The need to establish reliable methods of predicting the response of aircraft during taxying on rough runways and the associated dynamic loads and fatigue damage has led to numerous theoretical and experimental investigations of this problem. The present paper is a development of the study reported in ref. (1) which considered the random response of a flexible aircraft to forces transmitted through thei main undercarriage. The purpose of this paper is to apply power spectral techniques to the computation of the response of a rigid aircraft in heave and pitch to runway roughness, taking account of non-linearities in damping in the main and nose undercarriage.

The Islander is extremely simple and has had few aerodynamic problems; the exception was a persistent elevator “buzz” in some aircraft which was annoying more than it was serious and the cause of which was never satisfactorily established, despite an investigation that took six to seven months and which included wind tunnel testing and elaborate flight instrumentation. It was eventually reduced to an acceptable level by improved detail engineering.

The NACA 23012 section that we use is not a popular section nowadays despite having a good CL max, low CMO and low CDO. Its main drawback is the abrupt stall it can give to a wing. The usual cure for this is to provide generous washout. We chose to confine our washout to the wing tip and, as no dihedral was necessary apart from the tips, we achieved a very simple rectangular box structure with no joints—both a stressman's and a production engineer's dream. It is not often that you can please them both.

The Legal Committee of the International Civil Aviation Organization met recently in Montreal and decided to recommend a modification of the Montreal Interim Agreement to provide for a novel rule of liability. The rule would make the carrier absolutely liable, regardless of whether the carrier was at fault. The only exception to the rule would be where the passenger or person claiming damages had himself caused or contributed to the accident. The limit of the air carrier's liability would be raised to $100 000.

I will attempt to outline not only the current state of the law of aviation, but to critically dissect those provisions of the proposed treaty which I believe to be incompatible with fundamental concepts of justice and equality, and violative of constitutional safeguards of the Constitution of the United States. Recognisably, some of these comments may be controversial, but it is hoped that they will provide luminosity concerning a complex subject and reduce polarisation of views.

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.

It is of some historical significance that, after 25 years or so, a body still primarily associated with the aeronautical construction industry, is sufficiently concerned with the economics of airport operation, as affected by transport aircraft design trends, to invite a paper of this sort. Naturally enough, design trends of aircraft and their effect on economics have concerned airport authorities to a lesser or greater degree for a large part of that 25 years but from their remote position those responsible for airport design and operation have seldom been able to exert any real pressures upon aircraft designers. In addition, the old idea of airports as providing a form of subsidised social service, not required to be viable, also led to a fatalistic acceptance by airport operators, at least in the UK, of the vagaries of aircraft designers in expressing their individual talents and idiosyncrasies in widely differing design criteria. However, this era is now past and many airlines are becoming aware that wide changes of aircraft design criteria can lead to considerable extra cost in areas unconnected with the pure aircraft engineering and operational environment.

I want to begin by reminding you of the old friend of all of us, the late Captain J. Laurence Pritchard, who did more than anyone to record and analyse aeronautical history as it was happening. It was he who, in 1930, pointed my nose in the right direction and suggested that I should write a book on metal aircraft construction. The writing of that book showed me the gaps in my knowledge and I had to fill these in before the book was finished. I want to pass on to you–and particularly the younger members—some wise advice that JLP gave me then: “If you do not know a subject and want to learn, write or lecture about it. Then you will teach yourself”.

The five hours flying training obtained under the above Royal Aeronautical Society Award was given at Bristow Helicopter Flying Training School, Army Air Corps Centre, Middle Wallop. In this instance the training consisted of seven approximately equal duration flights in a Westland built Bell 47G-4 helicopter.

My flying experience prior to this award consisted of two short helicopter flights as a passenger apart from scheduled airline flights. I therefore found the flying a thoroughly enjoyable personal experience, and think the flying training will be of some professional value to my career as a helicopter engineer. It is difficult, however, to qualify this training in terms of benefit to my future work since the experience has primarily led to an environmental appreciation of the helicopter in flight.

Planning for the development of a future air traffic control system, or for the improvement of an existing system, requires a substantiated appreciation of the capacity and performance of the present system and of the projected future system.

With the growing volume of air traffic and the advancement of modern technology, ATC planners are concerned with making decisions relating to the organisation, development and control of an increasingly complex and sophisticated dynamic system. In many instances it is no longer possible to decide solely on the traditional basis of experience, intuition and “rule of thumb”, especially when the decision involves the selection of the best of several alternatives, involves the employment of very large sums in capital investment and affects the safety and security of large numbers of human lives. Under these circumstances it has become essential to turn to the Operational Research techniques which have been developed and which are now readily available to derive data on which sound decisions may be based.

The sound of a rotorcraft is very complex in nature since it is a combination of the sound produced by several individual sources, which in the main generate acoustic energy by more than one mechanism. Externally, the important sources are rotor noise and engine noise; while internally transmission system (gear) noise is an additional source. The frequency ranges associated with the various sources on a rotorcraft are summarised on the narrowband spectrum shown in Fig. 1. Main rotor noise is treated as two separate entities, rotational and broadband noise, while the tail rotor noise (if applicable) is dominated by its rotational components.

The following discussion is limited to gas-turbine-engined rotorcraft as, except for some of the small light-weight helicopters, the majority are powered by this type of engine. It is worth noting that on a piston-engined helicopter, the engine itself is the main noise generator, with the primary source being the exhaust noise emanating from the periodic expulsion of the hot gases of combustion. This produces harmonics at the engine firing frequency as indicated on Fig. 1, and in addition to being of high amplitude is very annoying since it occurs in the 200-1000 Hz range.

