alan arnold griffith, 1893-1963 -...

Alan Arnold Griffith, 1893-1963

A. A. Rubbra

1964, 117-136, published 1 November101964 Biogr. Mems Fell. R. Soc.

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ALAN ARNOLD GRIFFITH

1893-1963

Alan Arnold Griffith was born in London on 13 June 1893.His father, George Griffith, explorer, journalist and author, was a widely

travelled man who had a varied and interesting career. Much of George Griffith’s time abroad was spent in South Africa where, as a special correspondent of the Daily Mail, he covered among other events, certain of Rhodes’s journeys. As an author, he dealt with both fact and fiction, the latter including historical novels, a prediction of the coming Russian Revolution, and imaginative ‘science fiction’.

In this connexion and in view of the pioneering work on the evolution of jet-lift which Alan Griffith was later to contribute to aeronautical science, it is of interest to recall an article on nineteenth century fiction which was published by Flight (21 December 1956). The article pointed out that, following the vogue of Jules Verne, a new movement in English popular fiction by a few of the younger writers, introduced imaginary flying machines.

One of these authors was Fred. T. Jane who later, in 1909, founded Jane’s All the world’s aircraft, now widely used throughout the world. Another writer published a series of romances in which flying machines figured prominently and sensationally; H. G. Wells described one of these stories as an ‘aeronautic masterpiece’. The inventions of the author of this novel of 1895 are depicted in graphic illustrations; strange looking aeroplanes having slatted wings and a streamlined fuselage. Forward propulsion was provided by a group of three airscrews on horizontal shafts at the rear and lift (presumably to augment the wings for vertical take-off) was provided by five airscrews on vertical shafts above the fuselage. The author of this book was George Griffith, Alan Griffith’s father.

By a most interesting coincidence, the leading article of the same issue of Flight gave the first published photograph and details of the vertical take-off research aircraft built to Ministry of Supply order, by Short Brothers and Harland of Belfast. Known as the Short S.C.l, this was the first aircraft in the world to embody Griffith’s jet-lift ideas for vertical take-off and landing, referred to later on in this memoir.

During Alan Griffith’s early childhood, the family moved to the Isle of Man where his father died when Alan was a child of only seven years. Alan’s widowed mother was left rather poor and hence his early education was somewhat unsettled; he received private tuition until 1906 when his more advanced schooling began at the Douglas Secondary School. He

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118 Biographical Memoirspassed the Cambridge Senior local examination in 1910, achieving a first- class pass with distinctions in physics, chemistry and applied mathematics. The following year he was awarded a ‘Sir W. H. T ate Science Scholarship* of £35 per annum for three years and entered the School of M echanical Engineering a t the University of Liverpool. In 1914 he acquired his B.Eng. with first-class honours in mechanical engineering, the ‘Rathbone M edal’ and the University Scholarship in Engineering tenable for one year of research. During that year he conducted an investigation into the surface resistance to heat between metals and gases. He advanced to his M.Eng. in 1917 and to his D.Eng. in 1921, both a t the same university.

In November 1925 he m arried Constance Vera Falkner the daughter of R. T. Falkner of the Royal Engineers and Elizabeth {nie Shepherd). Their first child, daughter Betty, was born in September 1926; she died tragically in 1946 when an undergraduate at K ing’s College. A second daughter, June, born in 1929, studied art at the Slade School and m arried one of her teachers; they now have four daughters. A son, John, was born in February 1938 and followed scientifically in his father’s footsteps, reading physics at King’s College, London. Following graduation, John remained at K ing’s for a further three years’ research in nuclear physics before taking up a Research Fellowship at Birmingham University where he submitted his Ph.D thesis and is now with the Cyclotron Group. He is m arried and has one child.

Returning to Griffith’s career subsequent to his graduation at Liverpool University, he joined the Royal Aircraft Factory (later known as the Royal Aircraft Establishment) in Ju ly 1915 and received a short general workshop training until November 1916. During the next four years he was successively Draughtsman, Technical Assistant and Senior Technical Assistant in the Physics and Instrum ent Departm ent at the Royal Aircraft Establishment, becoming a Senior Scientific Officer of the departm ent in April 1920.

During this period, in December 1917, a jo in t paper by A. A. Griffith, M.Eng., and G. I. Taylor, M.A., entitled ‘The use of soap films in solving torsion problems’ was read before the Institution of M echanical Engineers and gained the Thomas Hawksley Gold Medal. This paper dealt with novel methods for the estimation of torsional stresses in sections of complicated shapes.

In principle, the soap film provides a means of finding solutions to the equation

7>2p^ 2 + - ^ 2 + a constant = 0.

Prandtl, in 1903, had pointed out the analogy that a soap film slightly displaced by a pressure difference and by constraints at its edges, assumed a surface profile which satisfied the equation

, i>2£ , pA



Hence the Z ordinates of the soap film multiplied by a suitable factor provide a solution of the equation.

A practical example of a similar equation results when finding the stresses in a twisted bar of uniform section.

Alan Arnold Griffith 119

* * 4 . * * 4 . 9 = 0.

The solution is achieved when ip has been found at all points of the section.

