Spin Investigation Of A 1/20-Scale Model Of An Unswept-Wing, Twin-Engine, Observation Airplane

An investigation was conducted in the Langley 20-foot free-spinning tunnel on a 1/20-scale model of an unswept-wing, twin-engine, observation airplane. The effects of control settings and movements on the erect spin and recovery characteristics for the normal loading and the most rearward center-of-gravity loading (external wing tanks full) were determined. Also, tests were made to determine the effect on the spin and recovery characteristics of a large radar store, of empty and full external wing tanks, and of an asymmetrical condition when one empty or one full external wing tank is carried. Spin-recovery parachute tests were also performed. The results of the tests indicate that erect spins obtained on the airplane for the normal loading should be satisfactorily terminated by rudder reversal to full against the spin, ailerons moved to with the spin, followed one-half turn later by forward movement of the stick to neutral. With the radar store, with wing tanks empty, or with an asymmetrical condition when one empty tank is on either wing, satisfactory recoveries can be obtained by using the same technique as for the normal loading. Recoveries for the model with a rearward center-of-gravity loading (external wing tanks full) or with a full tank on the wing inboard of the spin axis will be slow to unsatisfactory with rudder reversal to full against the spin followed by brisk forward stick movement. With a full tank on the wing outboard of the spin axis, the recoveries will be satisfactory. Spins in the landing configuration should be terminated by first retracting the flaps, slats, and landing gear, after which recovery should be attempted immediately by using the recovery technique recommended for the normal loading condition. Inverted spins can be satisfactorily terminated by rudder reversal to full against the spin followed by neutralization of the longitudinal and lateral controls. A 12.7-foot-diameter tail parachute with a towline length of 21.7 feet and a drag coefficient of 0.65 should be satisfactory for recoveries from erect and inverted demonstration spins when used simultaneously with movement of rudder to neutral.