P-40 turn rate/Flight model check

[Holtzauge]

@Holtzauge - should leave you to reply to posts directed to you, apologies. Thought you had gone off to do something else. 

 

No problem and thanks because I interpreted your post as an effort to get the thread back on track and as such it was much appreciated.

[unreasonable]

Yup I see what you mean and I think I misinterpreted figure 5: The text under figure 6 is quite clear on the point so as you say so there seems to be more to this after all......

 

But having looked at the dearly departed Klaus_Mann's post - and Zach's which backs it up with more glider knowledge, I think it may well be this phenomenon rather than anything different, just exhibited to a much greater degree and/or at a lower AoA/AoY than the graph is showing.

 

Ie we can get to the outside of the P-S curve where the total really does show an severe under-reading of speed at relatively low AoAs, when combined with low speeds: just as in the glider cases demonstrated.

 

I am fairly comfortable now, given this data and analysis, in agreeing with Z that this should be treated as a general issue - in which case the "mystery" of the P-40 stall speeds goes away. I have to admit I would still like to have a more definitive explanation of why the physics in the paper forecasts a small error, while the glider example shows a large error, just in case we are still missing something crucial.

 

I must say though that Venturi highlighting the the problem of manual stall speeds and their implications has led to a very interesting discussion, and perhaps a better understanding of the difficulties in interpreting BoX results alongside RL data, at least from my POV, so +100 to him, even if he is not necessarily getting the answers he might have preferred. (So far ) 

[Kurfurst]

Well I'm sorry to hear you think I'm doing it wrong but there are different ways of doing turn analysis and the one I'm using uses the Clmax at the glide as a base. For me the convention has always been to use the power off Clmax as a base so I would love to hear how you do it since you say I'm doing it wrong. What is your method Kurfurst?

 

That being said I too get a much higher Clmax with power on just like M. B. Morgan and in my C++ simulation I get a power off Clmax of 1.36 and a full power on Clmax of around 1.8 much like M. B. Morgan does.

 

As to the "anomalies" of my P-40 calculation you talk about what are those? My estimate (24.5 s) is currently within 1% of the current IL-2 estimate of 24.3 s so we both have it wrong then? Can you please outline where the Il-2 developers and I got this wrong and what the "anomalies" are?

 

And what are the "pitfalls" of RAE TN 1106? Did we all miss something there?

 

Well, I think you need to start with Post number 6. https://forum.il2sturmovik.com/topic/25323-p-40-turn-rateflight-model-check/?p=392002

 

Now, the actual valid data for the P-40 appears to be 18 secs for the C model and 19,2 secs for the E model. Yes, I know you have penchant for dismissing real world data when it doesn't suits you, but let's just not ignore the real world for a moment.

 

Sure, there are multiple ways of arriving at full throttle Clmax. Since you are very silent about how you got it, I must suppose that you have made a number assumptions (without solid base of auxilarry data) in the process of recalculating it from gliding Clmax, all which introduced a significant amount of error tolerance into your calculations, you got in the end a result that was 26% off from the real values.

 

As to what caused it, you are the only one to know that for sure. Picking the wrong Clmax? Accidentally miscalculating it? Making a series of error-prone assumptions and simplifications in the intermediate calculations? Making an error in the formulae itself? Or perhaps a number of interpretation errors/overlook of details for the data in the original documents (see your thread on G-2 climb rate for examples), or simply choosing to believe only the data that suits the results you wish to be correct? Or simply choosing a too wide brush size in MS Paint?

 

We do not know for sure. We know however that its well off the real world data that is very, very simple to measure without too much room for error.

 

In the end what matters somehow you got 24,3 secs, which is as much as 26 % off from the real values. Well, if you can't see what the anomaly is, I am afraid its a case of not seeing the forest for the trees.

[JtD]

Just for the record, I'm dismissing the 19.2 seconds as well. With the information at hand, there's just no way to accept it.

 

If you calculate the overall efficiency of the P-40E in a turn like that, even assuming clmaxes heavily increased by propeller slip stream, you end up at efficiencies above 60% (same approach as described in the other topic). For reference, other aircraft are somewhere around 40%-50% using real life numbers. A P-40E-1 at 1150hp and 3840kg will not sustain a turnrate of 360°/19,2s at 1000m in a standard atmosphere. It's just not in the physics.