Griffith demonstrated that the conditions are easily reproduced on a soap film stretched across a hole which has been cut to the shape of the cross- section of the twisted b a r ; the film being blown out slightly by reduction of the air pressure on one side.

Values of ip were found by plotting the contour lines of the blown film.He also showed that the elastic problem of ascertaining the shearing

stress in a cantilever beam of uniform section with an end load, may be solved by the soap film method as well as the stressing in torsion of hollow bars of irregular section. The need for the determination of stresses in the aerofoil sections of airscrew blading and other problems had originally led to the above work and the methods propounded by Griffith were proved to be exceedingly accurate and convenient.

In the discussion of the paper, M r Henry Fowler, C.B.E. (later Lt.-Gol. Sir Henry Fowler, K.B.E.), said that the authors had conferred a very considerable benefit, not only upon the aeronautical industry, bu t upon engineering generally. Professor A. H . Gibson remarked that it was practically the only real advance in our knowledge of the general problem of torsion since the investigations of Saint-Venant, the Chairm an (The Institution President, Michael Longridge) stated that ‘the reading of the paper was a great compliment to the Institution’. D r H. S. Hele Shaw, F.R.S., and D r L. Bairstow, C.B.E., F.R.S., were among several who commented favourably on the paper. O n the same subject, he also contributed a paper ‘The use of soap films in solving stress problems’ a t the International Congress for Applied Mechanics at Delft (Holland) in April 1924, which followed work done earlier and jointly with G. I. Taylor (later Sir Geoffrey Taylor). Griffith’s prolonged and intensive work on the estimation of stresses, using the soap film technique, earned him the nickname of ‘Bubble Griffith’ at the Royal Aircraft Establishment.

In 1920 he produced what is perhaps one of his best known contributions to the science of the behaviour of materials. This was his paper ‘Theory of rupture’ (Phil. Trans. A, 1920).

Commenting on this, M r Glenny of the National Gas Turbine Establishment states ‘Griffith’s earlier theories were devised to resolve the discrepancies between ideal and observed strength by postulating that materials contained cracks or other lattice flaws that set up local concentrations of stress. The



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importance of Griffith’s work was in pointing out that cracks could cause rupture. All subsequent theories of fracture strength took into account the existence of micro-cracks, dislocations, etc., either pre-existing in the material or generated in the process of deformation. Griffith’s contribution is the forerunner of all theories based on the presence of flaws to account for loss of strength. I t applies particularly to amorphous material and has been modified to account for the behaviour of crystalline materials particularly in view of the fact that deformation in materials is discontinuous. Secondary issues from Griffith’s work are that he was the first to draw attention to surface condition, i.e. stress concentration as a factor in strength. One favourable point in Griffith’s crack theory is that it explains the different behaviour of brittle materials in tension, torsion and compression.’

Sir Geoffrey Taylor recently made the following comment on this work: ‘The work on stress concentration led A. A. Griffith to realize that cracks

can theoretically produce infinite stress at their ends. A theory which tried to explain the weakness of materials by imagining them to be full of cracks encounters the difficulty that cracks, the curvature of whose ends are of molecular dimensions, would reduce the strength far below what is actually observed. Griffith’s great contribution to ideas about the strength of materials was that he realized that the weakening of a material by a crack could be treated as an equilibrium problem in which the reduction in strain energy of a material containing a crack, when the crack extends, could be equated to the increase in surface energy due to the increase in surface area.’

In this connexion it is also interesting to note that in October 1963, a paper by Sir Geoffrey Taylor was read before an American meeting on the history of technology; the connexion between the Griffith crack conception and dislocation, was described in the paper. In addition to the above it is of interest that Griffith also worked on glass fibres and other materials in bonded form utilizing the high strength of filaments, thus anticipating the fibreglass and other developments of the present day.

Griffith occupied the position of Senior Scientific Officer for eight years; Sir Ben Lockspeiser was one of his colleagues for part of this time. During this period, his work on airscrews led Griffith to the study of the gas turbine and to one of his greatest contributions to the science of aircraft propulsion. He realized that the blades of existing turbines were creating wasteful turbulence by working in a stalled condition and he was the first to suggest that it would be better to treat turbine blades as aerofoils and base their design on aerodynamic theory. Furthermore, he showed that in an axial compressor serious losses limited the angle through which the air flow could be turned and that successive stages of compression would be necessary; hence his staunch advocacy of the multi-stage axial design.

These proposals for securing high efficiency in gas turbines were detailed in Griffith’s classic report No. H 1111 for the Royal Aircraft Establishment in Ju ly 1926, ‘An aerodynamic theory of turbine design’. In this, now famous paper, he demonstrated that the axial gas turbine was feasible as a power

Biographical Memoirs



1 2 1

unit for aircraft propulsion and determined the basis for a complete design.It is of interest to quote one or two passages from Griffith’s paper:‘The comparatively low efficiency of turbines and turbo-compressors is

the only serious obstacle to the development of a successful internal combustion turbine suitable for use on aircraft. The causes of this low efficiency have therefore been investigated.

