The desire to fly is no new growth in humanity. For countless years men have longed to emulate the birds—"To soar upward and glide, free as a bird, over smiling fields, leafy woods, and mirror-like lakes," as a great pioneer of aviation said. Great scholars and thinkers of old, such as Horace, Homer, Pindar, Tasso, and all the glorious line, dreamt of flight, but it has been left for the present century to see those dreams fulfilled.
Early writers of the fourth century saw the possibility of aerial navigation, but those who tried to put their theories in practice were beset by so many difficulties that they rarely succeeded in leaving the ground.
Most of the early pioneers of aviation believed that if a man wanted to fly he must provide himself with a pair of wings similar to those of a large bird. The story goes that a certain abbot told King James IV of Scotland that he would fly from Stirling Castle to Paris. He made for himself powerful wings of eagles' feathers, which he fixed to his body and launched himself into the air. As might be expected, he fell and broke his legs.
But although the muscles of man are of insufficient strength to bear him in the air, it has been found possible, by using a motor engine, to give to man the power of flight which his natural weakness denied him.
Scientists estimate that to raise a man of about 12 stone in the air and enable him to fly there would be required an immense pair of wings over 20 feet in span. In comparison with the weight of a man a bird's weight is remarkably small—the largest bird does not weigh much more than 20 pounds—but its wing muscles are infinitely stronger in proportion than the shoulder and arm muscles of a man.
As we shall see in a succeeding chapter, the "wing" theory was persevered with for many years some two or three centuries ago, and later on it was of much use in providing data for the gradual development of the modern aeroplane.
Hitherto we have traced the gradual development of the balloon right from the early days of aeronautics, when the brothers Montgolfier constructed their hot-air balloon, down to the most modern dirigible. It is now our purpose, in this and subsequent chapters, to follow the course of the pioneers of aviation.
It must not be supposed that the invention of the steerable balloon was greatly in advance of that of the heavier-than-air machine. Indeed, developments in both the dirigible airship and the aeroplane have taken place side by side. In some cases men like Santos Dumont have given earnest attention to both forms of air-craft, and produced practical results with both. Thus, after the famous Brazilian aeronaut had won the Deutsch prize for a flight in an air-ship round the Eiffel tower, he immediately set to work to construct an aeroplane which he subsequently piloted at Bagatelle and was awarded the first "Deutsch prize" for aviation.
It is generally agreed that the undoubted inventor of the aeroplane, practically in the form in which it now appears, was an English engineer, Sir George Cayley. Just over a hundred years ago this clever Englishman worked out complete plans for an aeroplane, which in many vital respects embodied the principal parts of the monoplane as it exists to-day.
There were wings which were inclined so that they formed a lifting plane; moreover, the wings were curved, or "cambered", similar to the wing of a bird, and, as we shall see in a later chapter, this curve is one of the salient features of the plane of a modern heavier-than-air machine. Sir George also advocated the screw propeller worked by some form of "explosion" motor, which at that time had not arrived. Indeed, if there had been a motor available it is quite possible that England would have led the way in aviation. But, unfortunately, owing to the absence of a powerful motor engine, Sir George's ideas could not be practically carried out till nearly a century later, and then Englishmen were forestalled by the Wright brothers, of America, as well as by several French inventors.
The distinguished French writer, Alphonse Berget, in his book, The Conquest of the Air, pays a striking tribute to our English inventor, and this, coming from a gentleman who is writing from a French point of view, makes the praise of great value. In alluding to Sir George, M. Berget says: "The inventor, the incontestable forerunner of aviation, was an Englishman, Sir George Cayley, and it was in 1809 that he described his project in detail in Nicholson's Journal.... His idea embodied 'everything'—the wings forming an oblique sail, the empennage, the spindle forms to diminish resistance, the screw-propeller, the 'explosion' motor,... he even described a means of securing automatic stability. Is not all that marvellous, and does it not constitute a complete specification for everything in aviation?
