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Volume 68 November 1975
721
United Services Section President Sir Francis Avery Jones CBE FRCP Meeting 6 March 1975
Problems of Ejection from Aircraft Restraint Harness Design Squadron Leader D C Reader (Royal Air Force Institute of Aviation Medicine, Farnborough, Hampshire) said that to ensure that ejection seats and occupants cleared all parts of the aircraft when ejecting at high speeds, considerable forces were required, which must be lower than the limits of human tolerance yet be sufficient to guarantee a safe ejection. An outline was given of the factors that govern human tolerance to brief acceleration and the levels of human tolerance in relation to ejection accelerations. Tolerance to the forces of ejection could be increased by efficient restraint, for which a harness was usually provided that gave restraint during flight and ejection and also functioned as a parachute harness. The features of restraint harness design that increased tolerance to acceleration were described and some methods of testing explained. The advantages and disadvantages of various types of ejection seat harness were discussed and future developments outlined.
Sources of Ejection Injury Group Captain A J Barwood (Royal Air Force Institute of Aviation Medicine, Farnborough, Hampshire) said that the modern ejection escape system could recover aircrew from a crippled aircraft from zero forward speed with a high sink rate close to ground level up to 650 knots (335 m s-1) at low level. The acceleration applied to the ejection seat to accomplish this, the exposure of the crew to high air blast, and the need to achieve full parachute deployment in the shortest possible time combined to make ejection a traumatic experience. The sources of injury were directly related to the mechanics of the ejection system.
The telescopic ejection gun was fired by pulling a handle on the front of the seat pan, or an upper handle which pulled a face blind over the head, or by another crew member without warning. Firing the gun first unlocked the seat, allowing it to separate under gun thrust from the aircraft. As the gun extended, secondary cartridges were exploded to sustain the thrust of the gun, which extended 72 inches (1828.8 mm) in 0.2 seconds. To achieve system capability, gun thrust had always been near the maximum for human tolerance; the combined effect of near maximal thrust, an incorrect posture and imperfect restraint could produce minor wedge fractures of the lower spine. Contouring of the seat back and base ensured the correct posture on the hard and non-compressible surface, and if the posture was maintained by a correctly adjusted harness, spinal injury should not occur. Some reduction of gun thrust had been achieved by the application of a rocket pack to modern ejection seats.
Injury from contact with parts of the aircraft, the cockpit canopy or its debris, loose items from a cockpit or items from another ejection system could occur but was largely eliminated by design and by sequencing. The system included clearance of the ejection path by jettison of the cockpit canopy, but the time factor was sometimes so critical that the canopy had to be broken by explosive means. Injury from canopy penetration might be produced by contact with structure or debris, or even spatter from the explosive unless protection was adequate. Air blast became a major factor at speeds of over 300 knots (155 m s-1), with an increasing risk of limb flailing. Leg restraint was used on all ejection seats and arm restraint was provided on the latest types. The head was protected from wind loads by the helmet and face mask, but
Volume 68 November 1975
721
United Services Section President Sir Francis Avery Jones CBE FRCP Meeting 6 March 1975
Problems of Ejection from Aircraft Restraint Harness Design Squadron Leader D C Reader (Royal Air Force Institute of Aviation Medicine, Farnborough, Hampshire) said that to ensure that ejection seats and occupants cleared all parts of the aircraft when ejecting at high speeds, considerable forces were required, which must be lower than the limits of human tolerance yet be sufficient to guarantee a safe ejection. An outline was given of the factors that govern human tolerance to brief acceleration and the levels of human tolerance in relation to ejection accelerations. Tolerance to the forces of ejection could be increased by efficient restraint, for which a harness was usually provided that gave restraint during flight and ejection and also functioned as a parachute harness. The features of restraint harness design that increased tolerance to acceleration were described and some methods of testing explained. The advantages and disadvantages of various types of ejection seat harness were discussed and future developments outlined.
Sources of Ejection Injury Group Captain A J Barwood (Royal Air Force Institute of Aviation Medicine, Farnborough, Hampshire) said that the modern ejection escape system could recover aircrew from a crippled aircraft from zero forward speed with a high sink rate close to ground level up to 650 knots (335 m s-1) at low level. The acceleration applied to the ejection seat to accomplish this, the exposure of the crew to high air blast, and the need to achieve full parachute deployment in the shortest possible time combined to make ejection a traumatic experience. The sources of injury were directly related to the mechanics of the ejection system.
The telescopic ejection gun was fired by pulling a handle on the front of the seat pan, or an upper handle which pulled a face blind over the head, or by another crew member without warning. Firing the gun first unlocked the seat, allowing it to separate under gun thrust from the aircraft. As the gun extended, secondary cartridges were exploded to sustain the thrust of the gun, which extended 72 inches (1828.8 mm) in 0.2 seconds. To achieve system capability, gun thrust had always been near the maximum for human tolerance; the combined effect of near maximal thrust, an incorrect posture and imperfect restraint could produce minor wedge fractures of the lower spine. Contouring of the seat back and base ensured the correct posture on the hard and non-compressible surface, and if the posture was maintained by a correctly adjusted harness, spinal injury should not occur. Some reduction of gun thrust had been achieved by the application of a rocket pack to modern ejection seats.
Injury from contact with parts of the aircraft, the cockpit canopy or its debris, loose items from a cockpit or items from another ejection system could occur but was largely eliminated by design and by sequencing. The system included clearance of the ejection path by jettison of the cockpit canopy, but the time factor was sometimes so critical that the canopy had to be broken by explosive means. Injury from canopy penetration might be produced by contact with structure or debris, or even spatter from the explosive unless protection was adequate. Air blast became a major factor at speeds of over 300 knots (155 m s-1), with an increasing risk of limb flailing. Leg restraint was used on all ejection seats and arm restraint was provided on the latest types. The head was protected from wind loads by the helmet and face mask, but
