Abstract: In order to improve the takeoff and landing aerodynamic characteristics of flying wing unmanned aircrafts, a novel low speed control device called the belly-flap is introduced. Low speed aerodynamic characteristics of the flying wing unmanned aircraft is studied by using CFD. The aerodynamic optimization design on the locations, deflection angles, and solidity of the belly-flap is carried out. The lift-off lift coefficient and moment coefficient are increased by the help of the belly-flap, and the takeoff and landing aerodynamic characteristics of the unmanned aircraft are improved.