The Enigma of the Aerofoil

Rival Theories in Aerodynamics, 1909-1930

David Bloor

• Publisher: University of Chicago Press
• Year: 2011
• Print ISBN: 9780226060958, 9780226060941
• eBook ISBN: 9780226060934
• Topic: History
• Subtopic: British History
• Index: History

Why do aircraft fly? How do their wings support them? In the early years of aviation, there was an intense dispute between British and German experts over the question of why and how an aircraft wing provides lift. The British, under the leadership of the great Cambridge mathematical physicist Lord Rayleigh, produced highly elaborate investigations of the nature of discontinuous flow, while the Germans, following Ludwig Prandtl in Göttingen, relied on the tradition called "technical mechanics" to explain the flow of air around a wing. Much of the basis of modern aerodynamics emerged from this remarkable episode, yet it has never been subject to a detailed historical and sociological analysis.

           

In The Enigma of the Aerofoil, David Bloor probes a neglected aspect of this important period in the history of aviation. Bloor draws upon papers by the participants—their restricted technical reports, meeting minutes, and personal correspondence, much of which has never before been published—and reveals the impact that the divergent mathematical traditions of Cambridge and Göttingen had on this great debate. Bloor also addresses why the British, even after discovering the failings of their own theory, remained resistant to the German circulation theory for more than a decade. The result is essential reading for anyone studying the history, philosophy, or sociology of science or technology—and for all those intrigued by flight.

1

Mathematicians versus Practical Men: The Founding of the Advisory Committee for Aeronautics

In the meantime every aeroplane is to be regarded as a collection of unsolved mathematical problems; and it would have been quite easy for these problems to have been solved years ago, before the first aeroplane flew.

G. H. BRYAN, “Researches in Aeronautical Mathematics” (1916)¹

The successful aeroplane, like many other pieces of mechanism, is a huge mass of compromise.

HOWARD T. WRIGHT, “Aeroplanes from an Engineer’s Point of View” (1912)²

The Advisory Committee for Aeronautics (the ACA) was founded in 1909. This Whitehall committee provided the scientific expertise that guided British research in aeronautics in the crucial years up to, and during, the Great War of 1914–18. From the outset the ACA was, and was intended to be, the brains in the body of British aeronautics.³ It offered to the emerging field of aviation the expertise of some of the country’s leading scientists and engineers. In 1919 it was renamed the Aeronautical Research Committee, and in this form the committee, and its successors, continued to perform its guiding role for many years. After 1909 the institutional structure of aeronautical research in Britain soon came to command respect abroad. When the United States government began to organize its own national research effort in aviation in 1915, it used the Advisory Committee as its model.⁴ The resulting American National Advisory Committee for Aeronautics, the NACA, was later turned into NASA, the National Aeronautics and Space Administration. The British structure, however, was abolished by the Thatcher administration in 1980, some seventy years after its inception.⁵

If the Advisory Committee for Aeronautics was meant to offer the best, there were some in Britain, especially in the early years, who argued that, in fact, it gave the worst. For these critics the ACA held back the field of British aeronautics and encouraged the wrong tendencies. The reason for these strongly divergent opinions was that aviation in general, and aeronautical science in particular, fell across some of the many cultural fault-lines running through British society. These fault lines were capable of unleashing powerful and destructive forces. From the moment of its inception the Advisory Committee was subject to the fraught relations, and conflicting interests, that divided those in government from those in industry; the representatives of the state from those seeking profit in the market place; the university-based academic scientist from the entrepreneur-engineer; the “mathematician” and “theorist” from the “practical man.” Throughout its entire life these structural tensions dominated the context in which the ACA had to work.⁶

“I Was at Cambridge on Saturday”

