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Another look at turn times

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Maybe I will write them a letter...

Sounds good. Maybe Kurfurst can validate the VDM Model numbers?
Holtzauge can you tell us how the correct description of this sort of data/diagramm is? If SchwarzeDreizehn write a inquiery to VDM, it will be useful to formulate this correctly.

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Did anyone test the turn rate in game? Could it be that the specification tab info is outdated if there were changes, like for example in the past FM patch?

In the P-40E section it lists a top speed of 601km/h at 5000 meters, which is too fast and close to the speed of the late N variant, but in game the plane does up to around 572 km/h at that altitude (and 575 km/h at 15000 feet, a bit lower than 5000 m), which is the correct top speed for the P-40E. I think this might have changed in the FM patch, alongside the the other changes the plane had, but the specification tab wasn't updated?

Edited by -=PHX=-SuperEtendard

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Devs still search for data of VDM propellers. anwser 882

https://forum.il2sturmovik.ru/topic/6203-obsuzhdenie-fm-v-obnovlenii-2012/page-23

 

What kind of data do they look for regarding the VDM prop ? I might have access to archived (Finnish) documentation with some on the VDM, and my Russian is too rusty to decipher what they need (and Google Translate might be misleading).

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What kind of data do they look for regarding the VDM prop ? I might have access to archived (Finnish) documentation with some on the VDM, and my Russian is too rusty to decipher what they need (and Google Translate might be misleading).

AnPetrovich told in DD138

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Just fell over this report whilst researching lift coefficients relevant for the F4U, F6F, Fw190, P-51 etc.: 

https://www.abbottaerospace.com/wpdm-package/naca-tn-1044-effect-of-mach-and-reynolds-numbers-on-maximum-lift-coefficient?wpdmdl=26904&ind=1480607408478

 

To sum up the findings of the report:

 

F6F, Fw190 & F4U (naca 23016-09) Clmax = ~1.40 (?) @ m 0.30 > ~1.35 @ m 0.35 > 1.24 m @ 0.40 > 1.17 m @ 0.45 > 1.03 @ m 0.5 

P-51........................(naca 66-2-215) Clmax = 1.17 @ m 0.30 > 1.08 @ m 0.35 > 1.05 @ m 0.40 > 1.03 m @ 0.45 > 1.05 @ m 0.5 

 

There's a Focke Wulf report which lists the CLmax of the Fw190 as being 1.58, but I believe this is probably based on windtunnel tests with a model wing at very low mach number. At real world Re numbers the CLmax appears to be around 1.35 @ mach 0.35 at least.

Edited by Panthera

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Just fell over this report whilst researching lift coefficients relevant for the F4U, F6F, Fw190, P-51 etc.: https://www.abbottae...d=1480607408478 To sum up the findings of the report: F6F, Fw190 & F4U (naca 23016-09) Clmax = ~1.40 (?) @ m 0.30 > ~1.35 @ m 0.35 > 1.24 m @ 0.40 > 1.17 m @ 0.45 > 1.03 @ m 0.5 P-51........................(naca 66-2-215) Clmax = 1.17 @ m 0.30 > 1.08 @ m 0.35 > 1.05 @ m 0.40 > 1.03 m @ 0.45 > 1.05 @ m 0.5 There's a Focke Wulf report which lists the CLmax of the Fw190 as being 1.58, but I believe this is probably based on windtunnel tests with a model wing at very low mach number. At real world Re numbers the CLmax appears to be around 1.35 @ mach 0.35 at least.

 

You are about 2 years late on that discussion :biggrin:

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You are about 2 years late on that discussion :biggrin:

 

Oh, well hopefully they got it right then  :biggrin:

 

Useful info for the upcoming P-51 though :)

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Would be nice with similar graphs for the other aircraft (109, Spitfire, Yak, La etc), but I am unable to locate any :-/

Edited by Panthera

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That said the ingame turn times are definitely suspect, the 109 in particular seems to seriously underperform.  

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Seeing as I haven't been a part of this forum for very long I was wondering wether these issues have at any point been addressed by the developers?

Edited by Panthera

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Btw, am I the only one who's noticed how well the MiG-3 turns? and at SL too even....

 

The developers definitely need to take a closer look at their Cd0, Cdi & Cl figures o.O

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Test them then and see if it overperforms/underperforms instead of just claiming they do because you think so.

