The Under Body of the Monoplane Shown, Plate XIII.
The slow, but on the whole, encouraging movement toward the successful flying machine was given a serious set back in 1872 by a book written by H. Von Humboldt announcing the result of his experiments. This well known scientist, whose name carried great weight, wrote that mechanical flight was impossible. He based his idea on the discovery that as the body increased in size the work or power required to lift it increased more rapidly than the size of the body. In other words, a very large bird or flying machine could not contain muscles strong enough or machinery strong enough to enable it to fly. He argued that no bird larger than the albatross, for instance, had ever lived, therefore no flying machines could ever be more than toys. The book was so discouraging that many aviators gave up their experiments and the science of aviation stood still.
It may be said to have been awakened, however, by the German scientist, Otto Lilenthal, whose book, published in 1886, at once attracted world wide attention. It was this book, incidentally, which inspired the Wright Brothers to begin their experiments. Lilenthal was not only a great scientist, but he worked on the principle that an ounce of actual experience was worth a ton of theory. In aviation, where the weight is all important, this saving was naturally of the greatest importance. Lilenthal built gliders, many of them, and put to actual test the theories which others had merely talked and figured about. Finally he set up an engine on a glider but the machine turned over and he was instantly killed. The scientific information he collected, however, proved of the highest value to those who later actually conquered the air.
Lilenthal built a hill fifty feet in height and shaped like a cone with sides slanting at an angle of thirty degrees. Here he proved by actual tests that he might fly no matter which way the wind blew and that an arched surface, driven against the wind, would rise from the ground and support his weight. A great deal of scientific information was collected and tabulated as well as the exact effect of the pressure of the air. He also changed the shape of the gliding surfaces, making them very long and narrow and driving them edgewise as in the first form of aëroplane. The aëroplane took shape in his hands. The success of these experiments encouraged aviators in many countries to imitate him, and so great was the interest aroused that even his fatal accident in 1896 did not discourage them. The successful flying machine was now actually in sight.
PLATE XV.
A Simple Model which Proves Steady in Flight.
For a time it was believed that Hiram S. Maxim would be the first to construct a flying machine which would actually fly. He had gone about the problem in a thoroughly scientific manner, sparing neither time nor expense. An elaborate apparatus was first constructed like a revolving derrick, to test accurately the lifting powers of various aëroplanes of various sizes and shapes flying at different angles, as well as the propelling force of many kinds of screws. The horizontal arm of this machine was thirty feet, nine inches long, so that it described a circle of 200 feet in circumference. The arm was driven by an engine at high speed.
The various aëroplane forms to be tested were attached to the extreme end of this arm, and driven by propellers of various shapes and sizes, exactly as they would be in actual flight. Every part of the machine, meanwhile, was so adjusted that the readings of the speed of the aëroplane, its lifting power, the exact force of the propeller, in fact, every detail, could be measured and recorded with scientific accuracy. This preliminary work proved to be of the highest value. The test showed, for instance, just what size the propeller should be for different size planes, and the exact pitch of the screw which would give the best results, the proper angle of elevation for the front plane, the resistance offered by various shaped planes, and the exact amount of power required for planes of different sizes. A delicate machine was also built to test the different kinds of fabrics used for covering the planes. The fabric was stretched over a small steel frame, mounted at a slight angle, in a blast of air. The tendency of the cloth to lift or drift was then accurately measured. The material which gave the greatest amount of lift and the least drift was used.
A large aëroplane was finally built in 1893. It weighed 7500 pounds, measured 104 feet in width, and was driven by a 360 horsepower engine. Compared with the clear cut, ship-shape air-craft of to-day this early model appears crude and cumbersome. The main plane was almost square in shape, while stability planes extended out from the sides. A series of four narrow planes, one above another, were carried below on either side. The machinery for driving was carried far below the main plane. The two large propellers were placed in the stern. The aëroplane was run along a double-tracked railroad 1800 feet in length, to gather sufficient momentum to cause it to rise. Almost any school-boy of to-day familiar with the aëroplane models could have told at a glance that the machine could not rise. When it was finally sent down the track at a good clip, the front wheels did actually rise a trifle but it immediately came down with a bad smash.