Through the latter part of the last century experiments were carried on with gliders. Among those who achieved much success in this field was the German, Otto Lilienthal, the “flying man,” who made remarkable glides in the early nineties. He would run along the crest of a hill, jump from a precipitous declivity and sail on the wings of his glider over the valley below, guiding his course up and down and from side to side with a rudder attached to the machine. It was his idea that the problem of aviation was to be solved by perfecting the glider so that it could be controlled in its downward flight and then adding a propelling power that would sustain it and lift it through the air.
After the death of Lilienthal by accident in 1896, others continued experiments along similar lines with the same purpose in view. Among these were Octave Chanute and A. M. Herring. They tried at first a monoplane glider and afterward one of five planes. This number they reduced to two. The rudder was made of movable horizontal and vertical blades. It was found that the glider with two planes, the biplane, was most satisfactory.
Herring made for this a compressed air engine and claimed that with this he accomplished a flight of seventy-three feet. There is some doubt, however, as to this claim and some question as to whether it was an upward flight or a downward glide.
[Aviation at the Beginning of the Present Century]
As briefly outlined here, such was the status of aviation at the beginning of the new century. Much progress had been made and substantial vantage ground had been gained, but the problem still awaited practical solution. At this point it may be well to consider some of the features of the problem and the devices thus far evolved by long years of investigation and experiment.
[The Kite]
One of the simplest forms of the aeroplane is the common kite. This takes various forms. It is usually made of a framework of three light strips of wood crossing a little above the center and secured at the outer ends by similar strips, or strong cord tautly drawn and making when covered with paper a six-sided figure. From the corners of the framework cords are drawn to a common point near the center and there firmly united. At this point of union is attached the twine which is held in the hand of the kite flyer. From the base of the kite is suspended a string with light horizontal paper rolls, each about the size of a lead pencil, tied at intervals of a few inches, and forming the tail which steadies the kite in air. The paper surface of the kite is the plane on which the pressure of the air current and the power applied to the string is to lift the kite upward. As this simple form of the kite has but one plane, it may be considered a monoplane. The box kite presents two such surfaces joined together at the sides by the ends of the “box,” and may therefore be called a biplane.
When the boy flies his kite he first determines the direction of the wind and runs in that direction. In other words he flies his kite against the wind. The pressure of the moving current against the under surface keeps the kite aloft. When the boy runs against the wind, moving the kite forward with him, this pressure is increased and the kite tends to rise higher and higher. If instead of the long string and the boy there could be placed with the kite itself a very light motor that would give to it the same forward impulse, the kite would float through the air without boy or string and we would have a small aeroplane flying machine--a monoplane. If there were two kites, with parallel surfaces a few inches apart, united with light framework so that the air would pass between them, we should have a biplane. For many years the great problem in aviation was to get an engine of sufficient lightness and power to propel monoplanes, biplanes and multiplanes at an upward angle through the air.
[The “Plane” Defined]
It may not be out of place here to consider what Constitutes a plane, as that term is used in aviation. It is that part of the aeroplane, the pressure of the air upon the surface of which, lifts and sustains the aeroplane aloft. The plane may take a variety of forms; it may be curved or its parts may meet in an angle; it may be uniform and unbroken in shape or divided into parts. The two wings of a bird would constitute a monoplane, when they are in a horizontal position for soaring, or when the tips are uplifted and they form an angle like a broad V, called a dihedral angle. If the aeroplane has two such planes, one back of the other, it is still called a monoplane, or, more definitely, a tandem monoplane; but if one of the planes is above the other it is called a biplane. A similar arrangement of three planes, one above the other, could be called a triplane and one of several planes a multiplane.