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76    U.S. CIVIL AERONAUTICS AUTHORITY

with the pilot considered as the axis of movement, which is the only basis for accurate orientation and control use analyses. (Refer again to the detailed explanation given previously.)
In order to demonstrate again the falsity of the idea of the change of function it may be well to have the student perform the following:
1. Establish a steep turn and then ease forward on the elevators. The nose will fall and slip will result as well. This is not because the elevators have forced the nose down but because the back pressure holding against the normal tendency of the nose to fall while in this attitude has been removed. The slip is due to the lack of centrifugal force required to compensate for the loss of effective lift as a result of the angle of the lift force to the pull of gravity.
In a steep turn this centrifugal force is applied almost solely by the elevators by shortening the radius of the turn. In doing this the nose swings toward the pilot or "up" with regard to his position of view. It is then apparent that this control has not changed its function.
The function of the elevators in the various degree of banks are as follows (see fig. 5) : In the shallower turns the main function of the elevators is the perfectly normal "up and down" adjustment of the nose and a very slight application of a turning action and centrifugal force. As the degree of bank increases the former function decreases and the latter increases, until in a true vertical the whole effect of the elevators would be the control of the radius and speed of the turn and consequently centrifugal force. In anything less than a 90° bank they still retain some of their normal "up and down" movement.
However, when the bank is steepened the pilot retains his same outlook with reference to the airplane, and the elevators still pull the nose toward him or push it away. This is true regardless of the attitude of the ship with reference to the ground.
While in the same steep turn with the elevators relaxed and the ship slipping, have the student attempt to maintain his altitude by applying "top" rudder. No matter how much pressure is used, the airplane will continue to slip. In fact, if the elevators are held in the same position, the more he applies top rudder the more pronounced the slip will be.
This is due to insufficient speed or power to maintain flight on the fuselage alone, and too little compensating centrifugal force. The rudder still moves the nose to the left or right of the pilot but it does not maintain altitude even though it moves the nose to the side which is normally referred to as "up."
Then while still in the same slip with the elevators relaxed and the rudder normal, have him exert the correct back pressure on the elevators. If properly executed, the nose will come back up and the loss of altitude will cease.
This is not due to the normal functioning of the elevators in bringing the nose "up" but is due to the reestablishment of centrifugal force by shortening the radius of the turn.
After the normal steep turn is resumed have the student remove his feet from the rudder and note that very little effect on level flight is produced. (This may not be possible in some ships of low horse-