 

They've already been tested by others, did you not read the thread?

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Now I originally wrote this in the general discussion subforum, but as correctly pointed out over there that really isn't the proper place to discuss the matter, thus I'm going to repost it in the proper subforum & thread:

 

Now I am in no way certain of what the main problem causing the 109's to underperform so badly in turns ingame is atm, but I if I was to base my assumption on the data sheets published by the developers (the ones showing all the aircraft performance specs etc), then it has something to do with using an incorrect max lift coefficient. I say this as the listed stall speeds don't match the real life ones at all.

 

To use an example the landing speed of the 109 K-4 was 150 km/h at 3,000 kg weight (power idle, gear & flaps down), which means the actual stall speed has to be lower (by at least 10 km/h) as you obviously don't want to stall on landing  ;)  Yet the considerably lighter Bf-109 G2 as pr. the published IL2 data sheets stalls out at 154 km/h gear & flaps down ingame.

 

That this is the culprit could also explain how performance figures such as speed & climb rate can remain accurate at the same time as you're nowhere near the Clmax in those flight conditions, but once you approach flight conditions where it becomes important then the FM starts to fall apart accuracy wise.

Edited by Panthera

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Btw, am I the only one who's noticed how well the MiG-3 turns? and at SL too even....

 

The developers definitely need to take a closer look at their Cd0, Cdi & Cl figures o.O

Dunno about Mig3 turn time at low alt in game but IRL Mig3 wasnt too good in these got 22s at 1km. Surly our Mig3 is too fast at the deck about 20-25 kph so maby it got also influence in better turn time. Mig3 was known as too heavy and not good in turn fight at low alt IRL.

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There was an interesting discussion about propeller efficiency and turn performance in this thread that was closed down since it was pointed out it belonged here in the FM section so I added the input I wanted to give in that thread here instead. I noticed that Panthera already tried to explain propeller efficiency in that thread and I agree with message he has been trying to get across but since there still seems to be a lot of scepticism both about this and my C++ simulation results I’d like to give my input as well. The DCS thread about propeller efficiency I have linked below also gives some insight into the how complex it is to model props and hopefully convey that the numbers I use have not been pulled out of a hat but actually have some research and though behind them.

 

Regarding the need for specific VDM data to do a proper Me-109 propeller model I certainly agree that that would be good to have but I disagree that it is needed to do a good enough Me-109 FM that is within a few percent of IRL: I actually had a good discussion about the P-51 propeller model with a DCS developer here a while back on the subject. Note that we both use generic NACA data as a base and that Yo-Yo in one reply states an opinion that I share a 100%: You can design a good prop using 3 or 4 blades and there are pros and cons with both solution but basically a well matched prop will come within a few percent of each other in terms of efficiency as long as you have a similar blade solidity (basically blade area x number of blades) that is matched to the power you are planning to run the prop with.

 

I for one think there is more at play here than the propeller efficiency to explain why the turn times in BoX in some cases is more than 20% too long and while I think it would be good to supply the VDM prop data if it can be found I’m more focused on the statement by the developers that the turn time of the Me-109 in some cases is around 2 s too long. This is the key thing here IMHO: The issue has been acknowledged and that is the important part. We don’t know the inner workings of the BoX FM but since the developers have acknowledged the issue and plan to fix it then that’s good enough for me.

 

Edit: Updated link to DCS P-51 propeller efficiency thread.

Edited by Holtzauge

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I will add that an incorrect CL max may be one of the issues that plagues the P 40E's inability to perform to it's historic ability, especially in the turn, (not withstanding the utterly restrictive and poorly implemented engine limits) so if the 109 suffers accordingly it is understandable how this could be one of the issues, along with prop modeling.

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I will add that an incorrect CL max may be one of the issues that plagues the P 40E's inability to perform to it's historic ability, especially in the turn, (not withstanding the utterly restrictive and poorly implemented engine limits) so if the 109 suffers accordingly it is understandable how this could be one of the issues, along with prop modeling.

 

Probably not. At least for the P-40 since the last FM revision, the CLmax is now the about the same as the Spitfire V's, depending as always on the weight range you choose. (1.32-1.35 P-40 vs 1.33-1.34 Spitfire V).  

