The military tactics of vertical envelopment require the transport of 8000 pounds of payload to a radius of 100 nautical miles at a speed of 150 knots. The aircraft should be able to hover at 6000 feet on a standard day and with one engine inoperative maintain level flight in turbulent air. The helicopter should be readily convertible to carry cargo or troops.

The CH-53A meets these requirements. Additional design constraints, including emergency water landing, rear loading, self-contained navigation system and weight and dimensions compatible with aircraft carriers have been imposed.

With special attention having been given to the vibrational environment two General Electric T-64 engines have been installed. The 72-foot diameter main rotor is equipped with six blades with 26 inch chord and a NACA 0012 aerofoil modified to improve the characteristics at high Mach number. To achieve low drag and interference the fuselage and rotors have been developed in the wind tunnel. Tail surfaces have been especially developed to provide good handling qualities. An automatic stabilisation system was provided to relieve the pilot of various flight duties and to permit him to give more attention to the military situation.

Special design procedures have been followed to control weight, drag, reliability and vibration. The final helicopter is within 3-7 per cent of the desired weight and the performance is in substantial accord with predictions. The vibration level is generally about ±0-10 g throughout the cockpit and cabin.

During the flight development phase the control system was modified to provide appropriate coupling to relieve the pilot and automatic flight control system of any unnecessary compensating control motions. The structural integrity tests revealed the need for improvement of the main rotor blade attachment spindle. The engine-to-transmission shafting required a damped support.

The finally developed version of the CH-53A meets the mission requirements already stated. The hovering ceiling on a standard day Is over 5000 feet. The maximum level flight speed is 170 kt. The handling qualities and vibration are superior to any helicopter previously built by Sikorsky Aircraft. The reliability and maintenance features have been demonstrated by extensive testing. The overhaul periods will be 1200 hours in early service operation; 5-5 direct maintenance man-hours per flight hour are required to accomplish all maintenance except overhaul of repairable components. The dynamic components have been developed to such a high degree of reliability that they will be overhauled “on condition” only and continued in service throughout the normal military usage.

In terms of commercial service, the CH-53A (S-65) will have a direct operating cost of approximately 4c per seat mile.

In the past decade considerable attention has been given to the possibility of using self-adaptive control systems to cope with the problem of providing stability augmentation to aircraft over extended flight envelopes. On the other hand, it has sometimes been considered that insufficient attention has been given to the design of autostabilisers with fixed parameters. The authors have applied recent developments In dynamic programming to the design of aircraft autostabilisers. The methods provide a highly systematic approach to the design of multi-loop systems which is especially useful for control of the lateral mode. Furthermore, the resulting optimum multiple feedback coefficients vary little throughout the flight envelope and the use of fixed parameters for the whole of the flight envelope appears to be possible. Aerodynamic data for two aircraft were used: a supersonic VTOL aircraft and a supersonic transport.

One of the novel problems presented by supersonic transports is the control of the complex powerplants needed to achieve optimum efficiency over a very wide range of forward speeds.

The subject is a large one and its proper understanding involves the disciplines of aerodynamics, thermodynamics, servo-theory and finally human engineering, because its end product is a set of knobs, levers, lights and dials which must be usable by the flight crew.

This paper is intended as an elementary introduction, using the special case of the Concorde as a basis. First, an attempt is made to give the aerodynamic and thermodynamic reasons for the large number of powerplant variables which the control systems must manipulate. On this basis, a functional specification of the control systems is established and, finally, the crew's job of propulsion management is described step-by-step in the course of a typical mission.

The present aerodynamic study of “hangar” type engine test cells originated with a request for assistance following difficulties experienced in the commissioning of a Dart engine-test facility. The major improvements obtained resulted from a systematic programme aimed at understanding the basic problems involved. Extensive use was made of model techniques during this investigation.

Detailed flow studies in two other hangar type cells, in successful operation, disclosed certain vortex features which were common to all three cells. Hence in view of a dearth of information on the aerodynamics of such cells, it was decided to deal with the general design problem and to sup-port the study with selected results from the experimental work referred to previously.

