Design and flight test study of a VTOL UAV

Abstract

The aim of this paper is to present the ongoing studies about design and fight testing of a fixed wing UAV which is able to take-off and land vertically. The UAV concept discussed in this study has three propeller engines. Two of them are ducted propellers and placed at each wing tips. The third engine is placed on the tail boom. The ducted propellers can rotate up to ninety degrees around the wing axis. The aircraft, which is planned to be built at the end of this study, will be able to take-off vertically, perform transition to conventional flight and land vertically. The aircraft will also have capability of conventional take-off, cruise flight and landing. In this study, the design considerations of the aircraft in terms of balance and stability ha been examined. The equations of motion of the aircraft have been modelled with nonlinear approach, and the hover and transition flight attitudes have been simulated via numerical calculations. It has been showed that the aircraft has an inherent unstable behavior during hover flight. Implementation of a Proportional and Integral (PI) control methodology in to the simulation provided artificial stability for both longitudinal and lateral motions. The transition flight equations have also been modelled and solved for open loop and closed loop control approaches. The rear motor thrust variations during tilting for both control approaches have been compared. A control algorithm which is implemented into a micro-controller onboard, has been developed for experimental studies. An indoor and an outdoor low cost test frames have been constructed. A single-closed loop and nested (cascade) closed loop control strategies have been applied to the test frames and artificial stability is achieved during hover flight experimentally. The simulation results of hover and transition flights are presented in this article. The current status and results of the hover flight experiments are also summarized. The transition and cruise flight studies are planned as future work