Given the situation that there is at present something of a resurgence of interest in airships as practical vehicles, and that most people in aeronautics today are not very familiar with lighter-than-air flight, particularly in its technical aspects, it seems worth setting down a brief survey of the special characteristics of airships, as a contribution to the general understanding.

The present article was written with this aim in mind. It refers mainly to non-rigid or pressure airships, reflecting the fact that in most applications these appear to be simpler and cheaper than rigid airships, even for very high volume. However, much of the text applies equally well to rigid ships, and it must be accepted that adopting the “rigid” approach can give a useful extra measure of design flexibility (e.g. for internal cargo stowage).

During the first dozen years of space flight, from Sputnik to the initial Apollo lunar landing, the costs of space exploration and utilisation were not a major constraining factor. Indeed, the difficulty of initially penetrating beyond the earth's atmosphere and then the rapid extension of this capability to lunar distances (and beyond for unmanned spacecraft) dictated approaches that emphasised the highest performance, lightest weight, and the utmost in reliability that could be attained from the state-of-the-art available. As might be expected, conditions have changed. People are expecting a maturing relationship between the benefits achieved from space flights and the costs to attain them. Fortunately, approaches have been identified and the technology exists to greatly reduce the costs of space activities without degradation of safety or mission success. Of equal importance, we have identified many areas of actual or potential direct benefits from the ability to enter and operate in space which should be further developed. They include global communications, meteorology, earth surveys, materials processing, medicine, as well as the intellectual stimulation of scientific investigation and exploration, and others.

The simplest practical type of flow involving separation is that past a smooth flat plate with uniform velocity U0 at inlet followed by a linear adverse velocity gradient dU/dx = Constant (Fig. 1). At first the boundary layer is laminar up to the transition point xL. The turbulent boundary layer then grows with uniform potential flow velocity U0 outside the boundary layer up to the point x1 From x1 downwards the boundary layer grows in the presence of an adverse pressure gradient and finally separates at the point xs.

Much has been said and written about the last-minute preparation of the Royal Air Force for war after Munich, and of how disaster was so narrowly averted by inspired activity to produce fighters and train fighter pilots. Albeit there was more than a little luck on our side in the inability of the enemy to exploit a unique opportunity to attack this country immediately upon the outbreak of war in September 1939. We really were too weak to have stopped them at that time.

We were not only unprepared in numbers, but also to some extent in terms of tactical thinking and training. One of my earliest recollections of the Service was finding with something of a shock that as a newcomer, and at 18 scarcely more than a schoolboy, I had different ideas about the tactical use of fighters to those being taught at the time.

The question to be considered is the following—starting with the aircraft flying at the minimum conventional flying speed at a given height above the ground, how should the controls be operated and the flight path chosen, in order to bring the aircraft to rest on the ground in an optimum fashion? Optimum fashion can mean different things at different times but, in this context it usually means the simultaneous loss of speed and height in such a way that obstacles are surmounted but the total transi tion distance, time, or fuel used are minimised. The problem is one which may be solved mathematically by variational methods following Hacker or Brüning, but the approach in this study is a simpler one and is based on an intuitive search for near-optimum solutions by means of physical arguments.

A finite element which allowed warping constraint effects in open tubes to be taken into account was developed in Ref. 3. Because of the assumption of linear variation of the warping constraint direct stresses along the length of the element its flexibility matrix was very simple, but approximate.

In this note the flexibility matrix for an “exact” element is derived which will give results which coincide exactly with those obtained from the theory given in Ref. 1. It is assumed that the applied torque and cross-sectional properties do not vary along the length of a given element, but variation from element to element is, of course, possible.

The continued trend of increased weight and landing speeds of modern aircraft has strengthened the demand for improved materials for the manufacture of aircraft brakes.

The aircraft brake is similar to the car disc brake since both represent a medium for the conversion of kinetic energy to heat energy by means of friction. There are, however, unique problems which confront the aircraft brake designer since he is required to provide an acceptable mechanism involving components of minimum weight. The present paper discusses some general aspects of aircraft brakes and deals in more detail with some of the materials and material requirements for aircraft brakes; in particular it is hoped to show the manner in which advanced materials can provide some answers to the problems of the most recent development in design.

