Originally posted by Wmaker
For the quote below I don't have it's original source. It was posted by Oleg Maddox to the http://www.simhq.com's IL-2 Sturmovik message board. Oleg said that it was from a western historian. I'm just posting it to show a different view on the matter.
"The printed maximum speed in all books for the NA P-51D Mustang is 437 mph at 25,000 ft. Absolute nonsense. The fastest speed ever actually RECORDED for a P-51 ocurred on 20 October 1944, over Henden RAF base, England. Following RAF complaints that the P-51 would not reach the printed speeds, no fewer than 12 Mustangs from various units--two right off the boat, as well--were tested with USAAF pilots. Both theodolite units and radar were used to measure the speed. The fastest run--I should mention after innumerable flights occupying the whole day--
was 416 mph in a P-51B (s/n 36799 "Carolina Hustler"); this speed was sustained only for 10 seconds before the engine became seriously over-boosted. The longest sustained maximum speed recorded was 405 mph for 55 seconds by a brand new P-51D at 23,000 ft. (s/n 472484). Most of the machines in this evaluation were incapable of exceeding 400 mph under any conditions whatever. The NII VVS tested their P-51B (L-L, s/n 35145) to a maximum of 392 mph at 25,500ft, and climb to 5000m of 6.5 mins. (yes, on 100 octane gas). I suspect that this was exactly correct, despite the fact that all Wetserners try to explain it away. These two events are the ONLY scientific evaluation of the Mustang by any non-Company (i.e. North American) entity in the entire history of the aircraft. Both evaluations prove that the Company was inflating their numbers for 'advertising' reasons...."
as to OLEG's information. I queried some folks in a newsgroup to th validity of OLEG's response in the IL2 thread.
here as follows FWIW--
Gruenhagen's book on the Mustang shows a max. level speed of 441 mph @ 30kft for
the P-51B with V-1650-3 (and probably no rear fuselage tank). I'd really want
to know what the atmospheric conditions were on the day in question, as all test
results are supposed to be normed to Standard atmosphere, and whether this was
done. The claim that "these two events are the ONLY scientific evaluation of
the Mustang by any non-Company entity in the entire history of the a/c" is
patently incorrect. For instance, there used to be a web link which had the
results of the speed and climb tests performed on the Mustang Mk. I (AG 351) at
Burtonwood by the RAF. Unfortunately that link's no longer active, but
Gruenhagen states that the a/c managed a top speed of 382 mph at its best
altitude of 14,000 feet (engine critical altitude of 11,300 ft.) during those
tests, reduced from the 390 achieved in company tests because the a/c had gotten
its camouflage paint as well as having other operational equipment added.
Elsewhere he lists the same speed at 13,700 feet, which may be the value
corrected to ISA. Either way the best speed altitudes were a hell of a lot
lower than the Merlin-powered models in high blower, which were also more
powerful. Higher altitude = thinner air = less form drag = higher speed, until
the power starts to fall off or mach effects (on the prop or airframe) become
significant.
The P-51A, with a more powerful engine (Allison V-1710-81 vice -39) is credited
by Gruenhagen with 409 mph at its best altitude of 10,000 feet, mainly because
the -81 has a War Emergency MP rating of 57"/3000 RPM at that altitude, vs. the
-39 engine's military rating of 44.2"/3000 RPM at 11,300 feet; the -81 can
maintain the 44.2"/3000 RPM up to about 17 or 18,000 feet (eyeballing the
graph). Again, both of these are well below the critical and best speed
altitudes of the Merlin models in high blower, as well as being down a couple of
hundred hp compared to the Merlin. The Merlin V-1650-3 engined models made
their best speed at 30kft (give or take a few hundred, allowing for the usual
variation), while the V-1650-7 models made theirs at 25,000 feet.
Guy
