Sir Henry Tizard’s work and–above all–his part in our survival in 1940–have been the subject of many memoirs since his death in 1959. The biography written by Ronald Clark at the invitation of Professor J. P. M. Tizard, Sir Henry’s eldest son, will shortly appear. This first Memorial Lecture of the Royal Aeronautical Society thus occurs when a full record of Tizard’s life is about to be made available, and there is therefore little point in the plain re-iteration of a condensed biography. Future Memorial Lecturers, as they inevitably grow more remote from personal contact with Tizard, may well choose to describe the advances of the future in those fields to which Tizard himself so notably contributed: science, defence, education and government. My purpose in this first Memorial Lecture is, therefore, to build a bridge between biography and those future fields in which Tizard’s example, although unlikely to be excelled, will be emulated and extended.

Rocket motors designed for operation in ground launched vehicles generally have nozzle expansion ratios giving optimum thrust at low altitude (about 20 000ft). At higher altitudes the jets are under-expanded and the thrust is less than the maximum available with nozzles of higher expansion ratio. Some of this lost thrust may be regained by suitable design of the propulsion bay geometry, without the low altitude disadvantages of high expansion ratio nozzles. In addition, where the vehicle is propelled by clustered motors, interaction between the jet effluxes at high altitudes can be used to develop an extra thrust acting on the base of the vehicle. The flow changes, from low to high altitude, leading to these effects are described.

The results of the first firings of Black Knight drew attention in this country to these effects. Model tests in both the U.K. and America have confirmed them and indicated various means by which the thrust of clustered rockets may be augmented; these are described and consideration is also given to the side effects of thrust augmentation on vehicle control and propulsion bay heating. A full scale experiment, planned for the end of 1962 is outlined and possible future applications are considered.

The separation or breakaway of over-expanded gas from a nozzle wall plays an important role in the estimation of the thrust from a rocket engine when run at altitudes considerably less than the design. A number of reports have been written on the subject but the agreement of test results has not appeared to be good.

In an effort to clarify the position, the Rocket Department of Bristol Siddeley Engines Ltd. has carried out tests on experimental combustion chambers having static pressure tappings in the nozzle divergent section. These tests have shown that, contrary to some previous suggestions, the pressure at which the gas separates is neither constant nor independent of the nozzle length. The paper, which includes results from other workers, divides the field into separation adjacent to the nozzle exit and also at positions where the area ratio is less than 80 per cent of the exit area ratio.

For the most part, consideration is given to conical nozzles having divergence half angles of 15° to 17°, but comment is made on the effects of divergence and other variables. A tentative suggestion as to the mechanism of separation is also made.

Finally, the effect of separation on the sea-level thrust of a nozzle designed for high altitude Is shown.

The United States Army is now engaged in the selection of a Light Observation Helicopter (commonly referred to as the LOH) from three competing designs. It is estimated that large quantities will be procured to fulfil an operational requirement during the 1966-1975 time period. The paper describes the overall programme by examining the basic requirement and the development concept. In addition, a description of the actual hardware being developed is given and some economic considerations of the modernisation of the observation fleet are discussed.

In the light of what was now known, the only change that might have been made in the programme would have been the elimination of the animal flight; actually, systems for manned flight were ready to “go” at that time. The lecturer considered that the ballistic part of the programme would still have been needed to get the people ready for this sort of thing as well as for checking the systems control and for developing the recovery technique. The sea landing approach was chosen because it was a simpler system to develop within the brief time schedule available and would provide the lowest impact loads on the pilot and spacecraft alike.

It has been remarked that in half a century the bomber aircraft has risen from insignificance to be a prime weapon of war and is sinking again into obsolescence without any general rules having ever been agreed setting limits to its use. What the First World War did for the aircraft the Second World War did for the rocket. Will it too be replaced by even more fearsome engines and reach its decline, escaping any general control?

In little over 20 years, the rocket has passed from being the smiled-on object of amateur experiment and failure to become a vehicle of enormous speed and range, with expenditure and engineering effort the only limits to its potentialities. The steps are worth recalling quickly. The first serious use of rockets was as short range missiles by the Red Army in the Second World War. There followed the successive breakthroughs of the V.2, the first satellites in orbit in 1957, impact on the Moon in 1959, men in orbit in 1961, a successful Venus probe in 1962,a manoeuvrable spacecraft in 1963 and, in February 1964, the launching of Saturn by the United States far surpassing any previous launching achievement either American or Russian.

In the early part of this century aircraft were flown only when the pilot could control them by reference to outside sources—the ground, the sky and the horizon. Soon, however, instruments were developed which enabled him to fly in cloud or darkness. The Second World War with its blackout enforced this need for total blind flying and, as a consequence instruments and techniques were perfected, ending with what was known as the standard blind flying panel. This has remained substantially unchanged in the majority of aircraft up to the present day. This paper reviews the presentation and the principles which led to its development and then discusses some recent developments in this interesting field. First it is necessary to look at the problem in more detail.

The advent of a new generation of turbojet powered transport aircraft with engines mounted on the rear fuselage has complicated the task of the aerodynamicist, particularly when an attempt is made to determine the individual contributions to the stability and aerodynamic loading of the aircraft. This paper gives some idea of the additional complexity which is directly attributable to the presence of these engine nacelles and their effects on manoeuvring tail loads. Where rational methods are available for determining these effects they are referred to or included.

The drag of an aerofoil is often conveniently measured with reasonable accuracy by traversing pitot and static tubes across the wake of the aerofoil and calculating the drag from either the analysis of Betz or that of Jones.

In a recent Technical Note, Bradshaw offered additional thought on an earlier note by Markland and myself. In doing so he wrote of the efficiency of a diffuser which was confused with the pressure recovery coefficient, Cp. In view of the great significance when designing engine intakes, combustion chambers, nuclear reactor plant and even heating and ventilating systems of even minute improvements in duct efficiency, the distinction is further discussed.

In a recent note in the Journal, Morley and Bryce discuss the problem of natural vibration with a damping force proportional to a power of the velocity. They address themselves particularly to the problem of interpreting experimental measurements, and mention an application of the study of an elasticity in metals. They were apparently unaware of previous analytic studies of this problem, and their analysis is somewhat inaccurate in indicating that the full-cycle logarithmic decrement rather than the half-cycle logarithmic decrement characterises the damping.

It is intended here to outline the previous analytic studies, to present the essential results, including those which can be directly employed in the interpretation of amplitude measurements, and to mention typical applications.

The vibrations of stiffened plates have been considered by Kirk and Mahalingam. Kirk has treated plates with several stiffeners and also a plate with a single stiffener. For plates with several stiffeners he uses the Rayleigh Method as employed by Warburton. The calculated frequencies have been shown to compare favourably with the experimental frequencies when the stiffness has been taken as ef3/3 for a stiffener. While considering the plate with a single stiffener he has replaced the stiffener by a line of massless springs the spring constant of which is determined on the basis of certain approximations. The Rayleigh method has then been applied to solve the simplified problem. A plate with two opposite edges free and the other two simply supported with a central stiffener parallel to the free edges has also been considered by Kirk.