Nonlinear Aeroelasticity of a Very Flexible Blended-Wing-Body Aircraft

TLDR

Blended‑wing‑body (BWB) aircraft with high‑aspect‑ratio wings are a key configuration for high‑altitude long‑endurance unmanned aerial vehicles (HALE UAV). The study investigates the coupled aeroelastic–flight‑dynamic stability and response of a modified BWB aircraft, including the effects of structural and aerodynamic nonlinearities and wing bending‑torsion coupling on stability and gust response. The authors model the very flexible BWB using a low‑order aeroelastic formulation with a nonlinear strain‑based beam finite‑element model, incorporating finite‑state unsteady subsonic aerodynamic loads coupled to all lifting surfaces, including the flexible body. The model reveals body‑freedom flutter behavior and shows how flutter differs when rigid‑body degrees of freedom are constrained, highlighting the limited applicability of wind‑tunnel aeroelastic results to free‑flight conditions.

Abstract

Blended-wing-body (BWB) aircraft with high-aspect-ratio wings is an important configuration for high-altitude long-endurance unmanned aerial vehicles (HALE UAV). Recently, Northrop Grumann created a wind tunnel model under the Air Force’s High Lift over Drag Active (HiLDA) Wing program to study the aeroelastic characteristics of blended-wing-body for a potential Sensorcraft concept. This paper presents a study on the coupled aeroelastic / flight dynamics stability and response of a BWB aircraft that is modified from the HiLDA experimental model. An effective method is used to model very flexible BWB vehicles based on a low-order aeroelastic formulation that is capable of capturing the important structural nonlinear effects and couplings with the flight dynamics degrees of freedom. A nonlinear strain-based beam finite element formulation is used. Finite-state unsteady subsonic aerodynamic loads are incorporated to be coupled with all lifting surfaces, including the flexible body. Based on the proposed model, body-freedom flutter is studied, and is compared with the flutter results with all or partial rigid-body degrees of freedom constrained. The applicability of wind tunnel aeroelastic results (where the rigid-body motion is limited) is discussed in view of the free flight conditions (with all 6 rigid-body degrees of freedom). Furthermore, effects of structural and aerodynamic nonlinearities as well as wing bending/torsion rigidity coupling on the stability and gust response are also studied in this paper.