 

 

Now I originally wrote this in the general discussion subforum, but as correctly pointed out over there that really isn't the proper place to discuss the matter, thus I'm going to repost it in the proper subforum & thread:

 

Now I am in no way certain of what the main problem causing the 109's to underperform so badly in turns ingame is atm, but I if I was to base my assumption on the data sheets published by the developers (the ones showing all the aircraft performance specs etc), then it has something to do with using an incorrect max lift coefficient. I say this as the listed stall speeds don't match the real life ones at all.

 

To use an example the landing speed of the 109 K-4 was 150 km/h at 3,000 kg weight (power idle, gear & flaps down), which means the actual stall speed has to be lower (by at least 10 km/h) as you obviously don't want to stall on landing  ;)  Yet the considerably lighter Bf-109 G2 as pr. the published IL2 data sheets stalls out at 154 km/h gear & flaps down ingame.

 

That this is the culprit could also explain how performance figures such as speed & climb rate can remain accurate at the same time as you're nowhere near the Clmax in those flight conditions, but once you approach flight conditions where it becomes important then the FM starts to fall apart accuracy wise.

 

Since the other thread is locked - presumably for straying into "FM is false" territory - you should calculate the CLmax for the 109s using the game performance data for stall speeds from the tech specs page. When I do that (in a spreadsheet for every plane) I get values for the 109 F2 and F4 of 1.38 to 1.41, using the clean configuration stall speeds.  Which I note was pretty much what you had assumed in a post in the "shower" thread.  

 

Whatever is causing the 109 turn time issue it is unlikely to be something so basic.

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Probably not. At least for the P-40 since the last FM revision, the CLmax is now the about the same as the Spitfire V's, depending as always on the weight range you choose. (1.32-1.35 P-40 vs 1.33-1.34 Spitfire V).

 

 

 

Since the other thread is locked - presumably for straying into "FM is false" territory - you should calculate the CLmax for the 109s using the game performance data for stall speeds from the tech specs page. When I do that (in a spreadsheet for every plane) I get values for the 109 F2 and F4 of 1.38 to 1.41, using the clean configuration stall speeds. Which I note was pretty much what you had assumed in a post in the "shower" thread.

 

Whatever is causing the 109 turn time issue it is unlikely to be something so basic.

 

It was with the G2 & G4 figures I noted a discrepancy.

 

Using the 165 km/h flight configuration figure from the IL2 data sheet I get a CLmax of 1.35 for the G4 (assuming a weight of 2,850 kg), which would definitely be too low - albeit the stalling speed with gear & flaps down are even more odd as the listed stalling speed of 153 km/h is 3 km/h faster than the real life recommended landing speed, which would be atleast 10 km/h above stalling speed.

 

By comparison I usually use a flight configuration CLmax of 1.45 for below 0.2 M and 1.41 above that, and these are based on the real life flight & windtunnel figures.

 

Thus I believe an inaccuracy in the CLmax figure used is probably atleast part of the reason (even if isn't the major one) behind the turn time issue, esp. since this coefficient can be inaccurate and have no effect on the accuracy of speed & climb rate performance, whilst by comparison an inaccuracy in prop efficiency would immediately cause issues in terms of accurately replicating those two performance aspects. 

Edited by Panthera

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BTW Panthera: You need to streamline your cow a bit: Looks like there is severe flow separation behind the front legs and tummy. In addition the brow rises too sharply just like the Spitfire front glass.   ;)

 

 

 

I know, but it was either that or a sacrifice in payload  :P   Also I needed an area of high pressure in the front to keep the nose/head from rising excessively with speed  :P

Edited by Panthera

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Apparently soviet testing also proved the 109F to be more maneuverable than the Yak-1 at 1,000 m, with a lower stalling speed also being noted:

 

"The Yak-1 was better than the Bf 109E, but inferior to the Bf 109F - its main opponent - in rate of climb at all altitudes, although it could complete a circle at the same speed (20–21 seconds at 1,000 meters). In comparison, a Bf 109, with its automatic wing slats, had a lower stall speed and was more stable in sharp turns and vertical aerobatic figures. A simulated combat between a Yak (with M-105PF engine) and a Bf 109F2 revealed that the Messerschmitt had only marginally superior manoeuvrability at 1,000 meters (3,300 ft), though the German fighter could gain substantial advantage over the Yak-1 within four or five nose-to-tail turns. "

