Toward the end of World War II, emergency parachute escapes from military aircraft were becoming increasingly difficult, and the introduction of jet-powered aircraft, with their vastly increased speed, virtually eliminated the possibility of a successful "over the side" bailout.
In 1944, James Martin, an aeronautical engineer, was invited by the Ministry of Aircraft Production in Britain to investigate the practicability of providing fighter aircraft with a means of assisted escape for the pilot in an emergency.
After investigating alternative schemes, it soon became apparent that this goal could be best achieved by forced ejection of the pilot’s seat, with the pilot sitting in it, and that the most effective way of forcing ejection would be by an explosive charge. After ejection, the pilot would fall away from the seat and open a parachute by pulling a rip cord in the usual way. This solution also fitted in with the requirement of the British Air Staff at that time that any ejection system "utilize existing safety equipment."
Operation
When an ejection seat is operated in an emergency, the seat, complete with the occupant, carrying a parachute and a pack of survival aids, is ejected from the aircraft by an ejection gun. The ejection gun is secured to the aircraft vertically behind the back of the seat and is powerful enough to hurl the seat well clear of the aircraft even at high speed.
Some seats are fitted with a rocket motor underneath the seat in addition to the ejection gun to increase the height attained by the seat. The rocket is fired as the seat leaves the aircraft, and the combined force of the gun and the rocket will propel the seat and occupant to a height of about 300 ft. (91 m), which is high enough to allow a parachute to open fully, even if the ejection is made from ground level with the aircraft stationary. This feature is a decided asset when installed in modern vertical takeoff and short takeoff aircraft.
To commence ejection, the pilot pulls a handle located between the knees or pulls a screen down over his or her face, starting the ejection sequence while also protecting the face from the air blast. This action jettisons or fractures the cockpit canopy and fires the primary cartridge in the ejection gun, which unlocks the seat and ejects it from the aircraft. If a rocket motor is fitted, it is fired as the ejection gun tubes separate, thus continuing the thrust imparted by the ejection gun.
After the seat has left the aircraft, a drogue (small parachute) attached to the top of the seat is deployed. To ensure quick and positive deployment of the drogue, it is pulled out of its container at the top of the seat with some force by a heavy bullet fired from a drogue gun. The object of the drogue is to stabilize the seat and slow it down to a speed at which the occupant’s parachute can be opened without fear of its bursting.
When the drogue has slowed the seat sufficiently, a barostatically controlled (pressure-sensitive) time release unit releases the drogue from the top of the seat, transferring its pull to the canopy of the occupant’s parachute, pulling it out of its pack. Simultaneously, the time-release unit releases the occupant’s safety harness from the seat, and the occupant is pulled clear by the opening parachute to make a normal parachute descent while the seat falls free without causing the pilot any obstruction.
Should the ejection take place above 10,000 ft. (3,048 m), the action of the time-release unit is delayed by the barostat control, which responds to atmospheric pressure in a similar way to an aneroid altimeter or barometer (atmospheric pressure falls as the altitude increases). By delaying the opening of the main parachute until this height, the seat and its occupant, stabilized by the drogue, descend quickly through the cold, rare-fied upper atmosphere. The seat incorporates a built-in oxygen supply for the occupant to breathe, which is turned on automatically during ejection. This entire sequence is automatically controlled from the time the pilot operates the seat until landing by parachute, but in the unlikely event of the mechanism failing, the pilot can intervene and open the parachute by a manual rip cord.
