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80     U. S. CIVIL AERONAUTICS AUTHORITY

Having already been initiated into stalls (during the confidence maneuvers) and in the use of the senses in the same manner as they are to be used in stalls (during glides and gliding turns), the student should have a good background on which to base his perfection of the use of the senses by practicing stalls. However, the instructor should again analyze and explain their use to him.
Vision is useful in a stall in checking the attitude of the airplane. However, this sense can be relied upon only when the airplane is in an unusual attitude; usually when the nose is being carried higher than the power and speed would normally warrant. The airplane can also be stalled from a normal attitude in which case vision cannot aid in sensing the stall.
Hearing is very important, since the pitch and intensity of the sounds incident to flight decrease as speed decreases. In the case of engine noises when power is being used, the loss of r. p. m. is particularly noticeable. The lessening of the noise made by the air passing over wires, struts, etc., is also noticeable, and when the stall is almost complete, particularly in some airplanes, vibration and its incident noises greatly increase.
Kinesthesia, or deep muscle, tendon, and joint sensing, is probably the most important and the best indicator to the trained and experienced pilot. If this sensitivity is properly developed it will warn of the slightest decrease in speed and progressively increase the intensity of its warning as speed decreases. This sensitivity includes not only the sensing of speed loss, but also the relaxation of control resistances to the pilot's pressures and the sensations caused by the aircraft in tending to mush or settle out from under him.
As speed is reduced, the live resistance of the controls becomes progressively less and less. The pressures exerted on the controls become movements of the controls and the lag between the movements of the controls and responses of the airplane becomes greater and greater, until in a complete stall all controls can be moved with almost no resistance throughout their range without visible or immediate effect on the attitude of the airplane.
Long before this point is reached the sensation of "settling" can be felt, and upon completion of the stall a sensation similar to the initial drop of a roller coaster is experienced.
It is apparent, then, that all senses are useful, but that the last two are probably more important and, of their very nature, require much more training before trained reactions to their stimuli becomes accurate, rapid, and subconscious.
All stalls require either altitude or power with which to gain speed for recovery, and both if one or the other is limited, which is usually the case. The more severe or complete the stall the more altitude or power, or both, is necessary for recovery. Therefore, since the longer it takes to sense the approach of a stall the more severe and complete the stall is likely to be, it is necessary that the student be taken to a safe altitude before their practice is started and that the first few stalls practiced be incomplete until the senses are developed to appreciate the rapidity of approach and the degree of stall likely to ensue as a result. This method will also tend to teach the student the relative nearness of a complete stall at operations near the critical speed.