Last year the Royal Aeronautical Society and the Wissenschaftliche Gesellschaft für Luftfahrt agreed to organise lectures in honour of Osborne Reynolds and Ludwig PrandtI, to be given every two years, and alternating between Great Britain and Germany. The purpose of these lectures will be to show how closely English and German aeronautical research is related, and to recall the great scientific work of Osborne Reynolds and Ludwig Prandtl for the benefit of the younger generation. Without their contributions our scientific and technical achievements in aeronautics today would hardly have been possible.

Today I have the great honour to present the first Reynolds-Prandtl Lecture, and I wish to thank the Royal Aeronautical Society and the Wissenschaftliche Gesellschaft für Luftfahrt for this high distinction.

The generation of electric charges in hydrocarbon fuels during transfer has been recognised for many years as an explosion hazard, and the oil companies have taken precautions against this danger as a matter of routine. Usually the hazard arises only in the early stages of handling, and is associated with the fast pumping of large quantities of product, particularly into large refinery tanks and tankers. The possibility of a hazard usually becomes less as the product approaches the consumer, owing to the successively smaller quantities pumped.

The aim of this paper is to give an outline of the background, development and V/STOL flying techniques of the Hawker P.1127. For security reasons it is not possible to release information on performance or numerical details of the control characteristics and hence it has been necessary to confine the material to a qualitative nature.

Vertical and short take-off and landing (V/STOL) ability of operational aircraft from unprepared areas enables air power to be concentrated at long range with a minimum reliance, on overseas bases. In the past such operations have been possible because of the existence of well-equipped overseas bases and long lines of communications.

Published statistics reveal an approximate six-fold increase since 1951 in commercial air transport activity over the North Atlantic. Scheduled passengers increased in number from 341,000 in 1951 to 1,919,000 in 1961; cargo increased from 7,700 tons to 53,000 tons; and mail carriage increased from 3,900 tons to 17,000 tons over the same period. For 1962 a further increase of 12 per cent in passenger traffic and 14 per cent in cargo is forecast. This rapid growth situation has not been accompanied by a corresponding increase in profits, however, as evidenced by a loss estimated in the millions in 1961 on the North Atlantic by the United States international air carriers alone, and an indeterminably greater amount by the foreign air carriers operating in this area. From the limited financial data available, it appears that, among all North Atlantic scheduled international air carriers, only Irish Airlines and Pan American experienced profitable operations for 1961.

Aerial top-dressing, or the spreading of inorganic fertilisers from aircraft, introduces stringent flying conditions at extremely low altitudes. During release of the fertiliser there are large load and centre-of-gravity changes, and aerodynamic effects the cause of which has hitherto been conjectural. The experiments described in this paper were aimed at obtaining a knowledge of the aerodynamic effects of the cloud of falling material beneath the plane, and the effects of air flow through the empty hopper. The implications upon aircraft design are discussed. The high accident rate experienced in this industry emphasises the necessity for the production of a suitable aircraft designed solely for top-dressing.

I should like to express my gratitude to the Society, on behalf of the Federal Aviation Agency of the United States, for the opportunity of participating in this meeting.

Before speaking of the lessons gained in Helicopter Air Traffiic Control some background information is necessary on the types of helicopter operations which are being conducted in the United States.

As in many countries, helicopter operations are conducted by both the military services and civil operators. The military operations are primarily those of a tactical training nature and search and rescue work. Civil helicopter operations are conducted mainly for transport and utility purposes.

In addition to numerous civil air taxi operators providing transport by helicopter, we have three commercial scheduled helicopter airlines; New York Airways, Chicago Airways, and Los Angeles Airways. These three helicopter airlines serve the aerodromes and residential communities in the metropolitan areas of the cities from which they derive their names. Utility helicopter flying includes such services as forest fire fighting, insecticide spraying of farm crops, power line inspection, and construction work, just to name a few.

When atmospheric testing of nuclear devices was resumed in the latter part of 1961 it was found that certain commercial aircraft were being contaminated by airborne radioactive debris to such a degree that decontamination was required, with associated protection of personnel. Some airlines seemed reluctant to publish detailed information on the position. BOAC, however, recognised the phenomenon as a virtually permanent one and in recent months has been setting a lead in developing the process of measurement and control from a somewhat academic exercise to a properly understood engineering routine. When the nature of the hazard is understood—and particularly the all-important distinction between external radiation and internal radiation—it can be seen that, in fact, passengers and crews are not at risk at all, and that handling and maintenance personnel need not be concerned if the contaminated surfaces are washed by an essentially wet process and personal hygiene rules are observed where necessary.

