The testing of model rotors in closed throat wind tunnels is known to present major problems in the form of tunnel wall interference when operating at low speed. However, it is precisely this region of the aircraft's flight envelope which is of prime importance when investigating areas such as transitional flight, hovering in winds and tail rotor performance and handling qualities. Although much work has been carried out in the past to determine wall interference factors for various model and tunnel configurations, there still exists a problem of flow breakdown due to the presence of tunnel boundaries, for which no corrections are possible. The aim of this experiment was to conduct a short and simple investigation, first to identify the flow breakdown condition for a finite sized rotor in a closed tunnel, then to assess the feasibility of at least delaying the onset of this limiting condition by selectively removing panels from the walls of the working section. Since the experiment was designed only to study gross flow effects, no attempt was made to include wall interference factors.

Non-destructive testing (NDT) is not a new procedure and it is not intended that, by choosing the thirty odd years since the War, the impression should be given that before 1945 little or no attention was paid to determining component, system or structural quality by non-destructive means.

Archimedes, having discovered the principle of flotation, applied it as a means of determining whether his King's new crown had been unduly alloyed with silver. He is therefore probably the first on record to practise what is now known as NDT.

During the preparation of this paper within the present stringent financial climate in the industry I have been deeply conscious of time and cost, since it is much more difficult these days to give the time and also to justify the cost of an activity of this nature.

Initially it was intended to examine the contribution of the aircraft designer to the improvement of those phases of the total journey over which the designer could have a direct influence. However, the organising committee had other thoughts and has requested that I should point up those aspects where, despite the efforts of the aircraft manufacturers to improve their product by reducing airborne times and real costs, many of the resulting benefits appear to have been frittered away and lost within the surface phases of the total system.

Aerodynamic heating, which is generally recognised as one of the most important aspects of the re-entry technology, plays an important role in the design of re-entry vehicles. Vehicles entering the earth's atmosphere at high velocities are subjected to severe heating. A number of methods are available for protecting the interior of a re-entering vehicle. However, preliminary studies indicate that, in general, utilisation of a charring ablator is one of the most effective thermal protection systems.

A space vehicle is usually required to maintain a specific orientation with respect to Earth. If flexible appendages (such as panels of solar cells) are associated with the vehicle, the problem of controlling the attitude of the spacecraft becomes more complex. In this paper, attention will be directed towards the control of this class of vehicle when the control law suggested by Hughes is employed. This approach requires that the attitude and its rate of change with time are available in satisfactorily noise-free forms. The measurement of attitude is physically possible, but the measurement of rate is not. Consequently a Luenberger state observer was employed by the authors to reconstruct the rate information. A similar approach was adopted earlier where an analogue model of the observer was employed. It was found that in some situations the design procedure for the observer stipulated that very large amplifier gains should be incorporated into the model, and great care was needed to avoid this problem.

Jet thrust at low speeds is notoriously inefficient, and ejectors have often been proposed as thrust augmenters in the hope of increasing the mass flow and momentum flux for a given expenditure of energy. Henri Coanda reported the development of a successful thrust augmenter (the Coanda nozzle) for the propulsion of ambulance sledges in Russia during the Second World War, and useful thrust augmentations with this were reported by Sproule and Robinson and Reba. These reports raised interest in the technical press, and large scale experimental programmes have been mounted by Lockheed Aircraft, Cornell Aeronautical Laboratory, Hiller Aircraft and others. However, no clear conclusions seem to have resulted. Although recent published analyses of the performance of ideal ejector thrust augmenters stress the importance of size and energy input, no detailed analysis of the many different definitions of thrust augmentation which appear in the literature, or of their practical implications, seems to be available.