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The Japanese Quiet Short Take Off and Landing experimental aircraft named ASKA was developed and flight tested during 1977 till 1989. The control system hard and software were examined by the functional mock-up with using the actual hardware. The small longitudinal limit cycle was observed in the closed loop test when the Pitch Control Wheel Steering software was on in the mock-up testing. In this paper, first, the method to analyze and to expect the limit cycle based on the describing function was shown. The limit cycle was induced due to the nonlinearities in the automatic control mechanism. The nonlinearities in the hardware were examined to make the model to simulate the system on the computer. The method was shown effective to predict the limit cycle in the mock-up. Second, with using the flight measured dynamics, the limit cycle was concluded as on border line between existing and not, which coincides with the actual flight result.

The Upper Surface Blowing STOL experimental aircraft ASKA, was developed and flight tested by the National Aerospace Laboratory of Japan. The ASKA operated well on the backside of the drag curve, and because of this flight path control was accomplished with the throttle lever (thrust) during approach and landing. To compensate for the sluggish flight path response caused by the thrust response lag, the flight path control law put in stability and control augmentation system. Flight tests were conducted to evaluate flight path and airspeed response characteristics. This paper describes ASKA's flight path and airspeed response characteristics, as well as construction of the flight path control system.