NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS LANGLEY FIELD VA LANGLEY AERONAUTICAL LABORATORY
Calculations have been made to determine the effects of spring and gravity moments in the control system on the longitudinal-stability characteristics of the Brewster XSBA-1 airplane, and the computed results have been verified by flight tests. It has been found that the type of stick-force variation with airspeed in a given flight condition may be changed within wide limits by use of weight or spring moments in the control system and that the stick forces required in maneuvers may be reduced by the use of weight moments. By the use of weight and spring moments in combination, both of these factors may be adjusted independently. Flight tests on the Brewster XSBA-1 airplane showed, however, that the maneuvering forces could not be reduced below a certain point without encountering an unstable condition in which the airplane diverged from straight flight into a dive with controls free. The use of a weight moment large enough to increase appreciably the moment of inertia of a control system was considered by the pilot to be undesirable.