On Aerial Navigation.

London: W. Stratford for W. Nicholson, 1809-10.

First edition, journal issues in the original printed wrappers, extremely rare thus, of “the first and the greatest classic of aviation history, laying the foundations of the science of aerodynamics” (PMM) and setting out the correct conception of the modern aeroplane. “‘The true inventor of the aeroplane and one of the most powerful geniuses in the history of aviation’: these are the words used by the French historian Charles Dollfus to describe Sir George Cayley (1773-1857), a scholarly Yorkshire baronet who until recently was virtually ignored by historians of applied science. Cayley, who lived and did most of his work at Brompton Hall, near Scarborough, first had his aeronautical investigations fired by the invention of the balloon in 1783 – when he was ten – and his active concern with flying lasted until his death in 1857. In the year 1796 he made a helicopter model on the lines of that invented by Launoy and Bienvenu, a device he later improved and modified. Then, within a few years, with no previous workers to guide him or suggest the lines of approach, he arrived at a correct conception of the modern aeroplane, and so laid the secure foundations for all subsequent developments in aviation. It was in the year 1799 that Cayley took his first and most decisive step towards inaugurating the concept of the modern aeroplane: the proper separation of the system of thrust from the system of lift. This was the crucial breakaway from the ornithopter tradition of previous centuries: it meant picturing the bird with its wings held rigid as if in gliding flight, and propelled by some form of auxiliary mechanism. Then, during the most fruitful decade of his life (1799-1809), Cayley made his basic experiments, which included testing both model and full-size gliders, and arrived at his mature conception of aircraft and aerodynamics. It was almost an accident that he gathered together his notes and published them. For it was in Nicholson’s Journal, for November 1809, February 1910, and March 1810, that there appeared Cayley’s triple paper ‘On Aerial Navigation’” (ibid.). ABPC/RBH lists only three copies in the last half-century, none of them in original printed wrappers.

“The 2007 discovery of sketches in Cayley's school notebooks (held in the archive of the Royal Aeronautical Society Library) revealed that even at school Cayley was developing his ideas on the theories of flight. It has been claimed that these images indicate that Cayley identified the principle of a lift-generating inclined plane as early as 1792” (Wikipedia, accessed May 15, 2019).

“It was in 1804 that Cayley began to write his famous paper on Aerial Navigation, a work he was not able to complete for four years … One hundred and fifty years after Cayley began his essay, von Karman wrote in his book Aerodynamics (published this year [1954]), ‘The idea that sustentation can be accomplished by moving inclined surfaces in the flight direction, provided we have mechanical power to compensate for the air resistance, was probably clearly defined for the first time by an Englishman, Sir George Cayley, in his papers published in 1809-10 on aerial navigation … in his paper he clearly defined and separated the problem of sustentation, or in modern scientific language the problem of lift, from the problem of drag’ … It was after a brief but significant discussion on the forces on a bird in gliding flight that Cayley made the statement: ‘The whole problem is confined within these limits—To make a surface support a given weight by the application of power to the resistance of the air.’ This paper provided the first clarification of ideas about mechanical flight and was the first to lay down the main principles.

“The resistance of a plane in a moving stream of air, at various angles of incidence, was unknown. In his paper Cayley refers to ‘many carefully repeated experiments’ to obtain the pressures on a plane, but it was not until the discovery of his note-book in 1933 that it was known how astonishing these experiments were. Cayley records that they were made with a home-made whirling arm apparatus, to find the pressure on a flat plate, one foot square, at angles of incidence from 3 deg to 18 deg, in 3 deg steps. He was well aware of the difficulties of obtaining exact results, and carried out further tests, using a model glider, with an adjustable tailplane and a movable centre of gravity, to test his results.

