P-40 turn rate/Flight model check

[Dr_Molem]

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.

 

Then i suppose you should know better than us that FMs made by V*N and I**_***e have nothing, like nothing to do with the ones made by M****s (P-40E is made by him).

[Cpt_Branko]

I'm not arguing the unusually high Clmax obtained is the correct one, I'm just considering it more likely that some other important detail of testing wasn't listed. It is possible that the PEC curves are wrong to an extent*, but attempting to calculate your own curve like that comes with some problems. I'd much prefer to get well done instrumented tests.

 

First problem, we really have no clue about the critical AoA of the airfoil, so without AoA at stall it's impossible to judge. I haven't found data on NACA 2215 anywhere, the closest being a 1932 (I think; very old) test of a number of airfoils which included 2212, on which the critical AoA was in the 16-17 range and Clmax in the 1.6 region. However the data is very scant, with little detail, and very old, and not for same airfoil.

 

The reason I think that something else is also partially the culprit rather than just the PEC at stall, is that the PEC curves cannot be entirely wrong, because for the higher airspeeds they were definitely tested and used. To get everything to "match" you get a curve which is either of impossible shape or which seriously disagrees with published at higher airspeeds (which wouldn't really work out, as I said).

 

Linear extrapolation (which is quite correct for the Bf-109 test with trailing pitot tube you mentioned) from tests of a service P-40E** where PEC was measured at 150, 175, 200, 225, etc suggests something like 0 to -1 at 90 mph, which is in good agreement with RAAF tests of P-40E as well.

 

In the end you really want detailed, instrumented tests and design documents sadly we do not have them for P-40 yet. Absent that, I'd be wary of going "aha!".

 

----

 

Anyway, just something else which occured to me reading the thread. From where do people actually get 1150 HP? You need engine power charts. The 1150 HP at military power settings is at critical altitude at maximum speed, which is nearly at 11k feet from memory. At 1km where, eg. Soviets tested turn times, this is of course lower. The 1150 HP at takeoff power settings (higher manifold pressure than military) is at sea level, and using the same manifold pressure at 1km would result in higher power output (eyeballing from the chart, 1250 - but this chart is not entirely appropriate, as it is for level flight). Same story for other regimes, for instance 57" Hg setting (cleared officially only in Dec 1942, though, so it wouldn't really make sense for BOM even though it could have been physically done as far as the engine goes) is 1470 HP at sea level - of course higher at 1km. 

 

* Really, a few mph of error at a lower range of airspeeds wouldn't matter to the pilot much for purposes of navigation.

** Unlike the British one, which, as they say, is not really representative of one on account of having less guns and different equipment, but they figure it should be close enough.

Edited January 29, 2017 by Cpt_Branko

[unreasonable]

Just deleted longer thread - this is more concise.

 

We have to try to understand what is going on given the data we have, not what we would like to have, since it seems likely that we will never get either a trailing pitot test for a P-40 or a full scale wind tunnel test. These are the only things that can definitively solve the paradox.

 

The RAE tests did not extrapolate PEC down to stall speed - they directly measured it. They extrapolated up from measurements taken at very low speeds.

 

If the RL P-40 is under-measuring IAS at stall - like the 109 and Spitfire in the RAE tests - the paradox disappears. If it is accurate, or over-measuring the paradox is unresolved.

 

There might be some other hidden variable, but I doubt it. The CLmax formula is simple, and we have investigated the weight issue thoroughly.

 

Anyway, if you have an alternative hypothesis please share it. In the meantime the developers have to make a decision about CLmax based on what they know, and as far as I can see from this discussion they are not obviously wrong. 

[Cpt_Branko]

 

The RAE tests did not extrapolate PEC down to stall speed - they directly measured it. They extrapolated up from measurements taken at very low speeds.

 

 

Well, we don't really know what and how they measured because details aren't given.

 

PEC curve being vastly different on the high end of the speed range means they wouldn't be able to navigate with the airplane, test top speed, anything really.

 

RAAF trials show a PEC curve which generally agrees with RAE tests at speeds of 150 mph and above, but reads out as -1 mph at 90 mph. US climbing trials from Dec 1941 include also PEC correction which when extrapolated down reads out as 0 mph at 90 mph, but is overall in reasonable agreement with RAAF and RAE curves at higher speeds. There is a strong possibility of RAE given curve being wrong, but not to the extent previously described in the thread.

