Umm,
To the best of my knowledge Concorde was certainly not a ‘direct offshoot’ of the XB-70. Although the flight profile of the two aircraft is very similar this is more a result of the design necessities of travelling supersonic in a large aircraft rather than a development of the XB-70 design into Concorde. Certainly both aircraft were developed at roughly the same time, with the B-70’s first public unveiling in May 1964, first flight September 21st 1964 and the concept being conceived in 1959, while Concorde was shown to the public in December 1967, flown on March 2nd 1969 and design work started in 1962, with original work on the concept of an SST begun in 1959. Certainly there was no co-operation between the USA and Europe on the design, as the US was attempting to build its own SST at the time and would have kept the information ‘in-house’.
While on the ground the profiles are similar, the XB-70’s delta wing was designed to lower the outer wing sections mechanically when needed. So, from take off to 300 knots it was a flat wing, up to Mach 1.4 the outer wings drop 25 degrees, and from there to Mach 3 they drop 65 degrees. This was done to improve the flight characteristics of the aircraft without requiring extra control surfaces and is a rather ingenious solution to the problem. Obviously such a system was impractical for a commercial aircraft and Concorde’s wing is fixed in one profile. In fact it’s a more complex design than it appears with over 5,000 hours of wind tunnel testing to ensure the wing would perform as required.
In short, while there is a case for the XB-70 providing some concepts and data that influenced SST development, it is probably more accurate to state that it proved these concepts that are themselves based on the (currently) inescapable realities of developing an aircraft of a certain size that can cruise at supersonic speeds.
As for the environmental law prohibiting supersonic flight over the US, this is perhaps one of the most sensitive points in the history of both Concorde and the American-designed SST, the Boeing 2707. On the 24th March 1971 the US Congress abandoned their SST project, leaving Concorde as the sole supersonic passenger aircraft. On the 18th December 1975 the House of Representatives votes 199 to 198 to put a six-month ban on Concorde landing in the USA. Ohio Senator, Clarence J Brown said concerning the ban "I see no reason to oppose the SST (meaning Concorde) just because we were stupid enough to get out of the SST business ourselves". The US Secretary of Transportation provided approval for a limited run service to Washington and New York on 4th February 1976. While the US was by no means alone in banning supersonic flight over their territory (a restriction which, naturally, doesn’t apply to military jets although their flights tend to take place away from population centres), there is a feeling, probably justified, that these concerns would not have come into being if their own SST had proved successful.
It should also be pointed out that Concorde is, now that she’s retired, the only profit-making supersonic passenger aircraft to ever go into service. As Tron said, it’s the combined cost of modifying the fleet following the Paris crash and a drastic increase in maintenance costs from Airbus forcing their retirement as active aircraft, not any technological reason.
Data Sources:
http://www.concordesst.com/
http://www.labiker.org/xb70.html
(Yes, I know, basing any research on only one source per subject = bad practice, but it’s Sunday morning and way too early to be doing a full-on research job).
