Just for comparison, try looking at the figures from different testings.
They are from;
* The Complete Aces High2 Fighter Turn Performance (http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=155592&highlight=complete+turn)
* The Complete Aces High 2 Fighter Turn performance (revised 2.06) (http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=166537&highlight=complete+turn)
These are the tests I've done during versions 2.05 to 2.06, before Mosq's version of testings were compiled for AH Fighter Comparisons page. They show somewhat different figures for the F4Us.
The below is a list of turn radius for planes engaged in full flaps, starting from the smallest turning plane, and listed upto the P-38J. Some of the planes are highlighted as a marker for comparing performance.
[b]A6M2: 104.6m[/b]
Hurricane Mk.I: 111.0m
A6M5: 115.3m
Spitfire Mk.I: 117.3m
Hurricane Mk.IIc: 123.8m
FM-2: 128.1m
Ki-84-I-Ko: 133.2m
[b]Spitfire Mk.IX: 134.3m[/b]
Spitfire Mk.V: 134.5m
Seafire Mk.II: 135.8m
F4F-4: 139.5m
Hurricane Mk.IId: 140.3m
Bf110C-4: 142.3m
[b]N1K2-J: 143.0m[/b]
[b]F4U-4: 144.7m[/b]
[b]Spitfire Mk.IX(50cal): 146.4m[/b]
P-38G: 148.6m
[b]F4U-1D: 148.7m[/b]
Bf110G-2: 149.5m
[b]F4U-1: 150.9m[/b]
[b]Bf109E-4: 151.1m[/b]
Spitfire Mk.XIV(50cal): 151.1m
Spitfire Mk.XIV: 152.4m
La-5FN 152.4m
La-7(3x20mm): 152.4m
La-7: 153.6m
[b]F4U-1C: 156.6m[/b]
[b]P-38J: 156.8m[/b]
My testings were done before the addition of some new planes and recent changes concerning some FM aspects. The main difference with my testings and Mosq's, is that I've made extensive use of some of the in-game features to minimize human error in determining the true turn radius of the planes.
As you can see, in these testings (before the FM change) the performance of the F4U was a bit more in line with the more common belief amongst AH gamers. The "1st Tier" of tight turning planes are the A6Ms and Hurricanes, and the Spitfires and the N1K2 makes up the "2nd Tier".
In the turn radius comparisons at AH Fighter Comparisons Page, the F4U-1 ranks somewhere between the "1st Tier" and the "2nd Tier", physically outturning Spits and N1Ks and Ki-84s in the pure radius.
This is especially interesting to note, since when I've first done these tests, I was already thinking the F4U turned too well - since the general turn radius performance was matching those of the Spit9 with 50cals and N1K2s. In other words, this was before the FM change, a different test figure from those of Mosq's, and still I was already thinking the F4Us turned too good.
So more or less, I'm thinking it could be said that the F4Us always had very generous flaps... and it was just unnoticed until recently.