HUMAN PROBLEMS IN AVIATION — BRONK 407 



prolonged for some seconds, loss of consciousness will follow. In less 

 severe maneuvers there may be no obvious symptoms, but the often- 

 repeated reduction of cerebral blood flow causes fatigue, irritability, 

 and inefficiency. To help the human body meet these stresses imposed 

 by the swift combat planes, belts and suits have been devised which aid 

 the heart, by preventing the pooling of blood in the lower parts of the 

 body. Without such devices the plane is but a futile object, unsuitable 

 for use. A pilot may execute maneuvers that cause repeated black-out 

 with no evidence of permanent damage, but he is a relatively ineffective 

 fighter under those circumstances. 



Aircraft maneuvers which are quite inadequate to produce such 

 cerebral effects exert forces on the human body which make Unreliable 

 the normal sensory mechanisms concerned with posture and position. 

 The force which holds the plane in a banked turn, or in a loop, also 

 acts upon the gravity receptors, the tension receptors in the muscles 

 and the tendons, and the sensory mechanisms in the semicircular canals 

 which detect rotation. These sensory pathways are then stimulated 

 by the resultant of this machine-exerted force and that of the earth's 

 gravitational field. Because the sensory mechanism is unable to re- 

 solve these two components of the stimulating force, a true sense of 

 orientation in space is lost. The false sense of position must then be 

 corrected by visual reference to the earth. And so, when clouds or 

 darkness interfere, the pilot becomes incapable of maintaining a de- 

 sired course relative to the surface of the earth. "The night is come; 

 be then the night obeyed" was accordingly the rule of aerial combat 

 in the First World War, as it was for the foot-soldier in the Homeric 

 battle between Hector and Ajax. 



Finally, however, the causes of man's inaptitude for directed flight 

 without visual contact with the earth were recognized. It was then 

 possible to devise instrumental aids to the senses, and flight through 

 clouds and darkness became safe and commonplace. Once again the 

 physiological characteristics of the flier had limited his full utilization 

 of the aircraft; once again medical scientists defined the need, and 

 physicists provided instruments such as the artificial horizon, the 

 bank-and-turn indicator, and the gyroscopic compass to supplement 

 the senses. And so, the scope of human flight was once again increased. 

 But, as we shall see, still more human problems were thus created. 



The development of instruments that make possible flight by night 

 has greatly extended the tactics and strategy of aerial war, for it 

 enables the airman to utilize nature's most effective form of camouflage. 

 Unfortunately, this advantage is also available to the enemy, and this, 

 then, requires a keen ability to see through darkness the dim form of 

 an enemy aircraft. Physicists are already at work extending the 

 range of night vision through radar, but in the meantime men fly and 

 fight with the aid of their natural vision. 



