DestinationMiles AwayArrival TimeBrighton5010.25a.m.Portsmouth6010.30a.m.Birmingham11310.57a.m.Leeds18811.34a.m.Liverpool20211.41a.m.Holyhead26212.11p.m.Edinburgh4001.20p.m.Aberdeen5402.30p.m.
What would become of the records established in the “Race to the North” and by American “fliers”?
And what about continental travel?
Assuming that the Channel Tunnel is built—perhaps a rather large assumption—Paris will be at our very doors. A commercial traveller will step into the lightning express at London, sleep for two hours and twenty-four minutes and wake, refreshed, to find the blue-smocked Paris porters bawling in his ear. Or even if we prefer to keep the “little silver streak” free from subterranean burrows, he will be able to catch the swift turbine steamers—of which more anon—at Dover, slip across to Calais in half-an-hour, and be at the French capital within four hours of quitting London. And if M. Romanoff’s standard be reached, the latest thing in hats despatched fromParis at noon may be worn in Regent Street before two o’clock.
Such speeds would indeed produce a revolution in travelling comparable to the substitution of the steam locomotive for the stage coach. As has been pithily said, the effect of steam was to make the bulk of population travel, whereas they had never travelled before, but the effect of the electric railway will be to make those who travel travel much further and much oftener.
In the year 1836 theSirius, a paddle-wheel vessel, crossed the Atlantic from Cork Harbour to New York in nineteen days. Contrast with the first steam-passage from the Old World to the New a return journey of theDeutschland, a North German liner, which in 1900 averaged over twenty-seven miles an hour between Sandy Hook and Plymouth, accomplishing the whole distance in the record time of five days seven hours thirty-eight minutes.
This growth of speed is even more remarkable than might appear from the mere comparison of figures. A body moving through water is so retarded by the inertia and friction of the fluid that to quicken its pace a force quite out of proportion to the increase of velocity must be exerted. The proportion cannot be reduced to an exact formula, but under certain conditions the speed and the power required advance in the ratio of their cubes; that is, to double a given rate of progress eight times the driving-power is needed; to treble it, twenty-seven times.
The mechanism of our fast modern vessels is in every way as superior to that which moved theSirius, as the beautifully-adjusted safety cycle is to the clumsy “boneshaker” which passed for a wonder among our grandfathers. A great improvement has also taken place in the art of building ships on lines calculated to offer least resistance to the water, and at the same time afford a good carrying capacity. The big liner, with its knife-edged bow and tapering hull, is by its shape alone eloquent of the high speed which has earned it the title of Ocean Greyhound; and as for the fastest craft of all, torpedo-destroyers, their designers seem to have kept in mind Euclid’s definition of a line—length without breadth. But whatever its shape, boat or ship may not shake itself free of Nature’s laws. Her restraining hand lies heavy upon it. A single man paddles his weight-carrying dinghy along easily at four miles an hour; eight men in the pink of condition, after arduous training, cannot urge their light, slender, racing shell more than twelve miles in the same time.
To understand how mail boats and “destroyers” attain, despite the enormous resistance of water, velocities that would shame many a train-service, we have only to visit the stokeholds and engine-rooms of our sea expresses and note the many devices of marine engineers by which fuel is converted into speed.
We enter the stokehold through air-locks, closing one door before we can open the other, and find ourselves among sweating, grimy men, stripped tothe waist. As though life itself depended upon it they shovel coal into the rapacious maws of furnaces glowing with a dazzling glare under the “forced-draught” sent down into the hold by the fans whirling overhead. The ignited furnace gases on their way to the outer air surrender a portion of their heat to the water from which they are separated by a skin of steel. Two kinds of marine boiler are used—the fire-tube and the water-tube. In fire-tube boilers the fire passes inside the tubes and the water outside; in water-tube boilers the reverse is the case, the crown and sides of the furnace being composed of sheaves of small parallel pipes through which water circulates. The latter type, as generating steam very quickly, and being able to bear very high pressures, is most often found in war vessels of all kinds. The quality sought in boiler construction is that the heating surface should be very large in proportion to the quantity of water to be heated. Special coal, anthracite or Welsh, is used in the navy on account of its great heating power and freedom from smoke; experiments have also been made with crude petroleum, or liquid fuel, which can be more quickly put on board than coal, requires the services of fewer stokers, and may be stored in odd corners unavailable as coal bunkers.