‘The circulation theory of aerodynamics has been applied to the problem of the design of turbine blading. It has been deduced that the main reason for the low efficiency of blades of current design is that they normally work under stalled conditions. Formulae for efficiency have been worked out on the basis of the new theory . . .

‘It appeared on consideration that the use of rotary members similar to airscrews would lead to much higher efficiencies than are at present obtainable from turbo-machines. With existing airscrews, propeller efficiencies as high as 0-8 to 0-85 can be readily obtained. By using airscrews as the rotary members of compressors, even higher efficiencies would be possible, since most of the translational energy in the slipstream would be recoverable in the stator blades. Moreover, the efficiency of airscrews can be predicted within narrow limits by the application of known aerodynamic principles, so that the conditions for maximum efficiency are comparatively easy to determine.

‘These considerations at once suggest the basis of a new method in designing turbo-machinery. The blades, instead of being regarded as the walls of channels, whose shape determines the velocity and pressure changes taking place in the fluid, are to be regarded as aerofoils and the changes in velocity and pressure are to be calculated from the blade reactions. These, in turn, can be found with the help of the known aerodynamic characteristics of the blade sections . . .

‘A point which emerges at once is that, since the angle through which the fluid stream can be efficiently turned by one row of blades is comparatively small, it will usually be necessary to use multi-stage designs in order to secure a high overall efficiency.’

The A.R.C. (then the Aeronautical Research Committee) discussed the paper and recommended experiments on a single-stage compressor and a single-stage turbine; this was constructed in 1927 under Griffith’s supervision.

The small test unit comprised a compressor and turbine mounted on one shaft and having blading of aerofoil section. The diameter of the rotor barrel was 3 in. and the internal diameter of the casing 4 in., giving a blade height of 0 • 5 in. less blade tip clearance; the blade section had a chord of 0 • 6 in.

W. G. Clothier carried out the tests of the unit in 1928 and produced his report, ‘Test of aerofoil section turbine blading’. The efficiency was measured over a range of speed and blade settings, the losses being supplied by means of an exhauster pump. The tests demonstrated that blading designed on the aerodynamic theory of Griffith’s 1926 paper yielded efficiencies that accorded

Alan Arnold Griffith



122well with his prediction and reached 91 per cent including blade, casing and rotor friction losses and windage on rotor ends but neglecting bearing friction losses, at speeds around 15 000 rev/min.

This was the first time that high efficiency was obtained from an axial type compressor, the type which now predominates in all high output high efficiency gas turbines; Griffith may be said to be the true originator of the multi-stage axial engine.

Following this Griffith became Principal Scientific Officer in charge of the Air Ministry Laboratory, South Kensington, in 1928 and in 1929 he evolved the contra-flow principle for a gas turbine described in his paper ‘The present position of the internal combustion turbine as a powerplant for aircraft’ ( A.M.L. Report 1050 A).

In an endeavour to avoid stalling conditions in the low pressure stages of a multi-stage axial compressor when starting, and the possibility of large scale vorticity being projected downstream and stalling the high pressure stages, Griffith discussed in his paper the possibility of subdivision as follows:

‘Now let the compressor and its turbine be subjected in turn to mechanical sub-division, i.e. there may be high, intermediate and low pressure turbines driving high, intermediate and low pressure compressors.

‘In any compressor of the kind considered, the departure of the flow pattern from the designed form depends on two factors, namely, the volumetric rate of flow and speed of rotation. I t is clear that mechanical subdivision outlined above, lessens the adverse effect of the first of these factors. I f therefore an arrangement can be found such that the several speeds of rotation are under all relevant conditions of running, suitably proportioned to the respective volumetric rates of flow, it follows that the adverse effect of change of flow pattern will be decreased. Hence the efficient range of conditions will be increased. I f now, the mechanical sub-division be carried to the limit so that each mechanically independent element consists of a single-stage turbine driving a single-stage compressor, the effect of compressibility on the flow pattern (apart from the effect on the aerodynamic properties of individual blade rows) may be for practical purposes entirely eliminated. The range of efficient running conditions will then be limited at the lower end only by the adverse scale effect and at the upper end only by the onset of the compressibility stall.’

Means whereby limiting sub-division may be realized are described in Griffith’s patent from which the following quotations are taken :

‘According to the present invention a turbo-compressor comprises rotating blade elements which are arranged so that the relative rates of rotation of the elements are inherently adjusted to prevent stalling of the blading. The result can be obtained by coupling the turbine blades working at any given pressure to the compressor blades working at approximately the same pressure.

‘Further, according to the present invention, a combined turbine and

Biographical Memoirs



compressor comprises rotating elements, each of which carries a row of turbine blades and a row of compressor blades. These elements are assembled in a common casing so that each can rotate freely and independently of the others in its own bearings . . .

‘Owing to the rotatable elements being independently rotatable any change of working conditions as aforementioned is inherently accommodated by the elements taking new speeds of rotation appropriate to the volumetric rates of flow through the several elements.

‘The arrangement according to the present invention is such that the air or gas which is being compressed flows successively through the several rows of compressor blades whilst the products of combustion (or externally-heated air) which, by expansion, supply the driving power flow successively through the several rows of turbine blades preferably in the opposite direction.’

