Effects of a Free-to-Roll Fuselage on Wing Flutter: Theory and Experiment

Abstract

A theoretical study of a wing-fuselage combination with a rigid-body roll degree of freedom for the fuselage and elastic modes for the wing is presented along with a companion wind-tunnel test. The full-span wing dynamics are modeled using a linear-plate wing structure theory. A component modal analysis is used to derive the full structural equations of motion for the wing-fuselage combination system. A three-dimensional time-domain vortex-lattice aerodynamic model is also used to investigate flutter of the linear aeroelastic system. The experimentally observed flutter mode is antisymmetric, although theory suggests that the symmetric-mode flutter velocity is only modestly higher than that for the antisymmetric modes. Correlation between theory and experiment for flutter velocity and frequency is good. The experimentally observed postflutter response is a limit-cycle oscillation, and this is worthy of further study using an appropriate nonlinear theory. Nomenclature A, B = vortex-lattice aerodynamic coefficient matrices c = wing chord (including the leading and trailing control surface chords) f s , f as = symmetric and asymmetric natural frequencies J f , J w = fuselage and wing rolling inertias, respectively L = wingspan km, kn = numbers of vortex elements on wing in x− directions, respectively kmm = total number of vortices on both the wing and wake in the x−, y− direction m = mass per wing plate area m b = swinging pendulum mass m k = generalized mass of wing associated with the kth eigenmode q k = generalized coordinate of wing associated with the kth eigenmode R x , R y , R z = rotation angles r f = radius of the slender body (fuselage) T = transfer matrix from the downwash on the local vortex-lattice mesh on the wing to the global vortex-lattice mesh t = time U = airspeed W = downwash of wing w = out-of-plane displacement of wing x, y = streamwise and spanwise coordinates x ja , x jb = x positions of the two jth trailing vortex segments y ja , y jb = y positions of the two jth trailing vortex segments β = rolling angle Γ = vortex strength Δp = pressure distribution on the wing Δt = Δx∕U, time step ψx; y k = transverse natural mode of wing associated with the kth eigenmode ω b = natural frequency of a swinging pendulum ω k = natural frequency of wing associated with the kth eigenmode · = d·∕dt

Experimental Aeroelastic Models Design and Wind Tunnel Testing for Correlation with New Theory

“…A three-dimensional time domain vortex lattice aerodynamic model is also used to investigate flutter of the linear aeroelastic system and results are correlated with experiment. See Reference [28] for more detail.…”

“…Based on this model a computational code has been developed and evaluated. (5) A free-to-roll fuselage flutter model [28]. From measured wind tunnel data, one evaluates the predicted symmetric and anti-symmetric flutter/LCO theory.…”

A Review of Wind Tunnel Based Virtual Flight Testing Techniques for Evaluation of Flight Control Systems

“…Wind tunnel 1-DOF test includes free-to-pitch (or freeto-yaw) wind tunnel test [19][20][21][22] and free-to-roll wind tunnel test [23][24][25]. They let the test model oscillate freely on a support apparatus under an initial condition and are usually used to identify free motion modes and dynamic stability derivatives.…”

Stability of Turbine Blades, Aircraft Wings and Their Acoustic Radiation

“…A full wing-fuselage coupling with rigid-body roll degree of freedom for fuselage and elastic modes for the wing is investigated by both numerical and experimental technique. It is found that the post flutter response is a limit-cycle oscillation [17]. An experimental method and numerical technique are developed to apprehend the transient response of multilayer composite rotating airfoil under a slicing-impact loading and birdlike struck is investigated [18,19] Flutter instability can be used to harvest energy for small electric devises.…”