I am honoured to have been invited to give this Third Cierva Memorial Lecture on a subject which has a general application to all forms of aircraft, and which is central to any consideration of the future of the helicopter.

Reliability is a problem, the extent and urgency of which can only be appreciated fully and at first hand by the operator of a large fleet of aircraft, but most of the discussions and documents which have helped to lay the basis for this paper are not for general publication. I believe that this has helped me to concentrate on the essentials of the problem, but there is a danger that the simple arguments on which the paper is based may not carry the emphasis needed to convey to my colleagues the critical attitude of the operators.

Before looking forward, the structural significance of the trend towards the rear-mounted engine must be considered. The reason for this trend stems from the need to obtain increased overall efficiency. The advent of the jet engine first of all made it possible to bring the engines inboard into the root, as on the Comet and Vulcan aircraft, and now, in the interest of obtaining higher aerodynamic efficiency, they have been moved aft towards the tail end of the fuselage. This allows a reduction of wing area, a consequent reduction in tailplane area, an overall reduction in drag and a consequent decrease in fuel consumption for a given performance.

The second lecture to be given before the Air Law Group of the Society "Legal Liabilities Arising out of Aircraft Design and Manufacture" was given on 19th December in the Lecture Theatre, 4 Hamilton Place, London, W.l. The Lecture was in two parts, Major K. M. Beaumont, C.B.E., D.S.O., M.A., A.F.R.Ae.S., F.R.S.A., F.R.P.S.L., speaking from the legal point of view and Mr. C. B. White, M.A., Hawker Siddeley Aviation Ltd., sneaking from the manufacturer's point of view. The Chair was taken by Mr. Walter Tye, O.B.E., B.Sc., F.R.Ae.S., Chief Technical Officer, Air Registration Board. The report of the Discussion was prepared by Mr. B. J. Davenport, B.A.

A method for describing the action of a pilot in mathematical terms is presented. The method applies for tracking tasks and gives a pilot describing function which can be used in conventional servo-analysis. Flight simulator data obtained in this way for a wide variety of aircraft longitudinal response characteristics are presented and the effect of these characteristics on the pilot's action is discussed fully. In order to illustrate that work of this kind can lead to a quantitative understanding of pilot's “handling qualities” opinion, the recorded pilot opinions are “predicted” from a knowledge of three simple aircraft characteristics.

The effect of the longitudinal membrane stress on the flexural edge stresses in a thin cylinder under axially symmetrical loading is considered. A general solution is given, and applied to two specific problems to illustrate the magnitude of the effect.

The 1346th Lecture to be delivered before the Society, “Structural Design of the X-15”, by Dr. R. L. Schleicher, was given on 18th April 1963 in the Society's Lecture Theatre with Mr. B. S. Shenstone, M.A.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.L, in the Chair. Introducing the lecturer, Mr. Shenstone said that Dr. Schleicher was Manager, Structures Engineering, at the Los Angeles Division of North American Aviation, Inc., and he had been with the firm since its inception in 1934. Dr. Schleicher was a graduate of Villanova University and held a degree of B.S. in M.E., and his D.Sc. had been conferred on him in 1957. He had nearly 34 years experience in aircraft structures engineering beginning in 1929. He had been Chief Structures Engineer at North American Aviation, Inc. on all the aircraft designed and built by the Los Angeles Division of that company and that included the X-15. He was a member of the Society for Experimental Stress Analysis and an Associate Fellow of the A.I.A.A. From 1943 to 1958 he had been a member of a number of NACA (now NASA) Committees and Sub-committees and had written a number of technical papers. He was currently serving on an Advisory Committee on Aircraft Structures for the U.S. Air Forces.

They were indeed grateful to Dr. Schleicher for coming all this way to lecture.

A review is made of recent research in the United States relating to runway slipperiness and to slush-drag or fluid-drag effects on aircraft ground performance. The formation of fluid spray and its drag effects on aircraft are traced from spray origin at the intersection of the tyre and runway to impingement on the aircraft over the complete aircraft ground-velocity range. Six manifestations of tyre hydroplaning are presented and discussed: fluid-drag peak, tyre spin-down, loss of aircraft directional stability, loss of aircraft braking traction, suppression of bow wave, and progressive detachment of the tyre footprint from the fluid-covered runway surface as ground speed is increased. A convenient formula for estimating tyre-hydroplaning speed is indicated to be

where Vp=hydroplaning speed, knots

p=tyre-inflation pressure, lb/sq in.

Comparison with available experimental data is shown. The effects of fluid viscosity and density on runway slipperiness are discussed. The effects of some runway-surface textures, tyre-tread patterns, and aircraft landing-gear wheel arrangements on slipperiness are described. The paper also includes indications of areas of interest that need further study.

