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FLIGHT INSTRUCTOR'S MANUAL      183

biplanes. This emphasizes that the wrong use of aileron is likely to have serious consequences. As a general rule if ailerons are to be used at all they should be used with the spin (stick to the inside of the spin), which is the opposite of the normal tendency. 

It has been found that many airplanes that spin normally with ailerons in neutral will get into uncontrollable (flat) spins with ailerons crosses. Approach of such uncontrollable spins is usually noted first in back pressure on the elevators (tendency for the stick to stay back) and this may occur with the nose well down. 

Thus it becomes apparent that use of ailerons is undesirable and should be avoided in spins except when their use is necessitated for recovery from otherwise uncontrollable spins. 

Improper rigging may also cause an aircraft that normally spins well to become a bad spinner. The most common cause for this is "wash in" (trailing edge down at the tips) of wings. The effect of this in spins is similar to crossing ailerons. Such "wash in" usually occurs as a result of rerigging the aircraft for balance by merely alternately "washing in" the heavy wing until both are "washing in," instead of making certain that one wing is rigged flat while the opposite is slightly "washed out."

Changes in the stagger of a biplane may cause the shifting of the center of pressure with relation to the center of gravity to such an extent as to make this condition critical, having the same effect as overloading the baggage compartment of the aircraft. 

Bad spinning characteristics may also be encountered in aircraft normally satisfactory if loads are carried that move the center of gravity aft of the rearmost limit for which it is approved. It should be borne in mind that balance data required for type approval assumes that each passenger's weight will not exceed 170 pounds, and operators should avoid carrying excessively students or pilots in rear seats during spins. 

With certain aircraft equipped with a retractable landing gear it may be difficult or impossible to accomplish recovery from prolonged spins with the wheels extended or in the "down" position. With some models extended flaps may have a similar result. Therefore reliable information regarding the spin characteristics of such aircraft should be obtained before intentional spins are performed. 

It is further earnestly recommended that all concerned familiarize themselves with the contents of N. A. C. A. Technical Note 555, PILOTING TECHNIQUE FOR RECOVERY FROM SPINS. Due to lack of space only the conclusions are reproduced here. These are primarily recommendations for pilots spin-testing aircraft, but many of the same principles apply to ordinary spin practices with aircraft known to be normal spinners. 

(a) During a spin, particularly during the last three or four turns of a prolonged spin, before recovery is attempted, the ailerons should be neutral and the elevator and rudder should be held all the way with the spin. 

(b) When applying controls for recovery, the rudder should be briskly moved to a position full against the spin and later, after at least one-half additional turn is made, the elevator should be briskly moved to the full down position. 

(c) In the event of a vicious spin, the applied controls for recovery should be held for at least five turns before attempting any other measure for promoting recovery. 

(d) Deliberate spins should be started at an altitude of at least 10,000 feet. 

(e) When any doubt exists regarding the recovery characteristics of an