Quote: "Most issues associated with structural loading are related to g. For all formal flight tests where these are measured they are normally done during woigs level pull ups from either level flight or dives according to the amount of power or thrust available."
Actually, this above part almost answers my question, as it clarifies quite well the way these wing bending tests would usually be done: If that assumption is made, and the tests are typically done this way, then this does mean it is possible that wing bending measurements in level flight turns has never been done on these particular types of old fighters...
I'm sure a whole range of wing bending tests have been done since on modern jet fighters while in flight, but maybe not on less "advanced" single engine piston-propeller aircrafts that are low-wing monoplanes, as that kind of instrumentation seems uncommon on such small types, or of such vintage, with similar power and wing position at least...
The reason why I believe dive pull-outs might not give a meaninglful indication of level turning wing loads is because diving would unload the prop disc during the pull-out phase.
I know very well (in great detail) that the prop disc's load is not seen as affecting the wingload during level turns at all (at least not independantly of forward speed), but I think the location of thrust origin so far down the nose could be wrongly assumed to have no effect on wingloading. (I realize for it to do so would mean something very complicated is happening)
There are two indications that make me lean towards this no-effect assumption being entirely wrong: First, the repeated mention by WWII fighter pilots of superior sustained turn rates with reduced power. This far, far below their "Corner Speed", which makes no sense, as CS is the speed of the highest possible turn rate, and you would want to be as close as possible to it in a turn, which inevitably means all the power available for these old types.
Second, I have reasons to believe, from numerous first hand accounts, and general condensed conclusions (from several frontline's worth of combat experience over several years), that the Spitfire, of all marks, at around 140/150/160 lbs per square feet of wingloading, actually has no hope to catch the FW-190A, at 215/230 lbs per square feet of wingloading, in sustained and level low-speed turns at medium-low altitudes: Contrary to widely accepted lore, the margin in favour of the heavier fighter over the lighter aircraft is in reality quite noticeable, and commented on by some pilots (many other pilots having evidently trouble believing it, even including, it seems, a few of its users) as long as speeds remain slow and the turning continuous, but that advantage is reversed when speeds are high and especially when the turning is abrupt, where the Spitfire then turns inside it quite easily until speeds again get slower.
Another observation is that the dive pull-out performance of the FW-190A is extremely poor: A 40° dive from 1200 m will, upon levelling off, produce a further 220 m (660 ft.) loss of altitude with a slight nose-up attitude, with a tremendous loss of speed as the aircraft decelerates violently "nose up" while still going down for a considerable distance, this with a "tendency to black-out the pilot" if speeds are high enough, yet Gs and the nose-up attitude (and thus the amount of deceleration while "mushing"), still responds to stick inputs...
High-speed turn performance is similarly poor but not quite as bad, with sometimes a similar "mushing" or a violent wing drop. Low-speed sustained turn performance is, on the other hand, excellent to superior, especially with reduced power, flaps and below 220 mph.
As can be seen, the correlation between dive pull-out performance and low-speed turns seems extremely poor.
All of these observations makes no sense according to current accepted flight physics, hence my question about actual wing bending measurements in level turns for these particular types of aircraft.
P.S. Of note is that the exact same type of relationship can be observed between the P-47D at 17 000 lbs and the Me-109G at 7 000lbs (about 15-20% lighter wingloading for the Me-109G), except that, in this case, the slow-speed sustained turn superiority of the P-47D is far larger compared to the Me-109G than is the case with the FW-190A vs the Spitfire (all Spitfire Marks being roughly similar on that aspect).
Note there are a lot of tests that conclude otherwise (except for Geman tests, which confirmed the P-47D's superiority in sustained turns to the Me-109G, and that of the FW-190A to the Me-109G as well), but I preferred large numbers of combat accounts because most controlled tests were contradictory among themselves, while combat seemed perfectly consistent in comparison.