Solent from Southsea to Ryde on the Isle of Wight for many years. Operations commenced on
24th July 1965 using the SR-N6 which carried just 38 passengers. Two modern 98 seat AP1-88
hovercraft now ply this route, and over 20 million passengers have used the service as of
2004.
Bell licenced and sold the SRN-5 as the Bell SK-5. There were deployed on trial to the
Vietnam War by the Navy as PACV patrol craft in the Mekong Delta where their mobility and
speed was unique. Advanced AACVs were developed with automated turrets and slab sides, but
use was eventually abandoned. Experience led to the proposed Bell SK-10 which was the basis
for the LCAC now deployed.
As well as Saunders Roe and Vickers (which combined in 1966 to form the British Hovercraft
Corporation), other commercial craft were developed during the 1960s in the UK by
Cushioncraft (part of the Britten-Norman Group) and Hovermarine (the latter being 'sidewall'
type hovercraft, where the sides of the hull projected down into the water to trap the
cushion of air).
In the late 1960s and early 1970s, Jean Bertin developed a hovercraft train dubbed the
Aérotrain in France. His I-80 prototype established the world speed record for overland air
cushion vehicles with a mean speed of 417.6 km/h (260 mp/h) and a top speed of 430 km/h (267
mp/h).
By 1970 the largest British hovercraft were in service, the Mountbatten class SR-N4 model,
each powered by four Rolls-Royce Proteus engines, regularly carrying cars and passengers
across the English Channel from Dover or Ramsgate to Calais. This service ceased in 2000
after years of competition with traditional ferries, catamarans, and the opening of the
Channel tunnel.
In 1998, the US Postal Service began using the British built Hoverwork AP.1-88 to haul mail,
freight, and passengers from Bethel, Alaska to and from eight small villages along the
Kuskokwim River. Bethel is far removed from the Alaska road system, thus making the
hovercraft an attractive alternative to the air based delivery methods used prior to
introduction of the hovercraft service. Hovercraft service is suspended for several weeks
each year while the river is beginning to freeze to minimize damage to the river ice
surface. The hovercraft is perfectly able to operate during the freeze-up period, however,
it could potentially break the ice creating hazards for the villagers using their
snowmobiles for transportation along the river during the early winter.
The commercial success of hovercraft suffered from rapid rises in fuel prices during the
late 1960s and 1970s following conflict in the Middle East. Alternative over-water vehicles
such as wave-piercing catamarans (marketed as the Seacat in Britain) use less fuel and can
perform most of the hovercraft's marine tasks. Although developed elsewhere in the world for
both civil and military purposes, except for the Solent Ryde to Southsea crossing,
hovercraft disappeared from the coastline of Britain until a range of Griffon Hovercraft
were bought by the Royal National Lifeboat Institution.
There are an increasing number of small homebuilt and kit-built hovercraft used for fun and
racing purposes, mainly on inland lakes and rivers but also in marshy areas and in some
estuaries.
Hovercraft typically have two (or more) separate engines (some craft, such as the SR-N6,
have one engine with a drive split through a gearbox). One engine drives the fan (aka the
impeller) which is responsible for lifting the vehicle by forcing air under the craft. One
or more additional engines are used to provide thrust in order to propel the craft in the
desired direction. Some hovercraft utilise ducting to allow one engine to perform both tasks
by directing some of the air to the skirt, the rest of the air passing out of the back to
push the craft forward.
Plasma display
A plasma display panel (PDP) is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. The gas discharge contains no mercury (contrary to the backlights of an AMLCD). An inert mixture of noble gases (neon and xenon) is used instead.
General characteristics
Plasma displays are bright (1000 lx or higher for the module), have a wide color
[edit]
Pros and cons
(comparison with LCD and Plasma)
Pros
* Slim design (Wall mountable)
* Larger than LCD screens
Cons
* Expensive, although cheaper than LCDs at larger sizes.
* Is subject to screen burn-in, but modern panels have a manufacturer rated lifespan of 50,000 or more hours.
* First 2000 hours is its brightest point. Every hour there after, the display gradually dims.
* At higher elevations, usually 6000 ft or higher, they exhibit noticeable humming.
[edit]
Functional details
The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, on both sides of the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate.
In a monochrome plasma panel, control circuitry charges the electrodes that cross paths at a cell, causing the plasma to ionize and emit photons between the electrodes. The ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.
