A pioneer experimenter once said that “it is easy to invent a flying machine; it is more difficult to build one—but to make one fly is everything.” As Lilienthal had seen, the Wrights also saw that, if ever they were to make progress in solving the problems of flight, they had not only to study them theoretically, but also to get up into the air in gliders and test their theories by actual practice. “If you are looking for perfect safety,” said Wilbur, “you will do well to sit on a fence and watch the birds; but if you really wish to learn, you must mount a machine and become acquainted with its tricks by actual trial.” Preferring the air to a fence, the brothers recognized that when undertaking to fly gliders their first major problem would be how to fly safely so they could live long enough to learn to fly a powered machine. Wilbur wrote his father: I do not intend to take dangerous chances, both because I have no wish to get hurt and because a fall would stop my experimenting, which I would not like at all. The man who wishes to keep at the problem long enough to really learn anything positively must not take dangerous risks. Carelessness and overconfidence are usually more dangerous than deliberately accepted risks. The problem of equilibrium was the second major problem that the brothers had to solve. They needed to devise measures to steer or control a flying machine both up and down and to each side. When the Wrights started their investigations they believed that others had already solved the problems of how to design wings, propellers, and motors. Only later did they realize that they must also correctly design both the wings and the propellers and build their own motor. Thus their third major problem became how to design wings sufficiently strong to support the weight of the machine, motor, and pilot to take the greatest advantage of air particles providing lift by streaming along the upper and lower surfaces of the wings. A fourth major problem that faced Wilbur and Orville was how to design a light-weight, high-powered engine and the propellers required to drive the machine through the air. They were to find that these problems were interrelated and that they would solve them only after 4½ years of spare-time study and experimentation. _First Experiments, 1899_ Wilbur and Orville realized that the motion of the air on a flying machine is frequently variable and tricky, causing the machine to rear up or down, or one wing to rise higher than the other, and the machine to become unstable. The problem—how to control a flying machine—was to find a method of restoring the machine’s equilibrium both up and down and to each side.