Noel Penny Turbines Ltd (NPT) is progressively extending its family of low cost turbojet and turboshaft engines for application to unmanned vehicle systems (UVS). The family now incorporates eight distinct engine types, spanning a jet range of 50 to 1200 Ibf sea level static thrust and a turboprop/ turboshaft range of 15 to 450 SHP. The scope of these basic engines enables a wide variety of application and installational requirements to be covered. The crucial first target is low manufacturing cost.

The object of this paper is to introduce this UVS engine family and highlight highly significant design and development features necessary to meet both operational requirements and low cost.

The development of the jet engine produced jet noise problems. Most of the understanding of jet noise was and is performed in universities. The fundamental and quite exceptional work of Lighthill was followed by that of Curie. Powell and Ffowcs Williams at Southampton in the early 1950s and was paralleled by experimental investigations on noise suppression by for example. Lilley at Cranfield. This university work was used to form the basis of a programme of research into jet engine noise at Ministry of Aviation establishments with considerable university inputs which established a commanding lead for the United Kingdom in the understanding of jet noise.

The formation of the Institute of Sound and Vibration Research at the University of Southampton under the inspiration of Professor E. J. Richards was a step which placed university research at a different level to that usually observed in the United Kingdom by concentrating in one place some 40-50 people all devoted to research and postgraduate education.

Universities should be able to do two things which industry may not be able to do, and which should be valuable. We are supposed to be able to have time to think instead of continuously meeting deadlines (this is hardly true anymore) and so we can:

1. 1. Take a risk and embark on a novel idea which may not come off. If the gamble works then we publish and promote it for the general good.

2. 2. Recognise that industry has to meet deadlines, and often produce an answer to a problem which is only partially understood. We can then look at the problem in depth, and with better understanding point the way to future development.

My brief is to talk about flight mechanics. But flight mechanics covers all aspects of flight, including aircraft performance, operation and integrity. To limit this talk, flight mechanics is restricted to those aspects of flight dynamics which are concerned with the controllability of aircraft. Even so, it is a wide topic essentially interdisciplinary, embracing inertia, aerodynamics, structural dynamics, engines, hydraulic and electrical systems, instrumentation and avionics. Furthermore, the term ‘aircraft’ needs to be interpreted in the broader sense of referring to aeroplanes, missiles and spacecraft. In the spirit of this meeting, we are looking at contributions from universities in the past and identifying current centres of activity.

I hope that it will be clear from the brief accounts you have just heard that not only have the universities in the UK made a major contribution to the status and health of the aerospace industry but, given a modicum of encouragement, they can continue to do so. Indeed, I maintain for reasons that I shall make clear that the part that they can and should play is of greater importance now than ever.

Ever since the birth of the aircraft industry the universities have been making a continual contribution to research and development in aerodynamics. For example between the wars the work of Professor Melvill Jones and his school had a direct impact on the design of aircraft as illustrated by the classical paper (see Fig. 1) ‘The Streamline Aeroplane’ which was presented to the Royal Aeronautical Society by Melvill Jones in January 1929. In the immediate post-war years the work of Professors Lighthill, Ward and others laid the foundation of calculation methods for supersonic aerodynamics which eventually led to the design of practical supersonic aircraft. In addition staff in the universities have produced a continuous stream of theoretical and experimental results which have been useful, both in design, and in the overall research programme of the aircraft industry. In particular this work has resulted in a large number of new test techniques including the design and development of wind tunnels for special purposes. It is this aspect of current work which will be discussed first.

Several workers have found evidence for the presence of longitudinal vortices in wind tunnel wall boundary layers near the centre line of each wall, although the only actual publication appears to be the reproduction of Bearman's work in Ref. 3. The phenomenon usually observed is shown in Fig. 1: the boundary layer is considerably thickened near the centre line. (This symmetrical and localised perturbation should be distinguished from the effect of non-uniformities in the wind tunnel screens which apparently also leads to longitudinal vortices, randomly spaced across the width of the working section). The hypothetical vortex pattern is also shown in Fig. 1: it arises because lateral pressure gradients in the wind tunnel contraction naturally deflect the slow-moving fluid in the boundary layer towards the centre line more strongly than the main ‘inviscid’ part of the flow, implying the generation of longitudinal vorticity: this is secondary flow of Prandtl's first kind.

The advantages of using heavy gases in wind tunnels—reduced power consumption and scale size — have been appreciated for some time. To be sure of correct scaling of the results from such a tunnel, the working fluid should have a specific-heat-ratio γ equal to that of air (γ = 1·4); such a fluid can be obtained as a mixture of a monatomic gas with a polyatomic one. Here, general principles for choosing such a mixture are discussed, and estimates are given for the savings in size and scale which may be expected (compared to a conventional tunnel), following earlier work of Chapman.