A small scaled flight demonstration model of a tilt rotor aircraft for the Smart UAV Program has been developed. The tethered hover test following the ground test on a test rig with 4 degrees of freedom has been performed prior to the flight test of the scaled model. During the flight test and tethered hover test, the performances of a rotor speed governor and a rate SAS have been evaluated. Because the pilot could not confirm the aircraft attitude at high speed flight condition at low tilt angle, the control structure was modified to attitude SCAS system in pitch and roll axis. All conversion flight tests were performed by pilot’s manual control and the attitude SCAS control law and rotor governor were fully engaged. The pilot had to input the tilt commands during coordinated turn flight in order for the aircraft not to exceed pilot’s visual range. The rate SAS feedback system was also enough to meet handling qualities requirement at all axis so that it would be work as a manual mode in emergency condition. During flight test, the control law has been modified to improve many unexpected aircraft responses. This paper presents the conversion flight test results of small scaled tilt rotor model and also shows the control law updates according to unexpected flight characteristics of tilt rotor aircraft.
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Kang et al. (2008) studied this question.