 

We're missing some information here. A high clmax would explain the good turn time to some extent, and since the 19.2s have bothered me for several years now, it would be really interesting to finally find an explanation where all things add up.

[Kurfurst]

How do you address though that this 19 secs agrees very well with accounts and assessments from both sides veterans, flight test conclusions though...? 

 

Its not like its difficult to measure how fast an aircraft makes a full, sustained turn. 

[Farky]

A P-40E-1 at 1150hp and 3840kg will not sustain a turnrate of 360°/19,2s at 1000m in a standard atmosphere. It's just not in the physics.

 

We're missing some information here. A high clmax would explain the good turn time to some extent, and since the 19.2s have bothered me for several years now, it would be really interesting to finally find an explanation where all things add up.

 

What if this is for instantaneous turn? Do we know for sure that this is time for sustained turn?

[JtD]

How do you address though that this 19 secs agrees very well with accounts and assessments from both sides veterans, flight test conclusions though...?

 

Its not like its difficult to measure how fast an aircraft makes a full, sustained turn.

It could be different aircraft condition and/or power regime. 3840kg/1150hp make 69% at a cl of 1.34. 3600kg/1500hp make 45% at the same cl. That corresponds roughly to full throttle at typical flying weights (6 guns, 50% fuel&ammo). From what I know, something like that would make sense.

 

Or, also possible, it's a particularity about the aircraft I fail to see. I'm totally open to that, but it needs to be comprehensible. Or apprehensible. Whatever the proper English word. It needs to make sense to me.

 

What if this is for instantaneous turn? Do we know for sure that this is time for sustained turn?

That's unlikely, because the Soviets tested it as a sustained turn. It is possible that they didn't test it very well and lost altitude or speed, but that would be sloppy. Like Kurfurst said, it's not too hard to test properly. Edited January 12, 2017 by JtD

[Holtzauge]

Well, I think you need to start with Post number 6. https://forum.il2sturmovik.com/topic/25323-p-40-turn-rateflight-model-check/?p=392002

 

Now, the actual valid data for the P-40 appears to be 18 secs for the C model and 19,2 secs for the E model. Yes, I know you have penchant for dismissing real world data when it doesn't suits you, but let's just not ignore the real world for a moment.

 

Sure, there are multiple ways of arriving at full throttle Clmax. Since you are very silent about how you got it, I must suppose that you have made a number assumptions (without solid base of auxilarry data) in the process of recalculating it from gliding Clmax, all which introduced a significant amount of error tolerance into your calculations, you got in the end a result that was 26% off from the real values.

 

As to what caused it, you are the only one to know that for sure. Picking the wrong Clmax? Accidentally miscalculating it? Making a series of error-prone assumptions and simplifications in the intermediate calculations? Making an error in the formulae itself? Or perhaps a number of interpretation errors/overlook of details for the data in the original documents (see your thread on G-2 climb rate for examples), or simply choosing to believe only the data that suits the results you wish to be correct? Or simply choosing a too wide brush size in MS Paint?

 

We do not know for sure. We know however that its well off the real world data that is very, very simple to measure without too much room for error.

 

In the end what matters somehow you got 24,3 secs, which is as much as 26 % off from the real values. Well, if you can't see what the anomaly is, I am afraid its a case of not seeing the forest for the trees.

 

Yup, you got me Kurfurst: As you say: I dismissed data that did not suit me, was silent about how I got the Clmax and then picked the wrong one, accidentally miscalculated, made a series of error-prone assumtions and simplifications, made an error in the formula itself, then a number of interpretation errors/overlook of details for the data in the original documents and then I chose to believe only in the data that suited my results and I wished to be true.

 

And then I topped it off by using a too wide brush in MS Paint..........

Just for the record, I'm dismissing the 19.2 seconds as well. With the information at hand, there's just no way to accept it.

 

If you calculate the overall efficiency of the P-40E in a turn like that, even assuming clmaxes heavily increased by propeller slip stream, you end up at efficiencies above 60% (same approach as described in the other topic). For reference, other aircraft are somewhere around 40%-50% using real life numbers. A P-40E-1 at 1150hp and 3840kg will not sustain a turnrate of 360°/19,2s at 1000m in a standard atmosphere. It's just not in the physics.

 

We're missing some information here. A high clmax would explain the good turn time to some extent, and since the 19.2s have bothered me for several years now, it would be really interesting to finally find an explanation where all things add up.

