Of the many kinds of fatigue of materials, this paper deals only with “The fatigue of ductile metals by the imposition of cyclic stresses.” It is the purpose of the paper to show that: —

1. (i) Metals have certain very human attributes.

2. (ii) They have both memory and temperament.

3. (iii) They remember with increasing resentment the stresses which have been imposed upon them.

4. (iv) They are extremely sensitive as to the appropriate moment at which to break.

The question arises of why a piece of any ductile metal, other than a ferrous one, free from any abrupt change of section, when subjected to cyclic stresses of any magnitude, however small, ultimately breaks although the maximum stress imposed is one which, if static, it could have borne indefinitely. The answer is—mainly because of its metallographic structure.

Before the Second World War there were few airfields in Great Britain with paved runways.

The grassed flight strips of the pre-war years could carry the wheel loads of the aircraft then in use with little maintenance, other than grass cutting and rolling clinker or stone into local soft patches. From 1939 onwards, the increasing weight of aircraft, and more intensive flying, made it necessary to construct airfields with paved runways to permit operation in all weathers.

From 1939 to 1945, 444 airfields were constructed with paved runways for the Royal Air Force at a cost of £200,000,000, excluding the cost of building construction. Since 1945 the emphasis has been upon airfields for civil use, and the great airfields at Idlewild, Boston, Johannesburg and London Airport have been built.

Louis Blériot's epic first flight across the Channel in 1909 was the inspiring inception to a new era of travel. Man's imagination was stirred by the fact that a tiny aeroplane had crossed the sea barrier, thus showing to the least thoughtful that no longer were oceans an obstacle to international communication.

With the subsequent rapid development of aviation the Channel crossing became a matter of course, but it was nine years before a long ocean crossing was made, when, in 1918, Alcock and Brown flew a Vickers Vimy from Newfoundland to Ireland, and it was thirteen years before Lindbergh again captured the world's imagination by his lone flight across the Atlantic.

There is no doubt of the value of pioneer flights such as these in stimulating aircraft development towards greater performance, reliability and suitability.

The emphasis in this paper is on design because the author is engaged on design work and, therefore, is more competent to deal with design than with manufacture. In any discourse on design, however, consideration must be given to the available capacity for manufacture, as this has a considerable bearing on the subject.

The influence exerted by the technical development of a vehicle on the design of the surface on which it travels is of considerable historical and social importance. Technical progress in the design of the road vehicle has never been matched by a similar development of the road, and in the past 50 years the discrepancy between the performance of the vehicle as dictated by road conditions, and the performance of which it is capable has been even more marked. The policy, forced upon society by national and international conditions, of compelling the vehicle to conform to the present standards of road design is highly restrictive and uneconomic, and such devices as pedestrian crossings, traffic lights and speed limits, are all evidences of failure to solve the problems of the simultaneous development of vehicle and road.

The behaviour of an elastic aircraft in flight may be divided into dynamic and static cases with an intermediate class of phenomena under the heading of stability. The dynamic category is concerned with flutter and divergence effects and since these are destructive when they occur they are naturally given precedence in the aeroelastic analysis of an aircraft.

Having eliminated these dynamic effects by suitable design it is natural to turn to the static case which assesses the manoeuvrability of the aircraft. With the advent of sweepback and the attainment of higher Mach numbers it becomes increasingly difficult to determine the behaviour of modern aircraft even when regarded as rigid.

To judge by the newspapers, the day of the turbine powered transport aircraft is already here. This is not to say that the piston engine is no longer required; probably it will be in use for many years to come, particularly for small aircraft, but new major designs must certainly be planned so as to take advantage of this revolutionary new form of prime mover.

Detailed investigations of the two-dimensional characteristics of thin aerofoil sections with small leading-edge radius have been made by Gault and McCullough. They found that at angles of incidence well below the stalling angle of the section, the laminar boundary layer separated from the surface near the nose, became transitional away from the surface, and re-attached to the aerofoil as a turbulent layer a little farther downstream. Beneath the separated layer, a “bubble” vortex was formed lying parallel to the leading edge, its rotation being such that the flow adjacent to the surface was towards the leading edge.

The Fortieth Wilbur Wright Memorial Lecture, “ Prophecy and Achievement in Aeronautics,” was given by Sir Harry Garner, K.B.E., C.B., M.A., F.R.Ae.S., before the Royal Aeronautical Society on Thursday 29th May 1952 at the Institution of Civil Engineers, Great George Street, S.W.I. Mr. G. H. Dowty, F.R.Ae.S., President of the Society, presided over the meeting which comprised some 350 members and guests.

Medals and Prizes awarded by the Council for 1951-1952 were presented before the Lecture.

This paper does not claim to reveal any epic discoveries. In fact the technical features discussed, if perhaps not well tried are certainly well known to designers and technicians in aeronautical development. Its purpose is rather to emphasise the need for concentration in development in certain directions in the light of up-to-date combat experience with the aid of rather limited, but surprising, information on design trends of modern enemy interceptor fighters.

It is hoped that this will assist the operators, who will readily appreciate the tactical aspects, to assimilate some of the technical implications and to be able to discuss them more freely with designers and technicians.

It is well known that jet aeroplanes operate most economically, from a fuel consumption point of view, at their service ceiling and that with fighters the struggle for altitude supremacy has always been paramount from the beginning.

