Neither of the brothers was content with mere study of the work of others. They collected all the theory available in the books published up to that time, and then built man-carrying gliders with which to test the data of Lilienthal and such other authorities as they had consulted. For two years they conducted outdoor experiments in order to test the truth or otherwise of what were enunciated as the principles of flight; after this they turned to laboratory experiments, constructing a wind tunnel in which they made thousands of tests with models of various forms of curved planes. From their experiments they tabulated thousands of readings, which Griffith Brewer remarks as giving results equally efficient with those of the elaborate tables prepared by learned institutions.

Wilbur Wright has set down the beginnings of the practical experiments made by the two brothers very clearly. 'The difficulties,' he says, 'which obstruct the pathway to success in flying machine construction are of three general classes: (1) Those which relate to the construction of the sustaining wings; (2) those which relate to the generation and application of the power required to drive the machine through the air; (3) those relating to the balancing and steering of the machine after it is actually in flight. Of these difficulties two are already to a certain extent solved. Men already know how to construct wings, or aeroplanes, which, when driven through the air at sufficient speed, will not only sustain the weight of the wings themselves, but also that of the engine and the engineer as well. Men also know how to build engines and' screws of sufficient lightness and power to drive these planes at sustaining speed. Inability to balance and steer still confronts students of the flying problem, although nearly ten years have passed (since Lilienthal's success). When this one feature has been worked out, the age of flying machines will have arrived, for all other difficulties are of minor importance.