 

Well it’s not only the P-40 number that is weird in the Russian turn rate estimates: While most of the other estimates make sense, it's not only the P-40 with its 18 to 19 s that sticks out since the tabulated Russian turn estimate for the Me-109E3 is 23.9 to 26 s which is way too high.

 

In addition, I agree with what you said here earlier on about the P-40:

 

This has been brought up like 85 times on this board already. Sustained turn times of less than 20s for a 4t aircraft with not even 1150hp are not plausible. Didn't happen. The document is worthless because it either contains wrong numbers, or incomplete information.

So given the Me-109E3 numbers and that there is simply no way a P-40 with the that weight and power will do a sustained turn in 19s given the physics if you take power/weight, wing loading and aspect ratio into account it’s either a typo or the Me-109E3 and P-40 numbers are mixed up or more unlikely the P-40 number is some momentaneous turn rate figure that has snuck into the table.

[Sgt_Joch]

gross engine horsepower is one factor, but I presume what you really need to look at is how much net power the propeller is effectively delivering as it slices through the air.

 

For example, the Allison V-1710 has a 2:1 reduction gear while the DB601A has a 1.55:1 reduction gear. What effect would that have?

Edited January 12, 2017 by Sgt_Joch

[Holtzauge]

gross engine horsepower is one factor, but I presume what you really need to look at is how much net power the propeller is effectively delivering as it slices through the air.

 

For example, the Allison V-1710 has a 2:1 reduction gear while the DB601A has a 1.55:1 reduction gear. What effect would that have?

 

True, you need to apply a propeller efficiency factor to the power but that alone cannot explain the strange P-40 and Me-109E3 numbers you see in the Russian estimates. The effect of the reduction ratio is that it reduces the propeller tip speed which when it comes into the supersonic range lowers the propeller efficiency, hence the need to reduce it with the gearing. However, the propeller is selected in conjunction with the reduction ratio so they match. Anyway, as a rule there seems to be little to choose in terms of efficiency between Axis and Allied propeller efficiency and this may have amounted to a few % between different designs at most mostly depending if they were more climb- or speed optimized, not if they were say like in this case from Germany or the US.

[Sgt_Joch]

maybe I should ask the question differently, namely what turn performance do players expect from a P-40E, is 19 or 24 seconds for a sustained or combat turn and with what parameters?

 

When I did some testing a few days back, with 50% fuel, it is easy to do a 19-20 second combat 360 turn, i.e start around 350-400 kmh and do one turn:

 

https://forum.il2sturmovik.com/topic/25323-p-40-turn-rateflight-model-check/?p=429469

 

In QMBs, it is easy to out turn 109E7, F2, F4, but that is a quick combat turn where you use E to get into a snap firing position.

 

A sustained turn is more difficult, you cannot gain on a 109F as with a Yak, but the 109s cannot out turn you either. A sustained turn is a dead end, since you will eventually exceed your combat power time and be left low, slow and dead.

 

It would be easier to test, if I knew what you are looking for.

Edited January 12, 2017 by Sgt_Joch

[Holtzauge]

I think that is the question: What should the turn time be? According to the developers, the currently modeled P-40 does a 360 degree turn at sea level in 24.5 s at a sustained speed of 270 Km/h. I get basically an identical result (24.3 s) in my C++ simulation. AFAIK other planes have been tested and found to conform the the developers numbers so I don't think we really need to test this on the P-40 right now.

 

In addition, as you say, in practice maybe you don't use it so much but I think the reason if it is 19 or 24.5 s is important is that if you model it to do 19 s instead of 24.5 it will retain energy much better and you would be able to pull much harder without loosing energy. However, just like I can model a P-40 to do 19 s in my C++ simulation if I wanted, I'm sure so can the developers in IL-2. However, this would affect a whole host of other performance numbers and you would see a much faster P-40 that had tremendous acceleration and climbed like a rocket.

 

So to be able to do 19 s turn time at sea level you need a certain mix of power/weight ratio, wing loading and a certain aspect ratio in the wing design. Now when it comes to sustained turn rate performance you can to some extent compensate one with the other in the above mix but if you combine the mix of the above that the P-40 brings to the table the 19 s at sea level is just not physically possible........

Edited January 12, 2017 by Holtzauge

[ZachariasX]

gross engine horsepower is one factor, but I presume what you really need to look at is how much net power the propeller is effectively delivering as it slices through the air.