"Thus it is necessary to inscribe the name of Sir George Cayley in letters of gold, in the first page of the aeroplane's history. Besides, the learned Englishman did not confine himself to 'drawing-paper': he built the first apparatus (without a motor) which gave him results highly promising. Then he built a second machine, this time with a motor, but unfortunately during the trials it was smashed to pieces."
But were these ideas of any practical value? How is it that he did not succeed in flying, if he had most of the component parts of an aeroplane as we know it to-day?
The answer to the second question is that Sir George did not fly, simply because there was no light petrol motor in existence; the crude motors in use were far too heavy, in proportion to the power developed, for service in a flying machine. It was recognized, not only by Sir George, but by many other English engineers in the first half of the nineteenth century, that as soon as a sufficiently powerful and light engine did appear, then half the battle of the conquest of the air would be won.
But his prophetic voice was of the utmost assistance to such inventors as Santos Dumont, the Wright brothers, M. Bleriot, and others now world-famed. It is quite safe to assume that they gave serious attention to the views held by Sir George, which were given to the world at large in a number of highly-interesting lectures and magazine articles. "Ideas" are the very foundation-stones of invention—if we may be allowed the figure of speech—and Englishmen are proud, and rightly proud, to number within their ranks the original inventor of the heavier-than-air machine.
For many years after the publication of Sir George Cayley's articles and lectures on aviation very little was done in the way of aerial experiments. True, about midway through the nineteenth century two clever engineers, Henson and Stringfellow, built a model aeroplane after the design outlined by Sir George; but though their model was not of much practical value, a little more valuable experience was accumulated which would be of service when the time should come; in other words, when the motor engine should arrive. This model can be seen at the Victoria and Albert Museum, at South Kensington.
A few years later Stringfellow designed a tiny steam-engine, which he fitted to an equally tiny monoplane, and it is said that by its aid he was able to obtain a very short flight through the air. As some recognition of his enterprise the Aeronautical Society, which was founded in 1866, awarded him a prize of L100 for his engine.
The idea of producing a practical form of flying machine was never abandoned entirely. Here and there experiments continued to be carried out, and certain valuable conclusions were arrived at. Many advanced thinkers and writers of half a century ago set forth their opinions on the possibilities of human flight. Some of them, like Emerson, not only believed that flight would come, but also stated why it had not arrived. Thus Emerson, when writing on the subject of air navigation about fifty years ago, remarked: "We think the population is not yet quite fit for them, and therefore there will be none. Our friend suggests so many inconveniences from piracy out of the high air to orchards and lone houses, and also to high fliers, and the total inadequacy of the present system of defence, that we have not the heart to break the sleep of the great public by the repetition of these details. When children come into the library we put the inkstand and the watch on the high shelf until they be a little older."
About the year 1870 a young German engineer, named Otto Lilienthal, began some experiments with a motorless glider, which in course of time were to make him world-famed. For nearly twenty years Lilienthal carried on his aerial research work in secrecy, and it was not until about the year 1890 that his experimental work was sufficiently advanced for him to give demonstrations in public.
The young German was a firm believer in what was known as the "soaring-plane" theory of flight. From the picture here given we can get some idea of his curious machine. It consisted of large wings, formed of thin osiers, over which was stretched light fabric. At the back were two horizontal rudders shaped somewhat like the long forked tail of a swallow, and over these was a large steering rudder. The wings were arranged around the glider's body. The whole apparatus weighed about 40 pounds.
Lilienthal's flights, or glides, were made from the top of a specially-constructed large mound, and in some cases from the summit of a low tower. The "birdman" would stand on the top of the mound, full to the wind, and run quickly forward with outstretched wings. When he thought he had gained sufficient momentum he jumped into the air, and the wings of the glider bore him through the air to the base of the mound.
To preserve the balance of his machine—always a most difficult feat—he swung his legs and hips to one side or the other, as occasion required, and, after hundreds of glides had been made, he became so skilful in maintaining the equilibrium of his machine that he was able to cover a distance, downhill, of 300 yards.
Later on, Lilienthal abandoned the glider, or elementary form of monoplane, and adopted a system of superposed planes, corresponding to the modern biplane. The promising career of this clever German was brought to an untimely end in 1896, when, in attempting to glide from a height of about 80 yards, his apparatus made a sudden downward swoop, and he broke his neck.