In 1931 Griffith moved back to the Royal Aircraft Establishment to take charge of engine research, but it was not until 1938, when he became Head of the Engine Department, that a decision was made by the Royal Aircraft Establishment to build an experimental compressor on the contra-flow principle.

Earlier on in 1936, Mr Hayne Constant returned to the Royal Aircraft Establishment from Imperial College where he had been a lecturer and joined Dr Griffith. Constant became interested in the gas turbine and collaborated with Griffith until 1938, doing considerable work on the study of aerofoil blading which he reported in his paper ‘Notes on the performance of cascades of aerofoils’ (E 3696, June 1939).

Following this work, the compressor referred to above was designed at the Royal Aircraft Establishment and manufactured by Armstrong Siddeley in 1939.

Apart from entry guide vanes, no stator rows were incorporated in the design, the nine stages rotated alternately in clockwise and anti-clockwise directions; each disk carrying a ring of compressor blades concentric with a ring of turbine blades. The tip diameter of the outer blades at the low pressure stage was 11*25 in. and at the high pressure stage 10*0 in. The disks were carried on ball bearings although Griffith states in his patent that air lubricated bearings might be employed.

The results obtained from this compressor on test are referred to in the following note contributed by Mr Hayne Constant dealing with his association with Griffith over this period.

‘I think that his work on the gas turbine was typical of his approach to engineering. He was never a man for whom half measures or pragmatic solutions based on empiricism had any attraction.

‘He was always after the elegant rational solution.‘His earlier studies of the performance of aerofoils in cascade had convinced

him of the practicability of the axial compressor and had forced him to the conclusion that the upper limit to the pressure ratio that such a compressor could develop was set by the staffing characteristics of the blades. To




overcome this limitation, which he believed to be fundamental, he invented the contra-flow turbo-compressor.

‘This machine consisted of a number of wheels mounted side by side on a shaft, and each carrying two annuli of blades, one outside the other. One annulus consisted of compressor blades, the other turbine blades.

‘The blading was so arranged that when hot compressed gases were forced through the turbine annuli in a generally axial direction the wheels were forced to rotate, each in the opposite direction to its neighbours.

‘This motion of the wheels induced a flow of air through the compressor annuli in the opposite axial direction to the hot gases, the degree of compression in the air being similar to but not identical with the loss of pressure in the turbine annuli. As a result of this there was usually a difference in pressure between the turbine annulus and the compressor annulus of a given wheel, so that a leakage flow occurred from one annulus to another in the gap between two adjacent wheels. At the time the first turbo-compressor was constructed there was insufficient knowledge of blade design available to make it possible to attain in fact the high performance predicted by Griffith theories. As a result the turbine blades produced less power and the compressor blades absorbed more power than predicted. In consequence the wheels could not be run up to their design speed, and gross pressure differences developed between the compressor and turbine annuli. These pressure differences resulted in large leakage flows which further depreciated the machine’s performance.

‘The moral of all this is that when designing turbo-machinery of this kind it always pays to be a pessimist. This Griffith was not; he always aimed at the stars. As a result it is probably fair to say that his biggest contribution was the inspiration which he gave to lesser men rather than his own personal achievements, great though these were.

‘My principal memory of Griffith is his remarkable capability for holding in his head the scientific data needed for his studies. Stimulated by a technical problem or an engineering requirement he would pace like a caged lion whatever space was available to him until an idea arrived.

‘Then, armed only with a copy of Kaye and Laby to supply empirical information, he would develop in his head the basic relations involved and use mental arithmetic to get a quantitive idea of their implication. If things looked promising he would then, and only then, jot down on a scrap of paper, using a lead pencil with the greatest economy, the solution to the problem accompanied by a graphical illustration.

‘He was an idealist in the sense that he regarded engineers as capable of whittling away all the losses and imperfections of machinery right down to the bare minimum imposed by the inescapable natural laws. This inevitably resulted in his ideas appearing to the outside world to be directed rather into the future. Sometimes, as in the case of the contra-flow compressor, it even had the result of actually pushing the attainment of a successful machine further into the future than was really necessary.

124 Biographical Memoirs



‘Griffith was a delightful man to work for. Not once during our time together did he utter a single word of reproof—not even when I was running an engine on vapourized petrol, a leak developed and I blew up the whole test bed.

‘He didn’t even complain when in my report on the incident I mentioned that I had warned him that it was a dangerous experiment to do.

‘He was a remarkable colleague; I have never had a better one.’In addition to the above work on the contra-flow gas turbine, Griffith had

during this period made a number of important contributions to the development of the piston engine which at that time held sway in the aircraft propulsion field. He was associated with a wide variety of patents covering flame traps, ice indicators, de-icing, fuel vaporizing and many piston engine features, and there is no doubt that his contributions greatly assisted the successful prosecution of the air effort during the second world war. One such item was his fuel metering system which is dealt with in the following note contributed by Neil Muir.

