Drag Assessment of Vertical Lift Propeller in Forward Flight for Electric Fixed-Wing VTOL Unmanned Aerial Vehicle

Abstract

A fixed-wing UAV that is capable of vertical takeoff/landing is a hybrid aerial vehicle that could take off as helicopter and then transition into conventional airplane for forward flight. There are several powertrain configurations for the VTOL aircraft, one of them is called Separate Lift Thrust (SLT) configuration where the forward flight uses different powertrain compared to the hover phase. Without complex mechanism to store the inactive hover powertrain, the hover powertrain components added a significant amount of aerodynamic drag during forward flight. This paper presents the assessment of the drag caused by the inactive propellers during the forward cruising flight phase. For this research, 26 propeller samples with diameter from 5 inch to 9 inch were used with various configuration and materials. They were then tested in wind tunnel facility and the resultant drag was measured. The results from the wind tunnel test shows that for lowest drag penalty, smaller propeller diameter with low pitch blade provide the lowest drag. Interestingly, from the results, it shows that there is a flight speed that can provide an optimum drag from the chosen propeller. A selection of optimum motor and battery can be made in the future based on result presented in this paper to further improve the performance of the UAV.