Now that Lillenthal's experiments had proved conclusively the efficiency of wings, or planes, as carrying surfaces, other engineers followed in his footsteps, and tried to improve on his good work.
The first "birdman" to use a glider in this country was Mr. Percy Pilcher who carried out his experiments at Cardross in Scotland. His glides were at first made with a form of apparatus very similar to that employed by Lilienthal, and in time he came to use much larger machines. So cumbersome, however, was his apparatus—it weighed nearly 4 stones—that with such a great weight upon his shoulders he could not run forward quickly enough to gain sufficient momentum to "carry off" from the hillside. To assist him in launching the apparatus the machine was towed by horses, and when sufficient impetus had been gained the tow-rope was cast off.
Three years after Lilienthal's death Pilcher met with a similar accident. While making a flight his glider was overturned, and the unfortunate "birdman" was dashed to death.
In America there were at this time two or three "human birds", one of the most famous being M. Octave Chanute. During the years 1895-7 Chanute made many flights in various types of gliding machines, some of which had as many as half a dozen planes arranged one above another. His best results, however, were obtained by the two-plane machine, resembling to a remarkable extent the modern biplane.
We have seen that the inventors of flying machines in the early days of aviation modelled their various craft somewhat in the form of a bird, and that many of them believed that if the conquest of the air was to be achieved man must copy nature and provide himself with wings.
Let us closely examine a modern monoplane and discover in what way it resembles the body of a bird in build.
First, there is the long and comparatively narrow body, or FUSELAGE, at the end of which is the rudder, corresponding to the bird's tail. The chassis, or under carriage, consisting of wheels, skids, &c., may well be compared with the legs of a bird, and the planes are very similar in construction to the bird's wings. But here the resemblance ends: the aeroplane does not fly, nor will it ever fly, as a bird flies.
If we carefully inspect the wing of a bird—say a large bird, such asthe crow—we shall find it curved or arched from front to back. Thiscurve, however, is somewhat irregular. At the front edge of the wingit is sharpest, and there is a gradual dip or slope backwards anddownwards. There is a special reason for this peculiar structure, as weshall see in a later chapter.Now it is quite evident that the inventors of aeroplanes havemodelled the planes of their craft on the bird's wing. Strictlyspeaking, the word "plane" is a misnomer when applied to the supportingstructure of an aeroplane. Euclid defines a plane, or a plane surface,as one in which, any two points being taken, the straight line betweenthem lies wholly in that surface. But the plane of a flying machine iscurved, or CAMBERED, and if one point were taken on the front of theso-called plane, and another on the back, a straight line joining thesetwo points could not possibly lie wholly on the surface.
All planes are not cambered to the same extent: some have a very small curvature; in others the curve is greatly pronounced. Planes of the former type are generally fitted to racing aeroplanes, because they offer less resistance to the air than do deeply-cambered planes. Indeed, it is in the degree of camber that the various types of flying machine show their chief diversity, just as the work of certain shipmasters is known by the particular lines of the bow and stern of the vessels which are built in their yards.
Birds fly by a flapping movement of their wings, or by soaring. We are quite familiar with both these actions: at one time the bird propels itself by means of powerful muscles attached to its wings by means of which the wings are flapped up and down; at another time the bird, with wings nicely adjusted so as to take advantage of all the peculiarities of the air currents, keeps them almost stationary, and soars or glides through the air.
The method of soaring alone has long since been proved to be impracticable as a means of carrying a machine through the air, unless, of course, one describes the natural glide of an aeroplane from a great height down to earth as soaring. But the flapping motion was not proved a failure until numerous experiments by early aviators had been tried.
Probably the most successful attempt at propulsion by this method was that of a French locksmith named Besnier. Over two hundred years ago he made for himself a pair of light wooden paddles, with blades at either end, somewhat similar in shape to the double paddle of a canoe. These he placed over his shoulders, his feet being attached by ropes to the hindmost paddles. Jumping off from some high place in the face of a stiff breeze, he violently worked his arms and legs, so that the paddles beat the air and gave him support. It is said that Besnier became so expert in the management of his simple apparatus that he was able to raise himself from the ground, and skim lightly over fields and rivers for a considerable distance.