From the boiler the steam passes to the engine-room, whither we will follow it. We are now in a bewildering maze of clanking, whirling machinery;our noses offended by the reek of oil, our ears deafened by the uproar of the moving metal, our eyes wearied by the efforts to follow the motions of the cranks and rods.
On either side of us is ranged a series of three or perhaps even four cylinders, of increasing size. The smallest, known as the high-pressure cylinder, receives steam direct from the boiler. It takes in through a slide-valve a supply for a stroke; its piston is driven from end to end; the piston-rod flies through the cylinder-end and transmits a rotary motion to a crank by means of a connecting-rod. The half-expanded steam is then ejected, not into the air as would happen on a locomotive, but into the next cylinder, which has a larger piston to compensate the reduction of pressure. Number two served, the steam does duty a third time in number three, and perhaps yet a fourth time before it reaches the condensers, where its sudden conversion into water by cold produces a vacuum suction in the last cylinder of the series. The secret of a marine engine’s strength and economy lies then in its treatment of the steam, which, like clothes in a numerous family, is not thought to have served its purpose till it has been used over and over again.
Reciprocating (i.e.cylinder) engines, though brought to a high pitch of efficiency, have grave disadvantages, the greatest among which is the annoyance caused by their intense vibration to allpersons in the vessel. A revolving body that is not exactly balanced runs unequally, and transmits a tremor to anything with which it may be in contact. Turn a cycle upside down and revolve the driving-wheel rapidly by means of the pedal. The whole machine soon begins to tremble violently, and dance up and down on the saddle springs, because one part of the wheel is heavier than the rest, the mere weight of the air-valve being sufficient to disturb the balance. Now consider what happens in the engine-room of high-powered vessels. On destroyers the screws make 400 revolutions a minute. That is to say, all the momentum of the pistons, cranks, rods, and valves (weighing tons), has to be arrested thirteen or fourteen times every second. However well the moving parts may be balanced, the vibration is felt from stem to stern of the vessel. Even on luxuriously-appointed liners, with engines running at a far slower speed, the throbbing of the screw (i.e.engines) is only too noticeable and productive of discomfort.
We shall be told, perhaps, that vibration is a necessary consequence of speed. This is true enough of all vehicles, such as railway trains, motor-cars, cycles, which are shaken by the irregularities of the unyielding surface over which they run, but does not apply universally to ships and boats. A sail or oar-propelled craft may be entirely free from vibration, whatever its speed, as the motions arising from waterare usually slow and deliberate. In fact, water in its calmer moods is an ideal medium to travel on, and the trouble begins only with the introduction of steam as motive force.
But even steam may be robbed of its power to annoy us. The steam-turbine has arrived. It works a screw propeller as smoothly as a dynamo, and at a speed that no cylinder engine could maintain for a minute without shaking itself to pieces.
The steam-turbine is most closely connected with the name of the Hon. Charles Parsons, son of Lord Rosse, the famous astronomer. He was the first to show, in his speedy littleTurbinia, the possibilities of the turbine when applied to steam navigation. The results have been such as to attract the attention of the whole shipbuilding world.
The principle of the turbine is seen in the ordinary windmill. To an axle revolving in a stationary bearing are attached vanes which oppose a current of air, water, or steam, at an angle to its course, and by it are moved sideways through a circular path. Mr. Parsons’ turbine has of course been specially adapted for the action of steam. It consists of a cylindrical, air-tight chest, inside which rotates a drum, fitted round its circumference with rows of curved vanes. The chest itself has fixed immovably to its inner side a corresponding number of vane rings, alternating with those on the drum, and so arranged as to deflect the steam on to the latter atthe most efficient angle. The diameter of the chest and drum is not constant, but increases towards the exhaust end, in order to give the expanding and weakening steam a larger leverage as it proceeds.
The steam entering the chest from the boiler at a pressure of some hundreds of pounds to the square inch strikes the first set of vanes on the drum, passes them and meets the first set of chest-vanes, is turned from its course on to the second set of drum-vanes, and so on to the other end of the chest. Its power arises entirely from its expansive velocity, which, rather than turn a number of sharp corners, will, if possible, compel the obstruction to move out of its way. If that obstruction be from any cause difficult to stir, the steam must pass round it until its pressure overcomes the inertia. Consequently the turbine differs from the cylinder engine in this respect, that steamcanpass through and be wasted without doing any work at all, whereas, unless the gear of a cylinder moves, and power is exerted, all steam ways are closed, and there is no waste. In practice, therefore, it is found that a turbine is most effective when running at high speed.
