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FLIGHT INSTRUCTOR'S MANUAL 43 to the right or left around the vertical axis of the airplane, even when this axis is canted off the vertical plane. Therefore, except when the airplane's wings are absolutely level, the rudder will have an "up and down" effect on the nose. This effect increases until it is absolute in a true vertical or 90° bank, as will be instantly apparent to anyone who analyzes the action of the controls. This brings out the fallacy of the theory that the elevator and rudder controls change function at 45°. (See fig. 5.) The foregoing further emphasizes the necessity for considering the pilot as the axis of movement and analyzing control action from that viewpoint, rather than as a function of gravity of "up and down." It also brings out the absolute necessity for the pilot at all times to maintain his position in the ship in the alignment with the vertical axis or, in other words, to "ride with the ship." From these factors, it will be seen that it is necessary to use the elevators to hold the nose level as soon as the ship starts to bank; the steeper the bank, the more the elevators must be used for this purpose. In shallow banks their action will be mainly to counteract the effects of the rudder and the slight angle of the lifting force. As the angle of bank increases the action of the elevators is less and less in counteracting the rudder and more and more in maintaining centrifugal force to overcome the decreasing effect of lift due to the increasing angle of the lifting force to the pull of gravity until finally, in a true vertical or 90° bank, this is their sole function, with the exception of fixing the radius of the turn. It will be noted of course that this action of the elevators requires the expenditure of more power from one source or another. The greater the degree of bank the more power expended. This may be obtained by the sacrifice of speed and usually is, except in turns where the throttle must be opened to maintain altitude and prevent mushing. Thus it will be seen that some speed, as well as lift, is lost in all turns. The greater the degree of bank, the greater the loss in both. This is a principle that must never be overlooked in gliding turns. During the recovery from a turn the procedure is just the opposite of that during the entry. It is merely the executing of a bank in the opposite direction neutralizing the one already established. There is, however, one notable difference. The rudder must be used more firmly since centrifugal force has been acting throughout the turn and is apposed by the effective area of the banked airplane. (That is, the profile area of the airplane in the turn.) Consequently during recovery, as the bank is decreased, this profile area is also decreased, until it reaches it minimum when the plane is level. If sufficient rudder is not used during this period of transition from bank to level, the airplane will be thrown sideways due to the uncounteracted centrifugal force, or in common terms, will "skid." Consequently it will be seen that in the recovery from a bank the function of the rudder is to hold the ship so that its flight path is straight ahead, rather than sideways. This may be demonstrated to the student easily and very forcibly by sharply recovering from a steep turn without the use of the rudder. The resulting wind blast and the tendency to be thrown to one side of the cockpit will be very apparent. The student should be allowed to repeat this himself with no rudder, and with vary degrees of 150310°-39-4