To ionize the gas in a color panel, the plasma display's computer charges the electrodes that intersect at that cell thousands of times in a small fraction of a second, charging each cell in turn. When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.
The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel. By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce colors across the entire visible spectrum. Plasma displays use the same phosphors as CRTs, accounting for the extremely accurate color reproduction.
[edit]
Contrast ratio claims
Contrast ratio indicates the difference between the brightest part of a picture and the darkest part of a picture, measured in discrete steps, at any given moment. The implication is that a higher contrast ratio means more picture detail. Contrast ratios for plasma displays are often advertised as high as 10000:1. On the surface, this is a great thing. In reality, there are no standardized tests for contrast ratio, meaning each manufacturer can publish virtually any number that they like. To illustrate, some manufacturers will measure contrast with the front glass removed, which accounts for some of the wild claims regarding their advertised ratios. For reference, the page you're reading now (on a computer monitor) is actually about 50:1. A printed page is about 80:1. A really good print at a movie theater will be about 500:1
General characteristics
Plasma displays are bright (1000 lx or higher for the module), have a wide color
[edit]
Pros and cons
(comparison with LCD and Plasma)
Pros
* Slim design (Wall mountable)
* Larger than LCD screens
Cons
* Expensive, although cheaper than LCDs at larger sizes.
* Is subject to screen burn-in, but modern panels have a manufacturer rated lifespan of 50,000 or more hours.
* First 2000 hours is its brightest point. Every hour there after, the display gradually dims.
* At higher elevations, usually 6000 ft or higher, they exhibit noticeable humming.
[edit]
Functional details
The xenon and neon gas in a plasma television is contained in hundreds of thousands of tiny cells positioned between two plates of glass. Long electrodes are also sandwiched between the glass plates, on both sides of the cells. The address electrodes sit behind the cells, along the rear glass plate. The transparent display electrodes, which are surrounded by an insulating dielectric material and covered by a magnesium oxide protective layer, are mounted above the cell, along the front glass plate.
In a monochrome plasma panel, control circuitry charges the electrodes that cross paths at a cell, causing the plasma to ionize and emit photons between the electrodes. The ionizing state can be maintained by applying a low-level voltage between all the horizontal and vertical electrodes - even after the ionizing voltage is removed. To erase a cell all voltage is removed from a pair of electrodes. This type of panel has inherent memory and does not use phosphors. A small amount of nitrogen is added to the neon to increase hysteresis.
To ionize the gas in a color panel, the plasma display's computer charges the electrodes that intersect at that cell thousands of times in a small fraction of a second, charging each cell in turn. When the intersecting electrodes are charged (with a voltage difference between them), an electric current flows through the gas in the cell. The current creates a rapid flow of charged particles, which stimulates the gas atoms to release ultraviolet photons.
The phosphors in a plasma display give off colored light when they are excited. Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel. By varying the pulses of current flowing through the different cells, the control system can increase or decrease the intensity of each subpixel color to create billions of different combinations of red, green and blue. In this way, the control system can produce colors across the entire visible spectrum. Plasma displays use the same phosphors as CRTs, accounting for the extremely accurate color reproduction.
[edit]
Contrast ratio claims
Contrast ratio indicates the difference between the brightest part of a picture and the darkest part of a picture, measured in discrete steps, at any given moment. The implication is that a higher contrast ratio means more picture detail. Contrast ratios for plasma displays are often advertised as high as 10000:1. On the surface, this is a great thing. In reality, there are no standardized tests for contrast ratio, meaning each manufacturer can publish virtually any number that they like. To illustrate, some manufacturers will measure contrast with the front glass removed, which accounts for some of the wild claims regarding their advertised ratios. For reference, the page you're reading now (on a computer monitor) is actually about 50:1. A printed page is about 80:1. A really good print at a movie theater will be about 500:1
Cannons
A cannon is any large tubular firearm designed to fire a heavy projectile over a considerable distance. The term can apply to a modern day rifled machine gun with a calibre of 20 mm or more (see autocannon).
Cannon also refers to a large, smooth-bored, muzzle-loading gun used before the advent of breech-loading, rifled guns firing explosive shells. Although a variety of such guns are commonly referred to as "cannon", the term specifically refers to a gun designed to fire a 42 lb shot as opposed to a "Demi-cannon" (32 lb), Culverin (18 lb) or Demi-culverin (9 lb).