The first steam-turbines were used to drive dynamos. In 1884 Mr. Parsons made a turbine in which fifteen wheels of increasing size moved at the astonishing rate of 300 revolutions per second, and developed 10 horse-power. In 1888 followed a 120 horse-power turbine, and in 1892 one of 2000 horse-power, provided with a condenser to produce suction. So successful were these steam fans for electrical work, pumping water and ventilating mines, that Mr. Parsons determined to test them as a means of propelling ships. A small vessel 100 feet long and 9 feet in beam was fitted with three turbines—high, medium, and low pressure, of a total 2000 horse-power—a proportion of motive force to tonnage hitherto not approached. Yet when tried over the test course theTurbinia, as the boat was fitly named, ran in a most disappointing fashion. The screws revolvedtoo fast, producing what is known ascavitation, or the scooping out of the water by the screws, so that they moved in a partial vacuum and utilised only a fraction of their force, from lack of anything to “bite” on. This defect was remedied by employing screws of coarser pitch and larger blade area, three of which were attached to each of the three propeller shafts. On a second trial theTurbiniaattained 32-3/4 knots over the “measured mile,” and later the astonishing speed of forty miles an hour, or double that of the fast Channel packets. At the Spithead Review in 1897 one of the most interesting sights was the little nimbleTurbiniarushing up and down the rows of majestic warships at the rate of an express train.
H.M.S. Torpedo Destroyer “Viper.” This vessel was the fastest afloat, attaining the enormous speed of 41 miles an hour. The screws were worked by turbines, giving 11,000 horse-power. She was wrecked on Alderney during the Naval Manœuvres of 1901.
H.M.S. Torpedo Destroyer “Viper.” This vessel was the fastest afloat, attaining the enormous speed of 41 miles an hour. The screws were worked by turbines, giving 11,000 horse-power. She was wrecked on Alderney during the Naval Manœuvres of 1901.
After this success Mr. Parsons erected works at Wallsend-on-Tyne for the special manufacture of turbines. The Admiralty soon placed with him anorder for a torpedo-destroyer—theViper—of 350 tons; which on its trial trip exceeded forty-one miles an hour at an estimated horse-power (11,000) equalling that of our largest battleships. A sister vessel, theCobra, of like size, proved as speedy. Misfortune, however, overtook both destroyers. TheViperwas wrecked August 3, 1901, on the coast of Alderney during the autumn naval manœuvres, and theCobrafoundered in a severe storm on September 12 of the same year in the North Sea. This double disaster casts no reflections on the turbine engines; being attributed to fog in the one case and to structural weakness in the other. The Admiralty has since ordered another turbine destroyer, and before many years are past we shall probably see all the great naval powers providing themselves with like craft to act as the “eyes of the fleet,” and travel at even higher speeds than those of theViperandCobra.
The turbine has been applied to mercantile as well as warlike purposes. There is at the present time a turbine-propelled steamer, theKing Edward, running in the Clyde on the Fairlie-Campbelltown route. This vessel, 250 feet long, 30 broad, 18 deep, contains three turbines. In each the steam is expanded fivefold, so that by the time it passes into the condensers it occupies 125 times its boiler volume. (On theViperthe steam entered the turbine through an inlet eight inches in diameter, andleft them by an outlet four feet square.) In cylinder engines thirty-fold expansion is considered a high ratio; hence the turbine extracts a great deal more power in proportion from its steam. As a turbine cannot be reversed, special turbines are attached to the two outside of the three propeller shafts to drive the vessel astern. The steamer attained 20-1/2 knots over the “Skelmorlie mile” in fair and calm weather, with 3500 horse-power produced at the turbines. TheKing Edwardis thus the fastest by two or three knots of all the Clyde steamers, as she is the most comfortable. We are assured that as far as the turbines are concerned it is impossible by placing the hand upon the steam-chest to tell whether the drum inside is revolving or not!
Every marine engine is judged by its economy in the consumption of coal. Except in times of national peril extra speed produced by an extravagant use of fuel would be severely avoided by all owners and captains of ships. At low speeds the turbine develops less power than cylinders from the same amount of steam, but when working at high velocity it gives at least equal results. A careful record kept by the managers of the Caledonian Steamship Company compares theKing Edwardwith theDuchess of Hamilton, a paddle steamer of equal tonnage used on the same route and built by the same firm. The record shows that though the paddle-boat ran a fraction of a mile further forevery ton of coal burnt in the furnaces, theKing Edwardaveraged two knots an hour faster, a superiority of speed quite out of proportion to the slight excess of fuel. Were theDuchessdriven at 18-1/2 knots instead of 16-1/2 her coal bill would far exceed that of the turbine.
