Alan Arnold Griffith
From Graces Guide
Alan Arnold Griffith (1893-1963) of Rolls-Royce was an English engineer who is best known for his work on stress and fracture in metals that is now known as metal fatigue, as well as being one of the first to develop a strong theoretical basis for the jet engine.
1893 June 13th. Born
Griffith took a first in mechanical engineering, followed by a Master’s Degree and a Doctorate from Liverpool University.
In 1915 he was accepted by the Royal Aircraft Factory as a trainee, before joining the Physics and Instrument Department the following year in what was now been renamed as the Royal Aircraft Establishment (RAE).
Some of Griffith's earlier works remain in widespread use today. In 1917 he and G. I. Taylor suggested the use of soap films as a way of studying stress problems. Using this method a soap bubble is stretched out between several strings representing the edges of the object under study, and the coloration of the film shows the patterns of stress. This method, and similar ones, were used well into the 1990s when computer power became generally available that could do the same experiment numerically.
Griffith is more famous for a theoretical study on the nature of stress and failure in metals. At the time it was generally taken that the strength of a material was E/10, where E was the Young's modulus for that material. However it was well known that those materials would often fail at 1,000 times less than this predicted value. Griffith discovered that there were many microscopic cracks in every material, and hypothesized that these cracks lowered the overall strength of the material. This was because any void in a solid concentrates stress, a fact already well known to machinists at the time. This concentration would allow the stress to reach E/10 at the head of the crack long before it would seem to for the material as a whole.
From this work Griffith formulated his own theory of brittle fracture, using elastic strain energy concepts. His theory described the behavior of crack propagation of an elliptical nature by considering the energy involved. The equation basically states that when a crack is able to propagate enough to fracture a material, that the gain in the surface energy is equal to the loss of strain energy, and is considered to be the primary equation to describe brittle fracture. Because the strain energy released is directly proportional to the square of the crack length, it is only when the crack is relatively short that its energy requirement for propagation exceeds the strain energy available to it. Beyond the critical Griffith crack length, the crack becomes dangerous.
The work, published in 1920 ("The phenomenon of rupture and flow in solids", Philosophical Transactions of the Royal Society, Vol. A221 pp.163-98), resulted in sweeping changes in many industries. Suddenly the "hardening" of materials due to processes such as cold-rolling were no longer mysterious. Aircraft designers immediately understood why their designs had failed even though they were built much stronger than was thought necessary at the time, and soon turned to polishing their metals in order to remove cracks. The result was a series of particularly beautiful designs in the 1930s, such as the Boeing 247. This work was later generalized by G. R. Irwin, in the 1950s, applying it to almost all materials, not just rigid ones.
In 1926 he published a seminal paper, An Aerodynamic Theory of Turbine Design. He demonstrated that the woeful performance of existing turbines was due to a flaw in their design which meant the blades were "flying stalled", and proposed a modern airfoil shape for the blades that would dramatically improve their performance. The paper went on to describe an engine using an axial compressor and two-stage turbine, the first stage driving the compressor, the second a power-take-off shaft that would be used to power a propeller. This early design was a forerunner of the turboprop engine but although he recognised the engine as suitable for aircraft use, Griffith did not propose jet propulsion with it.
1928 As a result of the paper, the Aeronautical Research Committee supported a small-scale experiment with a single-stage axial compressor and single-stage axial turbine. Work was completed in 1928 with a working testbed design, but for some reason at that point work stopped.
1928 Griffith became the principal scientific officer in charge of the new Air Ministry Laboratory in South Kensington. There he invented the contraflow gas turbine, which used two sets of compressor disks rotating in opposite directions, one "inside" the other. This is as opposed to the more normal design in which the compressors blow the air against a stator, essentially a non-moving compressor disk. The effect on compression efficiency was noticeable, but so was the effect on complexity of the engine.
At about this time Frank Whittle wrote his thesis on turbine engines, using a centrifugal compressor and single-stage turbine, the leftover power in the exhaust being used to power the aircraft directly. Whittle sent his paper to the Air Ministry in 1930, who passed it on to Griffith for comment. After pointing out an error in Whittle's calculations, he stated that the large frontal size of the compressor would make it impractical for aircraft use, and that the exhaust itself would provide little thrust (ie as a jet). The Air Ministry replied to Whittle saying they were not interested in the design. Whittle was crestfallen, but was convinced by Johnny Johnson to pursue the idea anyway. Luckily for all involved, Whittle patented his design in 1930 and was able to start Power Jets in 1935 to develop it.
1931 he returned to the RAE to take charge of engine research, but it was not until 1938, when he became head of the Engine Department, that work on developing an axial-flow engine actually started. Joined by Hayne Constant, they started work on Griffith's original non-contraflow design, working with steam turbine manufacturer Metropolitan-Vickers (Metrovick).
1939 His pioneering work came to the notice of Ernest Walter Hives, then general manager of Rolls-Royce, and as a result, Griffith became research engineer at Derby, directly responsible to Hives for aero-engine research. He remained with Rolls-Royce for the rest of his working life.
After a short period Whittle's work at Power Jets started to make major progress and Griffith was forced to re-evaluate his stance on using the jet directly for propulsion.
A quick redesign in early 1940 resulted in the Metrovick F.2, which ran for the first time later that year. The F.2 was ready for flight tests in 1943 with a thrust of 2,150 lbf, and flew as replacement engines on a Gloster Meteor, the F.2/40 in November. The smaller engine resulted in a design that looked considerably more like the Me 262, and had improved performance. Nevertheless the engine was considered too complex, and not put into production.
Griffith's original rejection of Whittle's concepts has long been commented on. It certainly set back development of the jet engine in England by several years. His motivations have long been the topic of curiosity, with many people suggesting that his endless quest for perfectionism was the main reason he didn't like Whittle's "ugly" little engine, or perhaps the belief that "his" design was innately superior.
Griffith worked at Rolls-Royce until 1960. He designed the AJ.65 axial turbojet which led to the development of the Avon engine, the company's first production axial turbojet. Griffith carried out pioneering research into vertical take-off and landing (VTOL) technology, culminating in the development of the Rolls-Royce Thrust Measuring Rig. The "flying bedstead" was essentially a framework carrying two Rolls-Royce Nene engines which not only gave direct lift for hovering but provided air from their compressors to the jets used for control. The first free flight of this device took place on 3 August 1954, when it rose about 10 feet and was controlled successfully. This led to the design by Short and Harland of the SC-1 aircraft in which four Rolls-Royce RB108 engines, designed specifically for jet lift, provided vertical take-off and one RB108 was used for propulsion. This aircraft first flew in March 1957 and achieved complete transition from jet-borne to wing-borne flight in April 1960.
1960 June: Griffith retired.
1963 October 13th. Died
1963 An Appreciation by Donald Eyre
"IN this appreciation, my aim is to paint a word portrait of Dr. Griffith in the setting in which I knew him, rather than to list his many academic attainments or his profuse output of papers on fascinating new lines of thought.
Fellowship of the Royal Society, a C.B.E. and other awards recognised his outstanding work which has been dealt with elsewhere, but his careful avoidance of publicity has resulted in little being known of him. Duffield Bank House, the Rolls-Royce guest house, is a quiet haven on the outskirts of the sedate village of Duffield a few miles from Derby. It is situated at the foot of low hills and at the side of the river Derwent. A very suitable spot for quiet concentration; and here a room was prepared as an office for Dr. A. A. Griffith when he joined the company as research engineer at the beginning of June, 1939. He was responsible to E. W. Hives (later Lord Hives, chairman) who, characteristically, instructed him to "Go on thinking". Since June, 1937, I had been sharing a design office at Duffield Bank House with two other designers on advanced project work; it was therefore only a short move when he (Lord Hives) asked me to work with Dr. Griffith as his designer . . . "To translate Dr. Griffith's ideas into Rolls-Royce design schemes".
When I joined Dr. Griffith, the furnishing of our office, in addition to the inevitable bookcase and filing cabinet, consisted of a table for Dr. Griffith, a drawing board and two empty tables for myself. I mention these items to highlight two unique points, firstly, Dr. Griffith 's table was positioned with a good space round it so that he had room to walk. Between sessions of work at his table, he would walk round in deep concentration, always with the same quiet, slow and even tread to which I soon became accustomed. A difficulty arose when it was decided to place the telephone on his table, the wire from the wall crossed his walking space and so a large piece of white paper was hung over the wire to remind him to reverse. He insisted on plain floor covering because a patterned material might divert his thoughts. The second point concerned my own furniture, the blank board and empty tables emphasise the fact that at the start of my work with Dr. Griffith, I was on entirely new ground and whereas a designer might normally have prints of design schemes bearing some slight relation to his current work, no drawings existed of any project similar to Dr. Griffith's.
