A folding wing is a tactical missile launching device that needs to be miniaturised to facilitate storage, transportation, and launching; save missile and transportation space; and improve the combat capability of weapon systems. This study investigates the aeroelastic characteristics of the secondary longitudinal folding wing during the unfolding process. First, the Lagrange equation is used to establish the structural dynamics model of the folding wing, the kinematics characteristics during the deformation process are analysed, and the unfolding movement of the folding wing is obtained using the dynamic equations in the process. Then, the generalised unsteady aerodynamic force is calculated using the dipole grid method, and the multi-body dynamics equation of the folding wing is obtained. The initial angular velocity required for the deployment of the folding wing is analysed through structural model simulation, and the influence of the initial angular velocity on the opening process is studied. Finally, aeroelastic flutter analysis is performed on the folding wing, and the physical model of the folding wing verified experimentally. Results show that the type of aeroelastic response is sensitive to the initial conditions and the way the folding wing opens.

We present a hybrid, semi-analytical approach to perform an eigenvalue-based flutter analysis of an Unmanned Aerial Vehicle (UAV) wing. The wing has a modern design that integrates metal and composite structures. The stiffness and natural frequency of the wing are calculated using a Finite Element (FE) model. The modal parameters are extracted by applying a recursive technique to the Lanczos method in the FE model. Subsequently, the modal parameters are used to evaluate the flutter boundaries in an analytical model based on the p-method. Two-degree-of-freedom bending and torsional flutter equations derived using Lagrange’s principle are transformed into an eigenvalue problem. The eigenvalue framework is used to evaluate the stability characteristics of the wing under various flight conditions. An extension of this eigenvalue framework is applied to determine the stability boundaries and corresponding critical flutter parameters at a range of altitudes. The stability characteristics and critical flutter speeds are also evaluated through computational analysis of a reduced-order model of the wing in NX Nastran using the k- and pk-methods. The results of the analytical and computational methods are found to show good agreement with each other. A parametric study is also carried out to analyse the effects of the structural member thickness on the wing flutter speeds. The results suggest that changing the spar thickness contributes most significantly to the flutter speeds, whereas increasing the rib thickness decreases the flutter speed at high thickness values.

Aeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.

In this paper, the dynamical behavior and stability of hanging micropipes conveying fluid with pinned-free boundary conditions are investigated. For a pinned-free rigid micropipe, the dynamical system is found to be stable for various flow velocities. Particular emphasis is placed on the effects of flow velocity, mass ratio and gravity on the dynamics and flutter instability of flexible micropipe system with pinned-free boundary conditions. The governing equations for flexible micropipes are discretized using the differential quadrature method (DQM), yielding a generalized eigenvalue problem which is then solved for various flow velocities, mass ratios and gravity parameters. It is shown that, with increasing flow velocity, the flexible micropipe with pinned-free boundary conditions is stable until it becomes unstable via a Hopf bifurcation leading to flutter. The system may lose stability first in the second or third mode, mainly depending on the selected value of mass ratio. The existence of mode exchange between the second and third modes is possible. The gravity parameter of positive values causes additional restoring force and hence enhances the stability of the micropipe system; however, it can generate the complexity of stability diagrams.

Efforts to develop the next generation of aircraft with ever-increasing levels of performance – higher, farther, faster, cheaper – face great technical challenges. One of these technical challenges is to reduce structural weight of the aircraft. Another is to look to aircraft configurations that have been unrealizable to date. Both of these paths can lead to a rigid flex coupling phenomenon that can result in anything from poor flying qualities to the loss of an aircraft due to flutter. This has led to a need to develop an integrated flight and aeroelastic control capability where structural dynamics are included in the synthesis of flight control laws. Studies have indicated that the application of an integrated flight and aeroelastic control approach to a SensorCraft high-altitude long-endurance vehicle would provide substantial performance improvement(1,2). Better flying qualities and an expanded flight envelope through multi-flutter mode control are two areas of improvement afforded by integrated flight and aeroelastic control. By itself, multi-flutter mode control transforms the flutter barrier from a point of catastrophic structural failure to a benign region of flight. This paper discusses the history and issues associated with the development of such an integrated flight and aeroelastic control system for the X-56A aircraft.

The stability behavior of the Leipholz’s type of laminated box columns with nonsymmetric lay-ups resting on elastic foundation is investigated using the finite element method. Based on the kinematic assumptions consistent with the Vlasov beam theory, a formal engineering approach of the mechanics of the laminated box columns with symmetric and nonsymmetric lay-ups is presented. The extended Hamilton’s principle is employed to obtain the elastic stiffness and mass matrices, the Rayleigh damping and elastic foundation matrices, the geometric stiffness matrix due to distributed axial force, and the load correction stiffness matrix accounting for the uniformly distributed nonconservative forces. The evaluation procedures for the critical values of divergence and flutter loads with/without internal and external damping effects are briefly presented. Numerical examples are carried out to validate the present theory with respect to the previously published results. Especially, the influences of the fiber angle change and damping on the divergence and flutter loads of the laminated box columns are parametrically investigated.

The transonic tail flutter and flap buzz under the wing-flap-tail configurations are analyzed utilizing a dynamic grid capability of unstructured Euler solver coupled with an appropriate aeroelastic solver. From the results, the presence of a forewing, either stationary or oscillating, has significant effect on the tail flutter characteristics. In particular, the tail motion may be in resonance with the oscillating wing before the onset of flutter, which is dangerous to the tail structure because of the large amplitude oscillations. Besides, a complicated aerodynamic and aeroelastic interference of the tail have been found due to the unsteady disturbance which is a strong variability of flow structure induced by the buzz of the flap. In the high transonic flow regime, the flap buzz with limit-cycle oscillations does occur, and the influence induced by the tail is not important. The increasing restoring force at the pivot where the flap joints with the wing will reduce the flap oscillations that improves the effect of the flap buzz.