The advent of air- and spaceflight vehicles and that of nuclear explosions as well as the trend of constantly increasing and higher structures have brought attention to the need for better understanding of the dynamic response of such a system. The knowledge of free and forced large amplitude vibrations of structures or parts of it, as well as the response of them to pulse excitations, are of pronounced influence upon their design. Whether one deals with aerospace structures or civil structures, such as bridges or buildings, one is faced with the prediction of loads due to some wind or gusts.

The problem considered in the present note is that of the laminar boundary layer created by the motion of a strong shock wave. Such shock-induced boundary layers occur in shock tube flows behind the primary moving shock wave. For structural reasons, shock tubes frequently do not have very large diameters, so that such boundary layers often adversely affect the quality and duration of the test gas flow. The latter problem is studied, for example, in ref. 1 and to attempt such a problem a fairly detailed knowledge of the behaviour of shock-induced boundary layers is required. Such basic boundary-layer studies have been described in refs. 3-8 and the situation which occurs when the shock wave is strong is investigated here. The boundary-layer equations are expanded in a series form which involves a small parameter. This small parameter is shown to be the ratio of the gas densities fore and aft of a strong shock wave.

The terms of reference required the Committee to take account of safety when formulating its proposals. As a starting point the Committee had the report of a Special Review (published in 1968) entitled “The Safety Performance of United Kingdom airline operators”.

With this in mind, Edwards formulated as part of the long-term objectives of civil aviation policy that safety should be “equal to the best in the world” (paragraph 1053) —but although a great deal of attention was given to air safety, the Committee admitted that it had “not felt competent to consider the technical aspects of safety in depth” (paragraph 840).

The calculation of the inviscid, incompressible flow past non-lifting three-dimensional bodies has been greatly facilitated by A. M. O. Smith and his collaborators, using distributions of elementary singularities over the surface of the body. There is considerable current interest in the extension of this work to lifting bodies, involving the representation of the real viscous wake by a vortex sheet of zero thickness in the inviscid model of the flow. In view of this interest, it is appropriate to consider the way in which such a vortex sheet behaves at the trailing edge of a wing with non-zero trailing-edge angle. Is the sheet tangential to the upper surface of the wing, to the lower surface, or to neither?

During the past decade, the theory of optimal control associated with linear multivariable systems having state and output equations of the respective forms

and

has been applied extensively to the design of controllers for a variety of aerospace systems. Such applications of this theory have been mainly concerned with the design of controllers that generate optimal control vectors, ẑ, which minimise performance indices of the form.

where Q and R are positive-definite matrices.

For some years now an increasing amount of experimental and theoretical work has been done to obtain a deeper understanding of separated vortex flow associated with slender wings. Most of it has been concerned with flat plates or thin wings.

Slender thin wings with leading-edge separation have high lift-dependent or vortex drags, and lift-dependent drag factors are usually well above unity. Thick symmetrical wings also have high values of lift-dependent drag factor. On a slender wing with leading edge separation, no leading edge thrust is obtained but by suitable! addition of thickness, the high suction peak underneath the main vortex can be made to act on a forward facing surface to give a reduction in drag.

Many authors have established that a finite wing in inviscid flow has a theoretical maximum lift coefficient. One formula based on a theoretical model of a rolled-up vortex system aft of an elliptically loaded wing is

where AR is the aspect ratio. Ref. 6 criticises the validity of eqn. (1) but at least eqn. (1) gives the order of magnitude of an inviscid CLmax.

Economic and investment opportunities in the light of, the Edwards Report! The subject must have been devised by an engineer. I do not understand it. What can economic opportunities mean? Economics is concerned with finding how best to apply the finite resources of mankind to its infinite wants. What opportunities of this kind does this Report give us? I think it will help make air transport more economic through its educating influence, principally on the powers-that-be.

