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Aviation History
1942
1942 - 0349.PDF
FEBRUARY 12TH, 1942 FLIGHT g 66 €T MEN of the AIR ON PILOTS FLATTENING OUT : AVOIDING THE PHYSIOLOGICAL ILL EFFECTS OF VIOLENT ACCELERATION By F. G. SHEFFIELD ON reflection it would appear somewhat strange that in the development of the art of flying man should have adopted a sitting posture. There would seem to be no natural precedent for this. Birds fly through the air , witf- *the longitudinal axis of ^^iJbody lying in the direc- : tion of flight. Apart from a few freakish exceptions, fish progress in water in the same attitude. Man himself adopts that position when swim ming. Presumably long familiarity with transport in carriages and more recent experience with motor vehicles led to the sitting position being adopted merely from custom and not for any reasoned consideration. Curiously enough, when Leonardo da Vinci, the fifteenth-century Florentine genius, studied the mechanics of bird flight and the pos sibility of human flight he logically assumed the prone position would be utilised. He made models to test his theories, and his sketches and notes on the subject are still in existence. At the beginning of this century, at the time when practical flight had just become possible, the Wright brothers in their earliest gliding experiments adopted the horizontal position. In practice, of course, the sitting position has been en tirely satisfactory for all normal' purposes until recent times. With slow and medium-speed craft operating only with smoothly executed manoeuvres there was no need to call for any change. With the advent of fighters and dive bombers capable.of speeds between 400 and 500 miles per hour and rapid and complicated combined manoeuvres the conditions have entirely changed, and the posture of the pilot has become a question of urgency. In actual fact, the performance of modern military machines has already outstripped the physiological capacity of the normal human structure. fin its essentials the problem is an r^oldone. Pilots in the High-speed Flight of Supermarine seaplanes com peting in the Schneider Cup contests were prone to "blacking-out" when executing close turns. For these con tests and certain aerobatics it was found advantageous to bind the legs and the stomach of the pilot in order to avoid discomfort and nausea. The Effect of Acceleration It should be noted that it is acceleration and not velocity that is liable to cause discomfort or injury to the pilot or crew of an aircraft. A normal man of sound constitution can easily stand an acceleration, in level flight, of 30 metres per second per second, and, providing this rate is maintained smoothly, he could, it is estimated, reach a velocity of 1,620 , kilometres per hour (approximately 1,000 miles per hour) in 15 seconds without ill effects. It is particularly in executing close turns at high speed and pulling out of dives that the most violent accelerations are likely to °ccur. Apart from the physical con dition of the pilot, there are three TACTICAL considerations in modem combat call for higher and still higher speeds from our military aircraft. Present- day machines can travel at more than 400 m.p.h: and dive at 500 m.p.h. or even, it is claimed, at 600 m.p.h. Through the ages the physical structure of man has been evolved to suit much lower speeds of locomotion. Mere velocity does not distress him, but violent acceleration and ultra-rapid change of the direction of motion can injure or even destroy him. Man cannot be redesigned—how can he be trained and adapted to meet these new demands? Can machines be developed in which the improved performance does not stress the pilot so drastically? main factors which determine the effect of acceleration on the human body. These are (1) direction of acceleration, (2) magnitude of the accelera tion, and (3) the period for which the acceleration is sus tained. In the usual sitting position the centrifugal force acts in a direction from the head to the seat. The body presses tighter to the aircraft seat, the limbs feel heavier, the blood more weighty and heart action correspondingly more laboured. The heart is a pumping device and, similar to any mechanical pump, it is more difficult for it to raise blood to the head against the force set up by centrifugal action. '' Blacking-Out' * Minor effects of this character are commonly noted by fliers when spiralling for any considerable period. Vary ing in intensity, symptoms of faintness, dizziness, nausea. 01 even vomiting may be experienced. "Blacking-out" is due to the same cause but of greater magnitude. The human vascular system is very elastic and when subjected to the pressures occasioned by rapid acceleration a large quantity of blood is stored in locally distended veins and arteries, and is thus temporarily withheld from circula tion. As a result, a reduced quantity of oxygen is supplied to the brain and, as a first symptom, vision is affected and then a black-out occurs. If the excessive accelera tion is continued, this is soon followed by a complete loss of consciousness. When the acceleration ceases vision rapidly recovers, but if loss of consciousness has occurred it will persist for several seconds. A simple indication may be given of the work which the heart is called upon to perform in various manoeuvres. Compared with that needed under normal conditions, at a wide turn in,a pas- An imaginative impression of a fighter-dive bomber with the pilot in the prone position. Controls will be on a miniature scale and necessarily servo-as-.isted, either hydraulically or electrically. Lying on an armour plate platform the pilot is enshrouded with an arched casing of armour plate which can, slide to the rear to facilitate entry.
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