Mutual interactions-between aerodynamic and structural forces cause aeroelasticity that is very important in aircraft wings. In this paper, instability of a wing in dynamic situation that is called flutter is considered for a composite wing in subsonic flows. The "Strip Theory" approach is used to calculate the aerodynamic forces along the wing. For this reason, displacements along the wing and flutter speed are determined using the "Assumed Mode Method ". In this method, the displacement along the wing is assumed by definite boundary conditions. The stored potential and kinetic energy in the wing, as well as the generalized aerodynamic forces and moments on the wing, are determined. By employing Lagrange’s equations, the wing motion is formulated. A Computer program has been developed to calculate the speed of the wing instability, the effects of the elastic axis and the center of gravity has been investigated on the stability of the wing. The flutter speed is calculated for a certain wing, which the data is available, and a suitable elastic axis has been determined for a specified center of gravity.

The investigation of the self-feeding forces impact on the structural displacements in turbulent wind is presented. This impact is dealt with as a ratio of the displacement variances with and without the self-feeding forces, and a formula is proposed for this ratio on a 2DOF section-model. The paper also presents a method to determine the softness of the flutter that affects significantly the impact of the self-feeding forces over the buffeting forces. This method highlights the influence of the flutter derivatives on how the structural parameters affect the softness.

This study addresses the prediction of the flutter speed for a double-sweep folding wing in subsonic airflow, an area less explored in past research. Two types of modeling are employed: structural and aerodynamic. The structural model treats the wing as an Euler-Bernoulli beam. For the aerodynamic model, Theodorsen's unsteady aerodynamic theory is used. This theory is initially in the frequency domain but is converted to the time domain using the Kussner function and a new formulation method. Kinetic energy, strain energy, and the work of aerodynamic forces are then calculated. The differential equations governing the wing structure are derived using Hamilton's principle. The wing's motion equation is obtained using assumed modes and the Galerkin method. The instability flutter speed is determined through the p-method, and graphs of frequency versus airflow velocity are plotted. The results indicate that using the Kussner function for variable airflow improves the accuracy of flutter speed prediction. The analysis of sweep angle changes on flutter speed and frequency revealed that sweep angle one has the least positive effect, while sweep angle two has the most positive effect on flutter speed and frequency, respectively.

In this work, wind tunnel experiments were conducted to evaluate the critical flutter speed of wings for three pertinent flight parameters (i) the aspect ratio (AR), (ii) the angle of attack (AoA), and (iii) the aircraft propeller excitation. Six symmetrical wings (NACA0012 design), of fixed chord length of 80 mm and varied AR from 8. 75 to 15, were used for this purpose. These wings were mounted horizontally in the wind tunnel as fixed-free condition. The airflow speed is increased slowly until the wing flutters. The results show that the critical flutter speed decreases when the AR increases. For higher AR, the effect of the AoA on the flutter speed is minimal. However, for low AR, the AoA is vital in delaying the flutter instability of the wing. This critical speed spans low to moderate Reynolds numbers based on the wing chord length (Rec =7×104-2×105) which corresponds to the speed range of High Altitude and Long Endurance (HALE) aircraft. In contrast, for a propeller excitation outside the resonance region of the wing, its effect of the on flutter characteristics is not noticeable.

The body freedom flutter phenomenon is one of the aeroelastic instabilities that occurs due to the coupling of the aeroelastic bending mode of the wing with the short-period mode in the flight dynamics of the aircraft. By using the aeroservoelastic model and applying closed loop control, this phenomenon can be suppressed in the operating conditions of the aircraft and the velocity of this event can be increased. The simplest model aircraft capable of displaying this instability includes the flexible wing and the planar flight dynamics model. For this purpose, the wing structure is modeled using the Euler-Bernoulli beam and, the theory of minimum variable state is used to model unstable aerodynamics to make the conditions suitable for modeling the system in state space. In the control section, the elevator is used as the control surface and LQR theory with Kalman filter is used to body freedom flutter suppression. Finally, the effect of adding a closed loop control to increase the body freedom flutter velocity and the limitations of this work are studied.

The presented paper investigates the flutter phenomenon in a rectangular-shaped plate in supersonic air flow. First, the phenomenon of flutter and its identification method based on the analysis of eigenvalues are presented. Then, using the assumptions of Kirchhoff plate, the plate motion equation is derived and coupled with the first-order piston aerodynamic model. Next, the coupled structure-fluid equation is solved in matrix form using the differential quadrature method (DQM). Using the DQM numerical method in matrix form provides advantages such as high accuracy for solving the flutter problem. The obtained results show that the first phenomenon of flutter in an aluminum plate with a length and width of 1 meter and a thickness of 5 mm with clamped-free-clamped-free boundary conditions occurs in dimensionless dynamic pressure 617 (equivalent to Mach 3.395). The presented formulation can be used as a benchmark for solving and calculating the flutter speed of various objects in the supersonic air flow.

In this study the vibration behavior of a laminated composite cantilever plate with an attached strip mass was studied. In order to extract flutter speed, the Rayleigh-Ritz method was used by choosing selected shape functions. In this method, strain energy of the plate is calculated and the effect of attached mass is considered as kinetic energy for the system. After reaching an eigenvalue problem then natural frequencies, the force vibration of the plate is analyzed by piston method and flutter speed for each case study is obtained. The effect of the attached mass length is shown. Moreover results have shown that flutter speed was reduced continuously by increasing the mass density. Also by considering a specific laminate with different orientation of layers flutter speed is obtained. At the end attached mass offset from clamped edge is analyzed. In this paper effect of attachment mass, mass length and mass position on plate flutter frequency is analyzed. The results obtained through this study reveal that strip mass density, attached mass length, orientation of composite layers and attached mass position can change the system critical dynamic pressure significantly.

In this article, the Flutter speed of a composite wing carrying two power engines is analyzed. The wing is modeled as a beam with two degrees of freedom, which is a cantilever, with two thrust as a follower force and mass of the engines. Wagner theory has been used for aerodynamic model and using the assumed mode, the wing dynamic equations of the motion has been achieved by Lagrange equations. Linear flutter speed according to the eigenvalues of the motion equations was calculated. In order to valid the results of present work, at first composite wing assumed without engines and then wing modeled with two engines that results are compared with published results and good agreement has been observed. Composite wing has been analyzed as one layer and also laminate layers, and effect of variables such as follower force, engines mass, position of engines and number of layers has been investigated and the results show that with increase in mass and force of engines and also with increases distance between engine and wing root, flutter speed decreases and with decrease distance between engines and leading edge, flutter speed increases.

In this article the composite wing aeroelastic instability speed is optimized by genetic algorithm relative to fiber angle for different layers and follower forces. Aircraft wing is modeled as a beam with two degrees of freedom, which is a cantilever, with thrust as a follower force and mass of the engine. For structural modeling of composite wing the layer theory has been used and unsteady flow assuming subsonic and incompressible flow was used for aerodynamic model in the time domain. Using the assumed mode the wing dynamic equations of the motion were derived by Lagrange equations. Linear flutter speed according to the eigenvalues of the motion equations was calculated. The process of flutter speed calculation has been converted to computer code in which the number of layers, angle of fibers in each layer, the mass of the engine, and the thrust are input variables and the flutter speed is its output. Using Genetic Algorithm, optimum flutter speed was obtained by changing the angle of fibers. Finally, the impact of the number of layers, the mass of the engine, and thrust on optimum flutter speed has been investigated.