A semi-empirical method is given, together with systematic data sufficient for estimating the maximum lift characteristics of wings at Mach numbers below 0·6. The method gives the effect of sweep, aspect ratio, taper ratio, camber, leading-edge radius, maximum-thickness position and Reynolds number. The accuracy is good for most wings at full-scale Reynolds numbers, but deteriorates for wings with trailing-edge angles greater than about 12° (which for conventional sections correspond with thickness/chord ratios about 0·140), and for heavily cambered sections.

Throughout the years that rotorcraft have been on the British Register of Civil Aircraft, the single reciprocating engined, single main rotor helicopter has been the predominant representative of this particular family of aircraft. These helicopters were certificated to the British Civil Airworthiness Requirements (BCAR), Section G, “Rotorcraft,” issued in January 1954, which was written in terms of such helicopters.

During the past few years there have been significant changes in rotorcraft design—the turbine engine has been introduced and the multi-engined type has become a reality.

Basic changes in the design trends of any type of aircraft must inevitably involve a re-appraisal of the appropriate requirements by the responsible airworthiness authority. The BCAR are subjected to a constant process of refinement and revision and, as a result of the development of new types, the Air Registration Board has been considering the airworthiness implications and preparing amendments to most parts of Section G, but I wish to discuss only Flight Requirements which are in the main contained in one Sub-Section of Section G—Sub-Section G2. From the recent revisions I have extracted only the significant changes, although there are still problem areas I would like to put on record.

My intention is to give a generalised résumé of the Flight Testing of the H.P.115 from the pilot's viewpoint. It is my belief that, in many respects, the flight testing of an aircraft, so far as the pilot is concerned, starts from its inception in that common sense pilot participation right from the word go can do much to help to ensure the ultimate success of the project. This is one of several reasons why, instead of just discussing what goes on up at the front end of the H.P.115 during flight. I shall trace briefly the growth of the aircraft. It is an interesting and, in many respects, an involved story: I will try to work along its main thread with occasional excursions into some of the more pertinent by-ways.

The author accepted the invitation to present this paper on the rash assumption that he would be able to present something new and useful on the tilt-wing. The Hiller Company (in partnership with Vought and Ryan) was the first to have received a fully-fledged development contract for evaluation quantities of any VTOL machine. The VHR-447 which was selected as the Army, Navy and Air Force XC-142A was a culmination of almost ten years of effort spent in the investigation and promotion of the tilt-wing “propello-plane” VTOL aircraft concept.

My Task is to express the manufacturer's point of view and his problems in this field. I can only speak of my own experiences in one Group, and that experience has been chiefly in the civil field. The observations which follow are therefore related mainly to civil aircraft.

In a previous life as a recently qualified solicitor I had the task of presenting to the head of a company, on behalf of my client, a cheque for more than £lm. This payment was made partly because my client's product had run into trouble and partly because there was uncertainty about the legal liability. My experiences in the Aircraft Industry have, therefore, been coloured by a considerable respect for any manufacturer's responsibilities for his product.

My Subiect is a highly specialised and rather adventurous one—the practice of night spraying of trees and agricultural crops from aircraft.

It may sound hazardous, as it is, and of course it is at present only attempted when biological or climatic factors make spraying by daylight undesirable or ineffective. It is also dependent on a favourable terrain, and the development of better equipment. Where these conditions are fulfilled, in certain cases night spraying may become part of the armoury of a number of spraying contractors, mainly in Africa and America.

The 55th Main Lecture to be given at a Branch centre, “Light and Executive Aircraft and Their Future Prospects in the United Kingdom,” by F. H. Robertson, A.F.R.Ae.S., Chief of Preliminary Design, Short Bros, and Harland Ltd., was held under the auspices of the Christchurch Branch on 12th December 1962. Mr. E. W. J. Gray, F.R.Ae.S., President of the Christchurch Branch, opened the proceedings by welcoming the President and Secretary of the Society and visitors from the Society's branches at Luton, Bristol and Cheltenham as well as visitors from Shoreham. Mr. Gray then asked the President, Mr. B. S. Shenstone, M.A.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.I., to preside for the rest of the meeting.

Introducing the lecturer, the President said that Mr. Robertson had spent five years with Vickers-Armstrongs Ltd., three in the works and two in the D.O., and then joined Hawker Aircraft in 1934 as a junior draughtsman; in 1936 he had gone to Aeronca Aircraft Ltd. for a year and in 1937 had joined Miles Aircraft Ltd. as senior draughtsman, becoming Chief of Experimental Design. From 1946-1952 he had been with Saunders-Roe Ltd., where he became Chief Project Engineer, and in 1952 had joined Short Bros, and Harland Ltd. After several years as Chief Project Designer, he became the Company's Chief Designer, Light Aircraft in 1959. He was now Chief of Preliminary Design. He was sure that Mr. Robertson was known to many of them, either personally or from things he had written, and they would know that he rarely said anything with which they could all agree. He thought that what Mr. Robertson would say in his lecture would be of the same order.

