The movable horizontal tail presented another knotty structural-design problem. Aerothermoelastic effects were severely complicated, since the movable surface could not be rigidly attached to the fuselage along the length of the inboard end. All loads had to be carried through the single pivot point, which made much more difficult the problem of maintaining adequate torsional rigidity. This problem was so predominant, in fact, that it was the basic factor governing the design of the horizontal tail. In order to achieve adequate stiffness, the external surface here is restrained much more than the wing surface, and the pillowing effect at high temperature is quite marked.
Dark areas indicate the higher temperature.
Light areas reveal internal structure. Despite the general information gained during design and construction, several interesting additional problems were uncovered during flight. It is not unusual that these problems occurred in regions of large aeroelastic and aerothermoelastic interactions, or in regions of large thermal stress. A classical example of the interaction among aerodynamic flow, thermodynamic properties of air, and elastic characteristics of structure was the local buckling at four locations, just aft of the leading edge of the wing, during the first significant high-temperature flight to Mach 5. This buckling occurred directly back of the expansion slots that had been cut in the leading edge of the wing.