In a recent paper (Ref. 1) Dr. Hilton proposed the use of manoeuvres for creating zones of “no boom” which could be employed to protect cities situated along the flight path of a supersonic aircraft. The basic idea was to make use of the fact that curved flight causes a local focus of shock waves and that, in regions closer to the centre of curvature than this focus, shocks do not form.

In investigating this intriguing suggestion, the author found it advantageous to abandon the Huygens-type construction used by Hilton and employ in its place a technique which permits plotting the shock front directly. In applying this approach to manoeuvres of the type proposed for shock avoidance, regions of single, double and even triple shocks were found, but no shockless region. The method used and the results obtained are outlined briefly in the following sections.

The obtuse corner of the skew plate is a singular point with a stress singularity growing in intensity with an increase in the angle of skew. For regaining the full rate of convergence of the finite element method the mesh around the singular point should be properly refined or the leading singular terms included in the finite element scheme. In any event a large number of unknowns may be required. For obtaining an accuracy of 1% in the 10th Eigenvalue of a clamped square plate discretised with the 16-degrees-of-freedom elements used in the present calculations, about 300 variables are required. For computational convenience calculations were carried out here with a uniform mesh requiring even a larger number of unknowns.

The main object of tests on models in wind tunnels is to obtain results of direct application to aircraft in flight. Unfortunately, the flow about a model in a wind tunnel is subject to constraints that are absent in flight, and so allowance must be made for these wind tunnel interference effects for the results to be meaningful.

There is a considerable body of information on the sources of wind tunnel interference and, so far as effects in steady flow are concerned, methods of estimating the corrections to be applied are generally available. They enable results of wind tunnel tests to be reduced to equivalent flight results with some measure of confidence. The situation is far less satisfactory for oscillating models. The additional interference effects due to frequency of the motion may be of too complex a nature or require too tedious a computation (particularly for a deforming model) for a reliable reduction of the results to flight conditions to be practicable.

This paper represents a second stage in a continuing theoretical study of aircraft longitudinal responses to random turbulence based on stationary random process theory. In previous papers the spectral gust alleviation factor for eg normal acceleration, was studied in detail. In the first, the aircraft was assumed to be rigid, responding only in heave, and the effects of unsteady aerodynamics were K, systematically considered. Wherever possible, comparisons were made with previously published work. For the published version the report was revised and expanded to include some results for the pitching aircraft but this analysis was not complete. This paper is concerned with a more complete analysis of the longitudinal responses of a rigid aircraft, free to heave and pitch, flying through random turbulence. The turbulence is assumed to have a power spectral density function described by the Dryden model.

The advent of SI units makes it necessary to revise many standard constants and numerical values which are familiar to a generation of aeronautical engineers whose education and practical experience have been solely with the British system of units.

Most affected by these changes are not so much those who spend all their time carrying out (computer-aided) calculations, but those who direct such work and whose personal calculations are limited to the backs of envelopes. The task, for the latter, of assessing and communicating data presented in unfamiliar units is very daunting, and the possibility, for them, of ever being able to think in the new units may seem remote.

I shall discuss two examples of possible future deep space missions but first of all let me fill in a little of the scientific background in order to give you some idea of the kind of questions that we would aim to answer by undertaking these projects. It is now rather more than twelve years since the first spacecraft were placed in independent orbit round the sun. These were Lunik I and Pioneer IV which were the first satellites to make measurements in space outside the earth's gravitational field. In these twelve years as a result of the succession of space probes which has followed we have learned a great deal about the physics of interplanetary space where the situation is dominated by the solar wind and magnetic fields which it carries out from the lower corona. Let me remind you of the salient facts.

Numerical solutions to unsteady flow problems have been developed, and often it is not possible to carry out a direct check on their accuracy. However, such a check was given in Ref. 3 using an analytical solution for zero spatial velocity gradient. The object of the present note is to present a different simple analytical solution which can be used as a special case for checking the accuracy of a numerical solution. Also, the solution is of interest itself as it corresponds to certain gas dynamic problems.