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42       U.S. CIVIL AERONAUTICS AUTHORITY

during the training period the degree of bank should be held accurately, and once a bank is assumed, the corrections for errors in the turn should be made with the rudder. If the bank is allowed to vary, the student will miss many important principles. Once the desired degree of bank is attained, it should be held.

Incorrect rigging of the airplane may exaggerate the overbooking tendency or eliminate it. For example: If the airplane is "left wing heavy," the overbooking tendency will be greatly increased in a left bank. In a right bank it may be neutralized, or even decreased, depending on the degree of left-wing heaviness. The student must be watched for signs of being overconscious of this principle, in which case he will oppose the bank with enough pressure on the opposite

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FIGURE 4.—Gravity and lift forces.

aileron to soon cause the turn to lose its identity. His normal reaction to banks and his inclination to keep himself perpendicular to the horizon regardless of the ship's attitude will increase this fault. However, during short turns, the degree of change in the bank as a result of this overbooking tendency will normally be very slight. Any precision and alertness engendered by the instructor's insistence that the student correct such slight changes will, in the beginning, be more than counteracted by the fact that the student will be made too conscious of his flying and perhaps apprehensive at a time when relaxation and ease need be developed more than precision. Precision can be attained later.

In any turn the nose of the airplane tends to fall and cause the airplane to lose altitude. This is due to a decrease of the effective lifting force. Normally, the lifting force is directly opposed to gravity. In a turn, however, the direction of the lifting force, which is always perpendicular to the wings of the airplane, changes, while the force of gravity remains in the same direction. (See fig. 4.)

The rudder applied in the direction of the turn also causes a downward "cant" of the nose if some means is not used to correct for it. It will be remembered that the rudder always moves the nose