LIMITS TO HUMAN FLIGHT — WIMPERIS 587 



to 12 times the gravitational acceleration, commonly known as 12 g. 

 It fortunately happens, however, that the human body shows warning 

 signs of distress long before thefairplane. When, for instance, an 

 acceleration force of 5 g. is encountered, the body is affected in the 

 same way as it would be were the blood suddenly increased to five 

 times its normal specific gravity. The effect, naturally, is that the 

 blood seeks a lower level, and by denuding the brain of its normal 

 share, causes the failure of visual faculties known as "blacking out." 

 This produces no permanent effect, but for the time being the pilot sees 

 nothing, and even though he still maintains control of the machine, it 

 is a control unguided by any visual information from either the instru- 

 ment board or the external world. Even higher accelerations than 

 this have been endured by pilots, though not with any degree of hap- 

 piness. I have read of an American experience of 11 g. requiring sub- 

 sequent hospital treatment, and of 15 g. leading to a complete crash, 

 though in the latter case it was difficult to distinguish between the 

 results of human failure and the failure of the airplane structure. 

 Nature does then impose a definite limit to the safe rate of pulling out 

 from a dive and that limit is a physiological one and difficult to modify 

 by human ingenuity. One alternative is to await the long process of 

 normal human evolution and another to induce pilots to adopt the 

 prone position when flying — the one change might take as long to 

 bring about as the other. 



It will be natural to ask what happens to the human frame when the 

 acceleration comes in the opposite direction, that is toward one's 

 head instead of toward one's feet. This is what happens in the 

 maneuver known as "the bunt," and there then arises a suffusion of 

 the brain by more than its normal supply of blood, leading to what is 

 known as the "redding out" of vision. This maneuver is, however, 

 always a dangerous one and on it authority frowns. 



We have lastly to consider what I mentioned first, the effect on 

 maneuver of the steadily rising air speeds of modern aircraft. The 

 relationship is a simple one. The measure of the acceleration which 

 has so marked a physiological effect is proportional to the product 

 of the angular rate of turn by the linear velocity. If, therefore, the 

 linear velocity be doubled, as has indeed happened over a com- 

 paratively short range of years in typical aircraft, the rate of maneuver 

 must be halved if the safe acceleration limit is not to be passed. It 

 follows from this that as machines become more and more speedy, 

 so they must become less and less maneuverable. The effect of this 

 on the dog fighting of the past is outside the scope of this address, 

 though it is an interesting subject on which to speculate. 



Let the speeds of aircraft increase as they may, the speed of nerve 

 impulses in the human pilot will remain unchanged, namely, about 

 100 meters per second. Moreover, as in other means of signalling, 