Now it has been shown that the enormous extent of wing required to support a man of average weight would be much too large to be flapped by man's arm muscles. But in this, as with everything else, we have succeeded in harnessing the forces of nature into our service as tools and machinery.
And is not this, after all, one of the chief, distinctions between man and the lower orders of creation? The latter fulfil most of their bodily requirements by muscular effort. If a horse wants to get from one place to another it walks; man can go on wheels. None of the lower animals makes a single tool to assist it in the various means of sustaining life; but man puts on his "thinking-cap", and invents useful machines and tools to enable him to assist or dispense with muscular movement.
Thus we find that in aviation man has designed the propeller, which, by its rapid revolutions derived from the motive power of the aerial engine, cuts a spiral pathway through the air and drives the light craft rapidly forward. The chief use of the planes is for support to the machine, and the chief duty of the pilot is to balance and steer the craft by the manipulation of the rudder, elevation and warping controls.
Though, as we have seen, most of the early attempts at aerial navigation were made by foreign engineers, yet we are proud to number among the ranks of the early inventors of heavier-than-air machines Sir Hiram Maxim, who, though an American by birth, has spent most of his life in Britain and may therefore be called a British inventor.
Perhaps to most of us this inventor's name is known more in connection with the famous "Maxim" gun, which he designed, and which was named after him. But as early as 1894, when the construction of aeroplanes was in a very backward state, Sir Hiram succeeded in making an interesting and ingenious aeroplane, which he proposed to drive by a particularly light steam-engine.
Sir Hiram's first machine, which was made in 1890, was designed to be guided by a double set of rails, one set arranged below and the other above its running wheels. The intention was to make the machine raise itself just off the ground rails, but yet be prevented from soaring by the set of guard rails above the wheels, which acted as a check on it. The motive force was given by a very powerful steam-engine of over 300 horse-power, and this drove two enormous propellers, some 17 feet in length. The total weight of the machine was 8000 pounds, but even with this enormous weight the engine was capable of raising the machine from the ground.
For three or four years Sir Hiram made numerous experiments with his aeroplane, but in 1894 it broke through the upper guard rail and turned itself over among the surrounding trees, wrecking itself badly.
But though the Maxim aeroplane did not yield very practical results, it proved that if a lighter but more powerful engine could be made, the chief difficulty iii the way of aerial flight would be removed. This was soon forthcoming in the invention of the petrol motor. In a lecture to the Scottish Aeronautical Society, delivered in Glasgow in November, 1913, Sir Hiram claimed to be the inventor of the first machine which actually rose from the earth. Before the distinguished inventor spoke of his own work in aviation he recalled experiments made by his father in 1856-7, when Sir Hiram was sixteen years of age. The flying machine designed by the elder Maxim consisted of a small platform, which it was proposed to lift directly into the air by the action of two screw-propellers revolving in reverse directions. For a motor the inventor intended to employ some kind of explosive material, gunpowder preferred, but the lecturer distinctly remembered that his father said that if an apparatus could be successfully navigated through the air it would be of such inevitable value as a military engine that no matter how much it might cost to run it would be used by Governments.
Of his own claim as an inventor of air-craft it would be well to quote Sir Hiram's actual words, as given by the Glasgow Herald, which contained a full report of the lecture.
"Some forty years ago, when I commenced to think of the subject, my first idea was to lift my machine by vertical propellers, and I actually commenced drawings and made calculations for a machine on that plan, using an oil motor, or something like a Brayton engine, for motive power. However, I was completely unable to work out any system which would not be too heavy to lift itself directly into the air, and it was only when I commenced to study the aeroplane system that it became apparent to me that it would be possible to make a machine light enough and powerful enough to raise itself without the agency of a balloon. From the first I was convinced that it would be quite out of the question to employ a balloon in any form. At that time the light high-speed petrol motor had no existence. The only power available being steam-engines, I made all my calculations with a view of using steam as the motive power. While I was studying the question of the possibility of making a flying machine that would actually fly, I became convinced that there was but one system to work on, and that was the aeroplane system. I made many calculations, and found that an aeroplane machine driven by a steam-engine ought to lift itself into the air."
