Elastic deformations control of highly flexible aircraft in trimmed flight and gust encounter

High-altitude, long-endurance unmanned aerial vehicles are inherently highly flexible, and therefore are more susceptible to very large structural deformation in trimmed flight and in atmospheric turbulence. This work aims to avoid these large wing deformations by incorporating and deflecting multiple redundant control surfaces along the leading and trailing edges of the wing. These surfaces are used both in trim optimization to constrain wing deformation to a user-defined value in steady trimmed flight, and in minimizing the dynamic response to gust encounter via a feedback controller. Trim optimization is performed using the simplex algorithm. Concurrently, a robust control scheme is designed and applied using H_∞loop shaping, to demonstrate that although the control surfaces are used for trimming the aircraft, they have enough authority left to effectively minimize elastic wing deformations during gust penetration. The above methodology is demonstrated on a highly flexible flying wing. Trim optimization effectively allows trimmed flight at various load factors in the flight envelope, while maintaining small structural deformations. The designed controller significantly reduces the maximum wing deflection experienced by a gust disturbance, which is bounded below a user specified value.