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High speed roll rates of Russian aircraft (with wooden wings) too high?


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#41 unreasonable

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Posted 17 April 2017 - 14:47

Certainly helpful to me - the little blue graph makes it very clear why a reversal speed that is impossible to reach can give useful information, even if approximate information, at lower speeds. But then I always find graphic representations easier to grasp than... pretty much anything really. I suppose it does matter what is the shape of that curve.

 

I have to admit though, after reading all this, I am still not clear whether the Yak 1 wing should be stronger than the 109 F wing, for instance, or perhaps I should say be more resistant to certain types of damage and stress combinations.   Having had my wings removed often enough while flying both types, I am fairly neutral about what happens in the game!


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#42 Holtzauge

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Posted 17 April 2017 - 15:50

Certainly helpful to me - the little blue graph makes it very clear why a reversal speed that is impossible to reach can give useful information, even if approximate information, at lower speeds. But then I always find graphic representations easier to grasp than... pretty much anything really. I suppose it does matter what is the shape of that curve.

 

I have to admit though, after reading all this, I am still not clear whether the Yak 1 wing should be stronger than the 109 F wing, for instance, or perhaps I should say be more resistant to certain types of damage and stress combinations.   Having had my wings removed often enough while flying both types, I am fairly neutral about what happens in the game!

 

Well I started out thinking (in the OP) that the Yak wing would be torsionaly weaker and have a lower aileron reversal speed but then JG13_opcode found the Russian pdf file with wood data in which JtD found a table which indicated that the torsion modulus for the wing skin was much higher than I estimated initially. So using the revised data the difference in wing twist between a wooden and aluminium wing (same design) dropped from a factor 5 to 1.6 and when you on top of that add that the Yak and La had a double spar then my conclusion from what we have so far is rather that there is currently no basis to say that the Russian fighters had a substantially lower aileron reversal speed like I was thinking initially. So, like in the P-40 case, it looks like we need some more data to get anywhere with this.

 

Would be nice if our friends in the Russian forum could come up with some Russian calculations and flight test data like the German ones we have for the Me-109F! ;)


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#43 BlitzPig_EL

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Posted 17 April 2017 - 15:50

I thought the discussion was about roll rates, not having wings ripped off?

 

At least that is how it started.

 

What Dave said needs to be considered.  It's possible that a wood wing and a metal wing could very well have the same maximum roll rate, yet the metal wing would achieve that maximum rate sooner because it does not flex as much on initial aileron application.

 

What we are faced with in the sim is mostly visual evidence of initial application of ailerons, typically in a defensive situation.  Now the thorny part...  Measuring maximum roll rate isn't exactly easy in a sim, measuring initial roll rate is multiple times harder.  Now add the fact that I have never seen an initial roll rate, or roll rate acceleration curve statistic for a WW2 fighter, we are left with nothing to compare our in game performance to, even if we could accurately measure it.

 

So, once again we are back to "feelings" based on a virtual dogfight, or multiple ones, with no way to verify anything because of all the unknowns... Was an abnormal joystick curve applied to give an edge to the opponent (no matter the plane type)?  Do different joysticks react differently to input?  Plus all the anomalies of internet connectivity, etc...  Add the effect of air speed to roll rates, and how closely, or not we are paying attention to the ASI during a dogfight, and as I said, it gets thorny.


Edited by BlitzPig_EL, 17 April 2017 - 15:51.

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#44 AndyJWest

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Posted 17 April 2017 - 17:29

If BoX provided the sort of telemetry that Devicelink did for the original IL-2, it might be possible to do some more objective testing, though I can state from personal experience that it is never as simple as you hope, and you often end up with more new questions, rather than the sort of definitive answer you expect. The developers have stated in the past that something of the sort may come at some point, but I don't think it is much of a priority - and even with it, we would still be stuck with not having much in the way of real-world data to compare our findings against. Ultimately we may have to accept that there are going to be some things in the simulation that are based more on what the developers consider 'reasonable' than on any verifiable data, and that lacking such data, we are likely to disagree amongst ourselves as to whether the developers are doing it right. Personally, I can't see any reason to conclude that anything is obviously 'wrong' in regard to roll rates, and as this thread has shown, it isn't going to be possible to make definitive assertions regarding say the effect of different methods of wing construction as a factor. There are too many unknowns, and you can't reduce it to e.g. a simple comparison of material characteristics.


Edited by AndyJWest, 17 April 2017 - 17:31.

