This paper presents the research carried out in testing the adaptive capability of the Modified State Observer (MSO) based control law for a general aviation aircraft through Laboratory Simulations, Hardware-In-Loop (HIL) Ground Tests and Flight Tests. Prior using MSO adaptations, a simplified Model Reference Adaptive dynamic inverse controller (MRAC), was tested in-flight on a General Aviation (GA) fly-by-wire test bed. The flight test results of the MRAC show good tracking but unacceptable throttle surging during the commanded flight path angle and airspeed. Based on simulation the surging is believed to be in response to noise in the measured airspeed. To overcome this problem, MSO based adaptation methodology is adopted to control the longitudinal dynamics of a typical general aviation aircraft. The advantage of MSO is that it adapts to estimation error, not modeling or tracking error. A Dryden Turbulence Model is included to simulate the turbulence experienced by the aircraft. The airspeed measured in the presence of turbulence makes an accurate simulation of aircraft's flight condition and hence the longitudinal responses in the laboratory. The random Power Lever Arm (PLA) surge seen during the simulation and flight test of the baseline MRAC controller was not observed in the simulation results of MSO adaptation controller. Based on appropriate laboratory and desktop bench simulation results, HIL Ground Test and Flight Test were carried out in Beechcraft Corporation. The tests were conducted for three cases - No failures, Elevator failure and Engine failure. The flight test results showed the MSO controller's ability to adapt and track the flight path angle and velocity commands without any significant PLA surge.
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