Conceptual design of a vtol box-wing uav with rotatable duct-fans

A conceptual design of a vertical take-off and landing (VTOL) fixed-wing Unmanned Aerial Vehicle (UAV) with high aspect ratio box-wing configuration is presented. Two rotatable duct-fans, which are driven by a turboshaft engine placed inside the fuselage, are installed at the center of the box-wing configuration symmetrically. The existence of the duct between the two wings diminishes the detrimental aerodynamic interaction of the fan blades and the wings. The power requirements of VTOL mode and cruise mode are satisfied through the rotation of duct-fans. Steady numerical simulations of the fundamental box-wing configuration without duct-fans are carried out to optimize lift-to-drag ratio. In the research of the configuration with duct-fans, the momentum source method is used to simulate the flow field characteristics around the duct-fans to uncover the aerodynamic characteristic of the conceptual design. The maximum and minimum velocity within the range of attack angle during the transition flight phase are given to ascertain corridor curves of transition mode. Numerical results demonstrate that, the conceptual design has strong longitudinal stability and low stall speed in horizonal flight and the transition phase is stable and controllable. Meanwhile, changing the direction and value of the duct-fan thrust properly can improve the aerodynamic characteristics of the UAV and generate an effective direct force control. The conceptual design can achieve an excellent flight performance through an optimal control strategy.