First essentials of classical flutter are demonstrated by a comprehensive study of the behaviour of a lifting surface with two degrees of freedom under the action of airforces limited to those in phase with displacement. Structural coupling between the coordinates is eliminated by taking the normal modes to be the deflection coordinates, and this results in conditions for stability with particularly concise forms. It is shown that the flutter stability can be seen to be very much a matter of the relative amplitudes of heave and pitch in the normal modes.

In-quadrature airforces are then introduced and it is shown that they have little effect when the flutter is severe. They are of more importance in the milder forms of flutter, the extreme of which are shown to be little different from instabilities in a single degree of freedom.

A displacement-based versatile and effective finite element analysis of sandwich panels is presented. The analysis is applicable to both small and large deflections. Allowance for the local bending stiffness of the faces is made. The procedure described is readily adapted to arbitrary laminated beams and plates. Selected example problems are given to illustrate the applicability of the formulation.

Supersonic cavity flows driven by a thick shear layer at Mach 1·5 and 2·5 are studied by solving the two-dimensional unsteady compressible Navier-Stokes equations in terms of mass-averaged variables. The length to depth ratio of the rectangular cavity is three. The numerical scheme used is the finite-difference algorithm by Brailovskaya. A two-layer eddy-viscosity turbulence model is used. The results are compared with experimental data. The computations show the self-sustained oscillations at Mach 1·5 and 2·5. The continuous formation and downstream shedding of leading edge vortices is demonstrated. The oscillatory modes are correctly predicted. The first mode is attributed to a large unsteady trailing edge vortex moving in the transverse direction. Based on the analysis, it is considered that the oscillation in the length to depth ratio three cavity is a longitudinal one and is controlled by a fluid dynamic mechanism rather than a purely acoustic one.