Search

An experimental investigation into the use of a bistable winglet to enhance the lift characteristics of a wing transitioning from lower to higher subsonic flow speeds is presented in this paper. The concept centers around the use of a specifically designed composite winglet, manufactured with an unsymmetric layup, which, when increasingly loaded, snaps between two stable states. Initially, during low-speed operation, the winglet is fixed in one stable state that is specifically designed to be cambered, thus enhancing the lift capability of the wing. At higher dynamic pressures, the winglet snaps to a configuration more intuitive and conventional to current winglet design. Results presented in this paper show the concept to be viable at enhancing the lift produced by a swept wing as aerodynamic loading increases before snap-through. During snap-through, however, the absence of any method of controlling the snap-through process generated significant dynamic loading that was transmitted, unhindered, throughout the entire test rig.

DOI: 10.2514/1.27720 This paper investigates a novel method for the control of 'morphing' aircraft. The concept consists of a pair of winglets with adjustable cant angle, independently actuated and mounted at the tips of a baseline flying wing. The general philosophy behind the concept was that for specific flight conditions such as a coordinated turn, the use of two control devices would be sufficient for adequate control. Computations with a vortex lattice model and subsequent wind-tunnel tests demonstrate the viability of the concept, with individual and/or dual winglet deflection producing multi-axis coupled control moments. Comparisons between the experimental and computational results showed reasonable to good agreement, with the major discrepancies thought to be due to wind-tunnel model aeroelastic effects.

A method to calculate the derivatives of the eigenvalues and eigenvectors of multiple-degree-of-freedom damped linear dynamic systems with respect to arbitrary design parameters is presented. In contrast to the traditional viscous damping model, a more general nonviscous damping model is considered. The nonviscous damping model is such that the damping forces depend on the past history of velocities via convolution integrals over given kernel functions. Because of the general nature of the damping, eigensolutions are generally complex valued, and eigenvectors do not satisfy the classical orthogonality relationship. The proposed method to calculate the eigenvector derivative depends only on the eigenvector concerned. Numerical examples are provided to illustrate the derived results.

A study was conducted to analyze characterize a technique for extracting second-order systems from state-space representations. The physical systems were modeled as second-order differential equations. The method supported the formation of a subset of displacement degrees of freedom from the outputs. In addition, a condition was given for the original input and output matrices needed to support a transformation.

This paper describes a method to transform linear dynamic systems from a state-space form to a second-order form. The method employs displacement degrees of freedom as an output and excitation as an input to derive structural dynamics equations.

Coordinate selection procedures based on Guyan reduction and Fisher information matrix help select optimal measurement location for experimental modal testing. Both models sequentially reduce the degrees of freedom of an original detailed finite element model till the number of degrees of freedom equals the number of locations desired. The coordinates to be eliminated are chosen automatically and the remainder are used for modal testing.

Available direct methods of model updating to calculate the damping and stiffness matrices of a structure were improved. The technique minimizes the change in the damping and stiffness matrices, with the constraint that the measured modal data is reproduced. However, the process does not ensure that the updated matrices will be positive definite, and the connectivity of the previous finite element model may be lost.