Arresting gear
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Arresting gear is the term used for any system designed to decelerate an aircraft as it lands. They are most commonly used on the flight deck of CATOBAR and STOBAR aircraft carriers, although similar systems can also be found at land-based airfields. The most recognisable form of arresting gear is a series of arrestor cables laid across the runway, although other systems use elastic barriers or slow aircraft via friction.
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[edit] Sea-based systems
The arrestor cable or arrestor wire is the most common form of arresting gear, and is one of the essential components of naval aviation. Arrestor cable systems were first invented by Hugh Robinson and utilized by Eugene Ely on his first landing on a ship - the armored cruiser USS Pennsylvania, on January 18, 1911. These early systems had cables run through pulleys and attached to dead weight, such as sandbags or ship's anchors. More modern arrestor cables were tested on HMS Courageous in June 1931. Henry Fancourt was the first pilot to land using the new system.
On aircraft carriers, the system consists of an oil hydraulic cylinder with two rows of aluminium wire rope sheaves connected to the body of the hydraulic cylinder and two rows of aluminium wire rope sheaves connected to the piston rod of the hydraulic cylinder. These rows are mounted in a head that moves horizontally in a frame. The cylinder is hydraulically connected to a pressure vessel via a special valve. A wire rope is reeved over the sheaves; this rope passes over the deck. Multiple systems (commonly four) are installed on a carrier for safety. When aircraft land, their tailhook catches into one of the wires and pulls on it, with the tenson compressing the hydraulic cylinder and pulling the aircraft to a stop. The amount of tension provided by the system is adjustible; if it is too weak, it will not stop the aircraft before the end of the flight deck, but if it is too strong, it may severely damage the aircraft. Pilots about to land are required to confirm their aircraft type and fuel state, so the cables can be set for the aircraft's landing weight. Aircraft coming in to land on a carrier are at full throttle; if the aircraft fails to catch an arrestor cable or the caught cable breaks, the aircraft needs to have sufficient power to gain lift and "bolter", or go around again.
[edit] Land-based systems
Land-based military airfields operating fighter or trainer aircraft also use arrestor systems, although they are not required for all landings. Instead, they are used for landing aircraft on short or temporary runways, for training naval aviators prior to carrier deployment, 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.
The system usually consists of two sets of gear called arresting engines with one each located on each side of the runway. These engines are interconnected by an arresting cable which is usually attached to a nylon tape which is wound on to a reel on each arresting engine. When the aircraft tailhook engages the cable, the tape reels start to turn. The arresting engines apply the braking force to the reels, 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.
Other methods for absorbing the energy of an aircraft arrestment include cables attached to heavy ship anchor chains and cables attached to bundles of woven textile material.
[edit] Other systems
Elastic nets known as barriers are commonly used as a backup system. These would catch the wings and fuselage of an aircraft and use an arresting engine or other methods such as anchor chains to slow the aircraft down. These systems are normally located in the overrun area of a runway. The development of the angled flight deck has reduced the need for net-based arresting gear on aircraft carriers.
On some land-based airfields, materials such as foam, dirt, mud, or gravel are located in pits at the end of a runway or distributed over the runway surface in an emergency. These materials are used to catch the landing gear or underside of an aircraft and slow it via rolling resistance or friction. At larger airports, a series of concrete blocks referred to as an Engineered Materials Arrestor System is used. Aircraft are stopped by the transfer of energy required to crush the blocks.
[edit] Non-aviation uses
Vehicle Arresting Systems (VAS) use similar technology as aircraft arresting systems. VAS provides point of entry perimeter security, stopping and containing motor vehicles. Applications for this type of system include highway run-off control, rail crossing disaster prevention and entry-denial/control for secure area lockdown and anti-terrorist safeguards.
[edit] External links
- Engineered Arresting Systems Corporation - land-based aircraft arresting gear.
- Successful wheels up landing of F-111C at Royal Australian Air Force base Amberley - Series of photographs depicting a RAAF F-111 landing with land-based arrestor cables following a landing gear failure.
- Guide To Mobile Aircraft Arresting System Installation - United States Air Force