 

For example, the Allison V-1710 has a 2:1 reduction gear while the DB601A has a 1.55:1 reduction gear. What effect would that have?

Not too much as long as the prop is balanced to the torque and the rpm. A faster turning prop however is not suitable at higher speeds as the tips will go supersonic sooner. But you can make it smaller, lighter. You get a weight advantage over a speed issue (usually at 500+ mph).

 

Reno racers use slow turning bigger props. RareBear is a good example for that.

[Solty]

I think that is the question: What should the turn time be? According to the developers, the currently modeled P-40 does a 360 degree turn at sea level in 24.5 s at a sustained speed of 270 Km/h. I get basically an identical result (24.3 s) in my C++ simulation. AFAIK other planes have been tested and found to conform the the developers numbers so I don't think we really need to test this on the P-40 right now.

 

In addition, as you say, in practice maybe you don't use it so much but I think the reason if it is 19 or 24.5 s is important is that if you model it to do 19 s instead of 24.5 it will retain energy much better and you would be able to pull much harder without loosing energy. However, just like I can model a P-40 to do 19 s in my C++ simulation if I wanted, I'm sure so can the developers in IL-2. However, this would affect a whole host of other performance numbers and you would see a much faster P-40 that had tremendous acceleration and climbed like a rocket.

 

So to be able to do 19 s turn time at sea level you need a certain mix of power/weight ratio, wing loading and a certain aspect ratio in the wing design. Now when it comes to sustained turn rate performance you can to some extent compensate one with the other in the above mix but if you combine the mix of the above that the P-40 brings to the table the 19 s at sea level is just not physically possible........

I think you shouldn't take 19sec as what 109E can do. The much heavier K4 can easily do 18sec.

 

The whole thing is based on few anectdotal references of pilots claiming that they were able to easily turn with 109s. Also one pilot had an oprtunity to fly and review the p40 and claims its the best maneuvering and turning airplane of the US (at around 200MPH IAS at least). Taking into consideration that Mustang D and, depending on load can do a turn in 19-23sec this would mean that it at least would have to beat the P51D, not to mention P38L, if we were to believe his judgement. But P40E has the lowest wing loading between 109G6 and P51D. And from what I've seen the K4 can easily turn at 18sec having the highest wing loading...

 

Could you check your simulation for P40M? Maybe that will be some indication.

Edited January 13, 2017 by =LD=Solty

[Holtzauge]

I think you shouldn't take 19sec as what 109E can do. The much heavier K4 can easily do 18sec.

 

The whole thing is based on few anectdotal references of pilots claiming that they were able to easily turn with 109s. Also one pilot had an oprtunity to fly and review the p40 and claims its the best maneuvering and turning airplane of the US (at around 200MPH IAS at least). Taking into consideration that Mustang D and, depending on load can do a turn in 19-23sec this would mean that it at least would have to beat the P51D, not to mention P38L, if we were to believe his judgement. But P40E has the lowest wing loading between 109G6 and P51D. And from what I've seen the K4 can easily turn at 18sec having the highest wing loading...

 

Could you check your simulation for P40M? Maybe that will be some indication.

 

Well I'm not saying that the Me-109E should do 19 s. In fact I think the Me-109E should do even below 18 s at sea level. But the Russian table says 18-19 s for the P-40 and is 23.9 to 26 s for the Me-109E. Clearly, both these numbers are simply off the charts and something is obviously wrong. Question is not if but why I think.

 

I was just observing that it you were to exchange the P-40 and Me-109E numbers in the Russian turn rate estimates things would make much more sense. But its futile I think to start speculating why the numbers don't make sense. Could be anything from the pilots misinterpreting the power setting to use in the test or doing a "combat turn" without holding the speed constant to measurement or transcription errors. We can only conclude that the P-40 and Me-109E figures don't make sense and try to find reliable data from other sources.

 

Even though these turn estimates is data that has been published by a respected organization some minor parts of it may still be wrong. Remember the NACA  Clmax figure of 1.15 and the RAE measurement of 1.36. Sometimes things just don't add up and you need to look closer. In addition, it bears remembering that all other numbers make sense in the Russian table AFAIK.

 

I have spent more than 30 years as an engineer and have seen my fair share of data that was wrong in my time. After all, everyone involved from the pilots who did the tests to the people who reviewed the publication before it was published are only human.......

