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On 6-Nov-2006, "Jim Macklin"
wrote:

I would expect that the maximum speed was 4,000-6,000 mph.

You'd be wrong. Mary Shafer, formally NASA's SR-71 Flying Qualities Lead
Engineer at Dryden Flight Research Center, Edwards, CA, posted a reply to
"Yeff" back on February 23, 1999 on rec.aviation.military:
"Yeff" wrote:
The story I always heard was that if any plane ever beat
the Blackbirds speed record we'd just take a bird up and
move the throttles forward a bit more and take it back.
Sooth or myth? Has an SR-71 ever flown at max speed?
(hoping against hope that Mary imparts more wisdom...)

Yes. But it required permission of the Commander on a per-flight
basis. The SR-71's usual limit is Mach 3.2, but flight at Mach 3.3
was allowed, and flown, with prior permission. There's no evidence
that anyone has ever flown faster than Mach 3.3 (although it's
possible that someone may have briefly dashed above 3.3, not cruised,
but it's not documented).
The cruise speed on the SR-71 is limited by CIT, compressor inlet
temperature. The limit is 427 degC, per the Dash-1. Since the SR-71
is designed to fly Mach 3.2 (standard atmosphere), this temperature is
reached at Mach 3.3, offering a fairly standard margin of safety. If
operational conditions require going Mach 3.3 it's possible. Rather
than flying Mach number, we fly CIT, cruising just a bit below the
limit. This usually works out to Mach 3.23 but that's because the
real atmosphere isn't the same as the standard atmosphere. Everything
about the airplane is designed for Mach 3.2, including the inlet spike
operation, etc. I've always assumed that the extra 0.1 Mach was a
bonus, discovered in flight test, because the calculations were on the
conservative side.
If you'll check in Deja News, you'll find that Lednicer worked it out
that the absolute airframe maximum is around Mach 3.5, because you get
the bow shock impinging on the wing above that. Unfortunately, this
can't be tested because the CIT limit is reached first.
--
Mary Shafer NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer Of course I don't speak for NASA


What a cool plane. I seen one in person at the Dayton Air Museum, it was
smaller than I thought. But they had the Valkyrie there to and that thing is
HUGE!

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DW