Study on Design and Transitional Flight of Tail-sitting Vtol Uav

A new design for a tail-sitting vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) was proposed. A nonlinear mathematical model of the vehicle dynamics was constructed by combining simple estimation methods. The flight characteristics were revealed through a trim analysis and an optimized transitional flight path analysis by using the mathematical model. The trim analysis revealed the existence of a minimum path angle to avoid stall in lowspeed flights. Although the value of the angle was positive without flaps or slats, these high lift devices (HLDs) improved this value. In particular, the slats provided a substantial improvement in the value of the angle and enabled a descent rate of 2.0 m/sec. In the optimized transitional flight path analysis, a level outbound transition without HLDs was achieved although a trimmed level flight at low speeds as was shown in the trim analysis was not possible; this was because the outbound transition was an accelerative flight. On the contrary, without HLDs, the vehicle could not avoid climbing during inbound transitions to avoid stall. The slats provided a satisfactory improvement during the transition and made a level inbound transition possible. These results showed the necessity of leading-edge slats for the proposed tail-sitting VTOL UAV.