IV
I have spoken, in describing the fixed-wing versus moving-wing battle, only of short air-lines, because I think the establishment of the successful short line will precede the establishment of the long.
It is argued that the saving in time effected by the flying-machine becomes valuable only in long journeys, so that no one would bother to go to an aerodrome and take an aeroplane in order to save half an hour or so, and that the train-service in England is so good that the aeroplane-service would be incapable of competing with it successfully. And, while the disadvantages of short air-services are magnified, the disadvantages of long air-services are forgotten or not appreciated.
At present a short journey of three or four hours by aeroplane is all that the average passenger can stand in comfort. There is no room for him to move about much in the present cabins, and the noise of the engines, wires, and airscrews is fatiguing to anyone not used to it. Moreover, the time-basis is not the only basis on which the traveller compares the merits of the means of travel at his disposal. The ship provides its passengers with social intercourse and a high degree of comfort. A long journey by sea is usually a pleasant, invigorating experience. On a journey by air, on the other hand, the passengers get no fresh air, they have no opportunity for making friends, for conversation, dancing, games, or any other of the fascinating trivialities which flavour life on board a passenger-steamer. The traveller offered the use of a long distance air-line, therefore, is invited to choose between, perhaps, three days discomfort and isolation in the cramped cabin of an aeroplane and three weeks social pleasure and invigorating laziness on board ship.
Now the disadvantages which attend long-distance air-travel in modern type machines are due almost entirely to the small size of passenger aircraft when compared with ships. The aeroplane will not be successful as a long-distance vehicle until it can give its passengers most of the pleasures they would get on board ship. It will not be able to give its passengers even a small fraction of those pleasures until it is as large as or nearly as large as the ship.
The pleasures of long-distance travel vary almost directly as the size of the vehicle. Can the aeroplane ever be made so large that it can offer its passengers the space and freedom of even a small-sized passenger-boat?
I do not think the aeroplane can ever become sufficiently big, but I do think the seaplane or the flying-boat can and will become sufficiently big to offer that degree of space and freedom.
I believe that aircraft will begin to compete successfully with boat and train in carrying the merchandize and passengers of the world only after the coming of the era of the hydro-aeroplane (I use this word to include both seaplane and flying-boat).
The longest flight ever made in one machine was made in a hydro-aeroplane. The largest machines ever built are hydro-aeroplanes. The heavier-than-air machines carrying the greatest weight are hydro-aeroplanes. I am confident that the era of the hydro-aeroplane will come, and that, until it comes, aircraft will not compete successfully with boat and train.
I have based my first conclusion, that the moving-wing aeroplane will become a powerful competitor of the fixed-wing aeroplane for short-distance air-transport, on flexibility. The moving-wing machine can go from door to door, no matter if the journey is partly over the sea and partly over the land. I base my second conclusion, that the hydro-aeroplane will become the pre-eminent vehicle for long-distance air-transport, on size. The hydro-aeroplane can be built as large as may be required.
If people are to journey even for one day in the same vehicle, they need space and freedom of movement. They need wide promenade decks, lounges, restaurants, cabins, smoking-rooms. They cannot be confined to a single basket chair.
For long-distance air-transport the sardine-theory so popular with our London transport controllers must be abandoned. The sardine-theory must be recognized for what it is, a system of getting more money out of the passenger by increasing his discomfort. The more you squeeze the passenger, the more the money oozes out of him.
The aeroplane cannot, I think, become very much larger than the largest machines of to-day because the support of much greater weights on the landing-wheels becomes difficult. At present there are machines in which each landing-wheel must carry 6 tons. If the weight were much increased, the three-point suspension on wheels and tail-skid would become impracticable. The provision of a caterpillar landing-gear and of aerodromes with prepared surfaces might be possible and might assist matters if machines, say eight or nine times the size of the present, were contemplated. But, to obtain the comfort required (and given by the ship) on a long voyage, the machines would need to be some fifty or a hundred times the size of the largest existing types. When those sizes were reached, the problems of supporting the weight on the ground and of manoeuvring on the ground, taking off, and landing would become exceedingly difficult to solve.