Sir Hiram then went on to say that it was the work of making an automatic gun which was the direct cause of his experiments with flying machines. To continue the report:
"One day I was approached by three gentlemen who were interested in the gun, and they asked me if it would be possible for me to build a flying machine, how long it would take, and how much it would cost. My reply was that it would take five years and would cost L50,000. The first three years would be devoted to developing a light internal-combustion engine, and the remaining two years to making a flying machine.
"Later on a considerable sum of money was placed at my disposal, and the experiments commenced, but unfortunately the gun business called for my attention abroad, and during the first two years of the experimental work I was out of England eighteen months.
"Although I had thought much of the internal-combustion engine it seemed to me that it would take too long to develop one and that it would be a hopeless task in my absence from England; so I decided that in my first experiments at least I would use a steam-engine. I therefore designed and made a steam-engine and boiler of which Mr. Charles Parsons has since said that, next to the Maxim gun, it developed more energy for its weight than any other heat engine ever made. That was true at the time, but is very wide of the mark now."
Speaking of motors, the veteran lecturer remarked: "Perhaps there was no problem in the world on which mathematicians had differed so widely as on the problem of flight. Twenty years ago experimenters said: 'Give us a motor that will develop 1 horse-power with the weight of a barnyard fowl, and we will very soon fly.' At the present moment they had motors which would develop over 2 horse-power and did not weigh more than a 12-pound barnyard fowl. These engines had been developed—I might say created—by the builders of motor cars. Extreme lightness had been gradually obtained by those making racing cars, and that had been intensified by aviators. In many cases a speed of 80 or 100 miles per hour had been attained, and machines had remained in the air for hours and had flown long distances. In some cases nearly a ton had been carried for a short distance."
Such words as these, coming from the lips of a great inventor, give us a deep insight into the working of the inventor's mind, and, incidentally, show us some of the difficulties which beset all pioneers in their tasks. The science of aviation is, indeed, greatly indebted to these early inventors, not the least of whom is the gallant Sir Hiram Maxim.
In the beginning of the twentieth century many of the leading European newspapers contained brief reports of aerial experiments which were being carried out at Dayton, in the State of Ohio, America. So wonderful were the results of these experiments, and so mysterious were the movements of the two brothers—Orville and Wilbur Wright—who conducted them, that many Europeans would not believe the reports.
No inventors have gone about their work more carefully, methodically, and secretly than did these two Americans, who, hidden from prying eyes, "far from the madding crowd", obtained results which brought them undying fame in the world of aviation.
For years they worked at their self-imposed task of constructing a flying machine which would really soar among the clouds. They had read brief accounts of the experiments carried out by Otto Lilienthal, and in many ways the ground had been well paved for them. It was their great ambition to become real "human birds"; "birds" that would not only glide along down the hillside, but would fly free and unfettered, choosing their aerial paths of travel and their places of destination.
Though there are few reliable accounts of their work in those remote American haunts, during the first six years of the present century, the main facts of their life-history are now well known, and we are able to trace their experiments, step by step, from the time when they constructed their first simple aeroplane down to the appearance of the marvellous biplane which has made them world-famed.
For some time the Wrights experimented with a glider, with which they accomplished even more wonderful results than those obtained by Lilienthal. These two young American engineers—bicycle-makers by trade—were never in a hurry. Step by step they made progress, first with kites, then with small gliders, and ultimately with a large one. The latter was launched into the air by men running forward with it until sufficient momentum had been gained for the craft to go forward on its own account.
The first aeroplane made by the two brothers was a very simple one, as was the method adopted to balance the craft. There were two main planes made of long spreads of canvas arranged one above another, and on the lower plane the pilot lay. A little plane in front of the man was known as the ELEVATOR, and it could be moved up and down by the pilot; when the elevator was tilted up, the aeroplane ascended, when lowered, the machine descended.