"Cannon" derives from the Latin canna—a tube. Bombard was earlier used for "cannon", but from the early 15th century came to refer only to the largest weapons. "Cannon" can serve both as the singular and plural of the noun.
Modern cannon
A modern artillery piece is generally referred to either as a "gun", or by the name of its specific type, such as a Howitzer.
Since World War II the term cannon is used to refer to a gun of around 20 mm to 125 mm calibre, sometimes with an automatic loading action capable of firing explosive ammunition, an auto-cannon.
The minimum calibre of a cannon, 20 mm, has been a de facto standard since WWII, when heavy machine guns of 12.7 mm (0.5 inches) and 13.2 mm calibre were used side by side with 20 mm and larger guns, the latter using explosive ammunition, e.g., RAF fighters with 20 mm Hispano cannon and Luftwaffe with 20 mm and 30 mm cannon. The Bofors 40 mm gun and Oerlikon 20 mm cannon are two examples largely used during the Second World War, and still in usage today.
Most nations use these modern (auto-) cannon on their lighter vehicles. Typical of the type is the 25 mm 'Bushmaster' cannon mounted on the LAV and Bradley armoured vehicles.
A cannon generally refers to a high velocity, low trajectory, direct fire weapon such as the main gun on most modern main battle tanks.
A howitzer generally refers to a weapon using a lower velocity than a cannon, which fires on a higher trajectory, and provides indirect fire.
These are both differentiated from a mortar, which fires a low velocity (by comparison) round at very high trajectory at much more limited range.
Projectiles fired from cannon
Round shot
A solid projectile made, in early times, from dressed stone but, by the 17th century, from iron. The most accurate projectile that could be fired by a smooth-bore cannon, used to batter the wooden hulls of opposing ships, forts, or fixed emplacements, and as a long-range anti-personnel weapon.
Chain shot or bar shot
Two sub-calibre round shot (a good deal smaller than the bore of the barrel) linked by a length of chain or a solid bar, and used to slash through the rigging and sails of an enemy ship so that it could no longer manoeuvre. It was inaccurate and only used at close range.
Canister shot (or case shot)
An anti-personnel weapon which included many small round shot or lead musket balls in a metal can, which broke up when fired, scattering the shot throughout the enemy personnel, like a large shotgun.
Shell
An anti-personnel weapon, similar to canister shot, but with a can that was much more robust and which also contained a fused explosive charge, trimmed to explode above the heads of the enemy, spreading shot and can fragments in the form of shrapnel over the enemy. First used in the 16th century as a siege weapon fired from mortars, and later as a battlefield weapon.
Grapeshot
An anti-personnel weapon, similar to canister shot, but with the shot being contained in a canvas bag, and generally of a larger calibre. So called because of the resemblance of the clustered shot in the bag to a cluster of grapes on the vine.
Carcass
An incendiary/antipersonnel projectile designed to burn fiercely and produce poisonous fumes. It was constructed of an iron frame bound with sack cloth and filled with various ingredients such as pitch, antimony, sulphur, saltpeter, tallow and venetian turpentine. It was ignited by the cannon's propellant charge, bursting on impact with the target and releasing noxious fumes while setting fire to its surroundings. It was effectively an early chemical weapon as well as an incendiary and area denial weapon.
Heated (or hot) shot
A process where the cannonball is heated red hot and shot at flammable targets with the intent of starting a fire.
Cannon also refers to a large, smooth-bored, muzzle-loading gun used before the advent of breech-loading, rifled guns firing explosive shells. Although a variety of such guns are commonly referred to as "cannon", the term specifically refers to a gun designed to fire a 42 lb shot as opposed to a "Demi-cannon" (32 lb), Culverin (18 lb) or Demi-culverin (9 lb).
"Cannon" derives from the Latin canna—a tube. Bombard was earlier used for "cannon", but from the early 15th century came to refer only to the largest weapons. "Cannon" can serve both as the singular and plural of the noun.
Modern cannon
A modern artillery piece is generally referred to either as a "gun", or by the name of its specific type, such as a Howitzer.
Since World War II the term cannon is used to refer to a gun of around 20 mm to 125 mm calibre, sometimes with an automatic loading action capable of firing explosive ammunition, an auto-cannon.
