Flight Dynamics of Highly Flexible Flying Wings

TLDR

The paper develops a theory for flight‑dynamic analysis of highly flexible aircraft configurations. The analysis couples large aircraft motion with geometrically nonlinear structural deformation under small strain, incorporates a large‑motion aerodynamic load model, and enables trim, stability, and nonlinear simulation of the aircraft. Simulations of a high‑aspect‑ratio flying‑wing show that large deformations during trim alter the flight‑dynamic characteristics, causing the short‑period mode to become two real roots and the phugoid mode to destabilize, ultimately leading to catastrophic instability.

Abstract

The paper presents a theory for flight-dynamic analysis of highly flexible 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 high-aspect-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 with a rigid aircraft. When the example aircraft is loaded sufficiently, the pair of complex-conjugate short-period roots merges to become two real roots, and the phugoid mode goes unstable. Furthermore, nonlinear flight simulation of the aircraft indicates that the phugoid instability leads to catastrophic consequences.