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#45 Dave

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Posted 18 April 2017 - 12:02

Thanks for the lecture but as an aeronautical engineer already having done the type of structural analysis you refer to above on aircraft structures I still think that doing ballpark estimates and having the kind of constructive dialogue we had so far in this thread can be helpful as well.

Not a lecture ... just a tongue in cheek suggestion that you can "analyze" this all you like piecemeal and by supposition but until you consider the whole you don't get even close to reality. As it happens I write this kind of software for a living.


The developers have stated in the past that something of the sort may come at some point, but I don't think it is much of a priority

I have personally requested this twice and both requests were responded to with an emphatic "no". 


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#46 Dave

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Posted 18 April 2017 - 12:13

So far we have been discussing aileron reversal speed and not the effects of inertia on roll acceleration.

Yeah I gathered that. My bad for going OT - The point I was trying to make is that you can't infer much about torsional stiffness from the materials alone - the construction (as you later concluded) plays an important role. I introduced angular momentum in roll because it is the price the Russians paid for wooden construction sufficiently stiff to resist the torsional forces you were talking about - mass.


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#47 Holtzauge

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Posted 18 April 2017 - 16:16

Not a lecture ... just a tongue in cheek suggestion that you can "analyze" this all you like piecemeal and by supposition but until you consider the whole you don't get even close to reality. As it happens I write this kind of software for a living.

 

Well rest assured that your opinion of what you call my analysis within citation marks is mirrored by mine on your level of “expertize” based on the framing of your arguments so far and that you happen to write this kind of software "for a living" is no more impressive than that I happen to have done FEM structural design using ANSYS and even done strip theory based calculation and dimensioning of a composite wing calculating exactly the type of torsional twist we have been discussing here. This is also why I know you can make just the type of material based ballpark estimates we have been doing here since I have been working as an aeronautical engineer “for a living”.

 

I think the discussion we were having in this thread up until now was constructive but the latest developments is very reminiscent of what happened here so unless something constructive pops up I think I’ll call it a day.


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#48 Dave

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Posted 19 April 2017 - 12:13

Well rest assured that your opinion of what you call my analysis within citation marks is mirrored by mine on your level of “expertize” based on the framing of your arguments so far and that you happen to write this kind of software "for a living" is no more impressive than that I happen to have done FEM structural design using ANSYS and even done strip theory based calculation and dimensioning of a composite wing calculating exactly the type of torsional twist we have been discussing here. This is also why I know you can make just the type of material based ballpark estimates we have been doing here since I have been working as an aeronautical engineer “for a living”.
 
I think the discussion we were having in this thread up until now was constructive but the latest developments is very reminiscent of what happened here so unless something constructive pops up I think I’ll call it a day.


Wow - you can just chill out a bit. I think you are reading more into my words than I wrote. And I certainly didn't mention my job as a dick size comparison. I just know from experience how large the discrepancies can be from the kind of analysis being done here and the actual results of an FEA and then again of the whole airframe in physical test. I don't need to "impress" you because frankly I don't give a shit how knowledgeable or experienced you might think I am.

In fact, if you shelved your defensiveness for a moment you might notice that I was agreeing with you, apologising for going off topic, and trying to explain why I even brought up roll rate in the first place.

Analyse was in quotes to indicate that I understood that you weren't actually claiming yours was a a detailed analysis - it wasn't a jibe. Why does everyone get so freakin touchy about everything and go off half cocked all the time as soon as you start discussing the FM.

PS - for the avoidance of doubt, that last one was a rhetorical question. Can't be too careful here it seems.
Incidentally, I didn't bother responding to JtD in the thread you linked because discussion by that point seemed futile and I didn't feel like wasting any more of my time.
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#49 Dave

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Posted 19 April 2017 - 12:42

This would be where you made the only comment on this thread which attempts to discount someone else's assertion based upon its author's vocation.

 

Thanks for the lecture but as an aeronautical engineer already having done the type of structural analysis you refer to above on aircraft structures I still think that doing ballpark estimates and having the kind of constructive dialogue we had so far in this thread can be helpful as well.

 

 

Below is the sum total of my "arguments" on this thread. It isn't clear what part of the "framing" of them you have an issue with. My remaining posts were direct responses to clarify your misunderstanding of my intent.

 

800mph is supersonic.