At the back was a rudder, also under control of the pilot. The pilot's feet, in a modern aeroplane, rest upon a bar working on a central swivel, and this moves the rudder. To turn to the left, the left foot is moved forward; to turn to the right the right foot.
But it was in the balancing control of their machine that the Wrights showed such great ingenuity. Running from the edges of the lower plane were some wires which met at a point where the pilot could control them. The edges of the plane were flexible; that is, they could be bent slightly either up or down, and this movement of the flexible plane is known as WING WARPING.
You know that when a cyclist is going round a curve his machine leans inwards. Perhaps some of you have seen motor races, such as those held at Brooklands; if so, you must have noticed that the track is banked very steeply at the corners, and when the motorist is going round these corners at, say, 80 miles an hour, his motor makes a considerable angle with the level ground, and looks as if it must topple over. The aeroplane acts in a similar manner, and, unless some means are taken to prevent it, it will turn over.
Let us now see how the pilot worked the "Wright" glider. Suppose the machine tilted down on one side, while in the air, the pilot would pull down, or warp, the edges of the planes on that side of the machine which was the lower. By an ingenious contrivance, when one side was warped down, the other was warped up, with the effect that the machine would be brought back into a horizontal position. (As we shall return to the subject of wing warping in a later chapter, we need not discuss it further here.)
It must not be imagined that as soon as the Wrights had constructed a glider fitted with this clever system of controlling mechanism they could fly when and where they liked. They had to practise for two or three years before they were satisfied with the results of their experiments: neglecting no detail, profiting by their failures, and moving logically from step to step. They never attempted an experiment rashly: there was always a reason for what they did. In fact, their success was due to systematic progress, achieved by wonderful perseverance.
But now, for a short time, we must leave the pioneer work of the Wright brothers, and turn to the invention of the petrol engine as applied to the motor car, an invention which was destined to have far-reaching results on the science of aviation.
We have several times remarked upon the great handicap placed upon the pioneers of aviation by the absence of a light but powerful motor engine. The invention of the internal-combustion engine may be said to have revolutionized the science of flying; had it appeared a century ago, there is no reason to doubt that Sir George Cayley would have produced an aeroplane giving as good results as the machines which have appeared during the last five or six years.
The motor engine and the aeroplane are inseparably connected; one is as necessary to the other as clay is to the potter's wheel, or coal to the blast-furnace. This being the case, it is well that we trace briefly the development of the engine during the last quarter of a century.
The original mechanical genius of the motoring industry was Gottlieb Daimler, the founder of the immense Daimler Motor Works of Coventry. Perhaps nothing in the world of industry has made more rapid strides during the last twenty years than automobilism. In 1900 our road traction was carried on by means of horses; now, especially in the large cities, it is already more than half mechanical, and at the present rate of progress it bids fair to be soon entirely horseless.
About the year 1885 Daimler was experimenting with models of a small motor engine, and the following year he fitted one of his most successful models to a light wagonette. The results were so satisfactory, that in 1888 he took out a patent for an internal-combustion engine—as the motor engine is technically called—and the principle on which this engine was worked aroused great enthusiasm on the Continent.
Soon a young French engineer, named Levassor, began to experiment with models of motor engines, and in 1889 he obtained, with others, the Daimler rights to construct similar engines in France. From now on, French engineers began to give serious attention to the new engine, and soon great improvements were made in it. All this time Britain held aloof from the motor-car; indeed, many Britons scoffed at the idea of mechanically-propelled vehicles, saying that the time and money required for their development would be wasted.
During the years 1888-1900 strange reports of smooth-moving, horseless cars, frequently appearing in public in France, began to reach Britain, and people wondered if the French had stolen a march on us, and if there were anything in the new invention after all. Our engineers had just begun to grasp the immense possibilities of Daimler's engine, but the Government gave them no encouragement.
At length the Hon. Evelyn Ellis, one of the first British motorists, introduced the "horseless carriage" into this country, and the following account of his early trips, which appeared in the Windsor and Eton Express of 27th July, 1895, may be interesting.
