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36   U. S. CIVIL AERONAUTICS AUTHORITY

students is the inability to maintain a constant degree of bank for any appreciable period, which is probably due to lack of understanding of the "over banking tendency" when turning and lack of automatic compensation for it.

As vision is the first sense through which the student obtains perception of the angle of bank, some means of visually recognizing the approximate degree of bank must be used. As an aid to diverting the student's attention from the nose, this reference point should not be on the nose.  The most natural and convenient reference is the leading edge of the upper wing, since it makes a long, straight line and its angle with the horizon can be readily and easily recognized and estimated. This, of course, should be the low wing in the bank.

In gentle turns the tip of the upper wing which is lowered will apparently rest on the horizon.

In medium turns the tip will be below the horizon, and the horizon will cut the line of the leading edge from somewhere near the tip to well toward the fuselage, depending on the degree of bank.

In steep banks the point where the horizon cuts the leading edge will range on up to the center of the fuselage, where, in a vertical, the leading edge of the center section will make a right angle with the horizon.

Before discussing the mechanics of the turn it must be remembered that all controls function by the reaction of the air flowing over them. Consequently if no pressures are exerted on them they will automatically streamline themselves, or maintain a position of balanced forces called "neutral." When pressures are exerted on the controls the corresponding surfaces are moved into the air flow and the reaction causes the ship to move or change its attitude in proportion to the amount of pressure applied and the duration of its application. Therefore the response of the airplane to the controls depends on the shading of the pressures exerted on the controls by the pilot. If slow response is desired, a light, short, and smooth pressure is exerted. If rapid response is desired, firmer and longer pressures must be exerted rather than more rapid movement of the controls. Among other things, "control touch" depends on the ability to shade the variation of pressures in proportion to the amount and rapidity of the response desired.

A student will probably never have done anything requiring the same kind of coordination of hands and feet, with kinesthetic control, that is necessary in turns. This should be taken into consideration by the instructor when turning practice is started, since he must not only aid the student in developing the proper new habits, but also aid him in breaking old ones.  Some individuals have a highly developed coordination, due to some line of endeavor they have been following, that offers serious difficulties when a new concept is to be acquired. Experience has shown that the preliminary instruction in turns should consist of exercises to establish the peculiar relationship of the required movements of the hands and feet, and that these movements then be reduced to pressures.

After being given the necessary verbal instructions and actual demonstrations, the student should be required to push the stick and the rudder in the same direction and at the same time until the coordinated movement of hands and feet is fairly well established.