• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.254-262
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• 2008

Several decades have passed since tiltrotor technology became a hot issue of debates between aircraft majors, policy maker and mass-media. Although most of those subjects have been officially probed or answered in objective way, biased articles or argues related with the adequacy of this technology still prevail in the way of tilt-rotor development programs, which are totally irrelevant and out-dated. This paper aims to help understanding on those issues in technically balanced manner and the cases of flight test mishaps.

• Journal of Aerospace System Engineering
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• v.11 no.6
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• pp.10-16
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• 2017

In order to improve the safety of the multi-copter, Korea Aerospace Research Institute (KARI) performed a wind-tunnel test using an octocopter with the maximum takeoff weight (MTOW) of 28 kg. The wind-tunnel test was performed with three different RPM ranges, 3,500, 4,500 and 5,500 rpm, and three different wind speeds, 3.5, 5 and 7 m/sec. The tested range of the angle of attacks was $-40^{\circ}$ to $20^{\circ}degree$ and ${\pm}90^{\circ}degree$. Vortex ring state (VRS) of the tested multi-copter was located around the vertical descending speed of 6 m/sec and the decrement of thrust was about 13 % at the time of testing. Compared with the single propeller wind-tunnel test result, the propeller efficiency of the octocopter dropped to 10 to 15% depending on the propeller RPM. It is hypothesized that the obtained aerodynamic characteristics by the wind-tunnel test will be used to improve the performance and wind resistance of the multi-copter.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.120-131
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• 2016

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).