Yet these problems are comparatively easy to solve in the large hydro-aeroplane. A large hydro-aeroplane with a high wing-loading could, if necessary, use the open sea as its aerodrome. Since the problem of the forced landing would definitely have been overcome by the power-unit arrangement, the large hydro-aeroplane would fly over land or sea. Its stations would be sea ports, lakes, or wide rivers.
The aeroplane both with moving and fixed wing will certainly grow in size; but nothing seems to me to indicate that it will be able to keep pace with the growth of the hydro-aeroplane. The growth of the hydro-aeroplane is foreshadowed in a French machine and a German machine which have appeared recently. The hundred-passenger hydro-aeroplane is a proven possibility. I can see no insuperable obstacle to the eventual arrival of the 1,000-passenger or the 2,000-passenger hydro-aeroplane. Moreover, the fog-landing problem is easier to solve in the sea-going than in the land-going fixed-wing aircraft. Good automatic landing devices are more easily designed for hydro-aeroplanes than for aeroplanes.
Mr O. E. Simmonds, of the design staff of a firm of British flying-boat constructors, said: “The largest successful flying-boats yet built have weighed about 30,000 lbs. I shall certainly feel that progress has been inordinately slow if we have not constructed a boat of 100,000 lbs. gross weight by the end of the next decade.”
The first real air-liner, carrying some five or six hundred passengers, will probably appear after or towards the end of the battle between fixed and moving-wing machines. And it will be a flying-boat. The unsolved problems attending high-altitude air-transport seem to be so difficult that I am inclined to believe that high altitude transport will not become a regular method in this generation.
The possibilities of machines capable of travelling at immense speeds in the rarefied air at a height of 15 miles or so from the ground are attractive. But, if a forecast is to be based on research-work actually accomplished at the time, it is made, then high-altitude flying must be excluded.
Among the problems which high-altitude flying involves and which seem to postpone its arrival to the distant future are: the infinitely variable pitch airscrew, the light, positive, infinitely variable gear (without ratchet final drive), the sealed cabin with self-contained ventilating system, the engine altitude supercharger, and the variable camber-wing. Among these the Leitner automatic infinitely variable pitch airscrew is one of the most interesting inventions ever made in airscrew design, but it is at present in its earliest stages. The Constantinesco torque-converter, which is an automatic infinitely variable gear, might be adaptable to aircraft. The sealed cabin presents great practical difficulties, as does the variable camber-wing.
From this brief parenthesis the difficulties of high-altitude transport will be apparent. It is almost certain to come, but its day is likely to be distant, and for that reason I have concentrated on possibilities less remote.
Now that the long and short distance air-liners have been dealt with, I will give a brief sketch of how the traveller will use these vehicles. If Mr X, who lives at Hampstead, desires to go to Melbourne, Australia, he will first pile his luggage onto a taxi and drive to the terminus of some moving-wing aircraft line. This terminus will be close to the centre of London: A highly developed moving-wing aircraft will take him to the coast. The machine will land on the quay beside which will float a flying-boat express. This machine will be a fixed-wing flying-boat of about 1,000 tons. It will be a monoplane, the wings growing from the hull at a sharp dihedral angle and then curving down until they are horizontal.
The engines will be particularly interesting. Most designers, even now, are endeavouring to eliminate reciprocating motion in petrol-engines. The trend of thought is towards substituting the sleeve-valve for the poppet-valve and towards increasing the number of cylinders. More and more inventors “invent” gas-turbines. Their engines have had varying degrees of failure, although a few, the Jean Mély turbine among them, are reported to have gained a measure of success. One of these inventors will soon be completely successful. The movement towards the rotary gas-engine is too vigorous and too general to remain for ever unfruitful. The gas-turbine will be the aero-engine of the future. It will be cooled by an evaporative system.