From my start in the Rolls-Royce drawing office early in 1920 to my introduction to Dr. Griffith, my power unit experience had been solely with piston engines, now I was required to prepare schemes for an internal combustion turbine as we called the first Rolls-Royce gas turbine engine. This new form of power unit, an axial contra-flow engine for aircraft propulsiot), was taking shape in Dr. Griffith's mind and my job was to create design drawings from his calculations, from discussion with him and from his very rough and spidery sketches. Although his written work was superbly clear and concise, his conversation was hesitant, quiet and, at the beginning of our association often above my comprehension being of an entirely new sphere of science. In these days, the gas turbine being a well known and successful power unit, having been used for aircraft propulsion for twenty years, it is difficult to recapture the atmosphere of those war days in early 1940 when several alternative schemes had to be prepared before deciding on the type to produce as a first test unit.
Having worked personally with Dr. Griffith for twenty-one years, I would attribute our very happy association entirely to his friendly manner, infectious enthusiasm and optimism, and his ability to inspire confidence by leaving my part of the work entirely in my hands. Dr. Griffith was rather tall and slim, his manner was calm and quiet and on first meeting him, one might be forgiven for expecting him to be always serious and with no time for other than necessary conversation. Within my first week with him, I realised that he had a delightful sense of humour and a most friendly manner. Some days would pass with very little or even no conversation between us, particularly during the initial stages of a fresh study; other days would be interspersed with wit and laughter relieving the hours of concentration.
To help me with this portrait, I must, as an amateur artist, introduce contrast to the centre of interest in the accepted manner. In the late 1920s and early 1930s, I was privileged to be a very junior member of the small group of designers working personally with Sir Henry Royce at his secluded house in West Wittering and alone with him at his villa in the South of France. Here is vivid contrast of brain application, yet with remarkable similarity of personality. Whereas Sir Henry Royce concentrated mainly on perfecting known mechanisms, continually striving to create the best possible in detail and function, Dr. Griffith continually worked on new ground laying down the broad main lines of advanced ideas and leaving the detail design to me. Both Sir Henry Royce and Dr. Griffith sought seclusion and carefully avoided publicity and acclaim, both had a happy sense of humour and a "Puckish" wit. Sir Henry Royce took a keen interest in music and pictorial art, practising water colour painting in his rnoments of relaxation. Dr. Griffith most emphatically was not in the least interested in art, and music was never a topic of our conversation. Both personalities were devoid of sentimentality but, although childless, Sir Henry Royce was always happy in the company of children who might accompany his visitors.
For most of his years with Rolls-Royce, Dr. Griffith lived in Derby and could only make week-end or short visits to his family who lived in Farnborough, they nevertheless held a very warm place in his heart. Our office was always free of pictures or pictorial calendars, but a special place had to be selected on the wall for an original and amusing little sketch, drawn and sent to him by his younger daughter. This sketch remained in front of him until his retirement. His son is following, scientifically, in his father's footsteps.
It may here, be of interest to recall that the aeronautical weekly, Flight (December 21, 1956), published an article on aeronautical fiction of the nineteenth century. They reproduced the imaginative futuristic illustrations of the flying machines created by the author for one book, described by H. G. Wells as an "aeronautic masterpiece" . The illustrations depicted strange looking aeroplanes having, in addition to wings and forward thrusting propellers, several vertical shafts driving lifting airscrews. The a uthor was George Griffith, Dr. A. A. Griffith's father.
Dr. Griffith was a founder-member of the Gas Turbine Collaboration Committee, and, until his retirement, was closely associated with the Aeronautical Research Council to whom he communicated most of his written papers. Of his many engine studies for aircraft, the first was an axial contra-flow engine. This incorporated fourteen high-pressure stages and six low-pressure stages driving ducted fans. Each stage was driven independently by turbine blades at the tip of the compressor blades; the discs rotated freely on a fixed shaft and matching difficulties were thus eliminated. Turbine cooling \¥a catered for by a deeply finned light alloy casing surrounded by cooling-air duct. The many advanced features of the engine included centrifugal fuel supply from a rotating burner in a hemispherical combustion chamber. The high-pressure section of the system was built and tested in 1941. A memorandum by Dr. Griffith in 1945 together with preliminary design schemes, formed the basis of the Rolls-Royce "Avon" engine and in 1946, his proposal for a bypass engine led to the Rolls-Royce "Conway" engine and the family of so-called turbofan engine in the United States.