[ACG_KaiLae]

If I wanted to buy the Curtiss-Wright docs from the smithsonian, which specific ones would I want to get?

[Holtzauge]

If I wanted to buy the Curtiss-Wright docs from the smithsonian, which specific ones would I want to get?

 

That is difficult to know without having a list of the titles of the reports and a summary of what they are about in front of you. I think you really need a complete list of what they have and then it’s a painstaking process of going through it page by page so you don’t miss anything. Even if you have the holdings digitized, you may miss interesting stuff because a keyword search may miss out on something interesting that your search does not net.

 

That being said, (I’m assuming here you are looking for data concerning Clmax and stalling speeds?) I would start looking with keywords like “handling” “characteristics” “Cl” “Cd” “aerodynamic” “coefficients” “weight” then of course “stall” “Clmax” but really, I think you need some sort of report summary like NASA has for the old NACA reports where you get a few lines of what the report is about. Even so equipped in my experience you are mostly disappointed because the report you download seldom contains what you are looking for….. And that is on the NTRS server, where you have rather good report summaries to begin with……

 

Finally, I don’t want to rain on the parade, but if the purpose of this is to find evidence of a substantially higher Clmax for the P-40 than the other aircraft in this sim I think we will all be disappointed. OTOH any new data is always welcome so if you feel like doing this I would really like seeing the results and also help out interpreting them so best of luck!

Edited January 14, 2017 by Holtzauge

[Farky]

Curtiss-Wright Corporation Records Finding Aid for NASM - http://sirismm.si.ed...M.XXXX.0067.pdf

[unreasonable]

A major research project just reading Farky's attachment! Some possibilities - those with more specific experience of researching air related stuff might have a comment?

 

 

Box 80, Folder 21 Curtiss P-40E, Inspection Report on Five-Foot Wind Tunnel Model, EXP-M-51/ P731-31, 8/13/41

 

Box 83, Folder 43 P-40N Flight Tests, FS-M-19-1535-A, 1/30/43

 

Box 84, Folder 11 Test of Curtiss P-40 Conducted at Manufacturers Plant, PHQ-M-19-1078-A, 5/9/40

 

Box 84, Folder 12 Speed Tests of P-40, PHQ-M-19-1078-A, 5/15/40

 

Box 84, Folder 13 Pilot's Comments on P-40 with a Gross Weight of 7740 Lbs, PHQ-M-19-1128- A, 8/24/40

 

Box 84, Folder 14 Flight Test of P-40E at Manufacturers Plant, PHQ-M-19-1227-A, 4/26/41

 

Box 84, Folder 15 Acceptance Performance Tests of P-40D, PHQ-M-19-1267-A, 7/21/41

 

Box 139, Folder 13 Report No. 8076, File No. none. "Wind Tunnel Tests on the 1/6 Scale Model" submitted by the Aerodynamics Dept., 6/5/1941 Models covered: P-40D

 

Box 139, Folder 18 Report No. 8132, File No. none. "Flight Test Report" submitted by the Aerodynamics Dept., 2/17/1941 Models covered: P-40 #197

[Holtzauge]

Good job Farky and unreasonable! Especially the flight tests reports look interesting I think and personally I would start with those. While the wind tunnel results may be interesting, the problem there is with the scaling if they were run with models which I suspect. So IMHO the flight tests would be the first to look at to see if they contained data of interest to us. Is there no way to find out some more than can read from the title? Can one from the NASM get a summary or synopsis for the selected items now that unreasonable has identified those that may be of interest?

[Holtzauge]

If not then I guess one could ask for a copy of the report summary or abstract for each report that looks interesting. Usually you can at least weed out those that definitely do not contain what you are looking for that way.

[unreasonable]

My list not exhaustive - since I was exhausted and went to bed. There may be other better ones.  Now I have FM insomnia....

[MiloMorai]

Out of curiosity, what are the turn diameters?

[unreasonable]

Out of curiosity, what are the turn diameters?

 

JtD's thread uses the turn data from Il-2 tech specs and has turn radius at best turn: is that what you mean?

 

https://forum.il2sturmovik.com/topic/25336-another-look-turn-times/

[Farky]

A major research project just reading Farky's attachment! Some possibilities - those with more specific experience of researching air related stuff might have a comment?

 

...

