340 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



2. There is no effect on climb due to wind except very near the 

 ground, and there the wind-velocity gradient increases the rate of 

 climb slightly when flying into the wind and decreases it slightly 

 when flying with the wind. 



3. A steady wind has no effect on turning except very near the 

 ground, when the wind-velocity gradient causes a slight tendency to 

 settle when turning away from a headwind and a slight tendency 

 to climb when turning into it. This is most noticeable in strong 

 winds and when flying at a large angle of attack or at minimum power. 



Summing up : A steady wind exercises no measurable effect on air- 

 plane performance at altitude — except, of course, on groundspeed 

 and direction of flight. Very near the ground, however, the effect 

 of wind-velocity gradient can be serious, particularly in the case of 

 a heavily loaded airplane. The danger is increased by a strong 

 tendency on the part of the pilot to pull the nose up or in beyond the 

 most efficient angle of attack. This increases any tendency to settle 

 and may even cause the airplane to stall and spin in. 



In the early and middle 1920's the Jones-Barany revolving chair 

 test was given to all military pilots as a part of their periodic physical 

 examination for flying. Normally this test was given with the pilot's 

 eyes open, and the flight surgeon looked for variations in times and 

 amount of the rhythmic side-to-side movement of the eyes called 

 nystagmus. 



In early 1926, Capt. — later Col. — David A. Myers, an outstanding 

 Air Corps flight surgeon, decided to augment the routine test by giv- 

 ing an additional test consisting of several rotations of the chair with 

 the pilot's eyes closed. After the rate of rotation became steady, a 

 normal pilot, with ej^es closed, could not tell which way he was turn- 

 ing. If the rate of rotation was slowed down and stabilized at a 

 somewhat lower speed, the pilot thought the rotation had been 

 stopped, and when the rotation actually was stopped he thought he 

 was turning in the opposite direction. 



The explanation is that man normally maintains his equilibrium by 

 sight, touch, hearing, muscle, and vestibular sense. Touch and hear- 

 ing are not important in flight orientation. By using the three re- 

 maining senses he can usually ascertain and maintain his position, 

 accurately sense the rate and direction of his motion, and generally 

 orient himself with relation to the earth. Sight is by far the most 

 reliable of these three senses, and when sight is lost, we must get our 

 sense of balance and motion from the muscles and from the fluid 

 movement sensors in the vestibular canals. If an individual is merely 

 displaced, the fluid motions return to zero very rapidly, but if one is 

 rotated, it may take from 5 to 25 seconds for the fluid motions to stop. 

 During this period an individual can experience a false sense of mo- 