 

 

No, what you can see is that, for the same thickness, a sheet of aluminium has 5 times the torsional stiffness of a sheet of plywood. There is more to a wing than its skin. And there is more to roll rate than wing material. A better argument would be that being heavier for the same design load, the wooden wings would add more mass further from the CG which should increase inertia, reducing the rates of rotational acceleration and deceleration for the same wing section, area, plan, and aileron geometry. Lots of variables in there and it really affects acceleration (ie snappiness) more than angular velocity limits.
I think the only way you're going to find out one way or another is to perform an FEA of forces (and therefore stresses and deformation) integrated over the entire airframe. The software will take you a while to write and you'll likely need to buy yourself some large scale compute cluster time - or maybe start learning CUDA and build a GPU-based home super computer.


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#50 Dave

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Posted 19 April 2017 - 12:48

And while I'm in the mood for quoting ... this would be the first sentence of the first post of this thread entitled

"High speed roll rates of Russian aircraft (with wooden wings) too high?" where you introduced roll-rate as the topic of discussion ...

 

 

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.

 

 

And this would be where you condescendingly pulled me up for discussing the effect of inertia on roll rate ...

 

 

No, I don’t agree about this being a better argument because you are muddying the waters by mixing two different effects here: So far we have been discussing aileron reversal speed and not the effects of inertia on roll acceleration. Roll acceleration and the effects of inertia are of course also interesting but aileron reversal speed is a separate phenomena as outlined here.

 

I guess I owe you an apology for apologising for introducing talk of roll rate to this discussion.


Edited by Dave, 19 April 2017 - 12:50.

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#51 unreasonable

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Posted 19 April 2017 - 13:20

Is that you, Crump?


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#52 Holtzauge

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Posted 19 April 2017 - 15:42

Is that you, Crump?

 

Or maybe it's just that that slot is empty? Nature abhors a vacuum.......


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#53 JtD

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Posted 19 April 2017 - 18:31

Is that you, Crump?

Impossible, because

I didn't bother responding to JtD

would never happen.

On the technical point, Dave's statement as such is true. A wooden wing equivalent to an aluminium one in terms of stiffness, strength and layout has a higher weight and will therefore reduce roll acceleration. In case of the aircraft in game, we can add the presence of a significant amount of fuel in the wings of Soviet fighters, which would emphasize the effect. There have been plenty of discussions on this issue already, typically dead ended.

It's true that this isn't really the point of this discussion. However, I for one wouldn't mind new info on any of these issues, even if it isn't 100% on topic.
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#54 JtD

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Posted 23 April 2017 - 07:33

Not really on torsional stiffness: Taken from this Soviet test report on a Bf109G2, I've taken the little data available and put them into a format we're more used to.

Input data is:
- roll rate per degree of aileron
- stick force per roll rate
Both given over speed only, in a linear relationship.

Issues with that:
- roll rate per degree of aileron is not linear
- roll rate per degree of aileron over speed is not linear
- stick force per roll rate over speed is not linear
- stick force per angle of aileron is not linear
- data is limited to speeds below 500/450/400 depending on type
- no statement about the altitude the figures are valid for
- I can't see how torsional stiffness is being factored in

All in all, the data is fairly superficial, but it's the only source I know that contains a side by side comparison of German, Soviet and US aircraft. So I hope it is still interesting.

I have used a force limit of 30kg for each aircraft. I've also assumed that degree of aileron refers to total deflection of both ailerons divided by two. I took the maximum aileron deflection out of the respective aircraft manuals.

Compared to NACA data of the P-39, the Soviet data has lower control forces and reaches higher maximum rolling velocities, but it's not totally different. Part of the differences are probably explained by the non-linearities that were in the US data, but not in the Soviet data.

Attached Files


Edited by JtD, 23 April 2017 - 07:35.

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#55 Holtzauge

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Posted 23 April 2017 - 11:57

Based on your calculations it looks like the Yak-9 is quite a bit better than the Me-109 in terms of roll then: If I understand the figures and what you are saying then this would be without the elastic deformation effects like aileron reversal so the absolute roll rates will of course be lower but then that applies to all aircraft, also for the Me-109. So as a basis of a ballpark comparison it’s quite a good chart and it's also interesting to see the Russian assessment of the I-16 and P-39 as well.

 

I did a post a while back where I posted a figure with the Me-109 roll characteristics which does include the effects of wing torsion and also the  give and flex in the control circuit. It’s quite interesting to see how much the Me-109 loses due to these effects compared to the Russian linear analysis. Using the figure I posted there it looks like there is a not to bad correlation with the Russian data if you look at the linear effects: If you take away the aeroelastic effects in the German chart it looks like you get a max roll rate of roughly 2, i.e. 115 deg/s at circa 500 km/h TAS so it’s not too far away from the Russian data.