Box 83, Folder 43 P-40N Flight Tests, FS-M-19-1535-A, 1/30/43

 

This report is available via wwiiaircraftperformance.org - http://www.wwiiaircraftperformance.org/P-40/P-40N_42-9987_FS-M-19-1535-A.pdf

 

 

Box 84, Folder 14 Flight Test of P-40E at Manufacturers Plant, PHQ-M-19-1227-A, 4/26/41

 

 

Actually test of P-40B, also available via wwiiaircraftperformance.org - http://www.wwiiaircraftperformance.org/P-40/P-40B_41-5205_PHQ-M-19-1227-A.pdf

 

Box 84, Folder 15 Acceptance Performance Tests of P-40D, PHQ-M-19-1267-A, 7/21/41

 

http://www.wwiiaircraftperformance.org/P-40/P-40D_40-362_PHQ-M-19-1267-A.pdf

 

 

Box 84, Folder 11 Test of Curtiss P-40 Conducted at Manufacturers Plant, PHQ-M-19-1078-A, 5/9/40

 

Box 84, Folder 12 Speed Tests of P-40, PHQ-M-19-1078-A, 5/15/40

 

Box 84, Folder 13 Pilot's Comments on P-40 with a Gross Weight of 7740 Lbs, PHQ-M-19-1128- A, 8/24/40

 

Box 139, Folder 18 Report No. 8132, File No. none. "Flight Test Report" submitted by the Aerodynamics Dept., 2/17/1941 Models covered: P-40 #197

 

These reports cover early P-40s (P-40B/C, Tomahawk).

 

 

Box 80, Folder 21 Curtiss P-40E, Inspection Report on Five-Foot Wind Tunnel Model, EXP-M-51/ P731-31, 8/13/41

 

Box 139, Folder 13 Report No. 8076, File No. none. "Wind Tunnel Tests on the 1/6 Scale Model" submitted by the Aerodynamics Dept., 6/5/1941 Models covered: P-40D

 

plus these -

 

Box 143, Folder 13 Report No. 8333, File No. none. "Stalling Tests on the 1/6 Scale Model" submitted by the Aerodynamics Dept., 8/8/1941 Models covered: P-40 & P-40D.

 

Box 155, Folder 11 Report No. 8732, File No. none. "Wind Tunnel Stalling & Directional Stability Tests" submitted by the Aerodynamics Dept., 5/29/1942 Models covered: P-40 1/6 Scale Model.

 

Unfortunately it is only 1/6 Scale Model ...

 

-------------------------------------------------------------------------------------

 

Box 137, Folder 25 Report No. 8031, File No. none. "Wing Analysis" submitted by the Structures Dept., 11/5/1940 Models covered: H-81-A. - this one looks very promising, although Curtiss Model H-81-A is Tomahawk.

[ACG_KaiLae]

So, I should order the below documents? Anything else? The titles are not that helpful to me to know what to get; remember I don't have an aeronautical background.

Box 80, Folder 21 Curtiss P-40E, Inspection Report on Five-Foot Wind Tunnel Model, EXP-M-51/ P731-31, 8/13/41

Box 139, Folder 13 Report No. 8076, File No. none. "Wind Tunnel Tests on the 1/6 Scale Model" submitted by the Aerodynamics Dept., 6/5/1941 Models covered: P-40D

 

 

 

 

plus these -

 

Box 143, Folder 13 Report No. 8333, File No. none. "Stalling Tests on the 1/6 Scale Model" submitted by the Aerodynamics Dept., 8/8/1941 Models covered: P-40 & P-40D.

 

Box 155, Folder 11 Report No. 8732, File No. none. "Wind Tunnel Stalling & Directional Stability Tests" submitted by the Aerodynamics Dept., 5/29/1942 Models covered: P-40 1/6 Scale Model.

 

Unfortunately it is only 1/6 Scale Model ...

 

-------------------------------------------------------------------------------------

 

Box 137, Folder 25 Report No. 8031, File No. none. "Wing Analysis" submitted by the Structures Dept., 11/5/1940 Models covered: H-81-A. - this one looks very promising, although Curtiss Model H-81-A is Tomahawk.

[Farky]

So, I should order the below documents? Anything else? The titles are not that helpful to me to know what to get; remember I don't have an aeronautical background.

 

Hard to say. Frankly, I'm not sure if any tests of 1/6 model in wind tunnel will be worth it, most probably not. When it comes to "Wing Analysis", is it probably rather "Stress Analysis" than "Aerodynamic Analysis".

