A Flight Investigation of the Spinning of the F4B-2 Biplane with Various Loads and Tail Surfaces

A flight investigation of the spinning of the F4B-2 single-seat fighter airplane was made for the purpose of finding modifications that would eliminate dangerous spin tendencies exhibited by this type of airplane in service. The effects on steady spins and on recoveries of changing the loading, enlarging the fin areas, changing the elevator plan form, and raising the horizontal surfaces, were determined. Five fin sizes, two elevator plan forms, and three vertical positions of the horizonal surfaces were tested with four airplane loading corresponding to different service conditions for which the airplane may be used. The effect on recovery of various methods of control manipulation and the immediate effect on various spin parameters of deflecting one or more of the controls from the normal setting were determined. The flight results were analyzed and compared with the results of spinning-balance tests of a model of the subject airplane.

The variations of loading did not materially affect the steady spin or the recovery. Increasing the fin area progressively improved ease of recovery but had little effect on the steady spin; and modifying the elevator to diminish interference had little beneficial effect. Raising the horizontal surfaces gave the most pronounced beneficial effect on recovery, making possible recoveries in less than one turn. The alterations made to the horizontal and vertical surfaces for the tests did not introduce undesirable flying characteristics. Flight tests and model tests were in general agreement but there were apparent discrepancies in certain details, particularly in regard to the comparative merits of several ways of manipulating the controls for recovery.

Dangerous spins were encountered during the tests as a result of displacing the controls, particularly the rudder, away from the usual position for the normal spin. Observations of the manner in which these dangerous spins were started indicated the probably conditions under which trouble had been experienced with this airplane in service.