Design and Transition of a Quad Rotor Tail-sitter VTOL UAV with Experimental Verification

This paper presents the design and development of a quad rotor tail-sitter VTOL UAV (Vertical Take-off and Landing Unmanned Aerial Vehicle). VTOL UAVs have the capability of flying as a fixed-wing aircraft as well as rotorcrafts. This concept may serve well for surveillance, reconnaissance and in hostile environments. Currently different platforms are being utilized by researchers for designing VTOL aircraft which primarily include tilt rotors that serve for vertical take-off and landing and transition is done for translation of hovering configuration to fixed-wing configuration. This paper includes a specific study of the transition mechanism for VTOL UAVs, its transition from hover configuration to fixed-wing configuration, different phases of VTOL design, different configurations of rotors, and flight controller platform used for autopilot for long surveillance missions. This research is then followed by a specific design of tail-sitter VTOL UAVs which include the UAV design which follows an integrated analysis approach in which take-off weight is estimated followed by wing loading and thrust to weight ratio calculations. Design phase include an airfoil analysis using XFLR5 software followed by CAD modelling of UAV and its aerodynamic analysis. This research is then focused on the transition of VTOL UAV from VTOL mode into fixed-wing mode and vice versa. Different parameters involved during this phase are specified. During fabrication phase different techniques were used which include 3D printing of internal airframe of aircraft, laser-cutting of airfoil contours and hotwire cutting of Styrofoam. These techniques were applied using laser cutting and hotwire cutting machines available at the College of Aeronautical Engineering. Fabrication is followed by a series of flight tests which include ground test where aircraft endurance was calculated. Afterwards transition test from hovering mode into fixed-wing mode was carried out. The drone was able to achieve all the desired features successfully.