HUMAN LIMITS IN FLIGHT? 
By Bryan H. C. MarrHews, C. B. E., M. A., Sc. D., F. R. S. 
Head of the R. A. F. Physiological Laboratory, Consultant in Physiology 
to the R. A. F. 
[With 3 plates] 
A modern aircraft will climb in a few minutes to heights at which 
the air is so thin that it will no longer support life. It can turn and 
maneuver so fast that the pilot may easily be rendered unconscious 
from the mechanical forces which it imposes on his body, and in an 
aircraft which is moving rapidly in three planes of space the pilot 
can be subjected to stresses beyond the limits which the human body 
can stand. 
The adaptation of which the human body is capable to new sur- 
roundings and conditions can play a considerable part in fitting man 
to these new conditions; for example, airsickness which many suffer 
on first flying in rough air or doing aerobatics, in most people soon 
passes off and they become adapted to motions which at first perplex 
and incapacitate them, though a few never become completely adapted. 
But there are several stresses placed on man in aircraft that cannot be 
met by any unconscious adaptation, which require equipment specially 
designed to meet them. Some of the necessities are obvious, such as 
windscreens to protect the man from the great wind pressures at 
high speed and a heat supply from the engine or special clothing to 
keep him warm in the Arctic cold of the stratosphere. His senses must 
be extended by a set of blind-flying instruments so that he may know 
his altitude and movement in space when in clouds or at night. He 
must learn to believe the instruments against his senses for these are 
no longer a reliable guide when he may be moving at varying speeds 
in any direction, in fact they will often be wrong. The human limit 
of visual range by day and especially by night is of paramount impor- 
tance in flying. 
But beside the stresses from wind pressure, cold, vibration, and 
noise, the pilot’s body must also be protected from other less obvious 
stresses and here I propose to deal particularly with the two greatest 
1 Reprinted by permission from the Proceedings of the Royal Institution of Great 
Britain, vol. 32, pt. 3, 1943. 
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