It was aerodynamics that presented the greatest difficulties, particularly in detail design. The configuration that would become conventional — engine in front, stabilizers in back — emerged quite quickly, encouraged not only by its inherent advantages but also by the success of the Bleriot XI that crossed the English Channel in 1909. But pilots of today would find most of the airplanes of that era unpleasant to fly — sluggish, heavy, unstable, underpowered, unresponsive and self-willed in various combinations. It took time, and the patient experimental work of NASA’s precursor, the National Advisory Committee for Aeronautics, and similar research establishments abroad, to find ways to make controls light and sensitive, to streamline wings and fuselages and their intersections, to tame adverse yaw and Dutch roll, to cowl and cool powerful engines and to develop the thousand other tricks that made today’s production of comfortable, fast and pleasant-handling airplanes routine. These were refinements, however; a basic understanding of the principles of lift, stability and control already existed well before the Wrights actually flew.