In the early nineties the air ship was engaging the attention of many inventors, and was making important strides in the hands of Mr. Maxim. This unrivalled mechanician, in stating the case, premises that a motive power has to be discovered which can develop at least as much power in proportion to its weight as a bird is able to develop. He asserts that a heavy bird, with relatively small wings--such as a goose--carries about 150 lb. to the horse power, while the albatross or the vulture, possessed of proportionately greater winged surface, can carry about 250 lbs. per horse power.
Professor Langley, of Washington, working contemporaneously, but independently of Mr. Maxim, had tried exhaustive experiments on a rotating arm (characteristically designated by Mr. Maxim a "merry-go-round"), thirty feet long, applying screw propellers. He used, for the most part, small planes, carrying loads of only two or three pounds, and, under these circumstances, the weight carried was at the rate of 250 lbs. per horse power. His important statements with regard to these trials are that one-horse power will transport a larger weight at twenty miles an hour than at ten, and a still larger at forty miles than at twenty, and so on; that "the sustaining pressure of the air on a plane moving at a small angle of inclination to a horizontal path is many times greater than would result from the formula implicitly given by Newton, while, whereas in land or marine transport increased speed is maintained only by a disproportionate expenditure of power within the limits of experiment, in aerial horizontal transport the higher speeds are more economical of power than the lower ones."
This Mr. Maxim is evidently ready to endorse, stating, in his own words, that birds obtain the greater part of their support by moving forward with sufficient velocity so as to be constantly resting on new air, the inertia of which has not been disturbed. Mr. Maxim's trials were on a scale comparable with all his mechanical achievements. He employed for his experiments a rotating arm, sweeping out a circle, the circumference of which was 200 feet. To the end of this arm he attached a cigar-shaped apparatus, driven by a screw, and arranged in such a manner that aero-planes could be attached to it at any angle. These planes were on a large scale, carrying weights of from 20 lbs. to 100 lbs. With this contrivance he found that, whatever push the screw communicated to the aero-plane, "the plane would lift in a vertical direction from ten to fifteen times as much as the horizontal push that it received from the screw, and which depended upon the angle at which the plane was set, and the speed at which the apparatus was travelling through the air." Next, having determined by experiment the power required to perform artificial flight, Mr. Maxim applied himself to designing the requisite motor. "I constructed," he states, "two sets of compound engines of tempered steel, all the parts being made very light and strong, and a steam generator of peculiar construction, the greater part of the heating surface consisting of small and thin copper tubes. For fuel I employed naphtha."
This Mr. Maxim wrote in 1892, adding that he was then experimenting with a large machine, having a spread of over 100 feet. Labour, skill, and money were lavishly devoted henceforward to the great task undertaken, and it was not long before the giant flying machine, the outcome of so much patient experimenting, was completed and put to a practical trial. Its weight was 7,500 lbs. The screw propellers were nearly 18 feet in diameter, each with two blades, while the engines were capable of being run up to 360 horse power. The entire machine was mounted on an inner railway track of 9 feet and an outer of 35 feet gauge, while above there was a reversed rail along which the machine would begin to run so soon as with increase of speed it commenced to lift itself off the inner track.
In one of the latest experiments it was found that when a speed of 42 miles an hour was attained all the wheels were running on the upper track, and revolving in the opposite direction from those on the lower track. However, after running about 1,000 feet, an axle tree doubled up, and immediately afterwards the upper track broke away, and the machine, becoming liberated, floated in the air, "giving those on board a sensation of being in a boat."
The experiment proved conclusively to the inventor that a machine could be made on a large scale, in which the lifting effect should be considerably greater than the weight of the machine, and this, too, when a steam engine was the motor.
When, therefore, in the years shortly following, the steam engine was for the purposes of aerial locomotion superseded by the lighter and more suitable petrol engine, the construction of a navigable air ship became vastly more practicable. Still, in Sir H. Maxim's opinion, lately expressed, "those who seek to navigate the air by machines lighter than the air have come, practically, to the end of their tether," while, on the other hand, "those who seek to navigate the air with machines heavier than the air have not even made a start as yet, and the possibilities before them are very great indeed."
As to the assertion that the aerial navigators last mentioned "have not even made a start as yet," we can only say that Sir H. Maxim speaks with far too much modesty. His own colossal labours in the direction of that mode of aerial flight, which he considers to be alone feasible, are of the first importance and value, and, as far as they have gone, exhaustive. Had his experiments been simply confined to his classical investigations of the proper form of the screw propeller his name would still have been handed down as a true pioneer in aeronautics. His work, however, covers far wider ground, and he has, in a variety of ways, furnished practical and reliable data, which must always be an indispensable guide to every future worker in the same field.