The political pressures that originally prompted Herbert Asquith’s Liberal administration to set up the Advisory Committee for Aeronautics can be epitomized by the reaction to the first cross-channel flight from France to England, made by Louis Blériot on July 25, 1909. Newspaper headlines declared that Britain was no longer an island. Blériot’s heroic feat was greeted with sporting cheers, but the depressing military implications of the flight were evident. The nation’s basic line of defense had been breached. The channel was no longer a moat that made the island an impregnable fortress. Blériot’s flight dramatically confirmed the warnings that had been voiced since the inception of “aerial navigation.” These reactions have been described in detail by the historian Alfred Gollin, who documents the atmosphere of alarm and the fear of invasion that gripped the country during the early years of the century, particularly with regard to the emerging power of Germany.⁷ There was anxiety, assiduously cultivated by the press, that Britain was falling behind in the race to exploit the military potential of the new flying machines: the airship and the airplane. The anxiety was expressed in newspaper reports of mysterious (and almost certainly nonexistent) Zeppelins lurking in the night skies over Ipswich and Cardiff.⁸

The government, represented by Richard Burdon Haldane (fig. 1.1), the secretary of state for war, did not participate in this sort of unseemly clamor. Haldane was a patrician and highly intellectual figure who combined his politics with philosophical writing and a successful legal career. Educated at the universities of Edinburgh and Göttingen, he was fluent in German, translated Schopenhauer, and had a passion for Hegel.⁹ To the fury of his critics the portly Haldane proceeded at his own steady pace. Much preoccupied with the long-overdue reform and rationalization of Britain’s major institutions, from the army to the universities, Haldane always insisted that a cautious and “scientific” approach was needed.¹⁰ Critics of the government policy on aeronautics called for the immediate purchase of foreign machines. Airships could be bought from France, and aircraft were on offer from the American Wright brothers, who had been the first to master powered flight. Haldane thought that Britain should go more cautiously, even if it meant going more slowly. He was disinclined to rely on the results of mere trial-and-error methods developed by others. In fact he looked down on those who proceeded in a merely empirical manner, devoid of guiding principles to broaden and deepen their understanding.¹¹

Haldane met the Wright brothers in May 1909 when they came to Europe touting for government contracts. An editorial in Flight, on May 8, hinted at inside information and expressed confidence in the outcome of the meeting: “On Monday, Messers Wilbur and Orville Wright paid a visit to Mr. Haldane, and, while naturally it is needful and fitting to preserve secrecy as regards official matters, it may be taken as assured that our Government will duly acquire Wright aeroplanes and the famous American brothers will themselves instruct the first pupils in England.”¹² In fact it was not assured. Despite much pressure and lobbying, Haldane declined to do a commercial deal with the Wrights. Rather, the minister concluded, Britain should follow the German example—or what he took to be the German example. The National Physical Laboratory at Teddington, outside London, had been founded in 1900 on the model of Helmholtz’s great, government-funded institute of physics in Berlin, the Physikalisch-Technische Reichsanstalt, and this was the pattern that Haldane wanted to see developed.¹³ The government must locate the best scientists that were available and set them to work on the fundamental problems of flight. The pioneers had got their machines into the air, but how and why they flew remained obscure. The working of a wing, for example, the secret of its lift, remained an unsolved problem, as did the basis of stability and control. Furthermore, it was unclear whether the future lay with heavier-than-air flight or airships. Like many others, Haldane was more impressed by airships, but scientists must address these issues in all their generality and then, with scientific theory leading practice, the best technology would be able to progress on sound principles. As Haldane put it, “the newspapers and the contractors keep clamouring for action first and thought afterwards, whereas the energy which is directed by reflection is the energy which really gives the most rapid and stable results.”¹⁴ The issue of the Wright brothers and their rebuff deserves comment. To Haldane’s critics the refusal to buy these aircraft seemed a gross error of judgment on the government’s part. In fact it was grounded in a defensible line of reasoning. The Wright machine was known to be clumsy and unstable. It could only take off along specially constructed rails, and the subsequent flight demanded great skill and ceaseless intervention by the pilot. As a British test pilot put it a few years later, in a report to the ACA on the flying qualities of different machines, it needed an “equilibrist of the first order” to keep the Wright machine in the air.¹⁵ (This judgment is corroborated by modern aerodynamic research conducted on the Wright machine.)¹⁶ The pilots of such aircraft would (1) require extensive training, (2) become exhausted on long flights, and (3) be so preoccupied that they could hardly perform any military task such as map reading, reconnaissance, or photography. The need was for aircraft that were easy to fly and would leave their pilots with spare mental and physical capacity. The British government’s view was that power in the air would go to the nation that possessed stable aircraft.¹⁷