Spalding and Chi have shown that their method of predicting the skin friction and momentum thickness for the compressible turbulent boundary layer with and without heat transfer gives good agreement with experimental data. For practical purposes a knowledge of the shape parameter, displacement thickness and boundary-layer thickness are also often required. In this note it is shown that the predictions of these additional boundary-layer parameters by extending the work of Spalding and Chi do not compare so favourably with experiment. New correlations have therefore been developed and are reported in this note which provides the basis of Item No. 68020 in the Royal Aeronautical Society Aerodynamics Sub- Series of Data Items.

Several authors have considered the lifting characteristics of various simple shapes at hypersonic speeds. Non-weiler has dealt with shapes derived from wedge flows, and Townend has considered a class of two-dimensional shapes with concave undersurfaces. Cole and Aroesty and Pike have both considered two-dimensional shapes which are perturbations of simple wedge flow. They show that slightly higher values of the lift-to-drag ratio than that of the wedge are obtainable. Cole and Aroesty apply hypersonic small disturbance theory, under the constraint of constant lift, and suggest that the optimum shape is a “multi-wedge”. They show further that the optimum of a more restricted class of shapes having undersurfaces made of two plane surfaces, has a slightly concave surface. Pike has applied a more accurate (second-order) perturbation theory to a class of shapes which consist of small deviations from a wedge. He finds that the optimum undersurface consists of two plane surfaces, and confirms Cole and Aroesty's result that it must be slightly concave, except perhaps at low Mach numbers below the hypersonic range. It must be remembered that these results depend upon the assumed constraint of constant lift.

The note is concerned with four points in the analysis of laminar shock-induced boundary-layers in undissociated gases. The first point concerns the restrictions imposed by the requirement that similar solutions be obtained. The second point concerns the properties of two simple solutions which can be obtained when the Prandtl number is unity. The third point concerns the accurate prediction of surface heat transfer rate in terms of surface shear stress. Here, an extension and correction to a method employed by Spence is presented. The fourth point concerns the accurate prediction of surface shear stress, a slight modification to an existing mean enthalpy method being suggested in an attempt to correlate most of the available data.

To save weight, designers of aircraft gas turbines aim to produce axial compressors with fewer rows of blades and greater mass flows per unit of frontal area. These improvements often consist of increases in blade tip speeds and reductions in the ratio of the hub to tip diameters. As the efficiency of transonic blading is partly dependent upon a low value of blade pitch/chord it is now frequently necessary to design a blade with a greater actual chord at the tip than at the hub.

In a vibrating system with a non-linear restoring force the effect of gravity, if it influences the equilibrium of motion, is not completely balanced by the static deflection force. This produces in most cases an increase of the magnitude of non-linearity because of the displacement of the static equilibrium point on the restoring force characteristic. The static deflection parameter thus offers a more complete definition of this effect and is consequently used in the vibration equation in preference to the force of gravity. Previous investigation of the free vibration indicates that the existence of a static deflection must result in considerable changes of the forced vibration response.

The purpose of this note is to report some recent observations of the tailoring conditions for combustion driven shock waves and to offer explanations for two distinctly different pressure histories recorded during the combustion process.

The technique of initiating strong waves utilising combustible driver gas mixtures, such as stoichiometric hydrogen and oxygen with a helium diluent, is now well established, see Gaydon and Hurle.

A Fast and efficient method has been developed to obtain the equilibrium composition of a flame at a given temperature, pressure and mixture strength. The Newton-Raphson iteration technique enables one to solve a set of simultaneous non-linear equations and in the present problem these are the equations relating the equilibrium partial pressures and equilibrium constants for the particular reaction and the conservation of atomic species in reactants and products. A trial solution is used to check the energy balance for the flame at the assumed temperature. The temperature is then suitably altered and the whole procedure is repeated till a reasonable agreement is obtained.

For many space applications, such as communication, weather, military, and scientific experiment satellites scanning precise regions, 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 in libra-tional 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.