Though he is now remembered as one of the 20th century's greatest thinkers, philosopher Ludwig Wittgenstein's early design of a unique aero-engine shows he was at ease with technology too.
"I could have done better myself," fumes Adolf Hitler in AN Wilson's 2007 novel 'Winnie and Wolf'. The Winnie in question is Winifred Wagner, the German composer's daughter-in-law. Wolf is the Führer. His disparaging statement refers to a unique aero-engine proposed, but never completed, by Ludwig Wittgenstein during his time as a research student at Manchester University from 1908 to 1911.
While Wittgenstein is now recognised as one of the West's most influential philosophers, he originally moved to England to carry out aeronautical research. This was on the back of a rigorous engineering education at the Technische Hochschule (Institute of Technology) in Charlottenburg, near Berlin, and a secondary schooling biased towards the technical at the Realschule (secondary school) in Linz where he counted Hitler among his fellow pupils.
Wittgenstein initially spent a short period at Manchester University's Glossop outstation, experimenting with the aerodynamic design of box-kites as used for upper atmosphere meteorological research. He soon moved to the engineering department to start work on his aero-engine. As the aircraft of the time were rather flimsy, the relatively heavy conventional airscrew piston engines commonly used caused several probelms.
Wittgenstein's idea did away with the need for a crankshaft by employing a propeller rotated by blade-tip jets. This was a similar scheme to that employed in Hero of Alexandria's 'aeolipile' steam turbine in 60AD: in brief, air and vapourised fuel are fed into the propeller hub and forced along hollow blades by centrifugal action into the blade tip combustion chambers, where the compressed mixture is ignited and emitted as a pressurised jet.
In principle the idea is sound, but in practice there would have been formidable technical problems, such as the injection of compressed air and gaseous fuel through rotating joints, the effect of the differing densities of fuel and air on the degree of centrifugal compression of the mixture, the ignition arrangement, and so on.
Wittgenstein, it appears, had no ideas to solve these issues and it is unlikely that the motor would have worked. Nevertheless, he patented the design – 'Improvements in propellers applicable for aerial machines. British Patent. No 27,087' – in 1910.
He began experimentation by constructing a 'variable-volume combustion chamber' – essentially, a water-cooled cylinder enclosing a piston that could be driven from one end to alter the cylinder's volume and thus vary the pressure of an ignited gaseous fuel-air mixture. The far end was mounted with a supersonic exhaust nozzle, which could be removed and replaced by one of different form. Such experiments were carried out in order to optimise the exit nozzle geometry of the envisaged tip-jet combustion chamber.
The department head at the time was Professor JE Petavel, an acknowledged expert on the design of high-pressure combustion chambers. Wittgenstein's drawings, now held by the Austrian National Library, Vienna, showed dimensional similarities with those featured in some of Petavel's scientific papers.
There are many myths surrounding Wittgenstein's work, a fact noted in an informative biographical sketch written by GH von Wright, a former student of the philosopher who would later take on his Cambridge chair. The short biographical introductions prefacing many books on Wittgenstein often contain inexact abbreviated mentions of his early aeronautical engineering phase which sometimes make it difficult to separate fact from fiction.
Another Wittgenstein student, RL Goodstein, who later became a professor at Leicester University, noted that "[Wittgenstein] experimented with rocket propulsion ... conducted on a stretch of railway track just south of Manchester". While Wittgenstein was certainly wealthy enough to have organised such an improbable test – he once had to be dissuaded by his fellow student and friend William Eccles from hiring a train to take them on a trip to the seaside after they had missed a scheduled one – it is very difficult to confirm. In fact, Eccles remains the prime source of material on Wittgenstein's activities at this time but he does not go beyond recalling the laboratory combustion chamber experiments, and then only briefly.
A further published account states that, "a variable-volume combustion chamber was built into the propeller shaft while reaction jets were attached to the tips of the blades – the prototype essentially worked". This may have been an initial intention, a stage in the development procedure, but again there is no record of it having taken place.
Wittgenstein's scheme anticipated by three decades developments in which blade-tip jets were used to drive the rotors of hybrid helicopters. The advantage over conventional helicopters is that the torqueless reaction on the aircraft's fuselage eliminates the need for a compensating tail rotor and its associated drive mechanisms.
