Accuracy of two nonlinear finite wing models in the aerodynamic prediction of wing sweep effects

The accuracy of quasi-three-dimensional (2.5D) nonlinear implementations of the lifting line and lifting surface theories in predicting the aerodynamic impact of a three-dimensional parameter such as wing sweep is assessed through a combined vortex element method and Reynolds-Averaged Navier-Stokes investigation. The wing geometry tested in this study is that of a medium-altitude long-endurance unmanned aerial vehicle, the Hydra Technologies S4 Éhecatl. Simulations are performed for subsonic incompressible flows that are representative of typical flight conditions encountered by the vehicle in cruise. Finite wing results for two Reynolds numbers of 1.0×10⁶ and 1.5×10⁶ at angles of attack 0°, 2°, 4° and 6° over a range of quarter-chord sweep angles between -12° and 12° show that both methods are capable of producing results in very close agreement with high-fidelity data when it comes to estimating aerodynamic performance at a point. However, the maxima and minima on the lift, drag, and lift-to-drag with sweep angle curves differ significantly, suggesting that the finite wing models are capable of estimating, but not generalizing, the behavior of a three-dimensional geometric wing characteristic.