It is indeed an honour and a pleasure to join with you in honouring the memory of one of the great pioneers in British aviation. When I read the story of Captain Frank Barnwell's life so ably presented by Major Bulman in the first of these lectures, I was struck by the indomitable spirit of a man who, at the age of 57, was still determined to flight test his own new design. It is the same type of spirit that sustained Alan Shepard through a decade of physical adversity to reach the moon at the age of 47 and perform on its surface with all of the vigour this mission required. It is this type of human spirit that has made all of the fabulous technical achievements possible, and it is this type of spirit that is an essential ingredient for the continued assault on the great unknowns that lie in murky darkness all along the frontiers of man's knowledge of himself and his universe.

An important growth of air traffic is recorded, as compared with other forms of traffic. Fig. 1 is an example of the domestic-intercity passenger travel market in the USA and is characteristic; showing (millions of passenger miles)

stagnation for waterways;
stagnation for autocars—buses;
decreasing for railroads;
expansion for airlines: annual growth rate of 10% over the past fifteen years, and acceleration since 1962: mean annual growth rate 18%.
It is also important to mention the expansion in freight, which is about 20% a year, i.e. doubled every four years.

Since they were introduced at the end of the Second World War, aircraft turbojets, with which the name of Sir Frank Whittle must be associated, were in fact the object of considerable progress in terms of performance improvement, although this was achieved at the cost of an increased complexity.

While preparing this paper from old log books, diaries, photographs, etc, I was struck not so much by the advances aviation has made in the past half-century, but by the enormous gulf that divides “flying” in those days from the present day. It is laughable for instance to record that our average speed over the ground for the whole Far East Flight was 70 kt—80 mph, the greatest height we achieved 5500 ft and we had to land for fuel 27 times between England and Singapore. It may be more efficient to be dragged through the air in a tin box at ten times that speed and height, but it is not nearly so much fun.

Another thing I realised was how the map of the world has altered in 43 years. Except for a few comparatively small gaps the whole of our flight was over British Empire territory or land dependent on it. Many of the countries we visited in 1927 would slam the door in our faces if we tried to go there in 1970.

The problem of obtaining proper flow spreading together with useful pressure recovery across rapidly expanding diffusers is of considerable practical importance. Many different approaches to this end have been reported in literature, e.g. vortex generators, screens or baffles, surface roughness, corrugations, etc., apart from the use of direct boundary-layer control. These methods have the common aim of preventing separation from the walls of the diffuser. With increasing expansion angle and area-ratio, however, the effectiveness of these methods either breaks down or is obtained at a high cost of pressure recovery.

Theoretical studies of the response of supersonic transport aircraft (SST) taxying and taking-off on uneven runways showed several years ago that the vertical acceleration in the cockpit of an SST of typical configuration would be greater than that in a subsonic transport on the same runway. The vibration would occur mainly at the frequency of bending of the fuselage, which might be 2 Hz, and would be forced by long, shallow undulations of the runway. These might have wavelengths of 50 ft to 300 ft (15 m to 90 m) and amplitudes of 1½ in to 4 in (0·04 m to 0·10 m) peak-to-peak, and are so unlike the usual concept of a rough surface that a different term, unevenness, is used to describe them.

In many applications of boundary-layer control by tangential blowing the surface downstream of the blowing slot is likely to be strongly curved. For example, this is the case when blowing around a bluff trailing edge is used to control the circulation around an aerofoil as described in ref. 1. The flow involved in such cases is that of a curved wall jet in an adverse pressure gradient. A knowledge of the radial and tangential pressure distributions in the curved wall jet is required if development of the flow and separation are to be predicted.

The problem of maintaining a satellite in a fixed orientation relative to the earth has led to the investigation of several methods of attitude control. In particular, the one involving passive stabilisation using gravity-gradient torque has aroused considerable interest. However, a major limitation of this manner of stabilisation is its inability to achieve station keeping to a high degree of accuracy. Furthermore, some form of external damping is necessary to recover an equilibrium configuration in a reasonably short period of time. Modi and Brereton investigated the energy dissipating mechanism which was an extension of the model proposed by Paul The numerical analysis of the system with small damper mass showed limit cycles associated with the system to be identical with one of the periodic solutions of the undamped case.

In common with other pneumatic and electronic cabin pressure control installations the two new pneumatic systems discussed in this paper have been designed to control cabin pressure automatically by throttling the out-flow of the cabin conditioning air. For those unfamiliar with the subject Fig. 1 shows diagrammatically a typical modern military aircraft installation. Both the systems discussed should however be of particular technical interest warranting general description, as for the first time with this type of equipment low cost and robust integrated fluidic circuits have been extensively used in their design. Patents covering these have now been granted in the United Kingdom, the United States and other countries.