Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
I really don't think your going to change my opinion, but this article adds some interesting information to the discussion, even though portions of the article contradict some of the mk IV flight test conclusions as far as stability is concerned.
"The P-51 was of special interest to the pioneers of supersonics because among fast World War II fighters, the Mustang seemed the most resistant to high-speed controllability problems. (??????really??????)
I assume this is your clever reposte to the quote? I suspect the inference is to contrast the dive characteristics of the Mustang to well documented 'nose tuck' transonic issues encountered in 47s, 38's and even Me 262 in the Mach Crit speed range. The Mustang did NOT 'tuck'.
Actually the reason stated below might be, but may not be, the real reason. The primary causes for 'tuck were one or both of a.) movement of the aerodynamic center aft with the shockwave, and b.) separation aft of the shockwave 'blanking out' the elevator and reducing the ability of the elevator to actually control pitch 'down' when the Moment Coefficient of the wing goes increasingly negative as the AC moves rearward.
Most non-laminar airfoils with a max thickness in the 25-30% range started flow separation where the velocity profile was max (in that 25% chord range - which also pretty much coincides with AC), whereas the NACA 45-100 max thickness was at 40% further aft of the AC. If the shock wave started aft of the AC, then it would not change the Moment Cioefficient of the airfoil in the same way as the 47 and 38. I do NOT know which explanation is the correct one.
Apparently its unique laminar-flow airfoil managed to keep the airflow attached despite shock wave-induced perturbations. The P-51 could dive faster, under control, than any other World War II fighter. In 1946 and '47, Chuck Yeager in a P-51D with full instrumentation and cohort Bob Hoover in a P-47 dove "straight down," wide open, "from as high as we could go," Yeager later wrote to a friend. Yeager reached Mach .81 in the Mustang and Hoover managed .805 in the bluff, radial engine Thunderbolt."
Bill S - The 51 Did have some issues with phugoid (porpoise) motion in the high subsonic regimes in a dive and the B/C model also exhibited yaw perturbations which if uncontrolled could lead to a tail failure. The addition of the ventral fin to the D and all previous versions of the B/C in the ETO was a reflection of changes to make the 51 safer in the .75 to .8+ M range. The metal elevator kit and stronger ammo doors were also added in kit form until standard production inclusions for the P51D-20
Being that Yeager wrote this, are we to suggest there is some biased here??
lol
I recognize the silliness of my last post. It is funny how we give one pilots account more merit than another. I understand that indicators say one thing, but if two pilots accounts suggest the P-47 could out dive a mustang, then they deserve some merit.
To settle all the horse pucky, here is that 0.861M info straight out of the RAE (Royal Aircraft Establishment) test reports.
Table III, column five....22 seconds into the dive.
http://img113.imageshack.us/img113/3523/sd12.jpg
To find how they calculated the TAS and mach, you probably need to go to a library and check out the RAE test reports of WW2.
You would know better than myself.
I thought it was inline with other tests performed by the RAE.
and while the CIAS doesn't account for compressibility, the chart makes no mention of how they came to conclusions of the TAS.
It is probably information thats burried at the buttom of another pile of paperwork stuffed in some military warehouse. I'm sure a trip to a large public library or university library, would have a book that provides those kind of details on the RAE reports.
In defense of the 'mighty' Thunderbolt, i would have to assume the calculations that lead to the figure of .85M that the 51D achieved would have to fall under the same scrutiny. In other words, they were probably calculated the same way, and perhaps both figures are inflated due to the limited instrumentation at the time of the tests. But again, that is something i'm not familiar with.
This is a great report.
It also demonstrates the zoom dive capabilities of the P-47D, which to my surprise, in this report, out preformed the Mustang in that particular category.
See..the Zoom Dive and Zoom from level flight results.
It is also an interesting comparison, because the Zeke was designed to turn fight, while the US line up, was designed for speed.
That's why the roll rates of all three planes became superior to the Zeke at a higher IAS.
It was no secret that the P-47D should not engage in a turn fight with a Zeke, and most of the more maneuverable Japanese plane set.
Instead they'd dive to get away, and climb up high above the enemy only to swoop down on them at a high rate of speed....then take the bird back up with the zoooooooooooom and get positioned to do it again.
There is also a potential flaw in using an airplane as a baseline for comparison of performance to other aircraft. Specifically, there is lack of dive angles for the planes, but if taken at face value, this is a very good report.
Good find.