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Ejector seat

In (mostly military) aircraft, the ejector 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 ejector seat deploys a parachute which descends safely to earth.

While a bungee-assisted escape from an aircraft took place in 1910, the ejector seat as we recognise it today was invented in Germany 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 ejector seats were developed during the war by Heinkel. 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 ejector 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 ejector seats for the crew was the Heinkel He 219 night fighter in 1942.

In late 1944, the Heinkel He 162 featured a new type of ejector 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 gasses 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.

After WW2, 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 24th, 1946, when Bernard Lynch ejected from a Gloster Meteor Mk III. Shortly afterwards, on August 17th, 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 a 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.

The F-104 Starfighter was equipped, uniquely, with a downward firing ejection seat as the T-tail was judged likely to cut the pilot in half. 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 ejector 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 embedded within the perspex of the canopy, which shatters it simultaneously with the firing of the seat.

By December 2003, Martin-Baker ejector seats had saved 7028 lives. The total figure for all types of seat is unknown but must be considerably higher.

The purpose of an ejection seat is pilot survival, not pilot comfort. Many pilots have suffered career-ending injuries while using ejector seats, including crushed vertebra. The pilot typically experiences a G force of about 12 to 14 as he is hurled out of the airplane.

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