Arresting gear
Overview
 
Arresting gear, or arrestor gear, is the name used for mechanical systems designed to rapidly decelerate
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 an aircraft as it lands
Landing
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...

. Arresting gear on aircraft carriers is an essential component of naval aviation
Naval aviation
Naval aviation is the application of manned military air power by navies, including ships that embark fixed-wing aircraft or helicopters. In contrast, maritime aviation is the operation of aircraft in a maritime role under the command of non-naval forces such as the former RAF Coastal Command or a...

, and it is most commonly used on CATOBAR
CATOBAR
CATOBAR is a system used for the launch and recovery of aircraft from the deck of an aircraft carrier...

 and STOBAR
STOBAR
STOBAR is a system used for the launch and recovery of aircraft from the deck of an aircraft carrier, combining elements of both STOVL and CATOBAR .Aircraft launch under their own power using a ski-jump to assist take-off STOBAR (Short Take Off But Arrested Recovery) is a system used for the...

 aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...

s. Similar systems are also found at land-based airfields for expeditionary or emergency use. Typical systems consist of a cable laid across the aircraft landing area, designed to be caught by an aircraft's tailhook
Tailhook
A tailhook, also arresting hook or arrester hook, is a device attached to the empennage of some military fixed wing aircraft...

.
Encyclopedia
Arresting gear, or arrestor gear, is the name used for mechanical systems designed to rapidly decelerate
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 an aircraft as it lands
Landing
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...

. Arresting gear on aircraft carriers is an essential component of naval aviation
Naval aviation
Naval aviation is the application of manned military air power by navies, including ships that embark fixed-wing aircraft or helicopters. In contrast, maritime aviation is the operation of aircraft in a maritime role under the command of non-naval forces such as the former RAF Coastal Command or a...

, and it is most commonly used on CATOBAR
CATOBAR
CATOBAR is a system used for the launch and recovery of aircraft from the deck of an aircraft carrier...

 and STOBAR
STOBAR
STOBAR is a system used for the launch and recovery of aircraft from the deck of an aircraft carrier, combining elements of both STOVL and CATOBAR .Aircraft launch under their own power using a ski-jump to assist take-off STOBAR (Short Take Off But Arrested Recovery) is a system used for the...

 aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...

s. Similar systems are also found at land-based airfields for expeditionary or emergency use. Typical systems consist of a cable laid across the aircraft landing area, designed to be caught by an aircraft's tailhook
Tailhook
A tailhook, also arresting hook or arrester hook, is a device attached to the empennage of some military fixed wing aircraft...

. During a normal arrestment, the tailhook engages the wire and the aircraft's kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 is transferred to whatever is attached to the ends of the wire. There are other related systems which use nets to catch aircraft wings or landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...

. These barricade and barrier systems are only used for emergency arrestments for aircraft without operable tailhooks.

History

Arresting cable systems were first invented by Hugh Robinson
Hugh Armstrong Robinson
Hugh Armstrong Robinson, born May 13, 1881–1963, Neosho, Missouri. Robinson was pioneer in the earliest days of aviation, combining his skills of inventor, pilot, and daredevil. Among other things, he is said to have been the third person to successfully fly an aircraft after the Wright Brothers...

 and were utilized by Eugene Ely on his first landing on a ship - the armored cruiser
Armored cruiser
The armored cruiser was a type of warship of the late 19th and early 20th centuries. Like other types of cruiser, the armored cruiser was a long-range, independent warship, capable of defeating any ship apart from a battleship, and fast enough to outrun any battleships it encountered.The first...

 USS Pennsylvania
USS Pennsylvania (ACR-4)
The second USS Pennsylvania , also referred to "Armored Cruiser No. 4", and later renamed Pittsburgh and numbered CA-4, was a United States Navy armored cruiser, the lead ship of her class....

, on January 18, 1911. These early systems had cables run through pulleys and attached to dead weights, such as sandbags. More modern arresting cables were tested on HMS Courageous
HMS Courageous (50)
HMS Courageous was the lead ship of the cruisers built for the Royal Navy during the First World War. Designed to support the Baltic Project championed by the First Sea Lord, John Fisher, the ship was very lightly armoured and armed with only a few heavy guns. Courageous was completed in late...

 in June 1931.

Modern U.S. Navy aircraft carriers have the Mark 7 Mod 3 arresting gear installed, which have the capability of recovering a 50000 pounds (22,679.6 kg) aircraft at an engaging speed of 130 knots in a distance of 340 feet (104 m). The system is designed to absorb theoretical maximum energy of 47,500,000 foot-pounds (64.4 MJ) at maximum cable run-out.