"If anyone cares to run over to Datchet, they will see the Hon. Evelyn Ellis, of Rosenau, careering round the roads, up hill and down dale, and without danger to life or limb, in his new motor carriage, which he brought over a short time ago from Paris.
"In appearance it is not unlike a four-wheeled dog-cart, except that the front part has a hood for use on long 'driving' tours, in the event of wet weather; it will accommodate four persons, one of whom, on the seat behind, would, of course, be the 'groom', a misnomer, perhaps, for carriage attendant. Under the front seat are receptacles, one for tools with which to repair damages, in the event of a breakdown on the road, and the other for a store of oil, petroleum, or naphtha in cans, from which to replenish the oil tank of the carriage on the journey, if it be a long one.
"Can it be easily driven? We cannot say that such a vehicle would be suitable for a lady, unless rubber-tyred wheels and other improvements are made to the carriage, for a grim grip of the steering handle and a keen eye are necessary for its safe guidance, more especially if the high road be rough. It never requires to be fed, and as it is, moreover, unsusceptible of fatigue, it is obviously the sort of vehicle that should soon achieve a widespread popularity in this country.
"It is a splendid hill climber, and, in fact, such a hill as that of Priest Hill (a pretty good test of its capabilities) shows that it climbs at a faster pace than a pedestrian can walk.
"A trip from Rosenau to Old Windsor, to the entrance of Beaumont College, up Priest Hill, descending the steep, rough, and treacherous hill on the opposite side by Woodside Farm, past the workhouse, through old Windsor, and back to Rosenau within an hour, amply demonstrated how perfectly under control this carriage is, while the sensation of being whirled rapidly along is decidedly pleasing."
Another pioneer of motorism was the Hon. C. S. Rolls, whose untimely death at Bournemouth in 1910, while taking part in the Bournemouth aviation meeting, was deeply deplored all over the country. Mr. Rolls made a tour of the country in a motor-car in 1895, with the double object of impressing people with the stupidity of the law with regard to locomotion, and of illustrating the practical possibilities of the motor. You may know that Mr. Rolls was the first man to fly across the Channel, and back again to Dover, without once alighting.
I suppose many of my readers are quite familiar with the working of a steam-engine. Probably you have owned models of steam-engines right from your earliest youth, and there are few boys who do not know how the railway engine works.
But though you may be quite familiar with the mechanism of this engine, it does not follow that you know how the petrol engine works, for the two are highly dissimilar. It is well, therefore, that we include a short description of the internal-combustion engine such as is applied to motor-cars, for then we shall be able to understand the principles of the aeroplane engine.
At present petrol is the chief fuel used for the motor engine. Numerous experiments have been tried with other fuels, such as benzine, but petrol yields the best results.
Petrol is distilled from oil which comes from wells bored deep down in the ground in Pennsylvania, in the south of Russia, in Burma, and elsewhere. Also it is distilled in Scotland from oil shale, from which paraffin oil and wax and similar substances are produced. When the oil is brought to the surface it contains many impurities, and in its native form is unsuitable for motor engines. The crude oil is composed of a number of different kinds of oil; some being light and clear, others heavy and thick.
To purify the oil it is placed in a large metal vessel or "still". Steam is first passed over the oil in the still, and this changes the lightest of the oils into vapours. These vapours are sent through a series of pipes surrounded with cold water, where they are cooled and become liquid again. Petrol is a mixture of these lighter products of the oil.
If petrol be placed in the air it readily turns into a vapour, and this vapour is extremely inflammable. For this reason petrol is always kept in sealed tins, and very large quantities are not allowed to be stored near large towns. The greatest care has to be exercised in the use of this "unsafe" spirit. For example, it is most dangerous to smoke when filling a tank with petrol, or to use the spirit near a naked light. Many motor-cars have been set on fire through the petrol leaking out of the tank in which it is carried.
