The paper presents a theory for flight dynamic analysis of highly flexible flying wing configurations. The analysis takes into account large aircraft motion coupled with geometrically nonlinear structural deformation subject only to a restriction to small strain. A large motion aerodynamic loads model is integrated into the analysis. The analysis can be used for complete aircraft analysis including trim, stability analysis linearized about the trimmed-state, and nonlinear simulation. Results are generated for a typical highaspect-ratio "flying wing" configuration. The results indicate that the aircraft undergoes large deformation during trim. The flight dynamic characteristics of the deformed aircraft are completely different as compared to a rigid aircraft. For the example aircraft, the phugoid mode is unstable and the classical short-period mode does not exist. Furthermore, nonlinear flight simulation of the aircraft indicates that the phugoid instability leads to catastrophic consequences.
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.
Aeroelastic instabilities are among the factors that may constrain the ight envelope of aircraft and, thus, must be considered during design. As future aircraft designs reduce weight and raise performance levels using directional material, thus leading to an increasingly exible aircraft, there is a need for reliable analysis that models all of the important characteristics of the uid-structure interaction problem. Such a model would be used in preliminary design and control synthesis. A theoretical basis has been established for a consistent analysisthat takes into account 1) material anisotropy, 2) geometrical nonlinearities of the structure, 3) unsteady ow behavior, and 4) dynamic stall for the complete aircraft. Such a formulation for aeroelastic analysis of a complete aircraft in subsonic ow is described. Linear results are presented and validated for the Goland wing (Goland, M., "The Flutter of a Uniform Cantilever Wing,"
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.
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