Edited by Panthera

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Apparently soviet testing also proved the 109F to be more maneuverable than the Yak-1 at 1,000 m, with a lower stalling speed also being noted:

 

"The Yak-1 was better than the Bf 109E, but inferior to the Bf 109F - its main opponent - in rate of climb at all altitudes, although it could complete a circle at the same speed (20–21 seconds at 1,000 meters). In comparison, a Bf 109, with its automatic wing slats, had a lower stall speed and was more stable in sharp turns and vertical aerobatic figures. A simulated combat between a Yak (with M-105PF engine) and a Bf 109F2 revealed that the Messerschmitt had only marginally superior manoeuvrability at 1,000 meters (3,300 ft), though the German fighter could gain substantial advantage over the Yak-1 within four or five nose-to-tail turns. "

 

That WIKI quote gets trotted out whenever someone new pops up who tries to argue that on top of all their other advantages, the 109 should out turn Yaks in slow turning fights.  :biggrin:

 

That is from an early test of a Yak production model that had cooling issues, since it was still using an inadequate oil cooling system. In the test, the Yak did not use full power.

 

The Yak-1b had a much improved oil cooling system and in simulated combat " outperformed [bf109] completely in turning fights ". A Yak-1b could do a 360 low altitude turn in 17-18 seconds according to Soviet tests. (reference: Gordon, Khazanov "Soviet Combat Aircraft", vol. 1, pp. 128-129).

Edited by Sgt_Joch

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It was with the G2 & G4 figures I noted a discrepancy.

 

Using the 165 km/h flight configuration figure from the IL2 data sheet I get a CLmax of 1.35 for the G4 (assuming a weight of 2,850 kg), which would definitely be too low - albeit the stalling speed with gear & flaps down are even more odd as the listed stalling speed of 153 km/h is 3 km/h faster than the real life recommended landing speed, which would be atleast 10 km/h above stalling speed.

 

By comparison I usually use a flight configuration CLmax of 1.45 for below 0.2 M and 1.41 above that, and these are based on the real life flight & windtunnel figures.

 

Thus I believe an inaccuracy in the CLmax figure used is probably atleast part of the reason (even if isn't the major one) behind the turn time issue, esp. since this coefficient can be inaccurate and have no effect on the accuracy of speed & climb rate performance, whilst by comparison an inaccuracy in prop efficiency would immediately cause issues in terms of accurately replicating those two performance aspects. 

 

I agree that there is an oddity in the G-4 numbers - but it depends which specific set of data you use. The tech specs have a range of stall speeds, and a range of weights. To get a standard comparison, I only looked at the flight configuration figures (ie F+G up) since these are most easily understood in comparison to the airfoil and are after all what matters in most flight - including turning flight. 

 

Pairing the maximum T/O weight with the top of the stall speed range I get 1.39 - almost identical to the G-2. At minimum operation weight, which I paired with the bottom of the speed range, I get 1.26 - which is an outlier. Note however, that this is only a matter of a 7kph increase in the listed stall speed. I do not know why this is so and it is an interesting question - possibly an error - but I doubt very much that this is because the team have somehow plugged in a wrong CLmax figure. We do not even know for sure if CLmax is even an input in the BoX model, as opposed to an output which is used as a check.

 

edit - If it is an error in this specific case - they should have plugged in 1.36 instead of 1.26 - this still does not address why the other 109s appear to have a recognized discrepancy in turn times.

 

I would point out - was responding in the "shower" thread just as it got locked ;) - that the comments I was making about the difference in the speeds seen in BoX and manual speeds is important and general: you should not confuse it with the position error correction issue that is relevant at higher speeds. This is mainly a speed function - the error at or close to stall is an AoA issue.  It is a grave mistake to brush it off as an error with one test - it was a repeated phenomenon noted also in the case of the Spitfire by the RAE and independently by US testers, the cause of which was understood and discussed in NACA reports. See the P-40 thread for details.

 

This is why I think it is instructive to look at the full range of BoX modelling to put individual points in context.  If you take the stall speed figures from manuals for any of the UK or US types and plug them in you get CLmax values that are impossible. 

 

Here are my most recent versions of this calculation - which include some non-BoX numbers as well as a comparison.

