The U2 had more in common with a glider than with a typical Air Force aircraft. It has a center wheel and a tail wheel, high-aspect ratio wings, no pressurization and the need for absolute maximum efficiency. Most modern gliders now have a wing-tip skid instead of wheels, but most U2 era gliders had wing tip wheels -- they just did not fall off when the glider left the ground. It is really quite amazing the efficiency compromises that are made to the wing when you put two main wheels in it. This aircraft rates with the most successful aircraft ever built.