The Wrights did extensive experimentation, on both models an full-sized prototypes. They built the first wind tunnel and developed calculations for lift and propeller thrust.

They also practiced fairly rapid design iteration, trying out ideas and adapting to actual experience. What they arrived at worked, though it was far from ideal and doesn't much resemble modern aircraft (beyond the notion of wings and the rough principles of control surfaces). Once other designers / engineers entered the field, and with more reliable engines, further iteration advanced rapidly.

Military aircraft played a significant role in WWI, only a decade after the Wright's first powered flight.