As an outcome of these first trials the Caledonian Company are launching a second turbine vessel. Three high-speed turbine yachts are also on the stocks; one of 700 tons, another of 1500 tons, and a third of 170 tons. The last, the property of Colonel M’Calmont, is designed for a speed of twenty-four knots.
Mr. Parsons claims for his system the following advantages: Greatly increased speed; increased carrying power of coal; economy in coal consumption; increased facilities for navigating shallow waters; greater stability of vessels; reduced weight of machinery (the turbines of theKing Edwardweigh but one-half of cylinders required to give the same power); cheapness of attending the machinery; absence of vibration, lessening wear and tear of the ship’s hull and assisting the accurate training of guns; lowered centre of gravity in the vessel, and consequent greater safety during times of war.
The inventor has suggested a cruiser of 2800 tons, engined up to 80,000 horse-power, to yield a speed of forty-four knots (about fifty miles) anhour. Figures such as these suggest that we may be on the eve of a revolution of ocean travel comparable to that made by the substitution of steam for wind power. Whether the steam-turbine will make for increased speed all round, or for greater economy, remains to be seen; but we may be assured of a higher degree of comfort. We can easily believe that improvements will follow in this as in other mechanical contrivances, and that the turbine’s efficiency has not yet reached a maximum; and even if our ocean expresses, naval and mercantile, do not attain the one-mile-a-minute standard, which is still regarded as creditable to the fastest methods of land locomotion, we look forward to a time in the near future when much higher speeds will prevail, and the tedium of long voyages be greatly shortened. Already there is talk of a service which shall reduce the trans-Atlantic journey to three-and-a-half days. The means are at hand to make it a fact.
Note.—In the recently-launched turbine destroyerVeloxa novel feature is the introduction of ordinary reciprocating engines fitted in conjunction with the steam turbines. These engines are of triple-compound type, and are coupled direct to the main turbines. They take steam from the boilers direct and exhaust into the high-pressure turbine. These reciprocating engines are for use at cruising speeds. When higher power is needed the steam will be admitted to the turbines direct from the boilers, and the cylinders be thrown out of gear.
Note.—In the recently-launched turbine destroyerVeloxa novel feature is the introduction of ordinary reciprocating engines fitted in conjunction with the steam turbines. These engines are of triple-compound type, and are coupled direct to the main turbines. They take steam from the boilers direct and exhaust into the high-pressure turbine. These reciprocating engines are for use at cruising speeds. When higher power is needed the steam will be admitted to the turbines direct from the boilers, and the cylinders be thrown out of gear.
Few, if any, problems have so strongly influenced the imagination and exercised the ingenuity of mankind as that of aërial navigation. There is something in our nature that rebels against being condemned to the condition of “featherless bipeds” when birds, bats, and even minute insects have the whole realm of air and the wide heavens open to them. Who has not, like Solomon, pondered upon “the way of a bird in the air” with feelings of envy and regret that he is chained to earth by his gross body; contrasting our laboured movements from point to point of the earth’s surface with the easy gliding of the feathered traveller? The unrealised wish has found expression in legends of Dædalus, Pegasus, in the “flying carpet” of the fairy tale, and in the pages of Jules Verne, in which last the adventurous Robur on his “Clipper of the Clouds” anticipates the future in a most startling fashion.
Aeromobilism—to use its most modern title—is regarded by the crowd as the mechanical counterpart of the Philosopher’s Stone or the Elixir of Life; a highly desirable but unattainablething. At times this incredulity is transformed by highly-coloured press reports into an equally unreasonable readiness to believe that the conquest of the air is completed, followed by a feeling of irritation that facts are not as they were represented in print.
The proper attitude is of course half-way between these extremes. Reflection will show us that money, time, and life itself would not have been freely and ungrudgingly given or risked by many men—hard-headed, practical men among them—in pursuit of a Will-o’-the-Wisp, especially in a century when scientific calculation tends always to calm down any too imaginative scheme. The existing state of the aërial problem may be compared to that of a railway truck which an insufficient number of men are trying to move. Ten men may make no impression on it, though they are putting out all their strength. Yet the arrival of an eleventh may enable them to overcome the truck’s inertia and move it at an increasing pace.