The tank which contains the petrol is placed under one of the seats of the motor-car, or at the rear; if in use on a motor-cycle it is arranged along the top bar of the frame, just in front of the driver. This tank is connected to the "carburettor", a little vessel having a small nozzle projecting upwards in its centre. The petrol trickles from the tank into the carburettor, and is kept at a constant level by means of a float which acts in a very similar way to the ballcock of a water cistern.
The carburettor is connected to the cylinder of the engine by another pipe, and there is valve which is opened by the engine itself and is closed by a spring. By an ingenious contrivance the valve is opened when the piston moves out of the cylinder, and a vacuum is created behind it and in the carburettor. This carries a fine spray of petrol to be sucked up through the nozzle. Air is also sucked into the carburettor, and the mixture of air and petrol spray produces an inflammable vapour which is drawn straight into the cylinder of the engine.
As soon as the piston moves back, the inlet valve is automatically closed and the vapour is compressed into the top of the cylinder. This is exploded by an electric spark, which is passed between two points inside the cylinder, and the force of the explosion drives the piston outwards again. On its return the "exhaust" or burnt gases are driven out through another valve, known as the "exhaust" valve.
Whether the engine has two, four, or six cylinders, the car is propelled in a similar way for all the pistons assist in turning one shaft, called the engine shaft, which runs along the centre of the car to the back axle.
The rapid explosions in the cylinder produce great heat, and the cylinders are kept cool by circulating water round them. When the water has become very hot it passes through a number of pipes, called the "radiator", placed in front of the car; the cold air rushing between the coils cools the water, so that it can be used over and over again.
No water is needed for the engine of a motor cycle. You will notice that the cylinders are enclosed by wide rings of metal, and these rings are quite sufficient to radiate the heat as quickly as it is generated.
We have seen that a very important part of the internal-combustion engine, as used on the motor-car, is the radiator, which prevents the engine from becoming overheated and thus ceasing to work. The higher the speed at which the engine runs the hotter does it become, and the greater the necessity for an efficient cooling apparatus.
But the motor on an aeroplane has to do much harder work than the motor used for driving the motor-car, while it maintains a much higher speed. Thus there is an even greater tendency for it to become overheated; and the great problem which inventors of aeroplane engines have had to face is the construction of a light but powerful engine equipped with some apparatus for keeping it cool.
Many different forms of aeroplane engines have been invented during the last few years. Some inventors preferred the radiator system of cooling the engine, but the tank containing the water, and the radiator itself, added considerably to the weight of the motor, and this, of course, was a serious drawback to its employment.
But in 1909 there appeared a most ingeniously-constructed engine which was destined to take a very prominent part in the progress of aviation. This was the famous "Gnome" engine, by means of which races almost innumerable have been won, and amazing records established.
We have already referred to the engine shaft of the motor-car, which is revolved by the pistons of the various fixed cylinders. In all aeroplane engines which had appeared before the Gnome the same principle of construction had been adopted; that is to say, the cylinders were fixed, and the engine shaft revolved.
But in the Gnome engine the reverse order of things takes place; the shaft is fixed, and the cylinders fly round it at a tremendous speed. Thus the rapid whirl in the air keeps the engine cool, and cumbersome tanks and unwieldy radiators can be dispensed with. This arrangement enabled the engine to be made very light and yet be of greater horse-power than that attained by previously-existing engines.
A further very important characteristic of the rotary-cylinder engine is that no flywheel is used; in a stationary engine it has been found necessary to have a fly-wheel in addition to the propeller. The rotary-cylinder engine acts as its own fly-wheel, thus again saving considerable weight.
The new engine astonished experts when they first examined it, and all sorts of disasters to it were predicted. It was of such revolutionary design that wiseacres shook their heads and said that any pilot who used it would be constantly in trouble with it. But during the last few years it has passed from one triumph to another, commencing with a long-distance record established by Henri Farman at Rheims, in 1909. It has since been used with success by aviators all the world over. That in the Aerial Derby of 1913—which was flown over a course Of 94 miles around London—six of the eleven machines which took part in the race were fitted with Gnome engines, and victory was achieved by Mr. Gustav Hamel, who drove an 80-horse-power Gnome, is conclusive evidence of the high value of this engine in aviation.