Fig. 18.—Flow of the wind over hills.
As waves roll across the surface of the sea, so in the aerial ocean are there breakers and eddies and many dangers unknown; and men cannot see, but only feel them. The air does not flow in regular streams over the earth’s surface; could we follow its movements with our eyes, we should see that it is full of whirls and eddies, with currents of warm air flowing upward, streams of cool air moving downward; and with all the obstructions on the face of the earth, such as hills and woods, causing an interruption and a disturbance in the air flowing over them ([Fig. 18]). The face of a cliff, for instance, will deflect a current upward, leaving a partial void at its summit; and into this void the air will rush in the form of a whirling eddy.
The man who would learn to fly has to launch himself into a treacherous, quickly-moving element; and one which, to add to his perils, he cannot see. The rower in a boat, who sets out upon a stormy sea, can watch the flow of the waves and turn the prow of his vessel to a breaker that threatens him. But the aerial navigator moves in a medium that is invisible; gusts that rush upon him are unseen; he is unaware of their onslaught until his craft heels before the shock. This risk, from the sudden sweeping up of an air-wave, was put clearly by Wilbur Wright when he wrote:
“A gust, coming on very suddenly, will strike the front of a machine and will throw it up before the back part is acted on at all. Or the right wing may encounter a wind of very different velocity and trend to the left wing.”
In the aerial sea a machine will pitch and roll as does a ship upon the water; and the man who would fly must learn to check his craft, should it threaten to overturn; must be ready instantly with some system of controlling gear so as to correct the influence of each driving gust. And his task is made the harder because his machine, when struck suddenly by a gust, may fall towards the earth at any angle. On the road, when one learns to ride a bicycle, the machine will topple to one side or the other; but a craft in the air may fall forward or backward as well as from side to side, or partly forward and partly backward—or may slip and dive at any possible angle, either forward or backward or upon either side. A pioneer wrote, after his first experience in learning to fly:
“It is rather like trying to steer a motor-car along an exceptionally greasy road; you seem to slip all ways at once; and to slip so quickly also that, unless you make the right balancing movements without an instant’s delay, you find your machine has gone beyond control.”
If he were to succeed, if he were to fly like a bird, then a man had to learn this art of balancing himself in the air. Futile it was, as has been shown, to build some powerfully-engined machine that no one could control; futile also, and perilous as well, to make a pair of wings and jump from a tower. Another way must be found, or the quest abandoned and admitted hopeless. Here was the need; and here too, as we shall tell, came the man; a man who was not famous, who worked without reward and struggled to find time for his experiments; who died before he could see the final triumph; yet who won a fame that cannot die, and whom men call “the father of the aeroplane.”
To Germany one turns in telling the story of this man’s work. He was an engineer, Otto Lilienthal by name, and from the days of his boyhood he and his brother Gustav, living in Anklam, a small German town, were builders of model aeroplanes and students of the flight of birds. When the boys were thirteen and fourteen years of age respectively, they designed a flying machine; and in describing it afterwards, Gustav Lilienthal wrote: