After thorough investigation and experiment, the objections to the three classes of ma chines named, which have been briefly out lined above. appear so formidable to the "Teat majority of the foremost workers for mechanic-al flight to-day that there now appears to them to be but one principle left, and upon this there is based an increasing hope that flight will be accomplished. This principle is the one which underlies' the aeroplane or aeroeurve; which is that when a thin surface is drawn through the air and is slightly inclined to its path, the equivalent of a pressure is developed on the side which is exposed to the air current— that is, the under side—which is much greater than the driving force which is necessary to pro duce it. If a surface arched ill the line of the motion be substituted for the plane, we have an aerocnrve, whose chief advantage is that it has a higher efficiency. Another advantage is that it is not necessary to incline an ac rocurve in order to develop a pressure on the hollow side when it. is moved through the air. The one advantage which the power machine of the :tem curve type has over the vertical screw is the fact that it can for the reasons just stated con vert the relatively small push of the screw pro pellers into a much larger lifting effect.
ll.ceent experiments with may be divided into two classes: (I) Experiments with models and (21 experiments with large devices capable of earrying a man. Perhaps the two most notable experimenters with models have been Sir Iliram Maxim of Engdand and Professor S. P. Langley of the ITnited States. Maxim's experiments been largely With Various forms of ;ai with the purpose of determining the most. efficient, and the model constructed by him was employed in testing the different sur faces. In a paper written in 189(1, Sir II rain Maxim summarizes some of the principal results of his experiments, as follows: "My experiment s have certainly demonstrated that a steam and boiler may he made which will generate a horse-power for every six pounds of weight, and that the whole motor, including the gas generator. the water supply, the minimiser, and the pumps may be all made to im:ble of 1 t pounds to the ho•se•power. They also show that well•made screwy propellers working in the air are fairly effieient, and that they obtain a sufficient grip upon the air to drive the machine forward at a high velocity: that very large aeroplanes. if well made and placed at a proper angle, will lift as much as 21/2 pounds per square foot at a velocity not greater than 40 miles an hour; also that it is possible for a machine to be made so light and at the same time so powerful that it will lift not only its own weight but a considerable amount besides, with no other energy except that derived from its own engines. Therefore there can be no question
but that a flying machine is now possible with out the aid of a balloon in any In 1891, Professor Langley published his now famous memoir entitled P,xpe•inicats in Aerodu namies, and in 1893 his equally celebrated book on The Internal Work of the Iliad. The experi ments upon which many of the statements in these hooks were based were begun in 1887, and from 1S91 to 1896 Professor Langley was more or less constantly at work perfecting a model flying machine, which finally culminated in his aPro• drone. This machine made a flight of three quarters of a mile on November 28, 1896, and is described as follows in the Aeronautical Annu al, 1897: "The weight, with fuel and water sufficient for the flights described, is about 30 pounds. The weight of the engine and boiler together is about 7 pounds. The power of the engine under full steam is rather more than one horse-power. There are two cylinders, each having a diameter of 11/4 inches.. The piston stroke is 2 inches. The two screws are 39 inches from tip to tip, and are made to revolve in opposite directions; the pitch is they are connected to the engines by bevel gears most carefully made; the shafts and gears are so arranged that the synchronous movement of the two screws is se cured. The boiler is a coil of copper tubing; the diameter of the coil externally is 3 inches: the diameter of the tubing externally is % inch; the pressure of steam when the aerodrome is in flight varies from 110 to 150 pounds to the square inch. The flame is produced by the won pile, which is a modification of the naphtha "blow-torch" used by plumbers; the heat of this flame is about 2000° F. Four pounds of water are carried at starting, and about ten ounces of naphtha. In action the boiler evaporates about one pound of water per minute." The two most valuable sets of experiments conducted with large aerocurves capable of car rying one man are those of Otto Lilienthal of Germany and Mr. Octave Chanute. a well known American engineer. Practically the same methods of carrying out their experiments were employed by both of these gentlemen, although the machines experimented with were quite dif ferent in form: and they are briefly described by Mr. Chanute, as follows: "The method of carrying on these adventures is for the operator to place himself within and under the apparatus, which should preferably be light enough to be easily carried on the shoul ders or by the hands, and to face the wind on a bill‘ide. The operator should in no wise be attached to the machine. Ile may be suspended by his arms, or sit upon a seat, or stanch on a dependent running board, but lie must be able to disengage himself instantly from the machine should anything go wrong, and be able to come down upon his legs in landing.