Aerodynamic Shape Optimization of Common Research Model Wing-Body-Tail Configuration

Wing shape is one of the main drivers of aircraft aerodynamic performance, so most aerodynamic shape optimization efforts have focused solely on the wing. However, the performance of the full aircraft configuration must account for the fact that the aircraft needs to be trimmed. Thus, to realize the full benefit of aerodynamic shape optimization, one should optimize the wing shape while including the full configuration and a trim constraint. To evaluate the benefit of this approach, we perform the aerodynamic shape optimization of the Common Research Model wing-body-tail configuration using gradient-based optimization with a Reynolds-averaged Navier-Stokes model that includes a discrete adjoint implementation. We investigate the aerodynamic shape optimization of the wing with a trim constraint that is satisfied by rotating the horizontal tail. We then optimize the same wing-body configuration without the tail but with an added trim drag penalty based on a surrogate model we created before the optimization. The drag coefficient is minimized subject to lift and trim constraints. We found that considering the trim during optimization is a better approach than using a fixed-wing moment constraint. We also show that the trim drag surrogate model we created yields a minimum drag coefficient that is within 1.2 counts of the minimum drag coefficient obtained by rotating the tail to satisfy the trim constraint. However, we recommend rotating the tail within the optimization process to obtain the best possible performance.