 

post-15424-0-59314700-1517457556_thumb.png

 

post-15424-0-19930400-1517457583_thumb.png

 

post-15424-0-63942200-1517457603_thumb.png

Edited by unreasonable

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Btw, am I the only one who's noticed how well the MiG-3 turns? and at SL too even....

 

The developers definitely need to take a closer look at their Cd0, Cdi & Cl figures o.O

 

Lead FM engineer on why opening testing to a larger base is unproductive 

 

"And that's why, in our case, it's extravagantly different. 

It will be wasteful to waste time responding to that stream of useless (for the developer) information that will rush from the "testers" if we open the Pandora's box. 

Why useless? Because we, the developers, are better than any user aware of all the problems in the FM (and we are working on them, but, alas, not over all at once, but in stages). And in this regard, there is not much point in "opening" our eyes to the fact that the aircraft X is faster at 10 km / h than it should be according to the report of Y."

 

Cheers, Dakpilot

  • Upvote 1

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That WIKI quote gets trotted out whenever someone new pops up who tries to argue that on top of all their other advantages, the 109 should out turn Yaks in slow turning fights. :biggrin:

 

That is from an early test of a Yak production model that had cooling issues, since it was still using an inadequate oil cooling system. In the test, the Yak did not use full power.

 

The Yak-1b had a much improved oil cooling system and in simulated combat " outperformed [bf109] completely in turning fights ". A Yak-1b could do a 360 low altitude turn in 17-18 seconds according to Soviet tests. (reference: Gordon, Khazanov "Soviet Combat Aircraft", vol. 1, pp. 128-129).

To be honest the lower stalling speed is what stuck out the most as that is definitely not the case ingame.

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Lead FM engineer on why opening testing to a larger base is unproductive 

 

"And that's why, in our case, it's extravagantly different. 

It will be wasteful to waste time responding to that stream of useless (for the developer) information that will rush from the "testers" if we open the Pandora's box. 

Why useless? Because we, the developers, are better than any user aware of all the problems in the FM (and we are working on them, but, alas, not over all at once, but in stages). And in this regard, there is not much point in "opening" our eyes to the fact that the aircraft X is faster at 10 km / h than it should be according to the report of Y."

 

Cheers, Dakpilot

"pls me109 engine limits 1.98 ata 30 minutes wartime emergency or else i stop playing. proof is xyz" 

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Even then you will not get this performance. Live from Berloga. Cheat fest.
gNNn2Au.jpg

oOonXnc.jpg

Edited by JG27_Kornezov

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To be honest the lower stalling speed is what stuck out the most as that is definitely not the case ingame.

 

In game specs Yak-1 -69 has higher stall speed than 109E and 109F2 also slightly higher than F4 but that was not a comparison in you ''quote''

 

69 series Yak is no doubt later model than in the comparison, so likely has lower stalling speed in same respect that 1b has slightly lower stall speed

 

Cheers, Dakpilot

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Hard to interpret those charts, but looking at the bottom one, extrapolating a 9.3 second turn is not on. The scale at the bottom is in 5 second increments. If you look just before the spike, the blue line (turn rate) goes above 20 degrees/s over about 10 seconds. Average turn rate during that period is about 30 degrees/s.

 

So that is 12 seconds for 360. But this is not a flat turn - speed goes from 500 to 800 kph in the same period then back to 650. The plane is diving while turning - not the same thing as the turn tests at all. 

 

 

Just by looking at the chart I would say that the steep drops after the extreme peaks, hint toward a lag or netcode porblems.

 

Could be that too, but even if it is not the question is what exactly is the "turn rate" in degrees per second actually measuring. If it is just heading, that can be changed very quickly by a diving plane rolling and corkscrewing - not at all comparable with a sustained level turn.

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In game specs Yak-1 -69 has higher stall speed than 109E and 109F2 also slightly higher than F4 but that was not a comparison in you ''quote''

 

69 series Yak is no doubt later model than in the comparison, so likely has lower stalling speed in same respect that 1b has slightly lower stall speed

 

Cheers, Dakpilot

 

 

 

No it's the stall speeds of the G series that are odd, and incidently it's also the G series that performs the worst turn time wise ingame in comparison with the real life data available. The ingame clean G2 currently turning like the gondola equipped G2 tested by the Soviets.

