It depends very much on the pilot who generated the test data. I have no trouble getting a Spit IX to a slightly smaller turn radius than the Spit VIII. The Mk.IX is simply lighter.
Most of the data was generated by Mosq. Most of it is accurate. However, when I do the same tests, I consistently get a smaller turn radius for the Spit IX and F6F-5. Sometimes, I think Mosq flies a bit too far into the stall, which results in larger circles. But, don't think that it is easy to do this testing. It isn't. It's damn difficult. It's difficult enough that a minor slip or error can result in significantly different numbers. Which is why two or more tests are better than one. Three is even more reliable. Always take the best result. Why? because you can always make the circle bigger, but there is a finite limit on how small it can be. The smallest is always the more accurate measurement.
The methodology of the testing has been posted to the Aircraft and Vehicle forum several times. You need a stop watch, calculator and the ability to fly a fighter to its absolute limit and keep it there for three consecutive circles (I haven't seen more than a few who can do this, by the way). Then, repeat the test two more times and take the best results. Now, you must be able to do all of the above in every fighter.. That takes huge amount of time, and an equal amount of practice.
Here's something to consider. As a Trainer, I hear guys state that "no one can turn" their particular fighter tighter (a smaller circle) than they can. I like to get them into a flat, continuous turn (either left or right) and we start to tighten it up with this guy on my six. With very few exceptions, most guys find out that they were nowhere near the smallest possible circle. Within four or five full turns, they find me on their six. This is why I preach the need to know the true limits of their aircraft, which is often well beyond the limits of the pilots. Many duels are decided by one pilot being able to wring more out of a fighter than the other pilot can. All else being equal, the guy who fly right on the edge of being out of control, and do so without so much as a wiggle, he will win the fight. Like good SA and good ACM skills, plane control skills are vital to being successful.
My regards,
Widewing
