For the purpose of this paper, certain fundamental parameters are assumed to be outside the control of the structures designer. It is, however, realised that the designer is often able to show that small changes in one or more of these parameters may have far-reaching effects.

These basic parameters include the aircraft size, weight, operating speed and altitude, aerodynamic characteristics and load factors. Fig. 1 shows how these combine together in various ways to give the loads acting on the structure, the temperature environment and the stiffness required to prevent aeroelastic disturbances.

A study of engineering problems encountered in the design of transparencies for supersonic aircraft is presented with a special emphasis on the effects of kinetic heating. The paper is written primarily with optical transparencies in mind but many of the general principles discussed are equally applicable to the design of radomes for elevated temperature applications.

The first parts of the paper consider briefly the methods of calculating temperature distribution in transparent panels subjected to kinetic heating (or cooling) and this leads naturally to discussion of the effects of the non-uniform temperature distribution, differential expansion and the edge restraints preventing thermal deformations. Methods of calculating thermal stresses are suggested through the concept of the “ self-equilibrating ” temperature distribution; the main attention, however, being concentrated on the derivation of simple engineering formulae rather than on the mathematical rigour of the solution.

The choice of design cases for combined pressure and thermal loading is considered and it is shown that, in general, deceleration manoeuvres combined with outward pressure constitute the design criteria for transparencies. The effects of various parameters on the magnitude of thermal stresses are analysed; these include the effects of altitude, temperature, deceleration and material properties. It is shown that, for given material and panel geometry, the thermal stresses depend mainly on the following parameters: total temperature change, acceleration (or deceleration), and the Biot number based on the panel thickness.

Practical design aspects are also considered, such as choice of materials, strength, panel geometry, mounting of panels and the fail-safe design. Finally, testing of transparencies under pressure and thermal loading is briefly discussed, together with possible methods of strain measurements, and a tentative proving procedure for transparencies is suggested.

This paper is concerned primarily with some of the practical difficulties encountered in connection with the prediction of kinetic heating temperatures. Attention will be concentrated upon methods for estimating temperatures and heat transfer rates for practical aircraft designed to fly at Mach numbers up to about five.

One factor common to all kinetic heating calculations is the variation of temperature through the thickness of the boundary layer, with consequent variation of viscosity. At Mach numbers above about 3, these temperature variations also lead to considerable variations of other properties of air—which are commonly assumed to remain constant—even in classical compressible flow aerodynamics. These factors complicate the aerodynamic equations.

The use of models for structural test investigations in the presence of kinetic heating effects is examined. The principal features of the complex process to be represented are discussed under the classifications external air flow, internal heat transfer, elastic response. Of these the second is found to influence most model design, and an analysis of a typical structure is included to illustrate the various contributions to internal heat transfer.

The aircraft designer must clearly ensure that his aircraft will fly in all climatic conditions normally to be expected. Over and above this, aircraft must be able to cope with a change in weather also.

Since the last war, research into the problem of ice accretion on aircraft has done much to widen understanding of this serious flying hazard. In the flight testing and development of ice protection systems for aircraft, however, one of the principal difficulties encountered is that of finding natural icing conditions sufficiently uniform through which to fly the test aircraft. Because of this it has been found more profitable not to seek natural conditions, but instead to fly in clear air at temperatures below 0°C, while spraying the test surface from a water spray rake fitted to the test aircraft.

If a plane oblique shock wave, inclined to the free stream at the angle ε, is produced in two-dimensional supersonic flow of Mach number M by (for example) a wedge which deflects the flow through an angle δ, the equation connecting these quantities may be written

In this form, δ is given explicitly when M, ε are fixed. Similarly, we may obtain M explicitly when ε, δ are fixed; equation (1) may be written (see, for example, Liepmann and Puckett, Equation 4.27)

The Basic Theory of the deflection of long, thin plates under normal pressure is extended to cover the effects of initial lateral tension or slackness in the plate and the effect of deformation of the supports at the edges of the plate under the lateral tension developed. The procedure is illustrated by application to a case of a plate under initial tension with its edges held apart elastically, and the computed values of the strains are compared with values measured experimentally. The application to an initially slack plate is also illustrated by a diagram.