Sir George Cayley


Source: FLIGHT, 12 November 1854
Title: Sir George Cayley - The Man : His Work
Author: J. Laurence, Pritchard, C.B.E., Hon. F.R.Ae.S.


The First Cayley Memorial Lecture was read before the Brough Branch of the Royal Aeronautical Society on Thursday of last week November 4th. The full lecture, which would take up over twenty pages of "Flight," is here summarized for us by the lecturer. As most of our readers will know, Capt. Pritchard was for many years - from 192S to 1951 - secretary of the R.Ae.S.

George Cayley dedicated most of his inventor work to the problem of flying. However, this very busy man, still found time - in his spare time so to say - to invent two hot air engines and a few other things. This article won't tell much about hot air engines, but was chosen because it tells a lot about the man.

Cayley was the first man to

(1) Clarify the confusion of ideas about mechanical flight, and to lay down the principles of heavier-than-air flight.
(2) Carry out experiments in aerodynamic research, for flying purposes, on the pressure on surfaces at various angles of incidence.
(3) Use models for flying research.
(4) Draw attention to the importance of streamlining and to outline the body of least resistance.
(5) Show and discuss the movement of the centre of pressure of a surface in an air stream.
(6) Discuss the problem of stability of an aeroplane, and to indicate methods to obtain stability.
(7) Draw attention to the effects of the dihedral angle for wings, and of a movable tail plane and rudder.
(8) Draw attention to the great importance of weight control.
(9) Design a light aeroplane wheel.
(10) Build a man-carrying glider.
(11) Point out that curved surfaces had a better lift than plane surfaces, and that there existed a region of "vacuity" on the top surface.
(12) Suggest the "internal explosion" (i.e. combustion) engine for aircraft.
(13) Suggest jet reaction for propelling and steering air vessels.
(14) Suggest the convertiplane, i.e. the combination of the fixed wing surface and vertical lift surfaces.
(15) Suggest water recovery for airships.
(16) Draw the attention of the importance of the power/weight ratio, and of finding a light prime mover.
(17) Invent the expansion air engine: Cayley's 1807 hot air engine and Cayley's 1837 hot air engine
(18) Invent the caterpillar tractor.

Few men have written a birthday ode to their wife on her eightieth birthday. Sir George Cayley married the beautiful daughter of his mathematical tutor in 1795, and lived happily ever afterwards. His birthday ode, after 58 years of married life, began:

"Full many a pleasing, many an anxious thought
his lengthened day of eighty years has brought."

You may well ask: "What has this to do with his aeronautical fame?"

This paper is an assessment of the man as well as his work, for on both must his place in history rest. How misjudged would Nelson have been if Lady Hamilton had never been taken off the secret list, or Napoleon if Josephine had been put on it?

Sir George Cayley succeeded to his father's estates in 1792, when he was only nineteen. He early showed his interest in scientific and engineering pursuits; but, as the lord of the Manor and a political and social figure in Yorkshire, he was not able to devote anything like the time he would have liked to his ideas. The chief of these were concerned with the problem of flying, about which nothing was known except in relation to balloons.

Three times in his long life he tried to found an aeronautical society, the first time in 1816 and the last in 1843, when he wrote: "I think it is a national disgrace... not to realize by public subscriptions the proper scientific experiments... which would secure to this country the glory of being the first to establish the dry navigation of the universal ocean of the terrestial atmosphere."

He was a founder-member of two important societies for promoting science and an interest in it, the Yorkshire Philosophical Society and the Scarborough Philosophical Society. Through the former, Cayley played his part in helping to found, in 1831, the British Association for the Advancement of Science. He remained a member of it during his lifetime.

Cayley's interests were wide. In the paper a detailed account is given of his many non-aeronautical activities. He was the inventor of the hot air engine (Cayley's 1807 hot air engine), which attracted the attention of leading engineers for half a century; and of the caterpillar tractor. "This invention," he wrote of the latter in 1825, "which may be called the universal railway, is for the purpose of forming locomotive vehicles by which the impediments and resistances of every sort of road, land, morass or water will be obviated or overcome."

Whether or not Cayley is the inventor of the hot air engine - as stated in this article - is questionable as other inventors have attempted to built hot air engines before him. Nonetheless this would not diminish his genius.

The coming of the railway, and the early disasters, aroused him to publish a number of papers on safety devices and improvements in construction. He was strongly of the opinion that the human factor should be eliminated as far as possible, and he drafted out an automatic block system of signal control on the railways, with constructional diagrams, and the further suggestion that "in case of fogs a bell should likewise be arranged as to ring on the train passing any post showing the red signal."

Perhaps the situation then, as far as the public was concerned, can be realized when Cayley wrote: "It is necessary to make it a positive law, that the up trains shall always keep to one set of rails, and the down trains to the other."

For over thirty years Cayley was the chairman, under the Muston Drainage Act, for the effective drainage of frequently flooded land in Yorkshire; he was the first to start the allotment system on his own estates, an example widely followed for many years. He directed his attention to optics for testing the purity of water, a method used successfully in .the investigation of the waters of the Thames; and published a paper for the acoustical design of a new Covent Garden Theatre. In 1804 he carried out experiments with six-pounder cannon shot. "My object at the time was to ascertain whether, by obviating as much as possible the resistance of the air, the range of cannon shot might be increased." One of the shells he designed was almost a replica of the bomb shapes with guiding fins used in the early stages of the 1939-45 war.