In the 1940s, Austrian Friedrich von Doblhoff designed a hybrid helicopter with a conventional airscrew engine for forward flight and a disengaged rotor acting in an autogyro mode. With the rotor engaged and the engine disconnected from the airscrew, it drove an air/gaseous fuel mixture through the rotor blades to be ignited in the blade-tip jet chambers, with the resulting helicopter action providing lift.
The Fairey Rotodyne (1960) also featured the use of airscrew engines mounted on a pair of stubby wings. Compressed air and gaseous fuel were fed into a pair of orthogonally mounted dual-blade rotors, each with blade-tip combustion chambers. This provided a measure of redundancy should the action of one rotor fail. In forward flight the rotors autorotated, adding to the lift from the stubby wings. Below about 80 knots, pitch control of the rotor blades made the aircraft perform as a helicopter, while varying the pitch of the individual wing-mounted propellers provided steering.
From an engineering point of view, the Fairey Rotodyne was an extremely complicated aircraft and very noisy. There was an initial interest from both the RAF and the carrier British European Airways, but the project was abandoned in 1962 and not long afterwards the company itself disappeared, a harbinger of what was to come for the British aircraft industry.
Perfecting the rotation
While Wittgenstein was working in isolation in the north of England, a considerable amount of pioneering activity was taking place further south in and around London and at Farnborough. Among them were aeronauts (those who construct powered aircraft and flew them) including Samuel F Cody and AV Roe. Whether or not Wittgenstein was aware of this parallel work is not recorded.
Wittgenstein's patent had within it the seeds of the centrifugal-flow gas turbine engine, later to be developed in the 1930s by Sir Frank Whittle. Centrifugal compression in Wittgenstein's propeller blade corresponds to that within the compressor stage of the gas turbine. The rotation of the propeller provides a mechanical feedback equivalent to that provided by the output stage of the gas turbine. The relationship between the two engines can be thought of as an engineering topological transformation. In fact, von Wright wrote that Wittgenstein told him "the problem on which he worked at Manchester has since become very urgent". Von Wright's assumption was that he was referring to the emergence of reaction engines in modern aircraft.
Commemorating the 50th anniversary of Wittgenstein's death in 2001, a small exhibition at the Royal Academy of Arts, London, was organised by the late architect of the new British Library and St Pancras, Sir Colin St John Wilson, and the late Sir Eduardo Paolozzi, both of whom were influenced by Wittgenstein's writings.
Photographs from the exhibition show what appears to be a four-bladed model of the aero-engine suspended from the ceiling. Since Wittgenstein never got as far as designing a propeller blade, never mind a complete aero-engine, one must assume that the model is hypothetical and was perhaps based on the patent, which mentions multiblade versions.
Other works featured in the exhibition included a model of the modernist house he designed for his sister Margarethe in the 1920s, and a model of a device he designed to monitor heart-beat pulse amplitude for the medical assessment of 'wound shock' during the Second World War.
It is generally agreed, however, that Wittgenstein spent little time on the aero-engine and soon shifted his attention to the complex mathematical problem of airscrew blade profile. This would eventually lead to a growing interest in mathematics and mathematical logic prompted by the reading of Bertrand Russell's 'Principles of Mathematics'.
At Manchester University, Wittgenstein attended lectures by hydrodynamics expert Professor Horace Lamb and mathematician JE Littlewood, who was later to take up a chair at Cambridge and enter into a famous partnership with GH Hardy. After attentively listening to these two notables and consulting them on several occasions, Wittgenstein was left hungry for more and travelled up to Cambridge to literally knock on Bertrand Russell's door. Russell requested that his impromptu visitor write a piece on a philosophical subject and was so impressed that he declared him a potential genius and let him in on his lectures.
During the First World War Wittgenstein was in the Austrian army, first on the Eastern Front and later in Italy, where he became a prisoner of war. During this time he completed his first major work of philosophy 'Tractatus Logico – Philosophicus'. On returning to Cambridge in 1929, where he made a considerable impact thanks to his charismatic, but sometimes forbidding, personality and fierce intelligence. He was elected professor of philosophy in 1939. Commenting on his 1929 return, economist John Maynard Keynes wrote "Well, God has arrived. I met him on the 5.15 train".
He would subsequently turn his hand to all manner of work including several teaching posts and even a stint as a hospital porter. But he never again returned to the design of the aero-engine, instead leaving it to languish alongside history's countless other 'what ifs'.