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Aviation History
1942
1942 - 0350.PDF
FLIGHT FEBRUARY 12TH, 1942 C" MEN OF THE AIR 90 SECONDS 8 B4- HP _——1— 11 -15 ^ 120-180 SECONDS V/////Y////////////A m 30 60 80 SECONDS 120 ISO 180 90 SECONDS Graphical representation of the enhanced ability of a pilot to withstand violent acceleration as the posture is changed from normal to prone position. To be face downwards appears to be the most practical solution. .senger plane 1$ to if times the energy is required, but ior a close fighting turn or a pull-out from a dive it may •be as much as eight times. What the Average Man Can Withstand Tests have shown that a normal healthy individual occupying the usual sitting position in an aircraft can be subjected to an acceleration of 5 to 6 g for a period of 3 to 4 seconds without ill effects.* Translated into practical operation this would mean that at a speed of 370 miles an hour the radius of a turn should not be less than about 550 yards. Obviously such a limitation is not admissible for modern fighters and dive-bombers. If our vascular system consisted of rigid tubes, such a distention as mentioned earlier could not occur, and circu lation would not be materially affected. This fact, how ever, must not lead to the conclusion that prosperous old City gentlemen who suffer from hardening of the arteries would make ideal fighter pilots. Whilst they may be con stitutionally sound, they do not necessarily possess sound constitutions. In theory it should be possible to minimise the effect of acceleration by supporting the body in a dense fluid sealed in a rigid tank. This idea would not seem capable of prac- * A freely falling body has a constant acceleration, termed "gravity acceleration" and usually indicated by " g." Its value is subject to slight variation in accordance with latitude and height above sea-level. Unless specifically corrected for these factors, the value of "g" is that for London— 32.2ft. /sec* or 32^2 feet per second per second. tical realisation. A step in this direction, however, is indi cated by a recent U.S. patent for a double-walled flying suit that can be filled with air or liquid under pressure to furnish an evenly distributed support for the wearer's body. It could, of course, be suitably equipped with a hood and serve also as a pressure suit for high altitude. The normal individual can withstand a further 0.5 to 1 % for the same period if the legs and stomach are bandaged. Further improvement is obtained if a substantial meal is taken some little time before experiencing the accelera tion. This arises from the fact that digestion automatic ally induces an accumulation of blood in the intestinal region, and thus avoids any large-scale displacements of the blood stream under the effects of acceleration. The inhaling of a C02/02 mixture is also of assistance, as it facilitates the circulation of blood in the brain. Advantageous Postures '-4£*rf By lowering the seat, raising the legs, bending the body forward to a crouched position, and making use of all the minor aids mentioned earlier, it is possible for the pilot to withstand acceleration of the order of 7 to 8 g. for a period of 3 to 4 seconds. To achieve any marked improve ment, however, it is necessary for the pilot to lie in a prone position. In this way centrifugal force at the turn or pull-out is exerted approximately at right angles to the line of the main blood vessels instead of being substantially parallel, as is the case when the pilot is sitting normally. Relative to the direction of this force, the height of the head above the heart is reduced, the displacement of blood is less sudden, and the ill effects much less marked. Labora tory researches, confirmed by practical experience, show that it is possible for accelerations of 11 to 15 g. to be with stood for 2 to 3 minutes with the pilot lying face down wards. A slight improvement to the extent of 1 g. for the same period is possible if the pilot reclines on his back. Under carefully controlled conditions it is possible for these periods to be somewhat extended. - Although to lie on the back is advantageous as regards acceleration, it is not so conducive to good breathing. In this respect it was found preferable to lie face downwards with the chest supported on the parachute pack. It is pre sumed that the action of the diaphragm is better in this position. Thus, to lie face downwards in a recumbent position would appear to offer the best compromise solution for acceleration, breathing, and also for facility of vision. Experiment showed that neither back nor face prone posi tion was more tiring to the pilot than the sitting posturf**> Specialised Training By specially designed courses of physical training and regular practice, much can be done to accustom the heart and the vascular system to accelerations which would nor mally cause distress or even hasmorrhage. In Russia special sequences of exercises have been developed and special training equipment produced for this purpose. One device known as the '' Triplex Trainer'' consists of three rings revolving one within the other in different planes. The pupil rotates the inner ring by continually changing his centre of mass. Meanwhile the medial and outer rings are set in motion, and thus the pupil is subjected to most complicated conditions of acceleration. So far this survey of the problem has resolved itself into an examination of the limitations which the human struc ture imposes upon the performance of aircraft. No useful purpose is served by producing high performance machines with large load factors if the crews are physically incapable of withstanding the effects of such a per formance. There is, however, a diametrically opposed, viewpoint to be considered. German researches and experiments are claimed to show that the human body can stand very high accelerations if the period of applica tion is strictly limited to less than one second. As high as 26 g. is feasible if maintained for no longer than one- fifth of a second. No present day machine could be pulled out of a dive in so short a time, and there is reason to
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