NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS LANGLEY FIELD VA LANGLEY AERONAUTICAL LABORATORY
Flight tests of a twin-engine midwing attack bomber and a single-engine low-wing fighter airplane showed both airplanes to have moderately high effective dihedral but different directional stability and control characteristics. The attack bomber had a high degree of directional stability and the variation of rudder force required for trim with speed was small. The fighter had considerably less directional stability than the attack bomber and the rudder forces required for trim as the speed and engine power were varied were relatively high. In flying the attack bomber, pilots did not observe any unusual or undesirable lateral control characteristics. On the other hand pilots reported control coordination was difficult with the fighter when changing speed or power, with the result that inadvertent sideslipping occurred. When this motion occurred the airplane tended to roll and the pilot was required to apply aileron forces continually. Pilots also considered the rough-air control characteristics objectionable because of the aileron forces that were required when inadvertent sideslipping occurred. When the rudder forces were reduced with a spring-tab rudder, pilots noted a marked improvement in the lateral and directional control characteristics.