"Let us remark how fruitful is the method of personal trial which we have always advised in preference to any calculation. This year, with his fourth apparatus, Blériot has not met with any damage to his aeroplane. [Well, not much anyway.] He made the trials himself and they quickly led to results, because each trial gave him an exact idea of what was to be corrected. That is the condition of success." Capt. Ferdinarnd Ferber, 1907
In this quote, Ferber managed to identify precisely the right conditions for success, and precisely the wrong method to obtain them. To succeed in inventing the airplane, you need to determine exactly what must be corrected with your current design. Building airplanes and then testing them in the field is the exactly the wrong method to do this.
At the end of their gliding experiments in 1901, the Wrights knew there was something wrong with their lift calculations. The 1901 glider had not generated the lift they computed it would. The two brothers considered testing another different glider, perhaps one of the Lilienthal gliders or the Chanute-Herring biplane. But they knew the information they could glean from such a crude test would not be sufficient. Soon, the Wrights turned to the wind tunnel to help them resolve the problem of lift.
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The Wrights were the first to make precise and accurate measurements of lift and drag in a wind tunnel. In the process, they discovered that the coefficient of lift that was commonly accepted was too high, and were able to identify a long and narrow wing shape that was far more efficient than the short stubby wing employed in their 1901 glider. The 1902 glider was the first aircraft that solved the fundamental problems of flight: lift and three-axis control. The pictures of the 1902 glider are unusually beautiful because they show humankind, for the first time, in sustained and controlled flight.
By calculation, not by field tests, the Wrights were able to realize an ageless dream. Blériot was able to succeed later only because the Wrights solved the fundamental problems, and left only the need for modest refinements. In 1903 the Wrights constructed a larger version of their 1902 glider, added a power plant, and made the first self-powered journeys into the sky.