“In this paper Cayley briefly touches upon the helicopter, the principle of which he demonstrates with a model using two sets of contra-rotating airscrews made from birds’ feathers. ‘For the mere purpose of ascent this is perhaps the best apparatus,’ he declares, ‘but speed is the great object of this invention, and this requires a different structure.’ He discusses the problem of the lateral and longitudinal stability of a fixed-wing machine and ‘aided by a remarkable circumstance that experiment alone could point out,’ shows that at very acute angles of incidence the centre of pressure moves considerably in front of the centre of gravity of a wing. This was the first statement made of the centre-of-pressure movement. Light construction, light engines, and minimum forward resistance were the key features of all Cayley’s ideas about heavier-than-air craft. ‘In thinking of how to construct the lightest possible wheel for aerial navigation cars,’ he wrote in 1808, ‘an entirely new mode of manufacturing this most useful part of locomotive machines occurred to me—vide, to do away with wooden spokes altogether, and refer the whole firmness of the wheel to the strength of the rim only, by the intervention of tight cording.’ In a later paper he pointed out that the wheel was an incumbrance during flight, a cogent reason why it should be as light as possible” (Pritchard, pp. 701-2).

“His emphasis on lightness led him to invent a new method of constructing lightweight wheels which is in common use today. For his landing wheels, he shifted the spoke’s forces from compression to tension by making them from tightly-stretched string, in effect ‘reinventing the wheel’. Wire soon replaced the string in practical applications and over time the wire wheel came into common use on bicycles, cars, aeroplanes and many other vehicles” (Wikipedia).

The first part of Cayley’s paper is devoted to issues of propulsion and aerodynamics. He noted that steam-engines would be a factor of ten too heavy to act as sources of propulsion and adds that “lightness is of so much value in this instance, that it is proper to notice the probability that exists of using the expansion of air by the sudden combustion of inflammable powders or fluids with great advantage … Probably a much cheaper engine of this sort might be produced by a gas-tight apparatus and by firing the inflammable air with a due proportion of common air under a piston.” He then gives a brief indication of what had been done, and what might be achieved, using spirit of tar or gas as the combustible fluids.

Turning to questions of aerodynamics, Cayley uses the example of bird-flight to explain the action of the lifting wing. The wing’s total resistance is taken to act perpendicularly to the wing’s surface, the triangle of forces then being employed so as to determine the wing’s lift and drag components. The lift, of course, is always known, being equal to the weight of the bird or aeroplane. According to Cayley’s assumption concerning resistance direction, the wing’s drag force is also known, being related to lift by the tangent of the wing’s incidence angle. However, there is a further “direct resistance” due to the bulk of the bird, or to the aeroplane’s remaining structure. He then turns to his belief in the superior lifting ability of the bird’s cambered wing and here provides a perceptive conjecture as to its cause. He suggests that, at the leading edge, the air’s upward motion over the upper surface’s convexity “creates a slight vacuity” there. Meanwhile, “the current is constantly received under the anterior edge of the surface, and directed upward into the cavity … The fluid accumulated thus within the cavity has to make its escape at the posterior edge of the surface, where it is directed considerably downward; and therefore has to overcome and displace a portion of the direct current passing with its full velocity immediately below it; hence whatever elasticity this effort requires operates upon the whole concavity of the surface, excepting a small portion of the anterior edge.” Here we meet for the first time some of the rudiments of our understanding that lift is created by the ability of a wing to remove leading edge upflow and then impart trailing edge downflow. The lift force is thus the consequent reaction on the wing due to its imposition of a vertically downward change of momentum to the air’s motion. The subject of “direct resistance” is returned to in the closing pages of part three of the paper. He comments that “It has been found by experiment, that the shape of the hinder part of the spindle is of as much importance as that of the front, in diminishing resistance. This arises from the partial vacuity created behind the obstructing body. If there be no solid to fill up this space, a deficiency of hydrostatic pressure exists within it, and is transferred to the spindle. This is seen distinctly near the rudder of a ship in full sail, where the water is much below the level of the surrounding sea. The cause here, being more evident, and uniform in its nature, may probably be obviated with better success; in as much as this portion of the spindle may not differ essentially from the simple cone. I fear however, that the whole of this subject is of so dark a nature, as to be more usefully investigated by experiment, than by reasoning.”

