Originally Posted by
ORAC
Different technology to Concorde, the XB-70 was a “wave rider” using compression lift to reach the required range - hence the fold-down wingtips.
“As the competition evolved, North American exploited an aerodynamic advance that gave it the determining edge. A supersonic aircraft could have its lift-over-drag ratio increased by positioning its wing to take advantage of the pressure field that occurs behind the shock wave generated by the protruding fuselage. In North American’s design, this phenomenon—called compression lift—provided a 30 percent increase in lift with no drag penalty. Compression lift appeared to contravene the engineering rule that you never get something for nothing, but it worked.”….
At least according to the book I have on the Valkyrie "VALKYRIE NORTH AMERICAN'S MACH 3 SUPERBOMBER" (Jenkins on Landis), the fold down wingtips are not directly related to the compression lift function - apparently that's a common misconception. The compression lift was done with the overall shape of the aircraft - the fold down wings were to improve directional stability at high speeds.
The XB-70 that was lost in the mid-air was the second one built - and had incorporated lessons learned from the first and was more heavily instrumented than the first. A coworker that had been at North American before coming to Boeing told me there is video of the mid-air but it was classified and never made public.
Pretty amazing some of the things we did back in the 1960's, when we didn't know what we couldn't do...