The first ten years following the end of the First World War saw a steady “run down” in the armed forces and during this period what still existed in the field of aero-engine development was inspired, mainly, by participation in long range pioneering flights, distance records and international speed events—such as the Schneider Trophy Contest.

Research and development were limited by the funds available and it was not until about 1935, when the Government decided on an “all out” policy to re-equip the Royal Air Force with equipment to match the growing aerial strength of Germany, that aero-engine development received the support it needed. It was somewhere in this period that marked the “renaissance” of the development of aero-engines.

The Kinship of the English-speaking peoples, our common heritage of democratic ideals, and our close military alliance have created a unique relationship between the British Commonwealth and the United States. I know we both value it highly.

I am mindful of this in, saying that I feel that I am among friends here and that I appreciate your warm hospitality. Incidentally, my father received the same warm hospitality from you a quarter of a century ago when he delivered the twenty-third Wilbur Wright Memorial Lecture in 1935.

A guided missile system is a very complex assembly of interacting sub-systems, and rarely fits into a neat mathematical framework; but the need for a sound theoretical background is perhaps even more acute in this than in other fields, because of the almost prohibitive cost of protracted experimentation and cut-and-try methods. A theoretical model—even an approximate one—can greatly reduce the amount of experimental work necessary to prove a system, since the less efficient arrangements can be eliminated without a shot being fired. The use of simulators and computers, although indispensable, is in no way a substitute for this theoretical understanding: for the computer solutions can be obtained only for specific cases, and are of limited use unless they can be generalised to apply to other situations.

Over the past years many questions which come under the broad heading of cloud physics have been put to the Meteorological Office by aircraft firms and others, questions on the water and ice crystal contents of clouds and the size distribution of raindrops are examples. These questions have invariably been easy to ask and at first sight the answers would appear to be straightforward, but almost equally invariably these simple questions have proved difficult to answer with precision and in many cases estimates only have been possible. This may well appear surprising and it is the purpose of this paper to indicate some of the difficulties encountered.

The Flow of Fluids through screens has been widely studied with particular importance being attached to the measurement of the pressure drop caused by a screen and its relation to the screen geometry and the flow conditions. The majority of the investigations have been carried out on wire gauze screens mounted in ducts with air passing through them, the static pressure being measured on either side of the gauze. Attempts have been made by Weighardt Annand and Grootenhuisto correlate the gauze geometry with the pressure drop and to enable the pressure loss over a given screen and with given flow conditions to be predicted.

It is shown that, for infinite sheared wings with symmetrical aerofoil sections, the value of the suction peak near the nose in incompressible flow depends primarily on the value of the lift coefficient and the nose radius and not on the angle of sweep.

When investigating the suitability of a basic wing section for an aircraft design with comparatively large aspect ratio, it is useful to know up to which lift coefficient one can expect the flow to be attached over the wing surface, and separation to occur at the trailing edge only. For aerofoils of small or moderate thickness-chord ratio, flow separation tends to occur first near the leading edge.