In part two of the paper Cayley addresses the problems of stability and control. He begins by describing the first successful parachute descent by André Jaques Garnerin (1769-1823) in 1797. Having no vent at its apex and therefore no doubt suffering alternate spillage around its canopy edge, Garnerin’s parachute produced a markedly oscillatory descent. This instability Cayley seizes on in his search for a means of providing lateral stability for aeroplanes. He believes this instability to be due merely to direct resistance differences across the canopy when tilted. Using a two-dimensional analogy, Cayley's argument is based entirely on the reduced resistance of a plate, at incidences less than normal to a stream, in comparison with the normal case. From this he argues that an inverted parachute canopy should be stable, a conclusion which he immediately applies to the aeroplane so as to suggest wing dihedral: Cayley has arrived at dihedral provision so as to enhance lateral stability.

Cayley then turns to longitudinal stability. Despite Cayley’s failure to grasp the stabilising function of the tailplane at this stage, he nonetheless realises the necessity of having a movable horizontal tail surface for the purposes of re-trimming for different flight speeds: “From a variety of experiments upon this subject I find, that, when the machine is going forward with a superabundant velocity, or that which would induce it to rise in its path, a very steady horizontal course is effected by a considerable depression of the rudder, which has the advantage of making use of this portion of the sail in aiding the support of the weight. When the velocity is becoming less, as in the act of alighting, then the rudder must gradually recede from this position, and even become elevated, for the purpose of preventing the machine from sinking too much in front, owing to the combined effect of the want of projectile force sufficient to sustain the centre of gravity in its usual position, and of the centre of support approaching the centre of the sail.” A further function of the tail, as Cayley sees it, is for steering: “The powers of the machine being previously balanced, if the least pressure be exerted by the current, either upon the upper or under surface of the rudder, according to the will of the aeronaut, it will cause the machine to rise or fall in its path, so long as the projectile force is continued with sufficient energy.”

Cayley’s thinking on structural design is contained entirely within the third part of the triple-paper, this being otherwise largely devoted to flapper propulsion systems. He offers the following general principles: “Diagonal bracing is the great principle for producing strength without accumulating weight; and, if performed by thin wires, looped at their ends, so as to receive several laps of cordage, produces but a trifling resistance to the air, and keeps tight in all weathers. When bracings are well applied, they make the poles, to which they are attached, bear endwise. The hollow form of the quill in birds is a very admirable structure for lightness combined with strength, where external bracings cannot be had; a tube being the best application of matter to resist as a lever; but the principle of bracing is so effectual, that, if properly applied, it will abundantly make up for the clumsiness of human invention in other respects; and should we combine both these principles, and give diagonal bracing to the tubular bamboo cane, surfaces might be constructed with a greater degree of strength and lightness, than any made use of in the wings of birds.” Cayley’s suggestion of diagonal wire bracing coupled to his earlier ideas on hollow tubular members proved apt advice, as later constructors were to demonstrate.

After the publication of the triple-paper, Cayley turned to a variety of other activities. He retained his interest in aeronautics but concentrated mainly on airships and ornithopter designs. Indeed, he remained largely silent on the aeroplane until prompted to return to it by the publication of Henson’s design for his ‘Aerial Steam Carriage’ in 1843. “Around 1843 he was the first to suggest the idea for a convertiplane, an idea which was published in a paper written that same year. At some time before 1849 he designed and built a biplane in which an unknown ten-year-old boy flew. Later, with the continued assistance of his grandson George John Cayley and his resident engineer Thomas Vick, he developed a larger scale glider (also probably fitted with ‘flappers’) which flew across Brompton Dale in front of Wydale Hall in 1853” (Wikipedia).

PMM 263. Norman 423 (complete journal volumes). Pritchard, ‘Sir George Cayley. The Man: His Work,’ Flight 66 (1954), pp. 701-703. Much of our description is adapted from Ackroyd, ‘Sir George Cayley: The Invention of the Aeroplane near Scarborough at the Time of Trafalgar,’ Journal of Aeronautical History 1 (2011), pp. 130-181.

In: Journal of Natural Philosophy, Chemistry and the Arts, Vol. 24, November 1809, pp. 164-174 with one folding engraved plate; Vol. 25, February 1810, pp. 81-87 and March 1810, pp. 161-173 with one folding engraved plate. Three vols., 8vo, pp. [4:advert] 2 plates [161] 162-239 [240]; [2:adverts] 2 plates [81] 82-159 [160]; 2 plates [161] 162-239 [240]. Original blue printed wrappers, uncut (somepaper restoration to spines, light staining to wrappers).

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