The belief that man could learn to fly by flapping wings up and down was not given up until very recently. Nearly all the early machines were built on this principle. Man can never fly as the birds do because his muscles are differently grouped. In the birds the strongest muscles, the driving power, are in the chest at the base of the wings where they are most needed. It is amusing to find that while the birds are always flying before our eyes no one has guessed their secrets. Many attempts have been made to wrest their secrets from them by attaching dynometers to their wings to measure the force of the muscles but little has been learned in this way. One scientist calculated that a goose exerts 200 horse power while another investigator figured out that it was one tenth of one horse power. Many of the theories of flight have been quite as far apart. A great variety of false notions about flying had to be tried and from all these failures man slowly learned the road he must follow.
CHAPTER II
DEVELOPING THE AEROPLANE
THE opening of the twentieth century found the world well prepared for actual conquest of the air. Aviation has been developed to an exact science. It had taken centuries of failure to teach man that he could not fly by flapping his wings like the birds but the idea was at last abandoned. The birds were still the models of the heavier-than-air machines, but man had at last learned to study them more intelligently. The marvellous development of modern mechanics, especially the building of light and efficient motors, was also of great importance. The theory of the aëroplane was rapidly gaining in favor.
It was thought at one time that since no birds weighed more than fifty pounds no flying machine heavier than this could ever fly. Some years ago Hiram S. Maxim pointed out, however, that if we had built our steam engines to imitate the horse, as we then hoped to build flying machines like the birds, we would have built locomotives which weighed only five tons, the weight of an elephant, which walked five miles an hour. The secret of flight evidently did not lie in closely imitating the familiar forms of flight. So far as man was interested it lay clearly in the soaring flights. When a bird flies with extended wings it does two things. It forms an aëroplane which supports its body, much the same as a kite, and it operates a propeller for driving this aëroplane forward. And so men finally learned to fly by borrowing a single principle from the birds.
It is claimed by some that the theory, and largely the form, of the modern successful aëroplane was first suggested by an English inventor, Sir George Cayley, as early as 1796. Cayley argued that a flat plane or surface when driven through the air inclined slightly upward would lift a considerable weight. He also suggested that a tail would help to steady the plane as well as steer it upward or downward. His ideas of propelling the aëroplane by screws driven by motors was also far in advance of his time, but the engines then in existence were much too heavy for the purpose and he never built a model.
Fifty years later, when the steam engine had been highly developed, these old plans were remembered and two engineers, Hensen and Stringfellow, actually built a flying machine on Cayley’s principles. This early aëroplane was of the monoplane form, made of oiled silk stretched over a frame of bamboo. A car to carry a steam engine, and presumably the passengers, was hung below this plane. The motive power was supplied by two propellers at the rear. The aëroplane carried a fan-shaped tail with a rudder for steering it sideways, placed beneath. The model is said to have actually flown for a short distance, but proved to be unstable.
From this time onward the experiments became more scientific and accurate. Reliable scientific data was accumulated which later enabled the aviators to build practical aëroplanes. A number of interesting experiments were made shortly afterward by a scientist named Wenham to prove that the lifting powers of a carrying surface might be increased by arranging small surfaces in tiers one above another. Wenham had watched the birds to some purpose, and decided that a single plane, large enough to support a man would be too large to control, but that a number of small surfaces would make the bird flight possible. Wenham built and patented a machine in 1866. He never flew but he collected a great deal of valuable information about the behavior of planes.
PLATE XIV.