Youngshin Kang, Bum-Jin Park, Am Cho, Chang-Sun Yoo, Sam-Ok Koo / Min-Jea Tahk
International Journal of Aeronautical and Space Sicences, vol. 17, no. 1, pp.120-131, 2016

Abstract : The full results of troubleshooting process related to the flight control system of a tilt-rotor type UAV in the flight tests are described. Flight tests were conducted in helicopter, conversion, and airplane modes. The vehicle was flown using automatic functions, which include speed-hold, altitude-hold, heading-hold, guidance modes, as well as automatic take-off and landing. Many unexpected problems occurred during the envelope expansion tests which were mostly under those automatic functions. The anomalies in helicopter mode include vortex ring state (VRS), long delay in the automatic take-off, and the initial overshoot in the automatic landing. In contrast, the anomalies in conversion mode are untrimmed AOS oscillation and the calibration errors of the air data sensors. The problems of low damping in rotor speed and roll rate responses are found in airplane mode. Once all of the known problems had been solved, the vehicle in airplane mode gradually reached the maximum design speed of 440km/h at the operation altitude of 3km. This paper also presents a comprehensive detailing of the control systems of the Tilt-rotor unmanned air vehicle (UAV).

Keyword : troubleshooting, tilt-rotor, flight test, flight control, vertical take-off and landing (VTOL)