276 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
which the heart has to raise the blood to his head can be reduced and 
the loss of it to his feet is again less if the feet are high. Another 
method of lessening the effect of this force which may be mentioned 
is to place the pilot in the prone position. The heart and head are 
then nearly at the same height and a man in this position can withstand 
some 10g, but this posture is a very fatiguing and inconvenient one 
for the control of an aircraft, though it is reminiscent of the very 
earliest airplanes in which the pilot frequently lay prone. The effect 
of posture on blacking-out is shown diagrammatically in figure 2. 
F 
——_—_ {tint or Lia! POS, Ss) tein me 
% 
% 
ACCELERATION ACTING UPTO 
3-4 SECONDS 
Ss 
3-4 SECONDS 
> 
——____—____—— NOI 1WY31399v JO NOILDIVIG 
UPTO 3 MINUTES 
u 
4 6 10 
UPTO 3 MINUTES 
4 6 6 10 a2 i 6 
EFFECT ON POSTURE ON BLACKING OUT 
Ficure 2.—Effect of posture on the tolerance of acceleration. (Data from Ruff.) 
The engineer has produced machines that are so strong and 
maneuverable that they can subject the pilot to forces beyond his 
tolerance and the useful limit in design for maneuverability at high 
speed changes from being an engineering limit to being a human 
limit. It would be useless for the aircraft designer to produce an 
airplane so strong and maneuverable that it could turn with a 
centrifugal acceleration of 20g because the pilot would not be con- 
scious to control it under these conditions; the ability to out-turn the 
enemy has an important tactical advantage in dog fighting, but to 
achieve this it is now necessary to look to the man rather than the 
machine. Figure 3 illustrates how the human limit makes it impos- 