Every new discovery of the scientific application of power brings us nearer to the day when the truck will move. We have metals of wonderful strength in proportion to their weight; pigmy motors containing the force of giants; a huge fund of mechanical experience to draw upon; in fact, to paraphrase the Jingo song, “We’ve got the things, we’ve got the men, we’ve got themoney too”—but we haven’t as yet got the machine that can mock the bird like the flying express mocks the strength and speed of horses.
The reason of this is not far to seek. The difficulties attending the creation of a successful flying-machine are immense, some unique, not being found in aquatic and terrestrial locomotion.
In the first place, the airship, flying-machine, aerostat, or whatever we please to call it, must not merely move, but also lift itself. Neither a ship nor a locomotive is called upon to do this. Its ability to lift itself must depend upon either the employment of large balloons or upon sheer power. In the first case the balloon will, by reason of its size, be unmanageable in a high wind; in the second case, a breakdown in the machinery would probably prove fatal.
Even supposing that our aerostat can lift itself successfully, we encounter the difficulties connected with steering in a medium traversed by ever-shifting currents of air, which demands of the helmsman a caution and capacity seldom required on land or water. Add to these the difficulties of leaving the ground and alighting safely upon it; and, what is more serious than all, the fact that though success can be attained only by experiment, experiment is in this case extremely expensive and risky, any failure often resulting in total ruin of the machine, and sometimes in loss of life. Thelist of those who have perished in the search for the power of flight is a very long one.
Yet in spite of these obstacles determined attempts have been and are being made to conquer the air. Men in a position to judge are confident that the day of conquest is not very far distant, and that the next generation may be as familiar with aerostats as we with motor-cars. Speculation as to the future is, however, here less profitable than a consideration of what has been already done in the direction of collecting forces for the final victory.
To begin at the beginning, we see that experimenters must be divided into two great classes: those who pin their faith to airships lighter than air,e.g.Santos Dumont, Zeppelin, Roze; and those who have small respect for balloons, and see the ideal air-craft in amachinelifted entirely by means of power and surfaces pressing the air after the manner of a kite. Sir Hiram Maxim and Professor S. P. Langley, Mr. Lawrence Hargrave, and Mr. Sydney Hollands are eminent members of the latter cult.
As soon as we get on the topic of steerable balloons the name of Mr. Santos Dumont looms large. But before dealing with his exploits we may notice the airship of Count Zeppelin, an ingenious and costly structure that was tested over Lake Constance in 1900.
The balloon was built in a large wooden shed,450 by 78 by 66 feet, that floated on the lake on ninety pontoons. The shed alone cost over £10,000.
The balloon itself was nearly 400 feet long, with a cylindrical diameter of 39 feet, except at its ends, which were conical, to offer as little resistance as possible to the air. Externally it afforded the appearance of a single-compartment bag, but in reality it was divided into seventeen parts, each gas-tight, so that an accident to one part of the fabric should not imperil the whole.
A framework of aluminium rods and rings gave the bag a partial rigidity.
Its capacity was 12,000 cubic yards of hydrogen gas, which, as our readers doubtless know, is much lighter though more expensive than ordinary coal-gas; each inflation costing several hundreds of pounds.
Under the balloon hung two cars of aluminium, the motors and the screws; and also a great sliding weight of 600 lbs. for altering the “tip” of the airship; and rudders to steer its course.
On June 30 a great number of scientific men and experts assembled to witness the behaviour of a balloon which had cost £20,000. For two days wind prevented a start, but on July 2, at 7.30p.m., the balloon emerged from its shed, and at eight o’clock commenced its first journey, with and against a light easterly wind for a distance of three and a half miles. A mishap to the steering-gear occurred earlyin the trip, and prevented the airship appearing to advantage, but a landing was effected easily and safely. In the following October the Count made a second attempt, returning against a wind blowing at three yards a second, or rather more than six miles an hour.
The air-ship of M. Santos-Dumont rounding the Eiffel Tower during its successful run for the Henri Deutsch Prize.
The air-ship of M. Santos-Dumont rounding the Eiffel Tower during its successful run for the Henri Deutsch Prize.
Owing to lack of funds the fate of the “Great Eastern” has overtaken the Zeppelin airship—to be broken up, and the parts sold.
The aged Count had demonstrated that a petroleum motor could be used in the neighbourhood of gas without danger. It was, however, reserved for a younger man to give a more decided proof of the steerableness of a balloon.
