FLIGHT TEST EVALUATION OF THE UF-XS JAPANESE STOL SEAPLANE

Abstract : The UF-XS Japanese STOL Seaplane was evaluated to determine the flying qualities in configurations PA, L, and TO at approach speeds in the vicinity of 55 kt and the hydrodynamic characteristics while on the water. The NASA Ames simulator showed good correlation with the airplane's aerodynamic characteristics. The airplane has neutral to unstable static longitudinal stability, weak directional stability, large adverse yaw, a long period moderately damped Dutch Roll mode, a divergent spiral mode, and trims for flight in a 13 degree left sideslip. An automatic stabilization equipment (ASE) makes the static longitudinal stability and spiral modes positive but does not improve the remaining items. Take-off and landing touchdown speed is 50 kt. The airplane has a hydrodynamic stable elevator range of 20 to 35 degrees up elevator. A 'digging in' and slight 'porpoising' tendency is exhibited at elevator positions less than 20 degrees. The airplane possesses good spray characteristics. The mission capability of a STOL seaplane should greatly improve with reduction in takeoff and landing speed; however, evaluation of the airplane at lower speeds was not possible due to several airplane limitations.