The thought that the highlights of history four centuries ago will repeat themselves in our time is growing, but the word and the wish are not enough. It will need to enter the heart and soul of the people and the nation, if another prolonged period of prosperity, highlighted by the deeds of the adventurous, is to be ushered in.

The 850th Lecture to be given before the Royal Aeronautical Society was delivered at the Institution of Civil Engineers, Great George Street, London, S.W.1, on 20th March 1952. Major G. P. Bulman, C.B.E., F.R.Ae.S. (Past President) presided and introduced the Lecturer, Group Captain E. A. Whiteley, D.F.C., B.A., A.F.R.Ae.S., Royal Air Force, who was attending the Joint Services Staff College and who, in addition to being a pilot, had qualified as an R.A.F. Engineering and Navigation Specialist and also held a British Civil Airline Pilot's Transport Licence and a Flight Navigator's Licence.

This paper deals with the application of the Transfer Function-Fourier (T.F.F.) Method to the calculation of longitudinal manoeuvring tail loads for aeroplanes.

It has been found that the tail loads computed by this method agree very well with those computed by the standard method outlined in Ref. 1. The main advantages of the T.F.F. method are the time saving and the convenience in handling an arbitrary elevator input. Having once calculated the transfer function between elevator input and tail angle of attack output, it may be used repeatedly to compute the longitudinal manoeuvring tail loads for various arbitrary elevator inputs. This is done by simply expressing the input as a Fourier series and multiplying each term in the series by the value of the transfer function for the corresponding frequency. Then the resulting output series is summed at enough points to obtain a plot of the transient output. This process can be done in approximately one hour of engineering time for each arbitrary elevator input, exclusive of machine calculating time. The machine (usually I.B.M.) calculating time is about half an hour per input. On the other hand, experience has shown that the engineering time required per input by the standard method is approximately forty hours for the first input, and approximately five hours for each additional input.

It is concluded that the calculation of longitudinal manoeuvring tail loads by the T.F.F. method is accurate, dependable, especially adaptable to machine methods, and can conveniently handle arbitrary inputs.

The application of aircraft to agriculture began in the 1920's; experiments in insecticide dispersal were made in Ohio in 1921 and a bulletin was issued by the U.S. Department of Agriculture on dusting cotton crops by means of Curtiss JN6H aeroplanes in 1924. Since then the idea has been developed, notably in countries of large area. In 1928, for example, crop dusting experiments were made in the United Kingdom but the results were not very encouraging because of the drift problem with comparatively small fields.

The purpose of this paper is to explain in simple terms the methods employed in, and the principles underlying, the technique of resonance testing and flutter calculations and to place that technique in its proper perspective within the framework of fighter aircraft design. No attempt is made to present original work, or to examine the more advanced aspects of the subject as both of these are considered to be outside the scope of the paper.

The reasons behind the growth in importance of resonance tests and flutter calculations are dealt with first. The technique of ground resonance tests is then given in detail. A few words follow on model resonance tests, the calculation of normal modes, and some aspects of flight resonance tests. The technique of flutter calculations is considered last of all, an attempt being made to give a simple explanation of “ flexure-torsion ” flutter, plus the basic theory of two-freedom flutter leading to the Lagrangian equations. The methods and instruments described in the paper may be regarded as typical, but as the subject is continually evolving they are far from final.

Some present trends in technique are mentioned, together with the difficulties experienced in dealing with the aerodynamic forces in the transonic region. It is essential that these forces be assessed, and the only known method is by experiment.

An investigation into the preparation of Data Sheets based on the work of Kuhn and Griffith at the N.A.C.A., revealed that it might be possible to present non-dimensional curves for the ultimate shear strength of aluminium alloy webs in incomplete diagonal tension, in a form similar to that of Structures Data Sheet 02.03.13, which are independent of material specifications. The values of “basic allowable shear stress” are founded on flat plate details from early experimental work and on estimated values for fully developed diagonal tension. Later work by Ross Levin provided further test results extending the range of diagonal tension developed, and the application of these to thick webs has been confirmed.

In this paper it is shown how, in an angular contact ball bearing, the motion of a ball depends on the dimensions, loading and speed of the bearing. In general, ball motion in an angular contact bearing differs from the simple motion usually visualised by including oscillatory occurrences, shown here analytically, graphically and visually. These oscillatory occurrences are shown to lead to premature fatigue of the bearing metal, as a function of the speed of rotation, thereby imposing the present limitations on maximum speed and “ life.”

It is further shown that only when the dimensions of an angular contact ball bearing are related in a certain way, a motion is produced in which the oscillatory phenomena are eliminated. These relations are given as functions of loading and speed in a system of equations and limiting conditions (hereafter referred to as “ Relations of the Dimensions ”).

In recent years it has grown customary for aircraft firms to put increasing effort into the prediction of flutter during the design stage. This design work, however, is chiefly related to wing flutter in which the control surfaces play little part, whereas the cases of flutter which most commonly occur in reality are those involving control surfaces. The reason for this is that the wing stiffness, and hence the wing weight, is often determined by considerations of main surface flutter. Control surface flutter, however, can often be prevented by methods which do not have a serious effect on the aircraft weight and which are often postponed until after the design stage. This paper will discuss what steps can be taken, both in the design stage and during the flight testing of a prototype, to prevent control surface flutter.