North American XB-70A Valkyrie forward fuselage assembly. Photo taken April 1, 1962. The center forward fuselage section is being lowered into place between the flight deck and aft upper fuselage sections. (U.S. Air Force photo)
The design and construction of the XB-70A had to account for the large variation in aircraft skin temperatures maximized by air friction during high speed flight. At Mach 3, skin temperatures ranged from about 400°F to more than 600°F. The interior framework surrounding the six YJ93 jet engines could reach temperatures of more than 900°F.
To solve the problems associated with aerodynamic heating at high speeds and radiant heating causes by the engines, the North American engineers designed the aircraft to be built largely of brazed stainless-steel honeycomb sandwich panels and titanium. Most of the fabrication, assembly and construction techniques associated with the steel honeycomb panels had to be "invented" during the project. In fact, one of the most important legacies of the Valkyrie program is the knowledge gained in high-strength, high-temperature materials use for high speed aircraft.
Because the crew compartment and forward equipment bay had to be cooled to "shirt sleeve" temperatures, the aircraft incorporated a sophisticated "transpiration" system that used engine bleed air to drive two refrigeration pumps which provided both the cooling air and the cabin pressurization necessary because the crewmen didn't wear pressure suits. The air was evenly distributed throughout the crew compartment by a vast number of little holes in the compartment walls, this prevented the unacceptable temperature gradient which would have resulted if a conventional duct and vent system was used (the vent area would be too cold and the areas furthest away from the vents would be too hot).
Many very complicated engineering problems had to be overcome during the design and construction of the XB-70. Many of the techniques developed specifically for the Valkyrie program form the basis for processes still in use today for high performance jet aircraft.