In 1900 M. Henri Deutsch, a member of the French Aero Club, founded a prize of £4000, to win which a competitor must start from the Aero Club Park, near the Seine in Paris, sail to and round the Eiffel Tower, and be back at the starting-point within a time-limit of half-an-hour.
M. Santos Dumont, a wealthy and plucky young Brazilian, had, previously to this offer, made several successful journeys in motor balloons in the neighbourhood of the Eiffel Tower. He therefore determined to make a bid for the prize with a specially constructed balloon “Santos Dumont V.” The third unsuccessful attempt ended in disaster to the airship, which fell on to the houses, but fortunately without injuring its occupant.
Another balloon—“Santos Dumont VI.”—was then built. On Saturday, October 19th, M. Dumont reached the Tower in nine minutes and recrossed the starting line in 20-1/2 more minutes, thus complying with the conditions of the prize with half-a-minute to spare. A dispute, however, arose as to whether the prize had been actually won, some of the committee contending that the balloon should have come to earth within the half-hour, instead of merely passing overhead; but finally the well-merited prize was awarded to the determined young aeronaut.
The successful airship was of moderate proportions as compared with that of Count Zeppelin. The cigar-shaped bag was 112 feet long and 20 feet in diameter, holding 715 cubic yards of gas. M. Dumont showed originality in furnishing it with a smaller balloon inside, which could be pumped full of air so as to counteract any leakage in the external bag and keep it taut. The motor, on which everything depended, was a four-cylinder petrol-driven engine, furnished with “water-jackets” to prevent over-heating. The motor turned a large screw—made of silk and stretched over light frames—200 times a minute, giving a driving force of 175 lbs. Behind, a rudder directed the airship, and in front hung down a long rope suspended by one end that could be drawn towards the centre of the frame to alter the trim of the ship. Theaeronaut stood in a large wicker basket flanked on either side by bags of sand ballast. The fact that the motor, once stopped, could only be restarted by coming to earth again added an element of great uncertainty to all his trips; and on one occasion the mis-firing of one of the cylinders almost brought about a collision with the Eiffel Tower.
From Paris M. Dumont went to Monaco at the invitation of the prince of that principality, and cruised about over the bay in his balloon. His fresh scheme was to cross to Corsica, but it was brought to an abrupt conclusion by a leakage of gas, which precipitated balloon and balloonist into the sea. Dumont was rescued, and at once set about new projects, including a visit to the Crystal Palace, where he would have made a series of ascents this summer (1902) but for damage done to the silk of the gas-bag by its immersion in salt water and the other vicissitudes it had passed through. Dumont’s most important achievement has been, like that of Count Zeppelin, the application of the gasolene motor to aeromobilism. In proportion to its size this form of motor develops a large amount of energy, and its mechanism is comparatively simple—a matter of great moment to the aeronaut. He has also shown that under favourable conditions a balloon may be steered against a head-wind, though not with the certainty that is desirable before air travel can be pronounced an even moderately simple undertaking.The fact that many inventors, such as Dr. Barton, M. Roze, Henri Deutsch, are fitting motors to balloons in the hopes of solving the aërial problem shows that the airship has still a strong hold on the minds of men. But on reviewing the successes of such combinations of lifting and driving power it must be confessed, with all due respect to M. Dumont, that they are somewhat meagre, and do not show any great advance.
The question is whether these men are not working on wrong lines, and whether their utmost endeavours and those of their successors will ever produce anything more than a very semi-successful craft. Their efforts appear foredoomed to failure. As Sir Hiram Maxim has observed, a balloon by its very nature is light and fragile, it is a mere bubble. If it were possible to construct a motor to develop 100 horse-power for every pound of its weight, it would still be impossible to navigate a balloon against a wind of more than a certain strength. The mere energy of the motor would crush the gas-bag against the pressure of the wind, deform it, and render it unmanageable. Balloons therefore must be at the mercy of the wind, and obliged to submit to it under conditions not always in accordance with the wish of the aeronaut.
Sir Hiram in condemning the airship was ready with a substitute. On looking round on the patterns of Nature, he concluded that, inasmuch as all thingsthat fly are heavier than air, the problem of aërial navigation must be solved by a machine whose natural tendency is to fall to the ground, and which can be sustained only by the exertion of great force. Its very weight would enable it to withstand, at least to a far greater extent than the airship, the varying currents of the air.
The lifting principle must be analogous to that by which a kite is suspended. A kite is prevented from rising beyond a certain height by a string, and the pressure of the wind working against it at an angle tends to lift it, like a soft wedge continuously driven under it. In practice it makes no difference whether the kite be stationary in a wind or towed rapidly through a dead calm; the wedge-like action of the air remains the same.
