Aerodynamic Characterization of Long Range VTOL UAV

Abstract

The blended-wing-body vertical takeoff and landing unmanned aerial vehicle (BWB VTOL UAV) combines the hovering and VTOL capabilities of a helicopter with the efficiency of a fixed-wing aircraft. The BWB utilizes a lift-generating fuselage that improves the lift produced by the craft, and therefore improving the overall efficiency. The body allows for the propulsion system necessary for VTOL to be housed in the fuselage. The purpose of this research is to understand the effects of planform shape on the aerodynamics of the UAV, and the ground effects and jet interactions due to having rotors submerged within the fuselage of the craft. Wind tunnel experimentation was performed on the fore- and aft-body positioned BWB models at Reynolds number flows of 1.18x105, 2.4x105, and 3.6x105. The results indicate that having a fore-positioned body with respect to the wings provides better stability and efficiency for long-range flights. Additional tests were conducted on just the wing of the UAV to better understand the lift, drag, and moment contributions from the lift-generating fuselage of the fore-BWB model. Although the addition of the fore-body did increase the drag, there were improvements in the lift, and there was better stability in terms of the pitching moment. The ground effects due to ducted propellers in the body were also studied. Motor thrust values were obtained with the UAV positioned at heights of 1, 2, and 3 duct diameters, where 1 diameter is 5 inches. From individual motor tests, the motor located at the nose of the craft showed favorable ground effects, while the motors located more centered in the body typically showed adverse ground effects. Two motor experiments did not show much improvement or loss of thrust at various heights from the ground. However, a comparison of the thrust values with ones obtained by summing the individual motor data provide insight on how the jets from each motor interact with each other. Depending on the combination of motors running, there were either lower or higher lift values observed indicating either negative or positive jet interactions respectively. Results for when all four motors are running show favorable ground effects. A comparison of these results with the thrust from the individual data indicates positive jet interactions between the four motors.