 

I think best thing to do is contact NASM and request aerodynamic data for Curtiss P-40D/E, particularly CLmax. NASM staff will research this for you, but i don't know how expensive it can be. Here are instructions how to make request - https://airandspace.si.edu/research/resources/reference-services

[ACG_KaiLae]

Is there specific wording that I should use, or will just stating any information relating aerodynamic data of a P-40D/E?

[unreasonable]

Just say you are specifically looking for calculations or measurements of the plane's CLmax and critical AoA?  The simpler the better with research requests in my experience.

 

 

On the more general topic, there is a thread in the Ru forum which discusses the issue of AoA/Yaw pitot error - or lack of it - in the game and the potential for confusion about stall speeds. Very similar to my conclusions, in as far as Google translate lets me deduce them  .

 

https://forum.il2sturmovik.ru/topic/5086-modelirovanie-trubki-pito-i-skorost-svalivan/

 

1./ZG1_Gil--- is estimating the error at stall as proportional to the square of the cosine of the AoA. In my own spreadsheet I just made the P-40s error at stall equal to error of the Bf109E as a % of the Bf pilot's reading, times the ratio of the P-40/Bf109 critical AoA.

 

Works out as 17 mph error (my method) which when added to manual 90 mph = 107 mph puts inside the upper range  in-game of 95-109mph, (which seems reasonable as the highest values most closely correspond to the weights used).

[ACG_KaiLae]

Thank you. A request has been made to the NASM. 

[Cpt_Branko]

Such attempt at inventing PEC correction which is very different from what is given is very misguided. It is given already in many manuals and tests.

 

I ran into such a situation where everyone got their panties in a twist about an airplane having a Clmax of 1.8, arguing that:

- Clearly given PEC charts are wrong.

- Clearly given stall speed is wrong.

 

The reason everyone got their panties in a twist was because they didn't read the fine print, that it was a power on stall speed. Gliding stall speed (in another document) was of course different and higher (and wikipedia article had a small mistake in wing area, too, come to think of it) and Clmax was entirely normal as a result. You can see a pretty drastic difference in stall speed (from point of view of calculating CLmax) with different power settings in some NACA tests (eg. determination of flight characteristics of the P-39 for instance).

 

Which is why you really want properly instrumented flight tests with all the details of how it was done, like NACA did for a number of airplanes (but sadly I did not see one for P-40 specifically), so you see in what exact configuration is the stall speed measured in the first place.

 

Also discrepancies of other sorts exist as well. Altitude at which plane was tested impacts reynolds number which impacts Clmax, and I don't think that it was possible to recalculate this to a standard altitude in 1940s, so if a plane was tested unusually high (as was the case in a captured 109 test which resulted in a lower than usual Clmax for the type) there was a difference of a few mph from normal. Again the discrepancy had an entirely logical reason.

 

Devil is in the details, usually, and the problem is that the details aren't always listed. However I would not simply discount historical record and just invent PEC correction which suits something even though it's completely different from all known data.

 

Ideal solution would be to dig in archives and try to find more detailed flight testing, really. With what is easily available this is just mostly guesswork how exactly should it work, not even airfoil data to go on with and the figures in tests contain very little detail how it was done.

Edited January 28, 2017 by Cpt_Branko

[ACG_KaiLae]

Bit of an update: I got an email today from Crump. He did go to the smithsonian and get the documents that we are looking for, something like 200 pages worth. Among those apparently from what he said is the design clmax of the aircraft. I hope to have access to these in a few days. He also said he was planning on going back and getting Allison engine information.

 

Hopefully, we can make significant progress in our inquiry shortly.

[unreasonable]

Such attempt at inventing PEC correction which is very different from what is given is very misguided. It is given already in many manuals and tests.

 

 

 

You clearly have not bothered to read the thread. There is no "inventing" of PEC corrections, but an attempt to understand a physical phenomenon, based on tests and data, as I will endeavour to summarize.

 

I have never seen a manual that gives PEC at stall speeds: they all go down only to approximately where the PEC value changes from +ve to -ve., much faster than stall. Same with most flight test PEC charts, barring the RAE tests I will come to in a moment. Plenty of them posted in this thread for the P-40: not one has measured data points anywhere near stall speed.

 

What we are talking about here is the error induced by high Pitch/yaw angles at stall. 