Maxim decided upon constructing what was practically a huge compound kite driven by very powerful motors.
But before setting to work on the machine itself he made some useful experiments to determine the necessary size of his kites or aeroplanes, and the force requisite to move them.
He accordingly built a “whirling-table,” consisting of a long arm mounted on a strong pivot at one end, and driven by a 10 horse-power engine. To the free end, which described a circle of 200 feet in circumference, he attached small aeroplanes, and by means of delicate balances discovered that at40 miles an hour the aeroplane would lift 133 lbs. per horse-power, and at 60 miles per hour every square foot of surface sustained 8 lbs. weight. He, in common with other experimenters on the same lines, became aware of the fact that if it took a certain strain to suspend a stationary weight in the air,to advance it rapidly as well as to suspend it took a smaller strain. Now, as on sea and land, increased speed means a very rapid increase in the force required, this is a point in favour of the flying-machine. Professor Langley found that a brass plate weighing a pound, when whirled at great speed, was supported in the air by a pulling pressure of less than one ounce. And, of course, as the speed increased the plate became more nearly horizontal, offering less resistance to the air.
It is on this behaviour of the aeroplane that the hopes of Maxim and others have been based. The swiftly moving aeroplane, coming constantly on to fresh air, the inertia of which had not been disturbed, would resemble the skater who can at high speed traverse ice that would not bear him at rest.
Maxim next turned his attention to the construction of the aeroplanes and engines. He made a special machine for testing fabrics, to decide which would be most suitable for stretching over strong frames to form the planes. The fabric must be light, very strong, and offer small frictional resistance to the air. The testing-machine was fitted with anozzle, through which air was forced at a known pace on to the substance under trial, which met the air current at a certain angle and by means of indicators showed the strength of its “lift” or tendency to rise, and that of its “drift” or tendency to move horizontally in the direction of the air-current. A piece of tin, mounted at an angle of one in ten to the air-current, showed a “lift” of ten times its “drift.” This proportion was made the standard. Experiments conducted on velvet, plush, silk, cotton and woollen goods proved that the drift of crape was several times that of its lift, but that fine linen had a lift equal to nine times its drift; while a sample of Spencer’s balloon fabric was as good as tin.
Accordingly he selected this balloon fabric to stretch over light but strong frames. The stretching of the material was no easy matter, as uneven tension distorted it; but eventually the aeroplanes were completed, tight as drumheads.
The large or central plane was 50 feet wide and 40 long; on either side were auxiliary planes, five pairs; giving a total area of 5400 square feet.
The steam-engine built to give the motive power was perhaps the most interesting feature of the whole construction. Maxim employed steam in preference to any other power as being one with which he was most familiar, and yielding most force in proportion to the weight of the apparatus. He designed and constructed a pair of high-pressure compoundengines, the high-pressure cylinders 5 inches in diameter, the low-pressure 8 inches, and both 1 foot stroke. Steam was supplied to the high-pressure cylinders at 320 lbs. per square inch from a tubular boiler heated by a gasolene burner so powerful in its action as to raise the pressure from 100 to 200 lbs. in a minute. The total weight of the boiler, burner, and engines developing 350 horse-power was 2000 lbs., or about 6 lbs. per horse-power.
The two screw-propellers driven by the engine measured 17 feet 11 inches in diameter.
The completed flying-machine, weighing 7500 lbs., was mounted on a railway-truck of 9-foot gauge, in Baldwyn’s Park, Kent, not far from the gun-factories for which Sir Hiram is famous. Outside and parallel to the 9-foot track was a second track, 35 feet across, with a reversed rail, so that as soon as the machine should rise from the inner track long spars furnished with flanged wheels at their extremities should press against the under side of the outer track and prevent the machine from rising too far. Dynamometers, or instruments for measuring strains, were fitted to decide the driving and lifting power of the screws. Experiments proved that with the engines working at full power the screw-thrust against the air was 2200 lbs., and the lifting force of the aeroplanes 10,000 lbs., or 1500 in excess of the machine’s weight.