The designer's task is always to choose the best compromise to meet the various conflicting requirements put upon him. This task is eased when these requirements and ways of meeting them are expressed precisely in numbers, which is so in most performance work, but rarely true of safety or reliability.

In these latter areas the feedback of operational information shows when a problem exists and how important it is. For existing aircraft a solution must often be sought by ad hoc tests before the results of fundamental research are available.

The emergence of electronic computers has brought about a revolution in the analysis of aircraft structures in the past decade which is now generally accepted throughout the Industry. But the major impact of computers on design has, in my opinion, not yet been realised and I hope, in this short paper, to show how powerful a tool they can become in the hands of imaginative design engineers. The direct benefits to the designer lie in the ability of the computers to perform large amounts of routine arithmetic in a short space of time. This capability enables us to obtain an insight into structural behaviour and to consider the influence of the aircraft environment and design alternatives from the earliest stages of design. By the development of general purpose computer programmes for handling routine calculations the structural designer can be freed from much of the laborious calculation associated with complex structures and he is able to devote more time to creative work. An even more important indirect benefit is the basic re-thinking of design processes which is necessary in order to reduce them to routine arithmetic. We begin to realise that many aspects of efficient design such as continuity, cost and weight can be introduced as quantitative parameters instead of relying on intuitive compromise.

During the period 1945-1960 many journals contained papers in which flight optimisation problems were solved by several different methods, The author has long felt that a review of these methods and the assumptions under which solutions have been obtained is needed, particularly by research workers who are new to this field of study and also because many of the techniques used for optimising flight within the atmosphere are applicable to the space flight problems of today.

The A. & A.E.E. has been associated with rotorcraft in this country almost from their earliest days. For example, the records show that a C30A Autogiro was evaluated at Martlesham Heath in 1935. After the outbreak of war responsibility for development work in the rotary wing field was assumed by the Airborne Forces Establishment (later the Airborne Forces Experimental Establishment) and the accounts of such developments as the Rotachute and the airborne jeep have since become well known. In 1945 the A.F.E.E. was declared to be the official testing establishment for prototype helicopters and this responsibility has remained until the present time. The A.F.E.E. was merged in 1951 with the A. & A.E.E., becoming the Airborne and Helicopter Division of the latter Establishment.

The Inaugural Lecture of the Air Law Group of the Society “Crime in Aircraft” by the Hon. Mr. Justice Wilberforce was given in the Lecture Theatre, 4 Hamilton Place, London W.l. on 31st October 1962. Mr. L. A. Wingfield, M.C., D.F.C., A.R.Ae.S., Solicitor to the Society, presided. Introducing the lecturer Mr. Wingfield said that the Hon. Mr. Justice Wilberforce was a Judge of the Supreme Court (Chancery Division). He had also been the leader for the United Kingdom at no less than four diplomatic Conferences on Air Law—Geneva in 1948, Rome in 1952, The Hague in 1955 and Guadalajara in 1961—he had also been the Chief United Kingdom member of the Legal Committee of I.C.A.O.; to find a more distinguished contribution to air law than Sir Richard's would be difficult.

The Society's Air Law Group arose indirectly from a lecture to the Society in January 1961 by Mr. H. Caplan on “The Law versus Science in Aeronautics”. The Group was formed in September of that year, and since its inception Sir Richard had acted as Chairman. One of the first tasks tackled by the Group had been the study of the draft convention adopted by I.C.A.O. at Munich in September 1959 on offences occurring on board aircraft. At the request of the Ministry of Aviation the Steering Committee of the Group, voicing an independent view, reported on the draft convention.

Not only was this the Group's inaugural lecture, it was also the first occasion in the Society's 96 years that it had been addressed by one of Her Majesty's Judges.

Before beginning his lecture the Hon. Mr. Justice Wilberforce congratulated the Society on its initiative in forming the Air Law Group and paid tribute to the Secretary of the Society, Dr. A. M. Ballantyne, T.D., B.Sc, F.R.Ae.S., F.A.I.A.A., Hon.F.C.A.S.I., for the work he had done and the assistance he had given in organising the Group.

The following report is taken from the tape recording of the lecture.

Incompressible turbulent flow in smooth pipe bends of circular-arc curvature and constant cross section is discussed. The effects of bend angle, radius ratio, duct cross-sectional shape and Reynolds number are considered. Particular attention is paid to the influence of the tangents on the flow and losses in a bend. In addition consideration is given to the definition and measurement of the bend loss.

A correlation of experimental pressure loss data is made. It is shown that large variations in experimental results, which cannot be ascribed to the effects of geometrical parameters or Reynolds number, are accounted for by the effects of the downstream tangent and position at which the pressure measurements were made. The inadequacy of existing experimental information is an obstacle to the presentation of comprehensive data on the effect of geometrical parameters on bend losses.