‘Griffith saw early the shortcomings of the choke controlled carburetter system of fuel feed and enunciated the theory underlying the proper relationship between engine speed, air consumption and density of charge. The basic work led to his invention of the speed/density system of fuel metering (R.A.E. carburetter), which permitted injection into the eye of the supercharger thus permitting required fuel/air ratio at all times and overcoming carburetter freezing troubles that beset the earlier system. Griffith’s work here brought British piston engine fuel metering and feeding into parity with the long-used and highly successful German system of direct fuel injection into the induction system or cylinder.’

Early in 1939 his advanced thinking and pioneering work on gas turbine design were brought to the attention of the General Manager of Rolls-Royce Limited, Mr E. W. Hives (later Lord Hives, Chairman). A meeting was arranged and subsequently Dr Griffith accepted the position of Research Engineer with Rolls-Royce, responsible to Mr Hives and working mainly on the initiation and prosecution of aero engine research.

On 1 June 1939 when Griffith joined Rolls-Royce, he received a characteristically brief instruction from Mr Hives, ‘Go on thinking.’ To provide ideal conditions for quiet thinking, Griffith was given a pleasant room in the Rolls-Royce guest house at Duffield, a village five miles from Derby.

He devoted the first six months to blade design calculations, performance estimates and general design study of several alternative turbine proposals suitable for aircraft propulsion and a designer was then assigned to him as personal assistant, to translate his ideas into design schemes. In view of Griffith’s earlier work at the Royal Aircraft Establishment, Farnborough, it is not surprising that his first engine design for Rolls-Royce comprised a multi-stage axial compressor and turbine combined on the contra-flow principle incorporating blades of improved aerodynamic design.




The engine incorporated fourteen high pressure stages followed by six low pressure stages driving ducted fans. The stages rotated freely on a fixed shaft, each in the opposite direction to its neighbours; there were no stator rows and therefore the rotational speed was low.

Radial and thrust bearings were provided for each stage disk which carried at its periphery a ring of compressor blades. A shroud ring was formed in segments at the root and tip of the compressor blades; on the outer shroud, each blade carried an integral turbine blade. Hence, each compressor stage was driven by the turbine blades which it carried at its tip.

The shrouds had sealing features formed between the stages and gas leakage from turbine to compressor was further reduced by arranging that the low pressure compressor stages were driven by the low pressure turbine stages. Since the stages rotated freely, their relative rates of rotation automatically adjusted to suit alterations from designed running conditions and hence matching difficulties were reduced.

After passing through the compressor blades of the fourteen high pressure stages, the air entered the combustion chamber which embodied many features of design originated by Dr Griffith, which were far in advance of contemporary practice.

The air was ducted from the compressor so that it passed radially outwards through a ring of blades carried on a disk which was thus rotated by the air flow. Fuel was fed from the centre of the disk to the blades and entered the combustion chamber as a fine spray thrown from the periphery of the rotating burner. A hemispherical combustion chamber surrounded the burner and conducted the expanding gas to the first, high pressure, turbine blades. Heat release from this combustion system was exceptionally high relative to the volume of the hemispherical chamber.

From the fourteen stages of this high pressure unit, the expanding gas was fed to the six disks or stages of the low pressure system. Here again, the six stages rotated freely on a fixed shaft and the turbine blade annulus surrounded the compressor blades. A further shroud ring was formed in segments at the turbine blade tips and carried the ducted fan blades.

The fourteen stage high pressure unit was built and tested, its first run being on 3 March 1942. Patent specification No. 4699/41 dated 8 April 1941 carries a full description and illustrations of this engine.

Parallel with the design and building of this first contra-flow turbine for aircraft propulsion, Griffith initiated many novel forms of test apparatus for verifying the correct functioning of the components.

The rotor bearings were tested by mounting a pair of disks and bearings on a short shaft carried on pedestal brackets; bucket recesses were machined at the rim of each of the disks which were then rotated at 5000 rev/min in opposite directions by air jets. Compressed air was also applied to give end thrust on the bearings and the base to which the pedestal brackets were attached was provided with means for controlled precession to apply gyroscopic loading.

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Wind tunnels for checking the aerodynamic performance of various blade profiles in cascade, a rotating burner test rig and open combustion chamber were other pieces of apparatus which embodied examples of Griffith’s ingenuity.

The accurate blade profiling techniques developed during the past twenty years, were not available in 1941 and the blades for the contra-flow engine were modified from design requirements to facilitate machining; thus jeopardizing their performance aerodynamically. The engine’s performance was limited by surging which was associated with low compressor efficiency.

Quoting from a test summary: ‘Big concessions were made to ease of manufacture in the design of the blades, e.g. constant camber and constant profile at all rad ii. . . There is little doubt that these factors were mainly responsible for the low compressor efficiency which in turn brought high blade incidence.’

Later, when accurate blade forming was possible, the simpler forms of gas turbine had progressed so satisfactorily that the need to return to the contra-flow principle did not arise.

The engine tests had shown that the contra-flow was a difficult engine to develop since the turbine and compressor components were indivisible and the urgent need in 1944 for a more simple and robust gas turbine comprising more orthodox components, led to the decision to suspend contra-flow tests and to develop the Whittle engine. The centrifugal compressor of the latter, being similar to the supercharger used on piston engines, needed a much shorter period of development.