One pound of water carries only 20 B.T.U., whereas 1 lb. of steam carries 966 B.T.U. Wing Commander Cave-Browne-Cave, in a paper read before the Royal Aeronautical Society, drew attention to the advantages for aircraft of evaporative engine cooling. He said: “By far the lightest way of conveying heat is as the latent heat of steam.” On test a standard aero-engine gave the same power and fuel-consumption with evaporative as with water-cooling. The greatest advantage will accrue in reduction of resistance. Panels in the aircraft surface will receive heat in the steam and thus the drag caused by water-radiators even of the wing or strut type, or air-cooled cylinders will be eliminated. The evaporative cooling system will not freeze up at the highest altitudes: it will probably maintain the engine at a more even working temperature than an air-cooling system, and the steam will provide a suitable means of heating the passenger cabins and pilot’s cockpit and of cooking.
The flying-boat to which Mr X is now having his luggage transferred then, has twelve evaporative-cooled gas-turbines housed in the wings, six on the starboard and six on the port side. Eight of them will drive tractor airscrews and four will drive propellers through torque-converters. There may be a system of concentrating the whole engine-power at three or four airscrews.
The entire machine, including the wing-coverings, will be built of metal. “I cannot conceive”, said M. Dewoitine, the French designer, “that the ultimate aeroplane can be in anything else but metal, in the same way that metal ships to-day completely replace the wooden ships of days gone by.” The living quarters in the hull would be arranged on labour-saving lines. The passengers would have drawing-room, dining-saloon, lounge, and promenade deck. The promenade deck on a long-distance air-express will be different from the promenade deck on a liner. It will be enclosed in the hull and will be lighted by a transparent roof and sides.
Mr X finds his cabin arranged in much the same way as in a ship, and, having settled his things, he goes up to the lounge, where the other passengers are congregating. A few minutes later, with a faint hum, two of the tractor-airscrews begin to revolve, and the flying-boat moves slowly away from the quay. Two more airscrews start revolving, and the machine, having taxied out, turns into wind. It pauses a moment as if it were taking breath, then the twelve air-screws spin faster and faster until they appear as discs of light. The machine moves forward heavily, a solid mass of metal, with the passengers watching from the windows of the promenade deck. It lumbers through the water, but throws up but little spray. Then it seems to stretch itself, throw back its head, and to rise bodily out of the water until it runs on the surface of—instead of in—the water. Already it appears lighter and less clumsy. Finally, after giving the water two or three parting pats, it takes to the air and, in spite of its great mass, instantly becomes an agile, graceful flying-machine.
The usual amusements, the usual eating, drinking, reading, and talking will employ the passengers’ time in the air. For the daily round goes on in much the same way ashore, afloat or aflight. The night flying is exhilarating, although there is, of course, almost no sense of speed. Though the sea is rough, the machine, at 4,000 ft. is as steady as a rock. As the first stopping place rushes towards the machine, the hum of the engines alters note and the machine dips in a gentle glide. The mouth of a river, with shipping on it and two more flying-boat expresses lying at a quay a short way up the river, comes into view. The machine wheels round and glides closer and closer to the water. Four of the airscrews give a short burst of speed, and then the hull rips the surface of the water with a hiss.
Soon afterwards Mr X has said good-bye to his voyage acquaintances who are disembarking, and the machine is off on the next stage.
The success of the large, long-distance flying-boat will mark the beginning of the concentration of fixed-wing machines on long-distance routes and the concentration of moving-wing machines on short, distance routes. The fixed-wing machine, finding it has no rival in the large flying-boat type and finding that it has a strong rival in the comparatively small land-going type (that rival being the moving-wing machine) will gradually remove itself from the short air-lines. The position will then be that all short air-lines are run by moving-wing land-going aircraft while all long air-lines are run by fixed-wing sea-going aircraft.
The real air-liner, as distinct from the commercial flying soap-box of to-day, will be an immense sea-going air-vessel. It will be a self-contained town offering greater attractions to the pleasure-seeker than any other kind of small town. When that machine makes its appearance the Air Age will have begun.