Everything being ready the machine was fastened to a dynamometer and steam run up until it strained at its tether with maximum power; when the moorings were suddenly released and it bounded forward at a terrific pace, so suddenly that some of the crew were flung violently down on to the platform. When a speed of 42 miles was reached the inner wheels left their track, and the outer wheels came into play. Unfortunately, the long 35-foot axletrees were too weak to bear the strain, and one of them broke. The upper track gave way, and for the first time in the history of the world a flying-machine actually left the ground fully equipped with engines, boiler, fuel, and a crew. The journey, however, was a short one, for part of the broken track fouled the screws, snapped a propeller blade and necessitated the shutting off of the steam, which done, the machine settled to earth, the wheels sinking into the sward and showing by the absence of any marks that it had come directly downwards and not run along the surface.
The inventor was prevented by other business, and by the want of a sufficiently large open space, from continuing his experiments, which had demonstrated that a large machine heavier than air could be made to lift itself and move at high speed. Misfortune alone prevented its true capacities being shown.
Another experimenter on similar lines, but on a less heroic scale than Sir Hiram Maxim, is ProfessorS. P. Langley, the secretary of the Smithsonian Institution, Washington. For sixteen years he has devoted himself to a persevering course of study of the flying-machine, and after oft-repeated failures has scored a decided success in his Aerodrome, which, though only a model, has made considerable flights. His researches have proved beyond doubt that the amount of energy required for flight is but one-fiftieth of what was formerly regarded as a minimum. A French mathematician had proved by figures that a swallow must develop the power of a horse to maintain its rapid flight! Professor Langley’s aerodrome has told a very different tale, affording another instance of the truth of the saying that an ounce of practice is worth a pound of theory.
A bird is nearly one thousand times heavier than the air it displaces. As a motor it develops huge power for its weight, and consumes a very large amount of fuel in doing so. An observant naturalist has calculated that the homely robin devours per diem, in proportion to its size, what would be to a man a sausage two hundred feet long and three inches thick! Any one who has watched birds pulling worms out of the garden lawn and swallowing them wholesale can readily credit this.
Professor Langley therefore concentrated himself on the production of an extremely light andat the same time powerful machine. Like Maxim, he turned to steam for motive-power, and by rigid economy of weight constructed an engine with boilers weighing 5 lbs., cylinders of 26 ozs., and an energy of 1 to 1-1/2 horse-power! Surely a masterpiece of mechanical workmanship! This he enclosed in a boat-shaped cover which hung from two pairs of aeroplanes 12-1/2 feet from tip to tip. The whole apparatus weighed nearly 30 lbs., of which one quarter represented the machinery. Experiments with smaller aerodromes warned the Professor that rigidity and balance were the two most difficult things to attain; also that the starting of the machine on its aerial course was far from an easy matter.
A soaring bird does not rise straight from the ground, but opens its wings and runs along the ground until the pressure of the air raises it sufficiently to give a full stroke of its pinions. Also it risesagainstthe wind to get the full benefit of its lifting force. Professor Langley hired a houseboat on the Potomac River, and on the top of it built an apparatus from which the aerodrome could be launched into space at high velocity.
On May 6, 1896, after a long wait for propitious weather, the aerodrome was despatched on a trial trip. It rose in the face of the wind and travelled for over half a mile at the rate of twenty-fivemiles an hour. The water and fuel being then exhausted it settled lightly on the water and was again launched. Its flight on both occasions was steady, and limited only by the rapid consumption of its power-producing elements. The Professor believes that larger machines would remain in the air for a long period and travel at speeds hitherto unknown to us.
In both the machines that we have considered the propulsive power was a screw. No counterpart of it is seen in Nature. This is not a valid argument against its employment, since no animal is furnished with driving-wheels, nor does any fish carry a revolving propeller in its tail. But some inventors are strongly in favour of copying Nature as regards the employment of wings. Mr. Sydney H. Hollands, an enthusiastic aeromobilist, has devised an ingenious cylinder-motor so arranged as to flap a pair of long wings, giving them a much stronger impulse on the down than on the up stroke. The pectoral muscles of a bird are reproduced by two strong springs which are extended by the upward motion of the wings and store up energy for the down-stroke. Close attention is also being paid to the actual shape of a bird’s wing, which is not flat but hollow on its under side, and at the front has a slightly downward dip. “Aerocurves” are therefore likely to supersede the “aeroplane,” for Nature would not have built bird’s wings as they are without an object. The theory of the aerocurve’s action is this: that the front of the wing, on striking the air, gives it a downwards motion, and if the wing were quite flat its rear portion would strike air already in motion, and therefore less buoyant. The curvature of a floating bird’s wings, which becomes more and more pronounced towards the rear, counteracts this yielding of the air by pressing harder upon it as it passes towards their hinder edge.