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FLIGHT INSTRUCTOR'S MANUAL    189

From the description of the usual method of entry, it will be seen that they may be accidentally entered, most easily, from an Immelman [[Immelmann]] turn improperly executed, during improper recovery from a vertical reversement, then from a loop, the slow roll, and the chandelle, all of which must be very seriously abused to cause such accidental entry but which do present the possibility. 

In some aircraft, violent use of stick and rudder during the recovery from a normal spin will throw the airplane over on its back and start an inverted spin. 

Misapplication of the controls at the termination of a whip-stall have caused accidental entry.
The following instructions for recovery are quoted from instructions issued by the Navy:

If the spin has been entered with power on, close the throttle immediately. Neutralize the rudder, neutralize the ailerons, draw the control stick aft firmly as far as it will go. These control dispositions will immediately resolve the spin into normal flight position by the execution of a half loop. Just prior to reaching normal flight position, still holding rudder and ailerons neutral move the control stick to position slightly forward of neutral, in order to maintain sufficient flying speed. 

Should the spin have been of long duration and fully developed, a full turn and a half or two may be required to stop the circular motion. But it is to be noted that the control disposition detailed above will stop the spin and bring the airplane back to normal flight, and impatience will not hasten the resolution. 

While all students should be made acquainted with the causes of accidental entries into this maneuver and the manner of recovery from them, unless proper equipment is available and such students desire to become exhibition pilots, no demonstrations should be given, or practice allowed. However, the possibility of recovery by a student who accidentally falls into one without any prior explanation or knowledge of them is very small unless such an accidental entry occurred above the usual altitudes of student training. 

HALD-ROLLS OR SPLIT S'S

There are two types of half-rolls, the half snap-roll, and the half-slow roll, and each serves as an introduction to its corresponding full-roll and each further develops precision in techniques and orientation in unusual attitudes. 

The half snap roll is more or less a mechanical maneuver so far as execution is concerned. However,  high degree of development of orientation and timing is required for proper recovery. This maneuver is really a half turn power spin, done with sufficient excess over the normal stalling speed to permit the maneuver to be accomplished on the horizontal plane rather than the vertical. 

Like the spin, snap rolls are the result of the reaction of the airplane to yawing moments induced by the rudder while the wings are unequally stalled. In the case of spins the stall results from loss of speed, but in the case of the snap rolls the angle of attack is suddenly changed to one above the stalling point by mechanical means and the roll ensues before the airplane, due to its inertia, can take up the flight path that it would be required to assume before the maximum angle of attack would be exceeded.