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188      U. S. CIVIL AERONAUTICS AUTHORITY

In airplanes of medium to high horsepower the torque effect of the clockwise rotation of the propeller is counteracted by "washing-in" the left wing and, in some cases by 
"washing-out" the right wing as well. The vertical fin is then offset to overcome the yawing effect caused by the difference in the drag of the two wings. However, the fin is set for cruising speed only, which means that it will not be correct at either full throttle or in a dive. Therefore, the rudder may have to be held to offset the difference in the yawing moment during such conditions. This means that the rudder pressures will have to be changed as speed is lost and in some cases it may even require a reversal of the original pressures used. Failure to appreciate these facts often leads to a wing becoming low during the loop due either to excessive use of the rudder or failure to use it.

Another cause for the right wing being low is the usual tendency to pull the stick slightly to the right in attempting to pull it straight back. However, any such tendency in the student's operation of the controls should have been eliminated long before any instruction in loops. 

The motor should not be throttled until the nose has definitely passed the horizon, and it should not be reopened until necessary to maintain cruising speed during the last phase of recovery. Proper handling of the throttle is of great assistance in the performance of good loops.

INVERTED SPINS

Inverted or "outside" spins are discussed here only for the purpose of acquainting the instructor, who may have no knowledge of them, with their causes, effects, and with the manner of recovery in case of accidental entry. They should also be explained to the student and any tendencies he may have or develop that might lead to their accidental performance should be promptly eliminated. Their practice should be avoided except in aircraft definitely known to be suitable for such maneuvers. They introduce unusual loads on the aircraft and in addition, many aircraft that will spin in a perfectly normal manner are uncontrollable in an inverted spin.

During an inverted spin, the airplane spins in the same fashion as it does in a normal spin, except that it is upside down and the pilot is on the outside of the turn instead of on the inside. The spin is usually a little flatter, or the nose a little higher, than is the case with the same airplane in a normal spin.

The usual method of entry is to stop the airplane on its back with the nose slightly high at the top of a loop, shove the stick full forward and apply full rudder in the direction in which it is desired to spin. 

Recovery is made by pulling the stick back and neutralizing the rudder, or giving opposite rudder.

During the execution of these maneuvers in some aircraft the centrifugal force is so great that the pilot will be thrown well out of the cockpit, even with a tight safety belt. In such instances the rudder cannot be reversed or even used, due to the inability of the pilot to keep his feet on it, unless stirrups are available. Fortunately, most aircraft will recover by use of the stick alone.

This maneuver offers another excellent reason why the safety belts should be adjusted to a tight fit, and their condition and attachments checked before doing acrobatics.