The minimum calibre of a cannon, 20 mm, has been a de facto standard since WWII, when heavy machine guns of 12.7 mm (0.5 inches) and 13.2 mm calibre were used side by side with 20 mm and larger guns, the latter using explosive ammunition, e.g., RAF fighters with 20 mm Hispano cannon and Luftwaffe with 20 mm and 30 mm cannon. The Bofors 40 mm gun and Oerlikon 20 mm cannon are two examples largely used during the Second World War, and still in usage today.
Most nations use these modern (auto-) cannon on their lighter vehicles. Typical of the type is the 25 mm 'Bushmaster' cannon mounted on the LAV and Bradley armoured vehicles.
A cannon generally refers to a high velocity, low trajectory, direct fire weapon such as the main gun on most modern main battle tanks.
A howitzer generally refers to a weapon using a lower velocity than a cannon, which fires on a higher trajectory, and provides indirect fire.
These are both differentiated from a mortar, which fires a low velocity (by comparison) round at very high trajectory at much more limited range.
Projectiles fired from cannon
Round shot
A solid projectile made, in early times, from dressed stone but, by the 17th century, from iron. The most accurate projectile that could be fired by a smooth-bore cannon, used to batter the wooden hulls of opposing ships, forts, or fixed emplacements, and as a long-range anti-personnel weapon.
Chain shot or bar shot
Two sub-calibre round shot (a good deal smaller than the bore of the barrel) linked by a length of chain or a solid bar, and used to slash through the rigging and sails of an enemy ship so that it could no longer manoeuvre. It was inaccurate and only used at close range.
Canister shot (or case shot)
An anti-personnel weapon which included many small round shot or lead musket balls in a metal can, which broke up when fired, scattering the shot throughout the enemy personnel, like a large shotgun.
Shell
An anti-personnel weapon, similar to canister shot, but with a can that was much more robust and which also contained a fused explosive charge, trimmed to explode above the heads of the enemy, spreading shot and can fragments in the form of shrapnel over the enemy. First used in the 16th century as a siege weapon fired from mortars, and later as a battlefield weapon.
Grapeshot
An anti-personnel weapon, similar to canister shot, but with the shot being contained in a canvas bag, and generally of a larger calibre. So called because of the resemblance of the clustered shot in the bag to a cluster of grapes on the vine.
Carcass
An incendiary/antipersonnel projectile designed to burn fiercely and produce poisonous fumes. It was constructed of an iron frame bound with sack cloth and filled with various ingredients such as pitch, antimony, sulphur, saltpeter, tallow and venetian turpentine. It was ignited by the cannon's propellant charge, bursting on impact with the target and releasing noxious fumes while setting fire to its surroundings. It was effectively an early chemical weapon as well as an incendiary and area denial weapon.
Heated (or hot) shot
A process where the cannonball is heated red hot and shot at flammable targets with the intent of starting a fire.
Bombs
A bomb is an explosive device that, although not containing more energy than ordinary fuel, except in the case of a nuclear weapon, generates and releases its energy very rapidly, as an explosion, a violent, destructive shock wave. It is usually some kind of container filled with explosive material, designed to cause random destruction when set off. The word comes from the Greek word βόμβος (bombos), an onomatopoetic term with approximately the same meaning as "boom" in English.
These are first and foremost weapons; the term "bomb" is not usually applied to explosive devices used for civilian purposes, such as construction or mining, although the people using the devices may or may not sometimes refer to them as bombs. Many military explosive devices are not called "bombs". The military mostly calls airdropped, unpowered explosive weapons "bombs," and such bombs are normally used by air forces and naval aviation. Other military explosive devices are called grenades, such as hand grenades), shells, depth charges, warheads when in missiles, or land mines.
They have been used for centuries in warfare and are a central part of a terrorist's arsenal. They fall into three distinct categories: conventional if filled with chemical explosives, dispersive if filled with submunitions, chemicals or other disruptive agents which are spread on or shortly before impact, or nuclear if relying on nuclear fission or nuclear fusion for their effect.
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, terrorist bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, they are generally referred to as improvised explosive devices (IEDs).
The most powerful bomb in existence is the hydrogen bomb, a nuclear weapon. The most powerful bombs ever used in combat were the two nuclear bombs dropped by the United States to attack Hiroshima and Nagasaki. The most powerful non-nuclear bomb is the United States Air Force's MOAB (Massive Ordnance Air Blast).