 

 

I agree that there is an oddity in the G-4 numbers - but it depends which specific set of data you use. The tech specs have a range of stall speeds, and a range of weights. To get a standard comparison, I only looked at the flight configuration figures (ie F+G up) since these are most easily understood in comparison to the airfoil and are after all what matters in most flight - including turning flight. 

 

Pairing the maximum T/O weight with the top of the stall speed range I get 1.39 - almost identical to the G-2. At minimum operation weight, which I paired with the bottom of the speed range, I get 1.26 - which is an outlier. Note however, that this is only a matter of a 7kph increase in the listed stall speed. I do not know why this is so and it is an interesting question - possibly an error - but I doubt very much that this is because the team have somehow plugged in a wrong CLmax figure. We do not even know for sure if CLmax is even an input in the BoX model, as opposed to an output which is used as a check.

 

edit - If it is an error in this specific case - they should have plugged in 1.36 instead of 1.26 - this still does not address why the other 109s appear to have a recognized discrepancy in turn times.

 

I would point out - was responding in the "shower" thread just as it got locked ;) - that the comments I was making about the difference in the speeds seen in BoX and manual speeds is important and general: you should not confuse it with the position error correction issue that is relevant at higher speeds. This is mainly a speed function - the error at or close to stall is an AoA issue.  It is a grave mistake to brush it off as an error with one test - it was a repeated phenomenon noted also in the case of the Spitfire by the RAE and independently by US testers, the cause of which was understood and discussed in NACA reports. See the P-40 thread for details.

 

This is why I think it is instructive to look at the full range of BoX modelling to put individual points in context.  If you take the stall speed figures from manuals for any of the UK or US types and plug them in you get CLmax values that are impossible. 

 

Here are my most recent versions of this calculation - which include some non-BoX numbers as well as a comparison.

 

attachicon.gifCLmax snip 1.PNG

 

attachicon.gifCLmax snip 2.PNG

 

attachicon.gifCLmax 3.PNG

 

Yes there's a difference between position error correction at speed and at low speed, and that due to the AoA as you mentioned. However the difference is pointed out in the German 109F & E manuals, where again the landing speeds are nowhere near 60 mph :)  The correction error was in the range of 10 km/h in this case.  Either way it should be noted that landing speed is always a good safe margin above stalling speed.

Edited by Panthera

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Are those recent charts done using Tacview?

 

 

No it's the stall speeds of the G series that are odd, and incidently it's also the G series that performs the worst turn time wise ingame in comparison with the real life data available. The ingame clean G2 currently turning like the gondola equipped G2 tested by the Soviets.

 

 

 

Russian tests of German aircraft done on 'superior' Russian fuel  ;)  :ph34r:

 

(in fact there was an article suggesting one 'outlying' performance discrepancy on a german test aircraft was due to using very high octane fuel from a good batch from Baku,

 

but I do not remember where or when I read that, but I am certain I did, although I put this down as unconfirmed and make no claims to accuracy  :o:  )

 

Cheers, Dakpilot

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No it's the stall speeds of the G series that are odd, and incidently it's also the G series that performs the worst turn time wise ingame in comparison with the real life data available. The ingame clean G2 currently turning like the gondola equipped G2 tested by the Soviets.

 

 

 

Yes there's a difference between position error correction at speed and at low speed, and that due to the AoA as you mentioned. However the difference is pointed out in the German 109F & E manuals, where again the landing speeds are nowhere near 60 mph :)  The correction error was in the range of 10 km/h in this case.  Either way it should be noted that landing speed is always a good safe margin above stalling speed.

 

Can you link please? I have neither. The 109 G manuals I have show no stall speeds at all.      Alternately summarize in a table - throwing the odd number into a post does not help to sort out what it is you are highlighting as evidence of a problem at all. 

 

The figures in my tables are all the clean configuration speeds - ie stall at Vmin with flaps and gear up.   Using landing speeds is going to cause all sorts of problems - stalling speed with F+G up is completely different to with F+G down.  So CL with flaps and gear down is radically different - much higher - to that in clean configuration, which is the whole point of flaps, and not going to help at all in understanding issues in normal flight CLmax, if indeed there are any., since we cannot compare the results with the data on the airfoil used in the wing.

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