 

It was measured in the RAE Bf109 E test using a trailing pitot, (the test is quoted in detail in this thread), and also mentioned in the RAE paper on the NACA Spitfire tests.

 

It shows that at power-off stall AoA the pilot's instrument's AIS is substantially less than that measured by a trailing pitot - 20mph in the 109 case. The Spitfire example shows a similar error. 

 

It is perfectly reasonable to assume that this is a general phenomenon, unless shown otherwise, given the essential similarity of most speed measuring systems used at the time.

 

It explains why manual stall speeds cannot be used to estimate CLmax without a further correction - and this further correction is not an extrapolation off a manual's PEC. If you use the manual's AIS to calculate CLmax you get results that are much higher than the CLmax of the wing - a physical impossibility. Using standard PEC charts and extrapolating PEC from them just makes things worse, since this will lead to an even lower estimate of TAS. (Unless you hold to the theory that everyone is just reading PEC charts the wrong way round, which I still find appealing!   )

 

So far we have only found the data on two tests measuring this phenomenon - the RAE Bf109 E and Spitfire tests. If there are others that would of course be useful, but the phenomenon that air speed indicators under-measure at high AoA or yaw in RL is established experimentally.  In Il-2 they do not, as you can test for yourself.  Therefore the AIS in game at stall is significantly different from that which a RL pilot would observe in his cockpit.

 

Both Gol---'s numbers and mine are simply rough estimates to quantify the known phenomenon of AIS error at high AoA from basic physical facts, based on the assumption that  AIS measured in game corresponds closely to the trailing pitot AIS as tested by the RAE. Ie they seek to see if the large differences between the stall speeds given in manuals and the AIS measured in IL-2 can be accounted for systematically. The answer is that they can. 

 

The broader problem is that by looking at data given in manuals people have deduced that the Il-2 FM is incorrect, when it looks as though what is incorrect (ie is a simplification that goes badly wrong in this type of case), is Il-2's modeling of air speed indicators.

 

 

edit - for AIS read IAS or ASI throughout! AIS is my mobile telephone provider....

Edited January 28, 2017 by unreasonable

[Holtzauge]

Excellent summary of where things stand unreasonable!

[BlitzPig_EL]

Bit of an update: I got an email today from Crump. He did go to the smithsonian and get the documents that we are looking for, something like 200 pages worth. Among those apparently from what he said is the design clmax of the aircraft. I hope to have access to these in a few days. He also said he was planning on going back and getting Allison engine information.

 

Hopefully, we can make significant progress in our inquiry shortly.

 

Good news.

 

Hopefully this will finally give us the info needed to make a realistic assessment of the P 40E in the sim, which is what the whole project was started for in the first place.

Pass my thanks to Crump if you would sir.

[-=PHX=-SuperEtendard]

This chart was posted by a flight model developer in WT ru forums, I would say take it with a grain of salt but maybe it has some info that may be correct/useful? (apparently according to this the 19 s turn time is with 56" boost, 22 s with 45.5")

 

 

 

[ICDP]

It would certainly make sense, the BoM P-40E takes a similar turn time at higher boost.

[=362nd_FS=Hiromachi]

Do not use those FM charts at any circumstances. The are extrapolated from flight model .blk files and represent the ingame performance and characteristics. Considering how inadvanced are the propeller airfoils implemented into wt engine and all kind of other limitations, not to mention "quality" of war thunder fm developers work I'd stay away from that. 

[-=PHX=-SuperEtendard]

Do not use those FM charts at any circumstances. The are extrapolated from flight model .blk files and represent the ingame performance and characteristics. Considering how inadvanced are the propeller airfoils implemented into wt engine and all kind of other limitations, not to mention "quality" of war thunder fm developers work I'd stay away from that. 

 

I dont think it's from the game files though, it's more of a data check because it's FM is going to be reworked for the next patch, and the dev posted this so ppl can see it and look at the new technical aspects of the FM. But I agree with you that it could contain some mistaken data (that's what the grain of salt is for )

[=362nd_FS=Hiromachi]

The idea of those FM charts is to indicate what can be expected from ingame model. They can differ slightly, but those are very general. I've been a Tech mod there almost 2 years ago and remember quite a bit of stuff related to that. I assume they improved a bit, but considering my friends opinions who still play it ... flight model department really doesnt care about quality. It's not a flight sim after all.