Oh, the P-51 is certainly NOT going at 400 MPH after a turn like that! This is apparently an 8 G limit turn...
Yes, it does significantly out-turn the Spit Mk XIV at these speeds, but may come out of the 180° at a much slower speed than the Mk XIV. I would say that IS in fact a certainty, given the Spit's wider turn and much better power-to-weight acceleration...
Those tests you cite DO say the Spits Mk IX/XIV out-turn the P-51 at ALL speeds, but then they also say the spits Mk IX/XIV out-roll the P-51 at ALL speeds untill a parity is reached at 400 MPH...
The fact that they say the P-51's turn is not improved by the use of flaps makes their entire methodology doubtful, as does the vagueness of their data-free comparative descriptions. In other hands, a more detailed Polish combat pilot description of the use of the P-51B's flaps states that it DID improve the turn rate, but made the stall more dangerous. An informative give-and-take description that is correlated for the first part by thousands of U.S. combat reports... (Interestingly, no American mentions the worsened stall characteristic, a bit of positive-only thinking here I think...)
In fact, many descriptions I have read of the P-51 states it had the best high-speed turn rate of any WW II fighter, but that this abrubtly ended somewhere above 400 MPH with wartime fabric elevators. (Metal-skinned elevators were almost exclusively post war; maybe they lowered the low-speed response compared to fabric skin?) The 109G could be superior to the fabric-tailed P-51 above 400 MPH, and Noth American duly copied the moveable tailplane for the Sabre...
Those Farnborough tests are not to be trusted; they completely fail to specify that the 109G performance numbers they quote had underwing gun gondolas INCLUDED for the 625 km/h War Emergency max. speed. At a minimum, the G-6 did 637-640 at 1.3 ata, and 650 at 1.42 ata. ( I suspect they didn't like the fact that this matches the Spitfire Mk IX with less power...) The G-2 did 640 at 1.3 ata, and they DID have a G-2 on hand. The climb rate is also just about the poorest data you could possibly get out of a Gustav; wing guns included etc... They certainly didn't use the climb rate of a clean G-2...
I think failing to even MENTION the 109's wing guns speaks volume about the mind-set these tests were made with... These are the vaguest, most warped comparisons tests I have seen out of WW II... Perhaps some Soviet tests can offer a challenge, but I think even they didn't go that far, and simply accurately recorded the performance of highly fine-tuned and hand-made Soviet prototypes...
The best example of this is the mysterious roll performance of the Spitfire, always described in Farnborough tests as being among the best around, despite in actual combat being one of the slowest of any fighter... Robert Johnson (of the P-47D's legendary 72" 470MPH TAS at 10 km..., so not entirely a spotless observer himself...), says that his 80°/sec P-47 could change sides "2-3" times before a Mk IX Spit could bank once; a perfect match to a Mk XII's specific roll data of 40-50°/sec at 300 MPH TAS (worsening after!), and in line with a Supermarine's test pilot's claim of only 2/3 of the Spit V's 60-78°/sec, meaning about 40-50°/sec for Mk IX/Mk XIV Spits...
Fo once, I'll believe Robert Johnson, and a mountain of other combat pilot impressions, axis and allied combined, that would dwarf the Himalayas...
Sadly, that Farnborough data was repeated in the famous, and otherwise very instructive, NACA 868 fig. 47 roll rate chart, BUT WITH THE MARK UNSPECIFIED, which is rather strange, since all the others allied types are precisely described...
The answer to this mystery seems to be that these test Spitfires had non-standard wings, and also it seems the Spitfire's roll benefits immensely from not carrying wing guns, further clouding the issue in modern airshows. I think the Spitfire's roll rate would also benefit from higher altitudes with the thinner air, which is why clipped wingtips were introduced for units specialized in the low-altitude combat role (the gain in speed was apparently minimal).
The very fact that clipped wingtips even EXISTED at all, and WERE widely operational on MkVs (such as Johnny Johnson's)even during D-Day (speed could not have been a major issue!), says everything you need to know about the near-criminal misinformation of these roll-rate tests... Maybe these claims were intended to confuse the Germans? The fact that these tests are so vaguely-worded may mean an intention to supply semi-public info, with tweaks to boost non-pilot morale? Whatever the case may be, these roll rate quotes are clearly in the land of the bizarre...
Going back to the P-51's turn rate, one of the things obvious to me is that the wingloading is not the final word to predict an aircraft's comparative turn radius. On that basis, I have given up stoically ignoring the thousands of combat reports that say the P-51B/C/D series, above 200 MPH at least, ALWAYS out-turned the 109G, and increasingly so as the speed went up (until above 400 MPH), while it did NOT do quite so well against the FW-190A at low levels, at least up to 250-300 MPH (and may have done significantly worse, especially against a broad wood prop, and long-chord aileron, FW-190A-8, below 250 MPH TAS!). The wing/power-loading is obviously completely misleading in all three aircrafts for the turn rate, although it does correctly predict that the 109G's spiral climb will be far superior...
There are many things I think we still don't know about these aircrafts, most crucially how wingload relates to turn performance, and how lag-time in stick/pitch or pitch/turn response affects the actual turn performance. (Any WWII gun camera footage is often notable for the huge lag-time in turn response after a bank is completed.)
Believe me, some of these obviously biased, and vague, British comparative tests do a lot more to cloud things up rather than the opposite...
Gaston.