Developments in Range instrumentation for trajectory measurement over the past ten years are reviewed, and some possible future developments discussed. Instrumentation systems considered include kine-theodolites, tracking radars, multi-station Doppler systems and interferometers. Some common sources of error are discussed; it is shown that atmospheric retraction variations may be the limiting factor on the accuracy of modern trajectory measuring systems.

The most important problems during the next five years will arise from requirements for very low level weapon systems, high precision tracking of small targets with fast response characteristics and long range high precision tracking of space vehicles. Developments to meet these requirements will lead to further requirements for completely automatic data processing for the high data rates needed. It seems probable that fewer completely new instrumentation systems will be developed during the next five years, more attention being given to reducing the size of airborne transponders and other equipment and increasing the reliability and accuracy of existing equipment. Systems using a common carrier lor telemetry signals and tracking may appear.

Considerable work on isolating sources of error in existing systems and reducing them is going on and will continue. This will be combined with more advanced post-flight analysis techniques during the next five years.

One of the most remarkable, successful and useful of the Society's activities during the second World War was a series of weekend conferences called to discuss problems arising directly out of the War. To the greater number of members of the Society these valuable conferences and their scope are unknown for they were all highly secret.

All the theories of air strategy and tactics and actual combat and bombing and reconnaissance and the rest of it, only put to the test in peacetime manoeuvres, were now being tried out under the bitter stress of war.

As The strength of aluminium alloys is increased, other desirable properties are increasingly sacrificed and, as with other metallic materials, a major difficulty in developing better strong alloys is to assess these other properties in terms which are satisfactory indices of service performance. This difficulty becomes more acute as strength is increased and further progress demands that supplier and user are in the closest possible agreement on methods of assessing the properties involved and on where the line must be drawn between acceptable and unacceptable material behaviour. Discussion of this aspect of strong light alloy development is always opportune and much of what is said in this paper is intended to provoke constructive discussion between supplier and user on this subject.

After some introductory remarks about Reynolds and Prandtl the results of some work in the field of the aerodynamics of propulsion plants will be described. In this context there are, first, cascade flows in which the influence of such parameters as Reynolds number, Mach number, axial pressure ratio, turbulence and boundary constraint have been studied. Investigations in the transonic and supersonic ranges will also be considered.

Flows with heat addition at both subsonic and supersonic speeds are then dealt with, including reaction-kinetic effects in the ignition of fuel and in the recombination processes in expanding jets.

The flow problems which arose in the development of the rocket test beds for the third stage of the ELDO rocket will be described and, in particular, the special rocket steam generators and flow problems associated with the strong cooling of the hot rocket gases will be discussed.

Next we shall deal with work on the flow processes in the acceleration of electrically-conducting gases. Some results are described of the self-magnetic—the Hall current—and the electrodeless electromagnetic acceleration.

Finally some problems of measurement techniques will be touched on.

Over the past ten years the RAF has cost the country an average of some £500 m per year. Of this sum about £200 m has been spent with the aircraft and electronic industries, of which about half has been for new aircraft and weapons, the remainder being needed for spares, modifications and ground equipment. A further £200 m is expended on service and civilian manpower, the majority of whom have been employed on the maintenance of technical equipments or are needed to provide direct support for personnel so employed. Thus we have a situation where something like £200 m a year—almost half of the total budget—is spent upon maintenance.

As the cost of modern weapons systems needed to achieve the necessary operational performance is increasing rapidly, the front line strength of the Royal Air Force will be weakened unless substantial savings in these maintenance costs can be made, and this in the face of increasing complexity of aircraft equipments.

The object of this paper is to present some of the user experience with the high strength aluminium alloys. The somewhat tarnished reputation of the Aluminium-Zinc-Magnesium alloys is undoubtedly due to their premature introduction; the very substantial weight savings offered by the relatively high static strength values proving too strong an attraction at the end of the war-time era dominated by short term considerations.

It will be appreciated that there is a wide range of alloys in this family. Table I lists the composition ranges of typical French, American and British specifications together with a proprietary alloy, of German origin, which is of particular interest. Manufacturers have their own favoured compositions within the permitted ranges. Fig. 1 shows diagrammatically the wide variation in percentage of the principal alloying elements zinc, magnesium and copper.