Prior to the introduction of the angled flight deck, two systems were used (in addition to deck cables) to keep landing aircraft from running into parked aircraft further forward on the flight deck: the barrier and the barricade. If the aircraft tailhook failed to catch a wire, its landing gear would be caught by a 3-4 foot high net known as the barrier. If the aircraft caught a wire upon touchdown, the barrier could be quickly lowered to allow aircraft to taxi over it. The final safety net was the barricade, a large, 15 foot (4.6 m) high net that prevented landing aircraft from crashing into other aircraft parked on the bow. Barriers are no longer in use, although ground based arresting gear are sometimes called "barriers". Barricades are still in use aboard carriers, but they are only rigged and used in emergencies.

Operation

A normal arrestment is accomplished when the arresting hook of an incoming aircraft engages one of the deck pendants. When a landing aircraft engages a deck pendant, the force of the forward motion of the landing aircraft is transferred to a purchase cable which is routed via sheaves to the arresting engine, located in a machinery room below the flight deck or on either side of the runway. As the deck pendant and the purchase cable are pulled out by the aircraft being arrested, the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 of the aircraft is transferred to mechanical energy of the cables, and the arresting engine transfers the mechanical energy of the cables to hydraulic energy. The arresting engine brings about a smooth, controlled stop of the landing aircraft. At the completion of the arrestment, the aircraft arresting hook is disengaged from the deck pendant, which is then retracted to its normal position.

Sea-based systems

Modern carriers typically have three or four arresting cables laid across the landing area. All U.S. carriers in the Nimitz-class
Nimitz class aircraft carrier
The Nimitz-class supercarriers are a class of ten nuclear-powered aircraft carriers in service with the United States Navy. With an overall length of and full-load displacements of over 100,000 long tons, they are the largest capital ships in the world...

 have four wires, with the exception of the USS Ronald Reagan
USS Ronald Reagan (CVN-76)
USS Ronald Reagan is a Nimitz-class nuclear-powered supercarrier in the service of the United States Navy. The ninth ship of her class, she is named in honor of former President Ronald Reagan, President of the United States from 1981 to 1989...

 and USS George H.W. Bush, which have only three. The Gerald R. Ford-class carriers will also have three. Aircraft coming in to land on a carrier are at approximately 85% of full throttle. At touchdown, the pilot advances the throttles to full power. If the aircraft fails to catch an arresting cable, a condition known as a "bolter
Bolter (aviation)
In naval aviation, a bolter is when an aircraft attempting to land on the flight deck of an aircraft carrier touches down, but fails to catch an arrestor cable and come to a stop...

", the aircraft has sufficient power to continue down the angled flight deck and become airborne again. Once the arresting gear stops the aircraft, the pilot brings the throttles back to idle, raises the hook and taxies clear.

Land-based systems

Land-based military airfields operating fighter
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

 or jet trainer
Trainer (aircraft)
A trainer is a class of aircraft designed specifically to facilitate in-flight training of pilots and aircrews. The use of a dedicated trainer aircraft with additional safety features—such as tandem flight controls, forgiving flight characteristics and a simplified cockpit arrangement—allows...

 aircraft also use arresting gear systems, although they are not required for all landings. Instead, they are used for landing aircraft on short or temporary runways, or for emergencies involving brake failure, steering problems or other situations in which using the full length of the runway is not possible or safe. There are three basic types of land based systems: permanent, expeditionary, and over-run gear.

Permanent systems are installed on nearly all U.S. military airfields operating fighter or jet trainer aircraft. Expeditionary systems are similar to permanent systems and are used for landing aircraft on short or temporary runways. Expeditionary systems are designed to be installed or uninstalled in only a few hours.

Overrun gear consisting of hook cables and/or elastic nets known as barriers are commonly used as a backup system. Barrier nets catch the wings and fuselage of an aircraft and use an arresting engine or other methods such as anchor chains or bundles of woven textile material to slow the aircraft down. On some land-based airfields where the overrun area is short, a series of concrete blocks referred to as an engineered materials arrestor system
Engineered Materials Arrestor System
An engineered materials arrestor system or engineered materials arresting system is a bed of engineered materials built at the end of a runway. Engineered materials are defined in FAA Advisory Circular No 150/5220-22A as "high energy absorbing materials of selected strength, which will reliably...

 is used. These materials are used to catch the landing gear of an aircraft and slow it via rolling resistance and friction. Aircraft are stopped by the transfer of energy required to crush the blocks.

Components

The major systems that make up typical arresting gear are the hook cable or pendants, purchase cables or tapes, sheaves, and engines.

