Ejector seat
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In (mostly military) aircraft, the ejection seat is a system designed to rescue the pilot or other crew in the event of the aircraft becoming unflyable. In most designs, the seat is propelled out of the aircraft by a rocket motor, carrying the pilot with it. The concept of an ejectable escape capsule has also been tried. Once clear of the aircraft, the ejection seat deploys a parachute, and descends back safely to earth.
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History
While a bungee-assisted escape from an aircraft took place in 1910, the ejection seat as we recognise it today was invented in Germany in 1938 and perfected during World War II. Prior to this, the only means of escape from an incapacitated aircraft was to jump clear, and in many cases this was difficult due to injury, the difficulty of egress from a confined space, the airflow past the aircraft and other factors.
The first ejection seats were developed independently during the second world war by Heinkel and SAAB. Early models were powered by compressed air and the first aircraft to be fitted with such a system was the Heinkel He 280 prototype jet fighter in 1941. One of the He 280 test pilots, Helmut Schenk, became the first person to escape from a stricken aircraft with an ejection seat on January 13, 1942 after his control surfaces iced up and became inoperable. This aircraft never reached production status, and the first operational type to provide ejection seats for the crew was the Heinkel He 219 Uhu night fighter in 1942.
In Sweden a version using compressed air was tested in 1941. A gunpowder ejection seat was developed by Bofors tested in 1943 for the Saab 21. The first test in the air was on a Saab 17 on 27 February 1944. [1]
In late 1944, the Heinkel He 162 featured a new type of ejection seat, this time fired by an explosive cartridge. In this system the seat rode on wheels set between two pipes running up the back of the cockpit. When lowered into position, caps at the top of the seat fitted over the pipes to close them. Cartridges, basically identical to shotgun shells, were placed in the bottom of the pipes, facing upward. When fired the gases would fill the pipes, "popping" the caps off the end and thereby forcing the seat to ride up the pipes on its wheels, and out of the aircraft. By wars end the Do-335 Pfeil, Me-262 Schwalbe and Me-163 Komet also were fitted with ejection seats.
After World War 2, the need for such systems became pressing, as aircraft speeds were getting ever higher, and it was not long before the sound barrier was broken. Manual escape at such speeds would be impossible. The United States Army Air Corps experimented with downward-ejecting systems operated by a spring, but it was the work of the British company Martin-Baker that was to prove crucial.
The first live flight test of the M-B system took place on July 24, 1946, when Bernard Lynch ejected from a Gloster Meteor Mk III. Shortly afterwards, on August 17, 1946, 1st Sgt. Larry Lambert was the first live US ejectee. M-B ejector seats were fitted to prototype and production aircraft from the late 1940s, and the first emergency use of a Martin-Baker seat occurred in 1949 while testing the Armstrong-Whitworth AW.52 Flying Wing.
Early seats used a solid propellant charge to drive the seat out, by exploding the charge inside a telescoping tube attached to the seat. Effectively the seat was fired from the aircraft like a bullet from a gun. As jet speeds increased still further, this method proved inadequate to get the pilot sufficiently clear of the airframe, so experiments with rocket propulsion began. The F-102 Delta Dagger was the first aircraft to be fitted with a rocket propelled seat, in 1958. MB developed a similar design, using multiple rocket units feeding a single nozzle. This had the advantage of being able to eject the pilot to a safe height even if the aircraft itself was on or very near the ground.
In the early 1960s, deployment began of rocket-powered ejection seats designed for bailout at supersonic speeds, in such planes as the F-106 Delta Dart. Six pilots have ejected at speeds exceeding 700 knots (805mph) and the highest altitude a M-B seat was deployed at was 57,000ft (from a Canberra in 1958). It has been rumoured but not confirmed that an SR-71 pilot ejected at Mach 3 at an altitude of 80,000ft. Despite these records, most ejections occur at fairly low speeds and at fairly low altitudes.
Pilot safety
The purpose of an ejection seat is pilot survival, not pilot comfort. Many pilots have suffered career-ending injuries while using ejection seats, including crushed vertebrae. The pilot typically experiences an acceleration of about 12 to 14 g (120 to 140 m/s²). Western seats usually impose lighter loads on the pilots; ex-Soviet technology often goes up to 20-22 g. Career-ending injuries are quite common, partly because eastern military pilots usually continue to fly into their late-40s or early-50s, while most western jet jockeys quit in their late-30's to pursue civilian life.
By December 2003, Martin-Baker ejection seats had saved 7028 lives. The total figure for all types of ejector seats is unknown, but must be considerably higher.
Non-standard ejection systems
The F-104 Starfighter was equipped, uniquely, with a downward firing ejection seat due to the hazard of the T-tail. In order to make this work, the pilot was equipped with "spurs" which were attached to cables that would pull the legs inwards so the pilot could be ejected. Note that such a system is of no use on or near the ground. Aircraft designed for low-level usage sometimes will have ejection seats which fire through the plastic of the canopy, as waiting for the canopy to be ejected is too slow. Many aircraft types (e.g. BAe Hawk) have an explosive cord (MDC - Miniature Detonation Cord) embedded within the perspex of the canopy, which shatters it simultaneously with the firing of the seat. Soviet Yak-38 VTOL naval fighter planes were equipped with automatically activated ejection seats, mandated by the notorious unreliability of their vertical lifting powerplants.
Some aircraft designs, such as the General Dynamics F-111, do not have individual ejection seats, but instead, the entire section of the airframe containing the crew can be ejected as a single capsule. In this system, very powerful rockets are used, and multiple large parachutes are used to bring the capsule down, in a manner very similar to the Launch Escape System of the Apollo spacecraft. On landing, an airbag system is used to cushion the landing, and this also acts as a flotation device if the capsule lands in water.
Ejection seats in other aircraft
The Kamov Ka-50 was the first helicopter to be fitted with an ejection seat. The system is very similar to that of a conventional fixed-wing aircraft; the main rotor is equipped with explosive bolts and is designed to disintegrate moments before the seat rocket is fired.
Controversially, the US space shuttle is not fitted with ejection seats nor an escape capsule system of any kind. (However the first four flights of the first shuttle, Columbia were with a crew of two, and the pilot and commander both had ejection seats on these flights. When the crew was increased, the seats were disabled, as having the pilot and commander eject while the rest of the crew died was not an option even considered)
The Soviet's shuttle "Buran" was planned to be fitted with K-36RB (K-36M-11F35) seats, but the first, unmanned, flight in 1988, on which the crew cabin was not yet installed, would be the only one.
The only spacecraft ever flown with installed ejection seats are the Soviet Vostok and American Gemini series. During the Vostok program, all the returning cosmonauts would eject as their capsule descended under parachutes at about 7,000 m (23,000 ft). This fact was kept secret for many years as the FAI rules at the time required that a pilot must land with the spacecraft to be considered an official spaceflight for the FAI record books.
Passenger planes are unlikely candidates to receive ejection technology any time soon. The weight, complexity and economic requirements prohibit fitting jetliners with seat or capsule based ejectors and the benefits are not obvious, because most accidents happen during take-off or landing. However, some ultralight and single-engine general aviation aircraft have been refitted with ballistically deployed parachutes recently. These canisterized packages support and lower the entire airframe to earth and thus could be considered an extreme capsule-based ejection system.
External links
fr:siège éjectable he:כסא מפלט it:Seggiolino eiettabile nl:Schietstoel ja:射出座席 fi:Heittoistuin