Until the end of 1944, Dr Griffith continued the study of various engine designs incorporating the contra-flow principle and devoted some time to air-borne bearings (1943) and to air-cooled turbine blades.

Early in 1945, while development of the Whittle type engines continued, Griffith commenced detailed study of a simple jet engine with axial compressor. He realized the need for an engine incorporating the latest ideas on axial compressor blading and that such a design would give reduced fuel consumption and a considerably reduced specific weight.

The particular blade design he proposed, permitted the use of a small rotor hub diameter at entry, together with a high tip speed and hence a large air flow capacity combined with a relatively small number of stages. Furthermore, the high speed compressor with a high compression ratio, could be driven by only a single stage turbine. These excellent features resulted in an engine of high performance, low weight and small diameter and a preliminary design scheme prepared under his supervision, was included in Griffith’s technical memorandum of June 1945.

This paper, which also mentioned the possibility of engine installation at the rear of an aircraft fuselage, became the basis of the Rolls-Royce ‘Avon’ engines.

With the achievement of a light, powerful engine of small diameter and the concept of location at the rear of the fuselage, Griffith conceived the




idea of a supersonic interceptor which could take-off vertically and a design layout was made in December 1945.

To reduce leading-edge wave drag, the engine air intakes were situated in the leading edges of the wings; the latter being swept forward slightly so that the deflexion through the intake shock wave directed the air towards the fuselage and engine. The nose of the fuselage was made sufficiently long to permit the nose-wave to clear the wing tips and the propelling je t filled the base of the fuselage, thus effectively eliminating base drag.

Several of Griffith’s contra-flow engines devised in 1943-1944 incorporated bypass flow and in 1946 he turned his attention to the application of bypass to the simple jet engine, in order to reduce the specific cruising fuel consumption and increase the thrust for take-off and initial climb.

Basically, the axial bypass je t engine consisted of a small high pressure compressor driven by a single stage high pressure turbine and a low pressure compressor driven by a two-stage low pressure turbine. The shaft for the low pressure system passing concentrically through the high pressure drive shaft; the low pressure compressor positioned ahead of the high pressure compressor and the low pressure turbine aft of the high pressure turbine.

The capacity of the high pressure compressor is designed to be considerably less than the delivery from the low pressure compressor and the excess air is bypassed to the jet pipe; hence the name bypass je t engine.

The bypass air lowers the mean jet-pipe temperature and renders this type of engine very suitable for the application of reheat. By applying reheat to raise the jet pipe temperature to that of a simple je t engine of similar maximum thrust, Griffith estimated a 23 per cent reduction in fuel consumption, a 25 per cent rise in take-off thrust and a 50 per cent increase in range due to the bypass design.

This investigation of the bypass principle and the engine design scheme completed early in 1947 formed the foundation for the Rolls-Royce ‘Conway’ engines.

Following the bypass engine design, Dr Griffith devoted some time to a more detailed consideration of some early thoughts which he had mentioned in his report dated April 1941, in which he compared piston engines and gas turbines . . .

‘The advantages accruing from a doubling of the available power, with half the power plant weight, need not be elaborated.

‘To exploit the possibilities of the new power unit to the fullest extent, however, it will almost certainly be necessary to resort to specially designed aircraft. Ideas on this subject are naturally somewhat embryonic at present, but one example may serve as an illustration.

‘With a normal ratio of power plant weight to all-up weight, the take-off thrust would considerably exceed the all-up weight. This suggests the possibility of a jum p take-off, a flap being provided behind the power unit which could be lowered so as to deflect the slip stream downwards . . . An




obvious further development is to use the flap for landing also, whereby ground speed might be brought practically to zero before touching down.*

(Griffith aptly described this as ‘Thistledown landing’).His interest in the possibility of vertical take-off and landing had been

intensified following a brief preliminary study for a small, lightweight expendable engine suitable for missile application. This strengthened his conviction that minimum weight could be attained by using several small engines in an aircraft in place of one or two engines of high thrust, provided that design and manufacture could comply with the ‘square-cube’ law; i.e. the engine’s weight decreases as the cube of its linear dimensions whereas its thrust only decreases as the square. Furthermore, examination of various aircraft designs showed that small engines could be accommodated in a greater variety of locations, both for propulsion and jet-lift.

He commenced a prolonged and thorough investigation of the size, weight and cost of small je t engines and found that they could be designed close to the square-cube law and thus give the optimum lift/weight ratio for vertical take-off applications. This led naturally to the next step, careful consideration of vertical take-off aircraft design; since jet-thrust would replace wing-lift for take-off, the wing area could be reduced to suit only the cruise condition.

His first aircraft proposal, using small lightweight engines, was to fulfil the particular role of a ship-borne aircraft where a wide range of speed and height with suitable endurance were essential. To combine high thrust for short or vertical take-off and high speed capability, with economical low- speed cruising, Griffith advocated the use of small engines in the wings and a heavier, economical bypass engine in the fuselage; the thrust of all engines being capable of downwards deflexion.

