Control allocation performance for blended wing body aircraft and its impact on control surface design

Due to highly redundant and strongly coupled control surface configurations of future aircraft, advanced control allocation algorithms have been proposed to optimize the allocation of control power to control surfaces. These algorithms typically assume linear control surface effectiveness. The effect of this assumption was tested by measuring the overall aerodynamic performance of several control allocation algorithms in a wind tunnel experiment with the Zero Emission Flying Testbed (ZEFT) blended wing body aircraft model, which was developed at Delft University of Technology. In addition, several aerodynamic analysis methods, including a 3D RANS CFD method, were tested on their ability to accurately predict the (non)linear control surface effects. The wind tunnel results showed that angle of attack (α) and control surface deflection angle (δ) had the strongest effect on control moment nonlinearities. Typical losses at maximum deflection angle were 10–30% compared to a linear assumption. Control surface interaction effects on the overall performance were limited. Some control allocation algorithms achieved only 50% of the requested moment in the wind tunnel. It is therefore recommended to include control allocation selection and performance evaluation in early design stages to avoid costly redesigns. The RANS CFD analysis showed promising results for tracking control moment response as a function of δ for all three moment axes.