The most powerful bomb ever was Tsar Bomba: ca. 50 Mt; it had a mass of 27 tons; it was dropped from a bomber for a test, but was for various reasons not very suitable for combat.
The first hydrogen "bomb" Ivy Mike (10.4 Mt) was even heavier in mass, 82 tons. It was too heavy to be deliverable by a plane or rocket, and therefore not very suitable for an attack.
Another type of bomb is called an EMP (Electro-Magnetic Pulse) and its primary function is to terminate all working electrical equipment in the vicinity. Its power can range from one machine to an entire state.
Delivery
The usual method of delivering military bombs to their target is by bombing, i.e. dropping them from a bomber airplane. Modern bombs, precision-guided munitions, may be guided after they leave an airplane by remote control, by autonomous guidance or (in the case of nuclear weapons) mounted on a guided missile.
Some bombs are equipped with a parachute, such as the World War Two "parafrag", which was an 11kg fragmentation bomb, the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with airburst nuclear weapons, and in the case that the aircraft releases the bomb at low altitude.
A hand grenade is delivered by being thrown. Grenades can also be projected by other means using a grenade launcher, such as being launched from the muzzle of a rifle using the M203 or the GP-30 or by attaching a rocket to the explosive grenade as in a rocket propelled grenade (RPG).
A bomb may also be positioned in advance and concealed, for example in a garbage container, car or truck as a car bomb, or by the roadside in a roadside bomb, in a building as a booby trap, or in lugguage and in a vehicle.
A bomb destroying a rail track just before a train arrives causes a train to derail. Apart from the damage to vehicles and people, a bomb exploding in a transport network often also damages, and is sometimes mainly intended to damage, that network. This applies for railways, bridges, runways, and ports, and to a lesser extent, depending on circumstances, to roads.
In the case of suicide bombing the bomb is often carried by the attacker on his or her body, or a in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if they were disturbed, they would explode within ten seconds.
[edit]
Detonation
The explosion of the bomb has to be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others.
[edit]
Bombing
Bombing may be directed at military targets; such as ships, logistic and transportation centres, warehouses or weapons industries such as armament factories. They may be detonated also at civilian targets, such as office buildings, commercial areas or whole cities. Bombing of particular targets such as ships, railroad trains or military vehicles such as tanks is called tactical bombing; bombing of areas such as military bases or infrastructure, such as bridges, industrial centres, transport facilities) is called strategic bombing. Strategic bombing of civilian targets is controversial and considered a war crime by most and a defining characteristic of terrorism by others, and may be considered terror bombing. Area or carpet bombing of cities using incendiary bombs may result in a firestorm and extensive casualties especially when the city is fire-prone, largely constructed of timber buildings or used to store flammable materials, and it is windy.
These are first and foremost weapons; the term "bomb" is not usually applied to explosive devices used for civilian purposes, such as construction or mining, although the people using the devices may or may not sometimes refer to them as bombs. Many military explosive devices are not called "bombs". The military mostly calls airdropped, unpowered explosive weapons "bombs," and such bombs are normally used by air forces and naval aviation. Other military explosive devices are called grenades, such as hand grenades), shells, depth charges, warheads when in missiles, or land mines.
They have been used for centuries in warfare and are a central part of a terrorist's arsenal. They fall into three distinct categories: conventional if filled with chemical explosives, dispersive if filled with submunitions, chemicals or other disruptive agents which are spread on or shortly before impact, or nuclear if relying on nuclear fission or nuclear fusion for their effect.
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, terrorist bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, they are generally referred to as improvised explosive devices (IEDs).
The most powerful bomb in existence is the hydrogen bomb, a nuclear weapon. The most powerful bombs ever used in combat were the two nuclear bombs dropped by the United States to attack Hiroshima and Nagasaki. The most powerful non-nuclear bomb is the United States Air Force's MOAB (Massive Ordnance Air Blast).
The most powerful bomb ever was Tsar Bomba: ca. 50 Mt; it had a mass of 27 tons; it was dropped from a bomber for a test, but was for various reasons not very suitable for combat.
The first hydrogen "bomb" Ivy Mike (10.4 Mt) was even heavier in mass, 82 tons. It was too heavy to be deliverable by a plane or rocket, and therefore not very suitable for an attack.