Dr. Griffith initiated the concept of V .T.O. L. which he named "Thistledown Landing", commencing with his successful investigation of the possibility of designing a small lightweight engine especially for vertical thrust and leading to the well-known "Flying Bedstead" and subsequent designs for many forms of V.T.O.L. aircraft. Concluding, I fully realise that it is customary in an appreciation to speak warmly, but can I summarise more clearly than to point out that, as a very keen designer, I was happy to reject all offers of change in order to continue working with Dr. Griffith on the stimulating products of his brain?"
"On Friday, October 11, this country lost its most acknowledged authority on propulsion for powered flight when Dr. A. A. Griffith, C.B.E., D.Eng., F.R.S., died at the age of seventy years. Formerly he was chief scientist to Rolls-Royce Ltd. He had a shy and retiring nature and he was not well known to many people, yet he exerted a great influence on the work of Rolls-Royce, and his ideas may well form the future pattern of aviation. His function as chief scientist was to consider the whole range of scientific progress in relation to the company's business. He provided new lines of thought for development by the various engineering teams within the company. The comparative seclusion in which he worked was not an idiosyncrasy but a practical necessity for the type of work he did.
From very early in his career Dr. Griffith was an advocate of the gas turbine engine for aircraft. At the Royal Aircraft Establishment, while still in his twenties, he studied the then new science of aerofoils and formulated new theories of compressor and turbine design. In 1926, on the basis of these theories, he proposed a gas turbine engine which he claimed would be lighter, smaller and more efficient than piston engines for aircraft. Dr. Griffith's proposal, unlike that of Sir Frank Whittle, whose work on jet propulsion began in 1928, was based on the axial type of compressor. Both men were right: Whittle's simpler centrifugal compressor enabled quicker development of the jet engine in the short run, but Griffith's belief in the superior efficiency of the axial type is vindicated by its subsequent adoption throughout the world. He might justly claim to be one of the fathers of the modern jet engine.
Dr. Griffith's best known proposals have stemmed from his belief in the possibilities of the axial gas turbine engine. He led the company's first investigations of gas turbines - then known as "internal combustion turbines" during the early years of the Second World War. It was a technical memorandum prepared by him in 1945 which was the basis of the "Avon" engine, the first Rolls-Royce jet with an axial compressor.
In 1946 he first put forward his proposals for a by-pass engine. The success of the "Conway" engine in the Boeing "707-420" and Douglas "DC-8/40" and the fact that the by-pass principles are now being followed by engine manufacturers throughout the world, is a complete vindication of the soundness of his proposals. His continuous exploration of the possibilities offered by new developments led Dr. Griffith to make many suggestions so farsighted as to appear almost fanciful to people unaware of the closely reasoned theory behind all his work. In 1941 before the first British jet aircraft had even flown he had foretold the development of vertical take-off based on the high power-to-weight ratios which he knew were possible with the axial jet engine. The Rolls-Royce "Flying Bedstead' and the Short "SC.1" are successive stages in the development of his idea. The supersonic jet lift airliner, which he first proposed nearly ten years ago, now seems far less incredible than it did to many then. There is a growing belief in the future of aircraft taking off vertically by jet lift, and these could well change the whole pattern of future aviation.
When Dr. Griffith was busy with a problem he could withdraw so completely within himself as to be oblivious of his surroundings. People who worked with him remember him walking to and fro around his office for hours on end without as much as a word. His staff had to mark the telephone cables with sheets of paper to prevent him from walking into them in his concentration. Although most of his work was concerned with theories and possibilities, Dr. Griffith was a practical man, able, when he was in a hurry, to go to a machine and himself make the parts for an experiment. He has always avoided any sort of public recognition of his work. He was of a naturally retiring disposition and he talked about his work very little. There were very few people able to keep up with his reasoning, and nearly all his work has been secret, precluding public discussion. This is why he gave no lectures or papers. By the time a subject could be aired publicly it was by his standards out of date and of little further interest.
Despite his avoidance of publicity, his work was recognised by Fellowship of the Royal Society in 1941, by a C.B.E. in 1948, and by the award of the Silver Medal of the Royal Aeronautical Society in 1955.
Throughout his career, Dr. Griffith has usually looked fifteen or twenty years ahead. His influence will continue as long as gas turbine aero engines are used, for they all incorporate some of his original thinking."
Sources of Information
- The Engineer 1963 Volume 216 Jul-Dec