In the long history of the Society many committees of Council have been appointed to advise the Council upon matters concerning the advancement of aeronautical science and engineering, and of the welfare of the Society and its members. Yet the most important committee of the Council ever appointed never gave any advice to the Council during its five years of office. In the whole of my experience, as secretary of the Council and its committees, no committee attained that complete ideal of unselfish endeavour, without any regard whatever for their own personal and business interests, as did The Advisory Committee of the Royal Aeronautical Society to the Ministers of Aircraft Production, which played such a great part in the 1939–1945 World War.

Present day structural forms and methods of fabrication have considerably increased the importance of wind as a design consideration. For estimations of the overall stability of a structure and of the local pressure distribution on the cladding, a knowledge of the maximum steady or time-averaged wind loads is usually sufficient. Mind tunnel tests to determine the wind loading coefficients are often made in smooth uniform flow, but for more accurate data account must be taken of the effects of the vertical gradient of wind speed and the turbulence of natural winds. Further research is needed into these effects and also into methods of obtaining a sufficient representation of the natural wind in the wind tunnel.

There are a number of ways by which wind excites structures into oscillation; among these are vortex excitation, galloping, proximity effects including buffeting, stalling flutter and classical flutter. The vortex and galloping excitation might be expected to be especially sensitive to the turbulence properties of the air flow. Also, in the absence of any mechanism for instability, atmospheric turbulence may directly excite oscillations through the random forcing by the pressure fluctuations which it produces. Further understanding of this problem must come through research into the effects of turbulence (and to the extent to which these effects may be disregarded), but the range of the conditions is so vast and complicated that it seems unlikely that sufficient aerodynamic and wind data will be accumulated to permit the response of a proposed structure to be calculated with reasonable certainty, and for major projects it is anticipated that comprehensive tests on aeroelastic models in wind tunnels with appropriate turbulent air flow will continue to offer the more reliable predictions.

The air flow around buildings is of concern inasmuch as it influences the dispersal of combustion and other gases from the smokestack and also in its effect on the speeds and turbulence of the wind over areas used by pedestrians. The erection of a tall building may cause an increase in wind speeds and gustiness at ground level. These problems of the external flow over buildings are readily examined in wind tunnels. For this purpose tunnels with large working sections are desirable to permit a sufficiently wide area of the neighbourhood to be represented.

The first two US/UK co-operative satellites, Ariel 1 and Ariel 2, were put into orbit in April 1962 and March 1964, and both functioned most successfully. The lecture describes the NASA Pulsed Frequency Modulated telemetry system, including the methods used to store and transmit the data to ground stations, the digitising techniques used to prepare these data for entry into a computer and, finally, the organisation of the central data handling operations to the point where the partially or wholly reduced results were handed over to the various experimenters for analysis.

The main purpose of the investigation has been to clarify the definition of hovercraft wavemaking resistance and to improve understanding of the physical mechanism. The most literal definition of wave resistance as the force which makes the waves is proposed and its practical and theoretical implications are considered. Various interim accounts of this work have already been written, but the time now seems appropriate to assemble and review the overall picture which is emerging.

The pattern of forces on a hovercraft over water is often difficult to analyse because of the complicated interaction between wavemaking, jet air momentum, cushion pressure, wetting and other effects. It is important, however, in making power predictions that the physical interpretation and corresponding scaling laws of the various forces should be understood. A significant feature of the present approach is that a positive and unambiguous basis for identifying the wavemaking force is offered and compared with theoretical predictions. This force, according to the definition proposed, is assured a proper compliance with the physical laws which govern the waves generated and the corresponding scaling and interference effects, which are predicted by theory.

Although I deem it a great honour to have been asked to give this lecture I will be perfectly honest and tell you that for a long time I resisted. 1964 is an important landmark in the Hatfield Branch history. It has been in existence for a quarter of a century and the developments which have taken place during this period in the Aeronautical World have been remarkable. The lecture also ranks as a Halford Memorial Lecture and so I felt that someone far better qualified than myself was needed in order to do justice to the joint occasion. However, I finally agreed and I would like you to know that this was not because some sudden inspiration gave me confidence that I was the man for the job, but rather because I felt that as the Hatfield Branch had done so much for me I should try and do something in return.