The small engines, mounted on wing flaps, could be used for thrust augmentation or, deflected downwards, for take-off; differential variation of fuel supply providing lateral control. The bypass engine provided sufficient thrust for economical cruising and its thrust could be deflected for lift during initial climb and for pitch control.

Analysis of this design showed that it lost one of the chief aerodynamic advantages of jet-lift, the ability to select a wing configuration without reference to take-off and landing. The high speed performance was compromised by the flap-mounted small engines dictating wing design, their line of thrust being required to lie close to the aircraft centre of gravity.

Griffith proceeded in his next study, to show that such a compromise was not a necessary feature of jet-lift aircraft. He conceived a supersonic intercepter aircraft having a narrow delta wing of small wave drag and low structure weight and ten small engines installed in the fuselage for take-off lift and forward propulsion. The engines were arranged in two groups, six forward and four aft, suitably positioned to balance in the jet-borne condition. The four aft engines discharged at the rear and the exhaust from the forward six engines was divided and fed to nozzles on either side of the fuselage. All nozzles were provided with rotatable deflectors which directed the jets




downwards for take-off. Aircraft control during the jet-borne phase was provided by differential throttle movement.

Following this scheme and based on a similar fundamental concept, several alternative designs were set down; each having groups of small engines whose efflux could be directed downwards for landing or taking-off and rearwards for providing propulsive thrust.

Many types of military, civil, supersonic and subsonic aircraft received Griffith’s careful study and he also devoted his thoughts to thick wings with suction to remove the turbulent boundary-layer air and so reduce drag.

Two important points common to most of the aircraft proposals Griffith had studied up to this stage, now came to light. Firstly, it became evident that for an aircraft designed for low supersonic drag, the power required for cruising was considerably less than the thrust necessary for jet-lift at low altitudes and forward speeds. This highlighted the need for an engine designed purely for these jet-lift conditions and hence, to provide all the lift-thrust from these special engines; the cruising engines being designed solely for propulsion. Thus, the lift-engines, having only one function to perform are much lighter than the dual purpose engines they replace.

Secondly, aircraft control when jet-borne had depended on manipulation of the throttles of the lift-engines separated laterally for roll control and fore and aft for variation of pitch.

In a paper for the Aeronautical Research Council (No. 14472), Thorpe showed that to get critical damping in the important pitch and roll freedoms, the necessary rate of throttle response was much higher than that available from current engines.

Consequent to Thorpe’s findings, Griffith proposed that the couples and forces needing rapid response should be provided by compressed air jets suitably located and directed and controlled by gyroscopic or other devices. The necessary compressed air being obtained by bleeding the compressors of the lifting engines.

To investigate this control system experimentally, Griffith required a source of compressed air capable of sustaining itself in the atmosphere. He envisaged a framework carrying two je t engines modified to provide the required control air, fuel for 18 minutes’ duration of hover, a pilot and the necessary instruments and equipment.

On 27 March 1952, a preliminary design drawing was commenced, using two Rolls-Royce ‘Nene’ engines arranged back to back with their exhaust pipes meeting at the centre of gravity of the test rig. Here, the pipes were fitted with cascades of deflecting vanes and the exhaust gases were directed downwards to provide vertical lift. Compressed air bled from the compressors was fed to downward pointing control nozzles fore and aft and on outrigger supports laterally. From the preliminary drawing, the total weight including fuel and pilot was estimated in order to verify that a test-rig design having a lift-thrust suitably in excess of weight, was possible.

The Aeronautical Research Council endorsed the suggestion that this




control test rig should be made and a contract for its construction was subsequently received.

On 3 July 1953, the completed rig was run out to a gantry for tethered preliminary tests and the engines given their initial running. Over the following twelve months, tethered lifts of increasing height and duration were made and various modifications introduced where necessary.

The first free flight of the rig was made on 3 August 1954, it rose 8 to 10 feet and was controlled successfully by the compressed air nozzles for a period of 8^ minutes. Many subsequent and trouble-free flights were made and clearly demonstrated the success of Griffith’s proposals for the control of vertical take-off aircraft. The appearance of the wingless flying apparatus immediately gave rise to its name, ‘Flying bedstead’.

Soon after the first free flight of the ‘Bedstead’, Rolls-Royce commenced the design of the RB.108 engine; the first small engine specifically for jet-lift. This engine was used in the Short Brothers and Harland ‘S .C .l’ aircraft, the first to apply Griffith’s lift and control ideas; four RB.108 engines provided lift for vertical take-off and one RB.108 was used for propulsion.

The S.C.l first flew in March 1957 and achieved complete transition from jet-borne to wing-borne flight and vice versa in April 1960.

Nine months before the first free flight of the ‘Bedstead’, Griffith, with characteristic optimism and confidence in its eventual success in proving his ideas, commenced a prolonged and detailed study of a supersonic jet-lift transport aircraft to cruise at 60 000 feet altitude at a speed of Mach 2*6.

This design had two groups of lift engines arranged in longitudinal rows at each side of a tubular pressurized cabin within an integral delta shaped wing; propulsion engines were housed in vertical rear fins. The lift engines were carried vertically on trunnions so that they could be tilted to give a forward thrust component after take-off or a braking thrust before vertical landing.