When asked to give the de Havilland Memorial Lecture I could have taken as my subject the general state of play in aerospace research and development, with special reference to what Farnborough and its outstations were up to. Geoffrey de Havilland was a Farnborough product—a fact of which we at the RAE are very proud—so such a theme might have been appropriate. But de Havilland was not only a gifted aircraft designer, he was also essentially a test pilot. The whole rather special atmosphere at Hatfield which he created and sustained—and which still survives his death—owes much to the fact that we had here in one man both a quite exceptional engineer and an experienced and highly critical pilot who was quite capable of evaluating his own products in the air. As a matter of interest, I have reproduced in Figs. 1(a), and 1(b), pages from one of his 1911 notebooks at Farnborough which have recently come to light; even in those early days the pilot/designer combination sings out.

In the author's R. J. Mitchell Memorial Lecture, presented to the Southampton Branch of the Royal Aeronautical Society in March 1969, the role of aircraft in future transport systems was examined. Since that time, three important trends or events have taken place. First and probably the most important, the environmental problems arising from the use of aircraft—noise, pollution and land use—have come to be major parameters in the design of new airliners. This trend has been highlighted by the recent issue of noise regulations by the Federal Aviation Administration (FAA) which new airliners have to meet before they can be certificated. These limits can be expected to become more stringent in future years. Secondly, the economic effects of congestion—both in the air and on the ground, at and around airports—have begun to be felt at major airports, especially at those in the Northeast Corridor of the United States. Finally, in the United Kingdom the Roskill Commission on the Third London Airport has recently issued its report.

The achievement of high propelling nozzle performance in supersonic flight is vital to the success of any aircraft designed to cruise supersonically for prolonged periods. For such projects, the payload fraction is small compared with subsonic aircraft, and the ratio of gross to net thrust is high. As a result, the penalty in range/payload performance for a shortfall in nozzle gross thrust efficiency is inevitably severe.

In view of the very wide scope of Operational Research in both the civil and defence fields, it is instructive to recall that it originated in wartime, as a means of increasing the operational effectiveness of combat forces. In the Second World War in particular it had a major effect on the efficient functional uses of the new radar equipment and achieved many other notable successes in increasing the effectiveness of our forces. It rapidly spread to all Services and in particular it was introduced into the Army through the formation in 1941 of the Army Operational Research Group, which in 1961 became the Army Operational Research Establishment, which in turn became in 1965 the tri-Service Defence Operational Analysis Establishment. Operational Research in wartime, functions in direct contact with the operational environment and the analytical predictions which it makes leads to direct application to the real world of war, the outcome in many cases being checked against the predictions. Operational Research in the original sense of investigation of operational factors continues to play a major part in peacetime in increasing the potential effectiveness of the services.

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.

There are several situations of practical importance where it is essential to maintain a satellite in a fixed orientation relative to the earth. Of the numerous methods proposed for such station keeping, gravity gradient stabilisation has gained considerable attention primarily due to the passive nature of the system. The pioneering work for pure gravity orientated satellites was carried out by Klemperer who obtained the exact solution for planar librations of a dumbbell satellite in circular orbit, and by Baker who found periodic solutions of the problem for small orbit eccentricity. Schechter attempted, with limited success, to extend Klemperer's solution to non-circular orbital motion by perturbation methods. Zlatousov et al and, more recently, Brereton and Modi successfully employed numerical methods, involving the use of the stroboscopic phase plane, to analyse motion in the large for orbits of arbitrary eccentricity.

The sonic boom from an aircraft in level supersonic flight has been studied extensively. What is perhaps not so well known is the effect of a curved flight path in causing a local focus of shock-waves, and accentuated boom, and more particularly the production of a zone of silence, or rather “no boom” in other localities closer to the centre of curvature of the curved flight path than the M=1 radius. A steady shock wave pattern cannot rotate at a subsonic speed. It remains to be determined whether the necessary aircraft flight paths can be tolerated by both passengers and aircraft.

The subject is not new, and was theoretically predicted by Bryan and Lamb in 1921, and verified experimentally by the present author in 1938, for the case of propellers or airscrews. Figure 1 shows the effect of progressively tightening the radius of turn of the aircraft.

In addition to direct solar radiation, this paper includes the effect of direct earth radiation, its albedo and shadow on the attitude dynamics of gravity orientated systems, thus extending the analysis of Part I down to the earth's effective atmosphere. The importance of these radiations was indicated by a preliminary force analysis, which revealed that they can exert a force comparable to that of direct solar radiation for close earth satellites. Thus, the need for a rigorous investigation including the effect of earth radiations on satellite attitude dynamics is evident.

Earth radiation forces were obtained in integral form by Clancy and Mitchell using elementary radiation principles. However, in a test on an IBM-7044 digital computer, it was found that the time required to evaluate these integrals renders a study of satellite attitude dynamics virtually impossible.

My connections with,the helicopter industry covered a period of some ten years, working principally on the jet reaction rotorcraft Fairey Rotodyne, and my only regret about this exceptional aircraft was that it never entered airline service. VTOL/STOL projects currently being bandied around today for civil use appear to'have made very slow progress in noise reduction since that time.

It was on this aircraft that I really got to grips with the noise problem, and with this experience behind me, my present task with Rolls-Royce became much more invigorating and refreshing. If for no other reason than, if you generate the noise, you are the principal agency which is required to set about removing it.

My present paper is really a factual presentation of the Ansty Noise Facility and its relationship with the general lowering of sound levels of the next generation of gas turbine engines. It is therefore slanted more to the fixed wing CTOL type of aircraft powerplant, although VTOL/STOL applications are now being studied at scale size.