Experimental Investigation into the Effect of Aerodynamic Add-ons on the Aerodynamic Characteristics of the Flying V

Abstract

This research has been performed with the purpose of understanding the cause of the unstable pitch break experienced by the Flying V at a lift coefficient of CL = 0.95. Without understanding and possibly elimination of the pitch break, the flying V’s usable maximum lift coefficient is lower and the pitching moment behavior and gust response unpredictable. Three possible solutions are investigated empirically, with the ultimate goal of eliminating the unstable pitch break. First, the application of a trip strip to the suction and pressure side of the wing is investigated. Second and third, the implementation of vortilons and fences is investigated. The experiments are performed in the TU Delft’s Open Jet Facility using a 4.6% scaled half-span model of the Flying V. The wind tunnel experiments are evaluated using force and moment data and flow visualization using tufts. The application of trip strips results in an increase in pitching moment coefficient up to a lift coefficient of CL = 0.65 and introduces the unstable pitch break at CL = 0.80 compared to CL = 0.95 for the clean wing. Flow visualizations showed an improvement in the flow over the outboard wing when the trip strips were applied. Combining both observations, it is recommended to apply the trip strips on the outboard wing of the Flying V scaled flight testing model only. Vortilons have shown to have no effect on the unstable pitch break. The combination of a vortilon and the trip strips could decrease the pitching moment coefficient of the flying V up to a lift coefficient of CL = 0.70, depending on the spanwise location of the vortilon. Placing a fence could result in a favorable pitching moment coefficient characteristic, depending on its spanwise location and size. A fence placed at the spanwise location of the leading edge kink results in a decrease of pitching moment coefficient between a lift coefficient of CL = 0.30 and 1.1. Furthermore, a fence located at the leading edge kink and spanning the entire suction surface chord postponed the unstable pitch break experienced by the Flying V. Therefore, it is recommended to install that fence on the Flying V scaled flight testing model.