 

One thing immediately piqued my curiosity about the RAE report. Behaviour at the stall differs from behaviour in a slow glide at same airspeed (behaviour in slow glide and behaviour at stall section of the report). Which suggests that stall test wasn't done in a throttle closed condition. In other word, stall speed in RAE report is pretty useless for point of view of judging power off Clmax.

 

This reminded me that I have the British report on the P-39 from a similar period, where I also have a flight test done by NACA with trailing pitot head and details of stall tests included. The British result, when PEC for the P-39 (obtained from a third test and extrapolated to stall speed... eh, I know) is applied to the measured stall speed, matches NACA test of power on stall very well and not the gliding condition one. 

 

In light of these two observations, it is very possible that in British testing of these American airplanes in 1941-42 (which was not even aimed at figuring out the Clmax of operational aircraft because these quantities were known at the time), power was kept on to keep the correct deceleration (decelerate too rapidly and your stall test will be again slightly skewed - hence instructions for test pilots do contain also the correct amount of speed loss per second when testing stall) and examine stall speed in practical conditions. (Come to think of it, it's also possible that NACA got worse results due to age of the airplane and possible difference in weight, when we discuss the P-39 test above, but not so likely).

 

In a nutshell, we actually have no accurate, reliable information about the stall speed of P-40 in gliding condition.

Edited January 29, 2017 by Cpt_Branko

[unreasonable]

Well, we don't really know what and how they measured because details aren't given.

 

 

 

Not sure if we are talking at cross purposes or not here: the RAE report on the Bf109 E makes it perfectly clear what they did in more detail than I have seen in any other test report anyone has posted. They calculated CLmax using power-off stall speed measured with a trailing pitot.

 

 

We all know we do not have any reliable tests on the P-40 E - if we did we would not need a 17 page thread.  That is why we are trying to see if there are general principles that we can use to understand the paradox that the stall speeds given in manuals are, on the face of it, impossible.

 

There are possible objections to the line of thinking I have outlined:

 

1)  RAE got the measurements of the 109 and the Spitfire badly wrong. They were, in fact, incompetent.

 

2) The RAE measurements are not wrong, but the experimentally proven result that pitot-static systems in these aircraft significantly under-measured airspeed at high AoA near to stall speeds cannot be extrapolated to the P-40 E  because the P-40 E's speed indicator was of a different design, calibration etc.

 

I find (1) highly unlikely. (2) is certainly possible, I do not know enough about the details of pitot installations to be sure.

 

The pattern is, however, in my view the same. Here are the Clmax calculated using manual figures for the Spitfire MkI and P-40 E, "pilot's" IAS for the 109E, and then the adjusted figures for Spitfire and 109 using the RAE test data. Use the cockpit IAS you get CLmax higher than the wing.

 

                      Manual         Tested

 

Spitfire Mk.I        2.04             1.32

Bf109 E              2.23             1.38

P-40 E               1.99                  ?  [1.32-1.35 in BoX]

[Cpt_Branko]

That indicated airspeed needed to be corrected was known at the time, is known now, and is absolutely not a contentious point. Of course you can't calculate CLmax based reading from the airspeed indicator or manual value without applying correction for pitot tube error, it will be entirely bogus.

 

The question is how to get this correction. Now, a reasonably (not entirely, but reasonably) accurate way is using a trailing pitot tube at stall. This is what RAE have done in their Bf-109 tests. A considerably less accurate way (after all, velocity comes in squared so 5 mph here and there makes a massive difference) is eyeballing it by extrapolation of position error at higher airspeeds (which were important to have for practical purposes). 

 

This is not the point.

 

The point I'm trying to make is this: an attempt to take Spitfire and Bf-109 PEC (which had very similar installation) and apply it to the P-40 will result in a correction error curve which either is U shaped or is dramatically different at medium and higher airspeed, neither of which are real possibilities (first is not physically plausible, second would mean that it's impossible to navigate in a P-40 with any success, that all speed tests which were done on it were also fudged, etc).  The explanation that the tests matches some value you expect to see if you use the curve from a Spitfire just doesn't work out, because then other tests will not match. 