Even before he met the Wrights, Haldane had sanctioned secret tests to be carried out at Blair Atholl, in the Scottish highlands, on a machine designed by a British inventor, J. W. Dunne.¹⁸ Dunne was a friend of H. G. Wells and later in life became well known for his metaphysical speculations on the nature of time.¹⁹ After his early military career had been terminated by ill health, Dunne turned to aviation and won the confidence of the superintendent of the Army Balloon Factory at Farnborough. Dunne’s airplane, unlike the Wrights’, was meant to be stable and, to achieve this he used a novel, swept-wing configuration. The tests, however, which took place in the summer of 1907 and 1908, were a failure, and the machine did not maintain sustained flight.²⁰ A retrospective report of the episode in the journal Aeronautics contained the fanciful claim that, after an indiscrete mention of the trials in the press, the Scottish estate where they took place was alive with foreigners who, it was implied, must have been German secret agents. “In two days the place was buzzing with Teutons.” Fortunately, the article continued, loyal local citizenry misdirected the unwanted foreign visitors so that the nation’s secrets remained secure.²¹ Flight even hinted that some of these alleged spies had been disposed of by the Scotch gillies, who acted as lookouts for the trials.²² Haldane’s worst suspicions about empirics and inventors, and everything to do with them, were confirmed by such goings on.²³ Dunne and his supporters were dismissed. It was time to bring in the scientists and develop a serious policy. Haldane had no intention of being deflected from this course just because the Wrights turned up in London.

Haldane had already laid out his ideas of a sound policy at the first meeting of a new subcommittee of the powerful Committee of Imperial Defence on December 1, 1908.²⁴ The prime minister had formed the subcommittee to report on three questions: (1) the military problem that aerial navigation posed to the country, (2) the naval and military advantages of airships and airplanes, and (3) the amount of money that should be spent and where that money should go. The chairman, Lord Esher, invited Haldane to open the proceedings. Haldane said it was important to have the navy and the army working together on these issues in order to provide the preconditions for real progress. Haldane meant by this the preconditions for developing a genuine, scientific understanding of aerial navigation and the problems it posed. He went on: “I was at Cambridge on Saturday, and I spent Sunday talking over some of these questions with Sir George Darwin, the mathematician. Some of them there have given a good deal of attention to this matter, and what strikes them—certainly what has struck me—is the little attempt which has been made, at any rate as far as the War Office is concerned, to answer these questions.” Nobody in the navy, he said, would think of building ships without testing models in water, but if there was ever a need for model work it was in aeronautics. Darwin had told him that the French had experimental establishments using artificial currents of air. In reply to a direct question, Darwin had also told him that there was a great deal of mathematical work that needed to be done. Haldane therefore asked the subcommittee to consider appointing a further committee of experts...

Table of contents

• Cover
• Copyright
• Title Page
• Contents
• List of Illustrations
• Acknowledgments
• Introduction: The Question to Be Answered
• 1 Mathematicians versus Practical Men: The Founding of the Advisory Committee for Aeronautics
• 2 The Air as an Ideal Fluid: Classical Hydrodynamics and the Foundations of Aerodynamics
• 3 Early British Work on Lift and Drag: Rayleigh Flow versus the Aerodynamics of Intuition
• 4 Lanchester’s Cyclic Theory of Lift and Its Early Reception
• 5 Two Traditions: Mathematical Physics and Technical Mechanics
• 6 Technische Mechanik in Action: Kutta’s Arc and the Joukowsky Wing
• 7 The Finite Wing: Ludwig Prandtl and the Göttingen School
• 8 “We Have Nothing to Learn from the Hun”: Realization Dawns
• 9 The Laws of Prandtl and the Laws of Nature
• 10 Pessimism, Positivism, and Relativism: Aerodynamic Knowledge in Context
• Notes
• Bibliography
• Index