A fast jet can move rapidly on ground, taking off into the medium of air where it can be manoeuvered in flight by the aerodynamic forces generated by the thrust of its engine and manoeuvrability by swift-responding control surfaces. Such movements of the aircraft affect its occupants, the aircrew (pilots and weapons system operators) due to the magnitude and rapidity of changes in the position and attitude of the aircraft, in turn, compromising the human performance capability in the unnatural environment of military or aerobatic flying.
The effects of acceleration forces on human body are the result of the inertial forces acting on a pilot. An understanding of human tolerance limits to different types of acceleration is important to protect and train pilots to perform optimally for mission accomplishment under debilitating and sustainable acceleration forces of high performance aircraft.
Acceleration is the rate of change of velocity. Therefore any change in either the magnitude of speed or the direction of motion results in acceleration. It is of the following types:-
- Linear acceleration: Change in magnitude of speed only, e.g. take-off, landing, ejection, parachute opening shock.
- Radial acceleration: Change in direction without any change in magnitude of speed; e.g. loop, pulling out of a dive.
- Angular acceleration: Change in both the direction and magnitude of velocity: e.g. spin, spiral.
As per the duration of acceleration, there are the following types of acceleration:-
- Short duration: 0.5 second or less; e.g. crash landing, impact.
- Intermediate duration: 0.5 – 2 sec.; e.g. ejection, parachute opening, assisted take-off, engaging arrester barrier, deck landing
- Long duration: more than 2 sec, which may last up to several minutes; e.g. aerial combat manoeuvres, space launch and re-entry.
Human tolerance to short duration acceleration is determined by the structural strength of the body, where as the physiological changes set the limit for the long duration acceleration.
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1. Ernsting’s Aviation Medicine. Rainford DJ, Gradwell DP (Editors). 4th Edition. Hodder Arnold, London 2006.
2. Fundamentals of Aerospace Medicine. DeHart RL, Davis JR (Editors). 3rd Edition. Lippincott, Williams & Wilkins, Philadelphia 2002.
Acknowledgement. Image courtesy Wikimedia Commons