Usually, a lot of forum roll rate discussions end up being about stick forces but there is another phenomena that comes into play as well, namely the aileron reversal speed. I won’t go into the details here but for those who are interested but unfamiliar with the term it can as most things in life nowadays be googled with success.

Comparing IRL data, the two German fighter plane types we have in BoX are quite different in this respect with the Fw-190 being one of the best with around 750 mph while the Me-109 (like the Spitfire!) is only a moderate performer in the order of 500-600 mph: Note that these are ballpark numbers for reference only and what I’m after here is how the Russian wooden winged aircraft fared so please avoid derailing this thread by nitpicking the other numbers!. Note that the aileron reversal speed is the theoretical limit and that roll performance is seriously degraded long before that: As an example, the Spitfire only retains circa 35% of its stiff wing rolling capability at 400 mph due to wing twist!

Now while wood is an excellent material for building airplanes with a good strength to weight ratio and excellent fatigue properties it does have a serious limitation: The resistance to bending and torsion in terms of deflection is miles away from that of metal. At lower speeds this is not much of an issue but at higher speeds it can become a serious problem.

Anyway, I have since I started flying in BoX tried to find some info on the aileron reversal speeds for the Russian wooden winged fighter as well. However I have come up short and even asking around has produced nothing.

Therefore, I have done some ballpark calculations to try to get a "feeling" for how a wooden wing compares to one in aluminium:

Russian Yak and LaGG plywood wing skin: Estimated average E modulus circa 9000 N/mm**2 (See data on Russian wood attached).

Dural Aluminium assumptions: E modulus 72000 N/mm**2, G modulus 27000 N/mm**2

For a ballpark estimate I rely on the so-called Bredt-Batho formula:

Twist derivate = T/(4xA**2) * Integral(ds/(G*t)

Where T is torsional load, A enclosed area, G the torsion modulus and t the skin thickness. Now ds integrated is the circumference of the enclosed area but in order to do a ballpark comparison assuming a wing of the same cross section we can conclude that it’s only the G modulus and the wing skin thickness we need to compare.

For the Russian plywood wing skin we as per above only have the E modulus which is in the order 9000 N/mm**2 but what we need is the G modulus which is not in the attachment but as far as I have been able to find out depending on the wood grain direction this is in the order of 12-15 times less than the E modulus. So my very rough estimate for the G modulus for the Russian wing skin is in the order of 600-750 N/mm**2.

Further, while the wing skin varies (circa 0.5 to 1.3 mm) on the German fighters I’m assuming its 0.8 on average and I’m assuming the wing plywood at 6 mm on the Russian planes.

So for a similar resistance to torsional deflection we need the G*t for wood to be the same. However, calculating G*t we get:

Aluminium: 27000*0.8= 21600 N/mm

Wood: 675*6= 4050 N/mm

If we factor these we can see that the aluminium wing is more than 5 times better at resisting torsional deflection than the wooden one.

My personal conclusion from this is twofold: One being that this may well be one of the reasons for the low Vne for the Russian fighters and two, that the Russian wooden winged fighters IRL probably had a low aileron reversal speed and consequently rolled very poorly at higher speeds, even worse than the Spitfire and Me-109 which were not known to do very well in this respect which is a bit at odds with what we see in BoX today I think.

Note my use of the words “may”, “probably” and “I think” above! I’m not saying I’m right and seeing some solid data would be lovely but until then I’m leaning towards the high speed roll rates of the BoX Russian wooden winged fighters being a bit on the high side.

And before someone lynches me for being a “Luftwhiner”, please read this and this post I made earlier on concerning my view of Russian wooden aircraft structural engineering!

So, what I’m hoping for here is a civil discussion with lots of nice input so that after a few pages we have a better understanding of how the Russian wooden winged fighters performed in this respect, and who knows, based on the high level of knowledge in this community, maybe even some constructive input to the developers.