For many space applications, it is necessary to maintain a satellite in a fixed orientation relative to the earth. Unfortunately, a correctly positioned satellite deviates with time from this preferred orientation due to perturbing environmental forces. This explains considerable interest librational stability study in recent times.

Among the numerous methods developed for librational control, a passive technique depending on the gradient of the gravitational field has gained attention. Depending on the orbital distance, environmental effects, such as, aerodynamic, radiation, and magnetic torques become significant compared to the gravity-gradient restoring moment. A need to determine the influence of these disturbing forces is thus evident.

For flows at Mach numbers much less than unity the fully-developed wall shear stress in a circular pipe may be determined directly from a knowledge of the pipe radius, R, and the measured gradient in static pressure along the pipe, dp/dx. At higher subsonic Mach numbers it is conventional to apply a one-dimensional compressibility correction to make allowance for the acceleration of the fluid arising from the progressive decrease in density along the pipe. The correction procedure is to determine a “frictional” pressure gradient, dpf/dx, associated with wall shear stresses alone.

In their earlier paper the first two authors have given a solution to the problem of bending of clamped skew plates. The solution was obtained using the eigenfunctions of a beam. They have shown in their discussion that their results agree with other investigators except Kennedy who has used Galerkin's method. It was surprising to note that though both the authors’ and Kennedy's methods converged well, the results did not agree for all the cases and the difference being maximum for the rhombic case. It was mentioned in the discussion that additional work was desirable to resolve the difference. Hence in this note results using a different approach have been presented both for clamped and simply supported isotropic skew plates subjected to uniformly distributed load and the results are compared with the available ones.

A wing of finite span in flight generates trailing vorticity which “rolls up” into two “discrete” vortices. During the rolling up process the trailing vorticity is displaced vertically downward (assuming that the aircraft is in horizontal flight) under the influence of the wing circulation and the self-induced downwash velocities. In this note a method is presented for the prediction of the spatial distribution of the trailing vorticity during the rolling up process, thus giving the overall downwash field behind the wing.

The amount of research carried out in the field of highly swept wings has reached massive proportions. No attempt is made to review the literature on this subject but it seems that despite all efforts, no method yet exists for calculating the lift of delta wings in subsonic flow where the trailing-edge condition makes true conical flow impossible. A recent paper by Nangia and Hancock, has attempted this very difficult problem but the method proposed is not yet suitable for general application. Greater success has been obtained in supersonic flow,see for example ref.2.

Various formulae have been obtained for the lift coefficient of delta wings in conical flow and the lift can be divided into two parts; the linear part where the flow is fully attached in the region of zero incidence and the nonlinear part where extra lift is obtained from the leading edge vortices. One typical formula is derived from a relatively simple theory by Edwards.

A general review of the state-of-the-art in relation to stability augmentation in aircraft design, with an attempt to produce a co-ordinated view on the philosophy of its application, is something that I have long felt I should like to see done—but not by myself. My initial reaction on being asked to present such a paper was that this would better come from those concerned with the development of auto-control systems, but on second thoughts, there appeared to be some merit in considering the situation from the point of view of one concerned with the more basic aspects of aircraft handling and operation, putting the emphasis, therefore, on what is required or desirable in these respects, rather than on how it might be achieved. This, then, is my first aim; to consider various possible areas of application of stability augmentation, and advanced control techniques, to aircraft design; my survey will not attempt to be comprehensive but rather, selectively illustrative; it will, however, extend out beyond the confines of pure aircraft design, to externally guided aircraft flight, and in particular automatic landing.