Another type of bomb is called an EMP (Electro-Magnetic Pulse) and its primary function is to terminate all working electrical equipment in the vicinity. Its power can range from one machine to an entire state.
Delivery
The usual method of delivering military bombs to their target is by bombing, i.e. dropping them from a bomber airplane. Modern bombs, precision-guided munitions, may be guided after they leave an airplane by remote control, by autonomous guidance or (in the case of nuclear weapons) mounted on a guided missile.
Some bombs are equipped with a parachute, such as the World War Two "parafrag", which was an 11kg fragmentation bomb, the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with airburst nuclear weapons, and in the case that the aircraft releases the bomb at low altitude.
A hand grenade is delivered by being thrown. Grenades can also be projected by other means using a grenade launcher, such as being launched from the muzzle of a rifle using the M203 or the GP-30 or by attaching a rocket to the explosive grenade as in a rocket propelled grenade (RPG).
A bomb may also be positioned in advance and concealed, for example in a garbage container, car or truck as a car bomb, or by the roadside in a roadside bomb, in a building as a booby trap, or in lugguage and in a vehicle.
A bomb destroying a rail track just before a train arrives causes a train to derail. Apart from the damage to vehicles and people, a bomb exploding in a transport network often also damages, and is sometimes mainly intended to damage, that network. This applies for railways, bridges, runways, and ports, and to a lesser extent, depending on circumstances, to roads.
In the case of suicide bombing the bomb is often carried by the attacker on his or her body, or a in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if they were disturbed, they would explode within ten seconds.
[edit]
Detonation
The explosion of the bomb has to be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others.
[edit]
Bombing
Bombing may be directed at military targets; such as ships, logistic and transportation centres, warehouses or weapons industries such as armament factories. They may be detonated also at civilian targets, such as office buildings, commercial areas or whole cities. Bombing of particular targets such as ships, railroad trains or military vehicles such as tanks is called tactical bombing; bombing of areas such as military bases or infrastructure, such as bridges, industrial centres, transport facilities) is called strategic bombing. Strategic bombing of civilian targets is controversial and considered a war crime by most and a defining characteristic of terrorism by others, and may be considered terror bombing. Area or carpet bombing of cities using incendiary bombs may result in a firestorm and extensive casualties especially when the city is fire-prone, largely constructed of timber buildings or used to store flammable materials, and it is windy.
Gas turbine in vehicles
Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles.
In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Colin Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag. The fictional Batmobile is often said to be powered by a gas turbine or a jet engine.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator.
Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.
[edit]
Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 FT-4 main propulsion engines, 2 FT-12 cruise engines and 3 Solar Saturn 750 KW generators.
The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.
An example of commercial usage of a gas turbine in a ship is the Stena Discovery, using the GE LM2500.
Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.
[edit]
Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.
On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.
In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Colin Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag. The fictional Batmobile is often said to be powered by a gas turbine or a jet engine.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator.
Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.
[edit]
Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 FT-4 main propulsion engines, 2 FT-12 cruise engines and 3 Solar Saturn 750 KW generators.
The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.
An example of commercial usage of a gas turbine in a ship is the Stena Discovery, using the GE LM2500.
Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.
[edit]
Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.
On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.
Space Shuttle
NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's current manned launch vehicle. The winged shuttle orbiter is launched vertically, usually carrying five to seven astronauts (although eight have been carried) and up to 22,700 kg (50,000 lb) of payload into low earth orbit. When its mission is complete, it re-enters the earth's atmosphere and makes an unpowered horizontal landing.
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
The Shuttle is the first orbital spacecraft designed for partial reusability. It is also so far the only winged manned spacecraft to achieve orbit and land. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the International Space Station to earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years' operational life.
The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the Crew Exploration Vehicle (CEV).
Description
The Shuttle is a partially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
The Orbiter resembles an airplane with double-delta wings, swept 81° at the inner leading edge and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 45° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the Orbiter during descent and landing.
The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highest flight deck seats the commander and pilot, with two mission specialists behind them. The mid-deck has three more seats for the rest of the crew members. The galley, toilet, sleep locations, storage lockers, and the side hatch for entering/exiting the vehicle are also located there, as is the airlock hatch. The airlock has another hatch into the payload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurize before a space walk.
The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights.
Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the Shuttle as well as push.
The Orbital Maneuvering System (OMS) provides orbital maneuvers, including insertion, circularization, transfer, rendezvous, abort to orbit, and abort once around.
