Flow visualization and detailed load measurements over a maneuvering UCAV 1303

Abstract

The unsteady aerodynamic performance of a maneuvering 1/72nd scale model of an unmanned combat air vehicle (UCAV) 1303 geometry has been studied in the Naval Postgraduate School water tunnel. Despite the numerous past publications on UCAV flows, none pertains to the UCAV maneuvering characteristics. Due to its nonslender wing, the flow features over the chosen aircraft are unique in that both features of highly yawed wings and of delta wings are present. Even though the speeds and Reynolds numbers are low in a water tunnel, the results of the present studies attest to the suitability of a water tunnel for performing such studies. Force measurements taken at various Reynolds numbers, model attitudes and maneuvering rates for comparison proved to be valid for data comparison to potential flight scenarios. The UCAV 1303 model has a 47 degrees leading edge sweep and a cranked trailing edge delta wing with a fuselage. Pitching and rolling maneuvers were performed in various combinations to demonstrate the real flight conditions of a maneuvering UCAV. A five-component strain-gage and flow monitoring software were used to determine force and moment coefficients in real time. These coefficients were analyzed and compared to previous flow visualization tests to correlate the various flow features recorded during that phase of the study, and to determine the overall stability of a delta wing UCAV. These plots demonstrate what is seen visually at Reynolds numbers from 1.17x104 to 2.94x104. Where the pitch break occurs on the wings during maneuvers is correlated and dependent on Reynolds number, as initially suspected. Performing unsteady maneuvers helped in retaining the approximate linear variation of lift coefficient to higher angles of attack. Roll maneuvers produced oscillatory side forces and moments at high angles of attack and roll, indicating potentially serious unsteady forces.