It is now some 20 years since aircraft noise became a significant public nuisance and every conceivable aspect of the problem has been scrutinised and discussed in a vast literature. The scope of the present paper, in relation to this broad canvas, will appear extremely narrow. Nothing will be found herein about such important questions as the influence of noise on the development of aviation, engine technology, operational procedures, reduction of noise by acoustical means, the economics of air transport, regulatory action, or the planning of airports. It is only necessary to make slight reference to these matters to sketch the framework within which a system of measurement and assessment of noise has developed. The circumscribed nature of these aspects, unfortunately, does not mean that they can be dealt with briefly or summarised easily.

A paper was read to the Test Pilots’ Group of the Royal Aeronautical Society in 1974 some months before the first Hawk flew in August of that year. On that occasion the paper consisted of some background information on how the aircraft came about, followed by a technical description and outline of the projected flight test programme. Now, some two years later, it is intended to describe the flight test programme in general terms from first flight up to the end of 1975. It is hoped that in due course some detailed aspects of this programme will be presented as a separate paper to the Test Pilots’ Group. Before starting on the flight test programme I intend to give a brief description of the aircraft for those who have not seen it before, and to refresh the memories of those who have.

Since the advent of air transport half a century ago, safety has been a dominating influence in aeroplane design. It is by no means the only factor. The successful designer is one who uses his talents to arrive at the best balance between the competing demands of speed, reliability, comfort, and cost, while satisfying the demands of safety.

The fundamental reason why the aeroplane places high demands on the designer, perhaps to a greater degree than is the case with surface vehicles, is that the aeroplane proceeds on its way in defiance of gravity. It has to be light enough to fly, and it cannot stop for running repairs. Working within the limitations of available materials and fuels, it took mankind a long time to discover how to make an aeroplane light enough to fly at all. It is a near miracle that some 70 years later, today's aircraft carry large loads for long distances with remarkable safety.

For many years, a first order understanding of aircraft performance has been possible from lift drag curves or forward speed/sinking speed curves for gliders. These presentations of performance are not sufficiently accurate for detailed aircraft performance analysis, but their understanding has enabled generations of aircraft engineers to grasp the importance of various aerodynamic parameters.

A new method of presenting the sailing vector triangles is described. When the locus of the possible vector triangles is drawn in the new presentation, a large portion approximates to a straight line parallel to or making a small angle with the Xaxis in the neighbourhood of the best speed to windward. A geometrical construction is given, which defines the best speed to windward point. It becomes self-evident that, as is well known, most yachts sail at nearly 45 degrees to the true wind when sailing at their best windward condition.

This note is concerned with the response of a pitot tube in the region of its interaction with a weak shock wave. It will be helpful if we distinguish immediately between our usage of the terms ‘pitot pressure’ and ‘normal shock recovery pressure’. We use the former to mean the experimental reading obtained from a pitot tube and the latter to mean the theoretical stagnation pressure downstream of a normal shock at the Mach number of a point in the flow.

Across an oblique shock, the normal shock recovery pressure changes discontinuously. However, in the course of a recent study of the impingement of supersonic jets on flat plates, the authors noticed that, as a pitot probe was traversed across a weak shock wave, not only was the discontinuity smoothed out by the finite size of the probe but also values of pitot pressure were obtained which were larger than the higher of the two values of normal shock recovery pressure.