The success of inter-city transport helicopter operation will depend on the ability to fly between small sites in city centres with good regularity. Any compromise, such as moving the site to the outskirts of the city or only being able to fly in fine weather, will destroy the advantage of the helicopter over other forms of transport. During the past decade there has been considerable progress in the improvement of helicopter flying qualities so that it is now possible to specify equipment which will enable a helicopter pilot to control his machine in all visibilities and most conditions of turbulence. Further developments in ice protection will enable the basic helicopter to be cleared as an airworthy vehicle for all-weather flight. However, there still remains the problem of navigation, which becomes particularly acute for the final instrument approach. Existing equipment, in particular the Decca Navigation System, can probably meet the case for aerial navigation at altitude, but to fly down an approach to low altitudes into a restricted site demands a higher standard of accuracy and reliability than is offered by any currently available equipment. This paper only deals with the blind approach down to a height of the order of 200 ft. above the landing pad. To extend this to blind landing would require an even higher degree of accuracy and reliability, which does not seem to be justified until some actual operational experience of a simpler blind approach system has been gained to establish whether or not there is a real need for blind landing. A blind approach system which will permit a cloud break height of 200 ft. to be followed by a visual approach and landing on ground lighting should offer at least as good a standard of weather regularity as is currently achieved by fixed-wing aircraft.

In any industry, success calls not only for a tool which is well adapted to its purpose, correctly maintained and efficiently used, but also for a tool which is unsurpassed by a better one.

This is also true of air transport. C. R. Smith (President, American Airlines Inc.) noted some time ago that an aircraft ceases to be efficient as soon as another aircraft becomes available that can do its specific job better. This axiom places emphasis on the selection of aircraft as one of the primary elements of success for airlines which, in order to survive economically, must have available the right number of aircraft of the right type at the right moment.

This is the result of two essential characteristics of air transport: intense competition and marginal profits.

One of the main differences between manned aircraft and missiles is that in the former the “short period” dynamic characteristics should usually be at least moderately stable, while in the latter considerable instability can be tolerated.

However, this requires that the missile control system should have high gain “synthetic” feedback. Consequently, problems of stability associated with high gain are introduced, which do not occur with such severity in the manned aircraft. Typical missile stability problems of this kind, such as those arising from structural flexibility and propellant sloshing, are discussed.

Ballistic missiles, because they are required to operate in conditions where aerodynamic forces are sometimes negligible, need to utilise non-aerodynamic control forces. This introduces special problems, which have a parallel only in VTOL aircraft. The long duration attitude control of satellites in the presence of very small disturbances also presents a problem not encountered in the aircraft field.

The uncertainty of human pilot response is discussed in relation to the difficulties of adequate aircraft control system simulation. Some remarks are also made on the interaction between control about various axes. These interactions are often fundamentally different between aircraft and missiles.

The problem of designing a three-dimensional contraction arose recently in the course of the projected construction of a new low-speed (200 ft. /sec), closed-return wind-tunnel at the Northampton College of Advanced Technology. A three-dimensional contraction was required of contraction ratio 7·4:1 to provide smooth low turbulence conversion to the working section speed within an axial length of 126 inches. The inlet and outlet (working-section) dimensions are shown in Fig. 1 and the sections are similar. It was decided to design the contraction on the basis of an equivalent axi-symmetric contraction whose inlet and outlet circular areas are equal to those of the corresponding irregular octagons and then adapt the derived contraction wall profile to the actual sectional contours. The resulting equivalent inlet and outlet radii are then 55·4 in. and 20·4 in. respectively. The problem was thus reduced to the design of an axi-symmetric contraction of given area ratio within a specified axial length, with favourable velocity characteristics for low turbulence flow in the working section. This latter specification implies the absence of adverse pressure gradients on the walls near the working section and a small percentual difference between axial and wall velocities at the inlet to the working section.

If we look at contemporary space vehicles which start their journeys from the surface of this planet, there is no doubt that the propulsion plant is the dominant feature. Physically it represents a major proportion of the total vehicle weight while the technical effort in attaining the necessary standards of performance and reliability has been of commensurate magnitude. It is clear also that the rocket motor has, at present, an unchallenged position as the chosen form of power unit. The question may well be asked in these circumstances what place there could be for an air-breathing power unit in such vehicles specifically intended to travel for most of their journey through the empty regions of space. Clearly the answer must be that such air-breathing units must function during the boost phase of space missions when there is air for them to breath so that the engines can add their quota of energy (kinetic plus potential) which is to be given to the vehicle in fulfilment of its task.

Although this talk, to conform to the general pattern of the Symposium has the word “Economics” in its title, the plain fact is that nobody at the present time is able to make a reliable assessment of the economics, in the usual financial sense, of ramjet launchers.