Cross deck pendant

Also known as arresting cables or wires, cross deck pendants are flexible steel cables which are spanned across the landing area to be engaged by the arresting hook
Tailhook
A tailhook, also arresting hook or arrester hook, is a device attached to the empennage of some military fixed wing aircraft...

 of an incoming aircraft. On aircraft carriers there are either three or four cables, numbered 1-4 from aft to forward. Pendants are made of 1 inch (25 mm), 1-1/4 (32 mm) inch or 1-3/8 inch (35mm) diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

 wire rope. Each wire rope is made up of numerous strands twisted about an oiled hemp
Hemp
Hemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...

 center core, which provides a "cushion" for each strand and also supplies cable lubrication. The cable ends are equipped with terminal couplings designed for quick detachment during replacement and are able to be rapidly detached and replaced (in about 2-3 minutes on aircraft carriers). On U.S. carriers, the arresting cables are removed and replaced after each 100 arrested landings. Individual cables are often removed and left "stripped" in order to perform maintenance on other components of the arresting gear during aircraft recoveries (using other, on line, systems). Wire supports raise the deck pendants several inches so that they may be picked up by the tailhook of a landing aircraft. The wire supports on carriers are merely curved steel leaf springs that can flex to allow an aircraft to taxi over the installed deck pendant. On land based systems, "donut" shaped rubber supports raise the cable off the runway surface a minimum of 2 inches (51 mm).

Purchase cables or tapes

The purchase cable is a wire rope that looks very similar to the arresting cable. They are much longer, however, and are not designed to be easily removed. There are two purchase cables per arresting cable, and they connect to each end of the arresting wire. Purchase cables connect the arresting wire to the arresting gear engines and "pay out" as the arresting wire is engaged by the aircraft. As an incoming aircraft engages the deck pendant, the purchase cable transmits the force of the landing aircraft from the deck gear to the arresting engine. On land based systems, heavy nylon tapes are used in place of purchase cables, but they serve the same function.

Sheaves

Purchase cables or tapes run through sheaves in the flight deck or alongside of the runway to the arresting engines. Damper sheaves act as hydraulic shock absorbers that provide for the increased landing speeds.

Arresting gear engines

Each pendant has its own engine systems that absorb and dispel the energies developed when a landing aircraft is arrested. Carriers use hydro-pneumatic systems, wherein oil fluid is forced out of a cylinder by a ram (that is connected to the purchase cable) through a control valve. A major development in arresting gear was the constant runout control valve, which controls the fluid flow from the engine cylinder to the accumulator and is designed to stop all aircraft with the same amount of runout regardless of the weight and speed. The aircraft's weight is set by the arresting gear engine operator. The operator is given the weight of the aircraft by the air officer in Primary Flight Control. The operator then sets the Constant Runout Control Valve to the appropriate weight setting for that aircraft. The pressure setting for the arresting gear engine remains at a constant pressure of about 400 pounds per square inch. The constant runout valve (CROV) stops the aircraft (as opposed to hydraulic pressure). Permanent and expeditionary land based systems usually consist of two arresting engines located on either side of the runway. The arresting engines apply braking force to reels holding the purchase tapes, which in turn slow the aircraft and bring it to a stop.

The two most common methods used by land based arresting engines to apply the braking force are the rotary friction brake and the rotary hydraulic (water twister) systems. The rotary friction brake is simply a hydraulic pump coupled to the reel which applies a graduated pressure to multi-disc brakes mounted on the reel. The rotary hydraulic system is a turbine inside a water/glycol filled housing coupled to the reel. The turbulence generated in the water/glycol mixture by the turbine during the arrestment provides the resistance to slow the reel and stop the aircraft. Once the aircraft is released from the cable, the tapes and cable are retracted by an internal combustion engine or electric motor installed on the arresting engine.

Spray-type arrest gear

In the early 1960s, the British developed a spray-type arrest gear system for both land and sea use. The engine had hydraulic cylinders that moved through water filled pipe, with a smaller pipe along side that has holes of various size along its length. The Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

claimed that there was no theoretical weight limit, but there was a speed limit.

Excessive runout during an arrestment is a condition known as a "two-block." This name is derived from naval parlance when all the line has been pulled through a pulley system, the two pulley blocks are touching, hence "two blocked". Excessive runout can be caused by improper arresting gear settings, excess aircraft gross weight, excess aircraft engagement speed, or excess airplane thrust applied during the arrestment.

Barricade

The barricade is an emergency recovery system used only when a normal (pendant) arrestment cannot be made. The barricade is normally in a stowed condition and rigged only when required. To rig a barricade, it is stretched across the flight deck between stanchions, which are raised from the flight deck. Rigging the barricade is routinely practiced by U.S. carrier flight deck personnel, and good crews can accomplish the task in under three minutes.

The barricade webbing consists of upper and lower horizontal loading straps joined to each other at the ends. Five vertical engaging straps, spaced 20 feet apart, are connected to each upper and lower load strap. The barricade webbing is raised to a height of approximately 20 feet. The barricade webbing engages the wings of the landing aircraft, wherein energy is transmitted from the barricade webbing through the purchase cable to the arresting engine. Following a barricade arrestment, the webbing and deck cables are discarded and the stanchions are lowered back into their recessed slots. Barricade engagements are rare, as tailhooks are designed to be extremely fail-safe, and an aircraft returning from combat with such severe damage would likely not be able to land.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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