Nonlinear Aeroelasticity and Flight Dynamics of High-altitude Long-endurance Aircraft

High-Altitude Long-Endurance (HALE) aircraft have wings with high aspect ratios. During operations of these aircraft, the wings can undergo large deflections. These large deflections can change the natural frequencies of the wing which, in turn, can produce noticeable changes in its aeroelastic behavior. This behavior can be accounted for only by using a rigorous nonlinear aeroelastic analysis. Results are obtained from such an analysis for aeroelastic behavior as well as overall flight dynamic characteristics of a complete aircraft model representative of HALE aircraft. When the nonlinear flexibility effects are taken into account in the calculation of trim and flight dynamics characteristics, the predicted aeroelastic behavior of the complete aircraft turns out to be very different from what it would be without such effects. The overall flight dynamic characteristics of the aircraft also change due to wing flexibility. For example, the results show that the trim solution as well as the short-period and phugoid modes are affected by wing flexibility.