The Albatross Wing
Major Low’s paper, the third Congress paper of the morning, was titled “The Circulation Theory of Lift, with an Example Worked out for an Albatross Wing-Profile.”99 The “albatross” of his title was not the bird but the name of a German aircraft company that had played a prominent role in the war.100 Low’s aim was to apply the circulation theory to an actual aircraft wing and to show the relation of the theory to drawing-office practice. He also wanted to straighten out one or two points of recent history. He began by reminding his listeners that the origin of the circulatory theory was grounded in the work of British physicists. Fifty years ago, said Low, Rayleigh had published his paper on the spin of the tennis ball and explained the force that made it veer by reference to the circulation around the ball. A similar idea, he said, was to be found in the work of P. G. Tait of Edinburgh (where Low had himself been a student, graduating with an honors degree in mathematics and natural philosophy in 1903).101 Low regaled his audience with a story about experiments, done in the dark cellars of the old Edinburgh University buildings, on the spin of golf balls. Tait was helped by his son, “the lamented Freddie Tait.” Freddie had been a professional golfer and, in the name of science, was required by his father to shoot golf balls through screens in order to trace their trajectory. On one occasion, in the gloom, he missed the screens. This resulted in the experimenters dodging around as the ball “ricocheted interminably off the walls of the cellar” (255).
This story was merely the disarming prelude to a point that was not intended to be amusing. Lanchester, Low went on, had boldly applied the idea of circulation to the wings of an aircraft and had given a thorough, descriptive account of the mechanism of flight. That was nearly twenty years ago. Why was it only now that the circulation theory was being taken seriously in the land of its origin? Low had an answer, and it was not a flattering one: “Had Rayleigh put forward the theory, how we should have vied with each other in the will to believe it, if not in power to understand it! But when it was offered by a man outside the circle of recognised physicists it was ignored” (255).
Leaving his audience to ponder this sociological point, Low went on to expound some of the basic techniques associated with the theory, confining himself to “strictly graphical and descriptive” methods. First, he gave a graphical method for transforming a circle into Joukowsky profiles and then tackled the more difficult, inverse task of going from a given aerofoil back to a circle or a close approximation to a circle. As before, Low was conveying to his audience the content of recent German material, this time using a postwar publication by Geckeler.102 Low showed how to start from the Albatross wing and, using drawing-office methods, map it back to an approximate circle by a series of trial-and-error steps. “There now remains only a routine of laying off and measuring straight lines on the drawing board to determine the velocity and hence the pressure at every point of the field” (273). Low assumed a velocity U = 10 m/sec and an air density of p = 1.2 kg/m3. Using the formula L = p U Г, he derived the data to construct a theoretical curve for the Albatross wing relating lift to angle of incidence. Because the formula was based on the assumption of an infinite span, the curve could not be compared directly with wind-tunnel data derived from a finite wing. Low then appealed to the Gottingen transformation formulas relating wings of the same section but different aspect ratio. This allowed him to recast known experimental data on the Albatross wing into its equivalent for an infinite wing. Low now had two curves that linked lift and incidence for the Albatross wing, one curve coming from wind-tunnel tests, the other derived from the circulation theory. For the range of -5° to +10° the two graphs were close together. The theory was supported by experiment. Given an arbitrary wing, a designer could now predict from the circulation theory the curve relating lift to angle of incidence at least up to the point of stall.
Having achieved his main goal, Low then returned to the theme with which he had begun. “In conclusion,” he said, “it is desired to call attention to the fact that this fundamental physical theory was first stated by an English writer, and then allowed to fall into complete neglect in the country of its origin, largely owing to the attitude taken up by some of Lanchester’s fellow members of the Advisory Committee for Aeronautics” (275). On this note the talk ended.
Calling the circulation account of lift a “fundamental physical theory” can only have been meant as a thrust at Bairstow, who had just explicitly denied it the status of being a fundamental theory. But the remarks blaming the Advisory Committee for Aeronautics for the neglect of Lanchester were even more pointed. The austere figure of Professor Sir Richard Glazebrook, who had been the chairman of the Advisory Committee, and who was thus the main focus of Low’s complaint, was present at the talk. In fact, he was more than present. He was presiding over the session at which Low had just delivered his paper.103