Dynamic Response of Highly Flexible Flying Wings

46th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2005

This paper introduces an approach to effectively model the nonlinear aeroelastic behavior of fully flexible aircraft. The study is conducted based on a nonlinear strainedbased finite element framework in which the developed low-order formulation captures the nonlinear (large) deflection behavior of the wings, and the unsteady subsonic aerodynamic forces acting on them. Instead of merely considering the nonlinearity of the wings, the paper will allow all members of the vehicle to be flexible. Due to their characteristics of being long and slender structures, the wings, tail, and fuselage of highly flexible aircraft can be modeled as beams undergoing three dimensional displacements and rotations. The cross-sectional stiffness and inertia properties of the beams are calculated along the span, and then incorporated into the 1-D nonlinear beam model. Finite-state unsteady subsonic aerodynamic loads are incorporated to be coupled with all lifting surfaces, so as to complete the state space aeroelastic model. Different Sensorcraft concepts are modeled and studied, including conventional single-wing and joined-wing aircraft configurations with flexible fuselage and tail. Based on the proposed models, roll responses and stabilities are studied and compared with linearized and rigidized models. At last, effects of the flexibility of the fuselage and tail on the roll maneuver and stability of the aircraft are presented.

AIAA Journal, 2010

An evaluation of aerodynamic and structural models is carried out for their application to flight dynamics of low-speed aircraft with very-flexible high-aspect-ratio wings. The structural dynamic approaches include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beam models, while thin-strip and vortexlattice methods are considered for the unsteady aerodynamics. We first show that all different beam finite-element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible-aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require 3-D descriptions (e.g., vortexlattice or similar).

2011

A modal solution is presented to the aeroelastic equations of very flexible wings in intrinsic form, that is written using inertial velocities and strains as primary variables. After assuming 2-D thin-airfoil aerodynamics on the wing sections, it is shown that the equations of motion can be written in canonical state-space form on the intrinsic modal coordinates without any matrix inversion and including only quadratic nonlinearities. Flutter characteristics are readily obtained from a linearized description of the dynamics equations, and the approach provides an efficient way of computing the nonlinear response with large wing displacements. Both situations are exemplified numerically on the Golang wing. The use of modal coordinates will serve to highlight some of the particular characteristics of the use of intrinsic beam solutions in aeroelastic problems with geometrical nonlinearities.

Journal of Aircraft, 2010

This paper presents a study on the coupled aeroelastic/flight dynamic stability and gust response of a blendedwing-body aircraft that derives from the U.S. Air Force's High Lift-Over-Drag Active (HiLDA) wing experimental model. An effective method is used to model very flexible blended-wing-body vehicles based on a low-order aeroelastic formulation that is capable of capturing the important structural nonlinear effects and couplings with the flight dynamic degrees of freedom. A nonlinear strain-based beam finite element formulation is used. Finite state unsteady subsonic aerodynamic loads are coupled to all lifting surfaces, including the flexible body. Based on the proposed model, aeroelastic stability is studied and 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 aircraft characteristics are also discussed in this paper.

15th Dynamics Specialists Conference, 2016

This paper details five aeroelastic modelling methods applied to the study of an example high aspect ratio wing subject to high loads resulting in large structural deformations. Each method is discussed in turn and example static results from each are compared. Overall agreement is illustrated between the methods for key quantities of interest although aerodynamic modelling choices regarding the orientation of aero forces is observed to play a significant role in the agreement between predicted distributed loads and deflections. Quantitative differences resulting from linearisation of the wing model are also presented and discussed. It is found that by linearising the problem, wing deflection, aerodynamic forces and root bending are all overestimated. Large differences are also observed between linear and nonlinear predictions of root twist, however the modelling of drag effects is deemed important to the exact nature of the observed discrepancy. Altogether, linearised assumptions are shown to have a noticeable impact on the accuracy of predicted results for the considered wing test case and are deemed unsuitable in isolation for the analysis of this class of flexible problem.

Journal of Aircraft, 2006

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.

Journal of Aircraft, 2008

An analysis and parametric study of the flight dynamics of highly flexible aircraft are presented. The analysis extends previous work of the authors, used to predict the atypical flight dynamic characteristics of highly flexible flying wings, to conventional configurations with one or more fuselages, wings and/or tails. The aircraft structure is represented as a collection of geometrically exact, intrinsic beam elements, with continuity conditions enforced where beams intersect. The only exception is that for simplicity, the vertical tail is represented as rigid. The structural model is coupled with an aerodynamic model consisting of 2-D, large-angle-of-attack, unsteady theory for the lifting surfaces, and a fuselage model based on application of slender-body theory to a cylindrical beam. In the parametric study, influences of various design parameters, such as different aircraft configurations, wing flexibility, horizontal tail aerodynamics and offset, are investigated for aeroelasticity and flight dynamics of highly flexible aircraft. Results for prototype configurations illustrate the relationships between design parameters and flight dynamic behavior.

AIAA Atmospheric Flight Mechanics Conference, 2009

This paper presents an integrated flight dynamic modeling method for flexible aircraft that captures coupled physics effects due to inertial forces, aeroelasticity, and propulsive forces that are normally present in flight. The present approach formulates the coupled flight dynamics using a structural dynamic modeling method that describes the elasticity of a flexible, twisted, swept wing using an equivalent beam-rod model. The structural dynamic model allows for three types of wing elastic motion: flapwise bending, chordwise bending, and torsion. Inertial force coupling with the wing elasticity is formulated to account for aircraft acceleration. The structural deflections create an effective aeroelastic angle of attack that affects the rigid-body motion of flexible aircraft. The aeroelastic effect contributes to aerodynamic damping forces that can influence aerodynamic stability. For wing-mounted engines, wing flexibility can cause the propulsive forces and moments to couple with the wing elastic motion. The integrated flight dynamics for a flexible aircraft are formulated by including generalized coordinate variables associated with the aeroelastic-propulsive forces and moments in the standard state-space form for six degree-of-freedom flight dynamics. A computational structural model for a generic transport aircraft has been created. The eigenvalue analysis is performed to compute aeroelastic frequencies and aerodynamic damping. The results will be used to construct an integrated flight dynamic model of a flexible generic transport aircraft.

49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br> 16th AIAA/ASME/AHS Adaptive Structures Conference<br> 10t, 2008

A low-order aeroelastic model is introduced for very flexible high-aspect-ratio wings with adaptive airfoils. A geometrically-nonlinear beam-like model capable of capturing plate-like deformations has been coupled with a 2-D finite-state aerodynamic model with arbitrary airfoil deformations. The proposed approach results in a natural extension to the conventional way of analyzing high-aspect-ratio wings, with very little additional complexity. The control effectiveness of camber deformation is numerically investigated in some simple situations, including thin isotropic and anisotropic plates and a straight wing with a constant NACA4406 airfoil.

AIAA SCITECH 2023 Forum

In the present work, we investigate dynamic interaction and response of flexible bio-inspired morphing wing structure to a low Reynolds aerodynamic load. The aspects of inspiration are as follows. First, the segmentation of the wing into rigid and flexible segments. Considering a leading edge constitution of bone and muscle. In addition to a flexible trailing edge composed