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. This paper is published in full, for the first time since its original publication, in the appendix to the lecture.

One hundred and fifty years after Cayley began his essay, von Karman wrote in his book Aerodynamics (published this year), "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."

"Lightness is of so much value," declared Cayley in his paper, after rejecting the steam engine as being too heavy for his ideas, "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."

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 notebook in 1933 diat 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.

Since this lecture was prepared, these experiments have been analysed by A. H. Yates ("Flight," October 22nd, 1954). He draws attention to the surprisingly good agreement of Cayley's results with modern theory as given by Flax and Lawrence at the 1951 Anglo American Conference.

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 heavierthan-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 meā€”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.

Cayley's next papers appeared in the famous Phil Mag. in 1816. In them he discussed airships: "A globe is by no means the best shape for obviating resistance; a greater extension in the line of its path, with a corresponding diminution in the section perpendicular to it, may be adopted with great advantage."

In his notebook he made a sketch of what he called "the solid of least resistance" based on the measurements of the trout. Von Karman, in his Aerodynamics, draws attention to the astonishing fact that Cayley's outline "almost exactly coincides wim certain low-drag airfoil sections." The figure shows Cayley's sketch and his points superimposed upon the N.A.C.A. aerofoil section 63A016-LB N-0016.

In his paper of May 1816 Cayley proposed an airship 432ft in length with a total lift of 163,000 lb. He allowed a weight of 160 lb/h.p./hr for a steam engine with coal and water, "and as the water is a considerable part of the whole, and can be recovered by permitting steam to pass within the double coats of the balloon and to be thus exposed to so extensive a cooling surface it is probable that/200 lb per horsepower will be more than sufficient for working twelve hours without any further supply of water or fuel."

This was a remarkable suggestion for water recovery in airships. He had suggested an inner skin of oiled silk to conserve the hydrogen and lessen the danger from accidental damage to the outside skin. Cayley calculated the speed at 20 m.p.h. and the range in calm air, carrying 50 men, to be 960 miles.

In his 1837 paper in the Mechanics Magazine he discussed other means of propelling an airship. One of these is of presentday interest: "Communicating centrifugal force to air by means of a hollow drum and fans by the steam engine is another means of getting a propelling power conveniently applicable in every direction that may be required; for by having a movable mouthpiece, from which the air escapes, the re-action will always be in the opposite direction."
Shades of the turbojet!

One of his more remarkable papers appeared in 1843. In it Cayley outlined what would now be known as the convertiplane. There were revolving blades for the take-off and airscrews for horizontal flight: "The first may be termed the elevating fliers, to distinguish them from the two smaller ones, set at a very different angle with their axis, and used for propelling the machine, when the others are stationary; both sets will be put into action gradually, or in any required degree by friction plates." The contra-rotating "elevating fliers" were arranged to eliminate torque, and set at a dihedral angle for lateral stability. This is Cayley's machine "capable of landing at any place capable of receiving it, and of ascending from that point," and "capable of remaining stationary, or nearly so, in the air," to use his own words.

Cayley's last-but-one contribution to the science of aeronautics was one he wrote in 1853 for the French Aeronautical Society. He was then in his eighty-first year. In it there is a description of experiments to ascertain the weight carried by a surface at a given angle of incidence when gliding. In one of these experiments with a larger glider he writes, "a boy of ten years was floated off the ground for several yards on descending a hill, and also for about the same space by some persons pulling the apparatus against a very slight breeze by a rope." After drawing attention to the difficulties and dangers of starting a glide, Cayley anticipated Lilienthal by proposing an artificial hill to be constructed for gliding experiments. In those carried out at Cayley's home, Brompton Hall, in 1852, Cayley's grand-daughter, who witnessed them, wrote, "The coachman went in the machine and landed on the west side at about the same level. The coachman got himself clear and when the watchers got across he shouted,

Please, Sir George, I wish to give notice. I was hired to drive, not to fly."

In 1855 Cayley wrote his last aeronautical paper, on an "Improve d Flying Top," December I5th, 1857.

This summary is necessarily inadequate; but, as Cayley's papers are more carefully studied, in the light of the knowledge of the time, I am sure his reputation as "the Father of British Aeronautics" will be enhanced.

He was a member of the Institution of Civil Engineers and regularly attended their meetings when in London. He travelled often on the Continent, and met and was friends with many of the leading scientists there. He was a man of great personal charm, an excellent mechanic, a man of imagination, and one who had the gift of being able to mix with kings and yet not lose the common touch. He was a fierce patriot, and wrote and spoke at length on the necessity of a national defence force. He advocated, indeed, in a long and reasoned pamphlet, the calling up of one-quarter of the available male population for twenty days each year. (He was himself a colonel in the Volunteers.) The words with which he finished his appeal, written in 1807 when there were threats Britain might be invaded by Napoleon, might have been written today:

Let us men embrace the opportunity of repose afforded to this country by the present position of continental affairs; and assiduously rear up a bulwark, that shall either present so majestic a front as may effectually daunt our aspiring enemy; or, should he attempt to assail us, may heap deserved ruin upon his head.