Reentry compounds the effects of aerodynamic and space flight with a maneuver that is more demanding of both pilot and aircraft than any heretofore encountered. Yet, though severely taxing, reentry flight has been mastered, and many previous unknowns no longer remain. Today, after 120 flights, and accumulated flying time of two hours at speeds above 3000 mph, the three X-15 airplanes show the effects of having pushed past man's complete understanding. Wrinkles and buckles mar the once-sleek fuselages. Gaps have been cut elsewhere.
Scars are visible where the skin of the wings has been hammered back in place.
The three X-15's appear old and tired after many pioneering flights. One of them has a vertical tail with a razor-sharp leading edge, a radical departure from the others. None of them has the vertical tail with which it first flew. Other changes are hidden, such as the added structure that stiffens the fuselage and vertical tail, and the electronics that now help operate the controls. The lower half of its vertical tail had to be jettisoned before landing, since, as the little head-on view makes clear, it otherwise would have protruded below the landing gear when the latter was extended.