 

Would be good also to understand more about the differences (if any?) between the Yak-1 and Yak-9 in terms of things that may affect the roll rate like aerodynamics, stick gearing and wing build up etc. to figure out how applicable that data is the Yak we have in-game.

 

Anyway good stuff and thanks for doing the calculations and graph! :good:


Edited by Holtzauge, 23 April 2017 - 12:05.

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#56 JtD

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Posted 23 April 2017 - 16:40

Forgot about that 109 chart, thanks for the reminder. It's interesting to see that the Bf109 data is indeed a fairly good match (at least much better than I had expected), assuming the 15° is the total aileron deflection divided by two.

Early Yak-1's had a +26/-11 range for the elevators, on Yak-9's it was +22/-12. It's possible that this was changed for the Yak-1 as well. Later -9's got a different wing tip, but I think the data is for the earlier ones. The landing gear was different between -1 and -9..

However, all in all there'd be little to chose between the two in terms of roll rate, just as there was in terms and speed and climb.
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#57 Holtzauge

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Posted 23 April 2017 - 18:57

Yes, it does look like there is little to choose between the two when comparing the linear stiff wing data, or rather that the Yak is somewhat better since the roll rate is always above the Me-109 and that the break point between deflection and force limited roll rate occurs at a higher speed. However, seeing how much the Me-109 loses due to wing twist and control circuit flex, circa 115-80=35 deg/s it seems, it would be interesting to see similar data on the Yak. Of course, the ballpark estimate we have in this thread does not indicate any big difference in torsional stiffness but then that is just what it is: an estimate and I would not be surprised if things turn out to be different than expected and I'm still really curious how well the Russian wooden planes handled high dynamic pressures.

 

Anyway, looks difficult to get anywhere closer without new data so I was thinking maybe to see if =MG=Dooplet11 or some of the other guys in the Russian forum have any ideas but I have not gotten around to it yet.


Edited by Holtzauge, 23 April 2017 - 18:58.

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#58 Caudron431Micha

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Posted 25 April 2017 - 09:28

 It's possible that this was changed for the Yak-1 as well. Later -9's got a different wing tip, but I think the data is for the earlier ones. The landing gear was different between -1 and -9..

However, all in all there'd be little to chose between the two in terms of roll rate, just as there was in terms and speed and climb.

 

As far as i know Yak1 and early Yak9  had different wing shapes and construction. In 42/43 there was no longer as much shortage on some metals and this could allow a mixed construction for the Yak9 (and before Yak7D/DI) wings: double longerons and other parts were metalic, the rest was similar to Yak1/7 AFAIK. Wing aspect and weight changed from 560 kg to 481 kg with the advantage of leaving a lot of room inside the wings. I suspect that this along with the different landing gear (didn't know that, have you more info on it?) in the Yak9 allowed installation of the more important fuel tanks that allowed the Yak9D and DD increased range.

 

http://vvs.hobbyvist...lev/FuelGauges/

 

If metal torsional effect vs wood is a decisive factor, then surely normal early YaK9 (also Yak7D/DI featuring lighter and mixed construction wing)  would be better in rate of roll than all wooden winged Yak1 and Yak7? if someone knowledgeable knew the rates of roll of these types maybe it could give us elements, after all these were very similar types.


Edited by Caudron431Micha, 25 April 2017 - 09:55.

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#59 Holtzauge

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Posted 26 April 2017 - 15:50

Interesting info on the Yak wings in the link so thanks for sharing. Concerning the impact on roll rates, I think it was mentioned before about the wing tanks: This will have a large impact on roll acceleration but not impact the max roll rate since this is due to the aerodynamic and wing stiffness characteristics as discussed before. So while the basic structural weight change in the wings will have an impact, the major effect will be due to the fuel in the wing tanks which will be there irrespective if the wings are mostly of wood or aluminium. However, if the basic structure is changed as what seems to be the case in the Yak 9 with more aluminium incorporated this will probably change the wing torsional stiffness and probably for the better as well as it can be assumed that a change introduced in later models would be for better not for worse.

 

However, in some ways I’m beginning to doubt we will get a good grip on roll rates because it’s becoming more and more clear that the Russian general design practice with different series incorporating different solutions will mean that even if we do get a number, this will probably only tell us about the characteristics of that particular Yak series and we would still be in the dark when it comes to the others. Still, would be nice with something, since now I don’t believe we have a since aileron reversal speed number for any Russian fighter for any series which seems a bit strange seeing all the other engineering and performance data out there……


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