Rockets have already demonstrated their ability to fill this role and assessments of the cost can be based upon real experience, as Mr. Rothrock's paper clearly shows. The use of ramjets for this duty, or more strictly for part of the duty, since we cannot hope to provide ramjet power all the way from take-off to orbit, remains problematical. The first step must be to prove the feasibility of using ramjets and only when some of the major problems on which feasibility hinges have been solved, can any really rational assessment of the probable cost be made.

The significance of joining flow regions with moving waves is discussed and a generalised treatment of simple, one dimensional, moving shock waves is presented analytically and in chart form. The problem is next considered with the shock wave replaced by different types of non-steep waves and their corresponding charts given.

Possible and impossible flow configurations are examined and the results presented in the form of a diagrammatic table. An alternative shock wave chart is described in an appendix and worked examples, showing the use of the charts, are presented.

The problem of the vibrations induced in an aircraft structure excited by jet noise has been solved mathematically in general terms by Powell and others. The most promising methods for dealing with a practical structure are those based on the normal mode approach. In these methods the response of the structure in each of its normal modes is first determined and then the total response is obtained by a summation of individual responses. Use of these methods on practical structures is tedious because of the large number of modes which must be considered and also the difficulty of calculating theoretically the normal modes of a practical stiffened structure.

“All-weather” operational requirements have added considerably to aircraft and missile design problems as the effects of various meteorological hazards, predominantly rain, are aggravated by high speed flight. The problem of rain erosion is reviewed with regard to the functional requirements of the components, the flight plan of the vehicle and the occurrence of rain over the geographical terrain of operation. The factors affecting rain erosion characteristics such as type of material, surface finish, shape of component, speed and rainfall intensity are discussed and empirical data derived. The influences on the problem of radar limitation in rain, the probability of rain occurrence and the effect of wind and wind-shear are mentioned. Details given of equipment for the simulation of rain erosion are concerned principally with the R.A.E. “whirling arm” and rocket runway high speed sled techniques. Correlation of test results from these facilities and flight tests are briefly discussed.

Degree of erosion of a material is defined in relation to the particular application of the material and details are given of the characteristics of numerous materials, both metals and non-metals. The utilisation of these materials for such applications as radomes, transparencies, high temperature materials, de-icing systems are briefly discussed together with methods of extending the rain erosion “life” of materials by design or by use of protective coatings.

The earliest known boats were propelled by oars. Sails were soon discovered, probably in Egypt, where a light, but steady, north wind blows up the Nile. The Egyptians found that by stretching a large mat across the ship they could proceed up the river. However, sails remained an auxiliary source of power until about 300 A.D. because they could be used only with a following wind. Fig. 1 shows an Egyptian ship of about 1600 B.C.

The next improvement came in China, where the square sail was turned fore and aft, enabling the boat to be sailed at an angle to the wind. Unfortunately the Chinese made no further improvements, and the junk, Fig. 2, has remained basically unchanged for about two thousand years.

The main objectives of Missile Evaluation Trials are a complete evaluation of the operational performance of the missile tested, a comprehensive assessment of the practical implications of regular operation of the weapon system from the user's point of view, and the feedback of scientific information to assist in future designs. This means that the trials must be planned to provide data on the following aspects: —

• (a) Scientific evaluation, i.e. determination of performance in the various conditions which will arise in operational use.

• (b) Technical evaluation, i.e. assessment of the detail design, workmanship, engineering and reliability and its influence on operational performance.

• (c) User evaluation, i.e. a practical critical examination of (and evolution of) handling and servicing procedures, personnel training requirements, installation requirements, logistics, and the numerous organisational steps necessary for the introduction of a new weapon into service.

Many things have been said in the past year or two about the value of using Blue Streak to launch satellites and probes into space. Practical sense has at last triumphed and we have recently learned, with a great feeling of relief, that the European Space Launcher Organisation (ESLO) is now to be convened and there is now little doubt that a multi-stage satellite launcher rocket will be developed based on Blue Streak.

Unfortunately, there has been much misconception and loose thinking surrounding the Blue Streak concept and much unreal speculation on its life expectancy, performance limitations and general capability—mostly under-estimates. I would like therefore to try to summarise the present situation regarding the rocket, its ground facilities and its space applications.

I feel that the title of this lecture needs clarification, because it would appear from it that aircraft reliability is necessary only in the interests of Flight Safety. Although safety is vital, the operational capability of the aircraft must also be considered because, as in a missile system, operational reliability is of paramount importance. An aircraft may be completely reliable from the Flight Safety aspect without necessarily having a reliable weapons system.

In the past few years, of course, much has been said about the need for reliability. Conventions have been held in this country and in other countries and it might be thought that the lesson has been so often and so well propounded that to discuss it again is hardly necessary. However, I hope to show that we still have some way to go before we even begin to approach the ideal.