Many alternative schemes were drawn under Griffith’s supervision and he made a close study of the aerodynamics of the integral delta wing with the object of evolving a shape which would reduce the afterbody drag.

One of his applications of vertical thrust using small lift-engines, was a ‘pick-a-back’ lift platform for taking-off and landing aircraft and he also devoted much thought to a jet-wing using longitudinal jet-sheets each side of a fuselage.

Dr Griffith expounded his ideas to representatives of the aircraft industry at a ‘Jet-lift Symposium’ in November 1953 and displayed drawings, models and a film of the bedstead operating in its gantry. He also contributed a paper to a similar symposium in Ottawa on 30 September 1957 during the Fifth Meeting of the Commonwealth Advisory Aeronautical Research Council.

Previously, in 1944 he spent four weeks in the United States and in 1952 undertook a three-month world tour accompanied by his daughter, visiting the U.S.A., Honolulu, New Zealand, Australia, India and Italy.




His brilliant work was recognized by Fellowship of the Royal Society in 1941, a C.B.E. in 1948, the aw ard of the Silver M edal of the Royal Aeronautical Society in 1955 and the Bleriot M edal in 1962.

Owing to the international situation prevailing during much of Griffith’s creative and original thinking in connexion with aero engine research, aircraft design, the use of hydrogen fuel, etc., his papers were com m unicated mainly to Rolls-Royce and the Aeronautical Research Council. Having restrictive classification, none were freely published and he refused m any requests for lectures from the Aeronautical and Scientific Societies; he felt that free discussion on such occasions was essential and tha t the necessary security regulations would render it impossible for him to deliver a lecture satisfactorily.

He was a founder m ember of the Gas Turbine Collaboration Committee and rendered distinguished service by valuable contributions to the deliberations of the Aeronautical Research Council, with whom he was closely associated for m any years prior to his retirem ent. His contributions are of real historical interest and, in some cases, represent pioneering work of the first importance.

The present Secretary of the Aeronautical Research Council (M r R. W. Gandy) stated in a brief supplementary note published by The Times on 30 October 1963 . . . ‘During the past eighteen years he served as a m em ber of many A.R.C. committees and for six years was a m em ber of the Council itself.

‘In every case his appointm ent was in a personal capacity and not as a representative of his firm, Rolls-Royce, a distinction rare in itself and a tribute to the independence of his judgem ent and the high respect in which he was held in aeronautical circles.

‘He also represented this country three times as a delegate to meetings of the Commonwealth Advisory Aeronautical Council.

‘His contributions to the work of these bodies were m any and varied and by no means limited to his own original papers, epoch-making though some of these were. I t has been said that he was outwardly a reserved m an but he had extraordinary charm in the presentation of his ideas and, among his fellow scientists, was of an attractively convivial disposition. He will be very greatly missed by all who knew him .’

His personal assistant, a designer, worked with him from 1939 until his retirem ent and attributes the 21 years’ happy association entirely to Griffith’s infectious enthusiasm and optimism and to the continuous flow of his stimulating new ideas.

Griffith, a m an of vision, tall, slim and generally of serious countenance, was always calm and quiet, reticent and somewhat aloof; yet those closely associated with him found a very charm ing and friendly personality always with a ready and ‘puckish’ wit. He had a dry sense of hum our which never seemed to be far below the surface. His argum ent was concise and to the point and he often took m ental short cuts which his opponents sometimes

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found it difficult to follow. He had a unique capacity for thinking on fundamental lines and following these through to their logical conclusion.

He carefully avoided publicity and acclaim and, after clearly describing a new idea in detail, made no attem pt to mobilize support for the project but left it with equanimity for others to accept or reject; relying on its quality being eventually appreciated. He was devoid of sentimentality and his reticence renders difficult the estimation of the part played in his life by religion or cultural interests, but one facet of his private thought was abundantly evident, his warm regard for his wife and children.

His younger daughter, June, while quite a child, showed considerable aptitude for pictorial art and an original and amusing little sketch which she sent to him, received a special place near his table and remained until his retirement.

At the end of June 1954 he took his son John to Sweden in order to observe an eclipse of the sun from an aircraft.

O n 13 January 1946, his family suffered a grievously tragic loss; his elder daughter, Betty, died suddenly at the age of nineteen as the result of a horse riding mishap. Griffith bore his grief with silent stoicism but the effort cost him dearly; for a long time after this loss, he wore a small badge in his lapel and when eventually he was asked its purpose, he merely replied ‘It was Betty’s’.

Soon after his retirement in June 1960, he was temporarily immobilized by hip trouble and entered hospital in January 1961 for diagnostic purposes, again in M arch and April he received attention in Chertsey and Farnborough hospitals.

After the latter part of 1961, there was some improvement in his condition and he continued his studies as a consultant for Rolls-Royce until September 1962.

In June it was necessary for him to return to hospital where, with much suffering very bravely borne, he passed away on 13 October.

His designer and five officials of Rolls-Royce attended his cremation at the Park Crematorium, Aldershot; mourning the passing of one of the greatest philosophers of the science of aircraft propulsion.

A. A. R ubbra


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