Page:Popular Science Monthly Volume 64.djvu/394

390 system of combined aeroplanes and lifting screws for flying apparatus.

A good deal of experimenting has been done with power-driven flying models. The more recent types have been actuated by twisted rubber threads, by compressed air and by steam, and the most notable experiments in order of date are those of Penaud, Tatin, Hargrave, Phillips, Langley and Tatin and Richet. The data for these (except the first) will be found by searchers in such matters in the London Times edition of the 'Encyclopaedia Britannica,' in the article on aeronautics. The most successful experiment was that of Professor Langley, who obtained in 1896 three flights of about three fourths of a mile each with steam-driven models, the apparatus alighting safely each time and being in condition to be flown again.

The one great fact which appears from all these various model experiments is that it requires a relatively enormous power to obtain support on the air. Omitting the cases in which the power was probably overestimated, the weights sustained were but 30 to 55 pounds to the horse power expended, thus comparing most unfavorably with the weights transported by land or by water; for a locomotive can haul about 4,000 pounds to the horse power upon a level track, and a steamer can propel a displacement of 4,000 pounds per horse power on the water at a speed of 14 miles an hour.

But models are, to a certain extent, misleading. They seldom fly twice alike and they do not unfold the vicissitudes of their flight. Moreover, the design for a small model is sometimes quite unsuited for a large machine, just as the design for a bridge of ten feet opening is unsuited for a span of one hundred feet.

After experimenting with models three celebrated inventors have passed on to full-sized machines, to carry a man. They are Maxim, Ader and Langley, and all three have been unsuccessful, simply because their apparatus did not possess the required stability. They might have flown had the required equilibrium and strength been duly provided.

At a cost of about $100,000, Sir Hiram Maxim built and tested in 1894 an enormous flying machine, to carry three men. It consisted in a combination of superposed aeroplanes, portions of which bagged under air pressure, and it was driven by two screws 17 feet 10 inches in diameter, actuated by a steam engine of 363 horse power with steam at 275 pounds pressure. The supporting surface was about 4,000 square feet, and the weight 8,000 pounds. The machine ran on a track of 8-feet gauge, and was prevented from unduly rising by a track above it of 30-feet gauge. At a speed of 36 miles per hour all the weight was sustained by the air, and on the last test the lifting effect became so great that the rear axle trees were doubled up and finally one of the front wheels tore up about 100 feet of the upper track ; when steam was shut off and the machine dropped to the ground