The Reaction Control System (RCS) provides attitude control and translation along the pitch, roll, and yaw axes during the flight phases of orbit insertion, orbit, and re-entry.
The Thermal Protection System (TPS) covers the outside of the Orbiter, protecting it from the cold soak of -121 °C (-250 °F) in space to the 1649 °C (3000 °F) heat of reentry
The orbiter structure is made primarily from aluminium alloy, although the engine thrust structure is made from titanium.
The External Tank (ET) provides 2.025 million liters (535,000 gallons) of liquid hydrogen and liquid oxygen propellant to the SSMEs. It is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) then breaks up on reentry. The ET is constructed mostly of aluminium-lithium alloy about 1/8 inch thick. Many people think that the ET is painted orange. In reality, the orange color is the true color of the tank's insulation. If it were painted, it would add another 1,000 lbs. of unnecessary payload.
Two Solid Rocket Boosters (SRBs) provide about 83% of the vehicle's thrust at liftoff and during the first stage ascent. They are jettisoned two minutes after launch at a height of about 150,000 feet (45.7 km), then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1/2 inch (1.27 cm) thick.
Computerized fly-by-wire digital flight control
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the shuttle Data Processing System (DPS).
The design goal of the shuttle DPS is fail operational/fail safe reliability. After a single failure the shuttle can continue the mission. After two failures it can land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. This should never happen, as embedded system avionic software is developed under totally different conditions from commercial software. For example, the number of code lines is tiny compared to a commercial operating system, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can fail, and the BFS exists for that contingency.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, but load software from tape cartridges.
In 1990 the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
[edit]
Other improvements
Internally the Shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to contemporary airliners like the Airbus A320. This is called a "glass cockpit". In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the Shuttle's mid-deck during Station resupply missions.
The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. However this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For STS-1 and STS-2 the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of Shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminium-lithium alloy. It weighs 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.
On the first four Shuttle missions, astronauts wore full-pressure Launch Entry Suit (LES) during ascent and descent. The pressured helmet was used from STS-5 until the loss of Challenger. The LES was reinstated when Shuttle flights resumed in 1988. The LES ended its service life in late 1995, replaced by the Advanced Crew Escape Suit (ACES).
[edit]
Technical data
Orbiter Specifications (for Endeavour, OV-105)
* Length: 122.17 ft (37.24 m)
* Wingspan: 78.06 ft (23.79 m)
* Height: 58.58 ft (17.25 m)
* Empty Weight: 151,205 lb (68,586.6 kg)
* Gross Liftoff Weight: 240,000 lb (109,000 kg)
* Maximum Landing Weight: 230,000 lb (104,000 kg)
* Main Engines: Three Rocketdyne Block 2 A SSMEs, each with a sea level thrust of 393,800 lbf (178,624 kgf / 1.75MN)
* Maximum Payload: 55,250 lb (25,061.4 kg)
* Payload Bay dimensions: 15 ft by 60 ft (4.6 m by 18.3 m)
* Operational Altitude: 100 to 520 nmi (185 to 1,000 km)
* Speed: 25,404 ft/s (7,743 m/s, 27,875 km/h, 17,321 mi/h)
* Crossrange: 1,085 nautical miles (2,009.4 km)
* Crew: Seven (Commander, Pilot, two Mission Specialists, and three Payload Specialists), two for minimum.
External Tank Specifications (for SLWT)
* Length: 153.8 ft (46.9 m)
* Diameter: 27.6 ft (8.4 m)
* Propellent Volume: 535,000 gallon
* Empty Weight: 58,500 lb (26,559 kg)
* Gross Liftoff Weight: 1.667 million lb (757,000 kg)
Solid Rocket Booster Specifications
* Length: 149.6 ft (45.6 m)
* Diameter: 12.17 ft (3.71 m)
* Empty Weight: 139,490 lb (63,272.7 kg)
* Gross Liftoff Weight: 1.3 million lb (590,000 kg)
* Thrust (sea level, liftoff): 2.8 million lbf (1,270,058 kgf / 12.46MN)
System Stack Specifications
* Height: 184.2 ft (56.14 m)
* Gross Liftoff Weight: 4.5 million lb (2.04 million kg)
* Total Liftoff Thrust: 6.781 million lbf (3.076 million kgf / 30.18MN)
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