Traffic across the ocean or a great lake offers to air travel the best time-saving inducement. To connect two places separated by one hundred and fifty miles of water, an average steamship needs ten hours. A passenger on it must spend at least one night away from home, while transacting his business. An air passenger covers the same distance in one and one-half to two hours, and can return on the same day. For such transport the seaplane and the flying boat will have their chance.
Besides the carriage of passengers, mails and valuable freight, aviation will have many additional functions. Maps may be made and checked with absolute accuracy by means of aërial photography. Another important function of the aëroplane and the aërial camera is to explore and prospect undeveloped districts. In places remote from the ordinary facilities of civilization aircraft may be used for the discovery of fire, flood and lawlessness. Already the Canadian Northwest Mounted Police have captured wrongdoers by means of aëroplane patrols.
Aircraft offer particular advantages as carriers in regions where the natural obstacles on the ground prohibit railway or road transport. In Alaska valuable metals and furs are brought to civilization on sleds drawn by dogs, over paths that are circuitous and dangerous. They could be taken in safety, and with an immense saving of time, by aëroplanes fitted with skids suitable for landing on ice and snow. Again, copper is transported from mines in the Andes by llamas, which are slow and must jog over devious tracks. Aëroplanes could make the journey directly and speedily, from mine to coast, without regard to precipice, marsh or forest.
South America is likely to be a happy hunting-ground for aëronautical pioneers. The mountain-range of the Andes, which for hundreds of miles sharply divides America into two parts, gives aviation an incontestable opportunity. The eastern section of South America could be brought days nearer the western section by high-climbing aircraft, which would provide a pleasant alternative to the roundabout, uncomfortable journeying now necessary. The air mails between the two great commercial centers of South America—Rio de Janeiro and Buenos Ayres—should also save many days of valuable time. Many owners of ranches and plantations in the Argentine, Uruguay, Paraguay and Brazil are buying aëroplanes to bring their isolated, up-country properties in closer contact with the towns.
Asia and Africa have similar geographical problems, to which air traffic might find a ready solution. Each of these continents has enormous areas that, because of the absence of good railways, are either unproductive or much less productive than their resources warrant. A few of many such cases are Turkestan, Central Arabia, parts of China, Siberia, Thibet, and the whole of Central Africa. Most of these are rich in minerals. Meanwhile, aëroplanes have flown between the desert marts of Damascus and Bagdad in eight to ten hours. These cities are not yet linked by railroad and a camel caravan over the Syrian desert covers the same route in two weeks to a month. The same conditions apply to the Gobi desert.
So far I have dealt with the future of commercial aëronautics almost entirely in terms of heavier-than-air machines. These—land planes, seaplanes and flying boats—have at present a useful radius of non-stop flight confined to distances of under one thousand miles. The limitation must remain until changes in the basic principles of aëroplane construction are so altered as to give a much greater speed in proportion to fuel consumption. One such change may be the introduction of wings with variable camber. This, by permitting variations in the angle of incidence, would make possible a quick ascent at a steep inclination, and a very fast forward speed once the required height had been attained. The benefits from variable camber could be increased by the introduction of a propeller with a variable pitch. Going still further in the same direction, we may find any day that one of the attempts in various countries to design and construct a successful helicopter has matured, producing a machine which, by reason of a very powerful propeller on a moveable shaft that can be inclined in any direction, will not only rise and descend vertically, but also may be made to travel forward at a great speed and to perform such acrobatic tricks as sudden halts, retreats and jumps.
All this, however, is surmise; and we are faced with the fact that until the design of aëroplanes differs radically from its present form, heavier-than-air flying apparatuses are limited as to maximum size by certain structural principles too complicated for explanation in this non-technical analysis. A further limitation is imposed by the space needed by the largest machines for leaving the ground or landing.
Within these bounds it has been found that the maximum capacity for passengers and freight does not greatly exceed one and one-half to two tons for a non-stop journey of five hundred miles in still air. Lesser distances do not increase the useful load appreciably, but greater distances decrease it; until for a radius of about twenty-five hundred miles the whole of the disposable lift is needed for fuel, and nothing else may be carried.
For long journeys over land, therefore, the aëroplane must come to earth for replenishment of fuel every five hundred miles. Even for this distance it cannot take more than one and one-half to two tons beyond the weight of fuel and crew. If heavier loads are to be transported, more machines must be used. Finally there comes a point at which a single airship, carrying a heavy freight over five hundred miles, is more economical than several aëroplanes. For non-stop flights of over one thousand miles the same considerations make the airship always more economical than the aëroplane.
Over the ocean the flying boat can beat the dirigible in time and cost up to five hundred miles. Even at one thousand miles it is a commercial proposition, but it must then have all in its favor. For longer distances the airship has no competitor. It may be deduced that in years to come, when the world's airways are in general operation, heavier-than-air machines will bring freight to the great airports, there to be transferred to dirigibles and by them carried to the earth's uttermost ends.