 

A simpler explanation is this: the tests are useless because they haven't been done nearly rigorously enough as it was not the purpose of the testing at all (else, they would have done it properly) and no details were reported. RAE report on P-40 is of extremely limited usefulness - obviously they weren't interested at all in testing Clmax of the P-40, and the report reflects this - so they noted just the indicated airspeed, no idea of the flight regime, if the plane was in a throttle fully closed position, nothing. Included position error correction chart contains little detail (and at low end of the speed spectrum does not agree with other reports anyway). 

 

-----

 

Even when they have been performed as correctly as they could have, there's the problem of accuracy. I would advise people not to take as gospel that CLmax of Bf109E is exacly 1.36, because, aside from possibilities of error, it is and it isn't. I mean, yes, it is, in a certain situation. For instance, it would appear the tests were done at 10000 ft altitude which will not match sea level value or value at some higher altitude because Re number is different. The test was done only once which is quite a red flag. So if you compare two planes you have to be wary of such detail how tests were done on one and how on the other. I mean the British wrote it as 1.4, not because they didn't know how to do division. It tells you volumes about the accuracy of measurement, even when you make an effort to do it right.

 

Really, trying to deduce backwards with very little reliable data what is the CLmax of WW2 fighters in power-off condition probably ends up being no more accurate than saying "we have no idea, let's say it was 1.4 at sea level and go for a coffee". At some point deducing and assuming, the errors grow to the extent the result you get is as reliable as reading animal entrails.

Edited January 29, 2017 by Cpt_Branko

[unreasonable]

That is all very well but misses the point of the thread completely - the developers have to stick some numbers into their model. They do not have the luxury of saying that it is all too hard.

 

No-one is saying that these calculations are exact - but an FM cannot use a range.

 

Currently, some posters have said that the current value in for P-40 CLmax Il-2 is too low, and they have used as evidence the undisputed fact that IAS stall speeds in the game are much higher than in the manual. 

 

But not applying a correction at stall similar to the 109 and Spitfire corrections derived from the RAE tests generates CLmax higher in fact than all the known airfoils as similar to that of the P 40 that we can find.

 

That is the paradox. So what should the P-40 E CLmax be in Il-2?  The developers have made a choice and incorporated it into the game. Is their choice reasonable or not? And if it is, how do you explain the subsequent difference in stall speeds?

 

That is the substance of the thread - do you actually have an opinion on this?

[ACG_KaiLae]

 

 

 

Items of interest:

 

A. Stall speed of AC listed at 84 MPH at sea level, clean. 

B. Weight listed as 8439 lbs for testing.

C. Stall speeds guaranteed to be within 3% in the document. I don't have the rest yet but this seems like a contract acceptance document.

D. Computed clmax given these conditions comes out to 1.4.

 

More later as available.

[unreasonable]

Items of interest:

 

A. Stall speed of AC listed at 84 MPH at sea level, clean. 

B. Weight listed as 8439 lbs for testing.

C. Stall speeds guaranteed to be within 3% in the document. I don't have the rest yet but this seems like a contract acceptance document.

D. Computed clmax given these conditions comes out to 1.4.

 

More later as available.

 

Thanks - more data is always good.

 

Using Clmax= W/(0.5* S*rho*Vmin^2), it comes out to 1.98 with a 84mph stall speed at those weights. Someone else please check my workings.

 

To get a speed correction to make it 1.4 you have to add 16 mph. Ie the TAS must be ~100 mph.

 

In other words, the IAS is under-measuring speed at stall. 16/84 = 19% ie this is not a +/- variation issue.

 

Then there is the question of why manual stall IAS is 90 compared to 84 here: are they different marks? What report are we looking at?  Is the "stall speed" F+G up or down?

 

Where does the 1.4 come from? It is not in the report - at least the posted pages.

Edited January 30, 2017 by unreasonable

[Cpt_Branko]

Reading civil air regulations of the day (well, ok, from 1960), they define stalling speed as minimum speed at which airplane is controllable, with the elevator control applied at a rate such that the airplane speed reduction does not exceed one knot per second, with power off. I think there's the requirement this is at the most unfavourable allowed loading.

 

So different definitions of stall speed are in use, only in relatively modern regulations they demand that reference stalling speed may not be lower than 1G stall speed.

 

Pretty sure that is a very reasonable cause of discrepancies why WW2 manual stall speeds are dodgy when translated to CLmax even when PEC is applied - they tell us when the pilot will lose control, not exact lift carrying capacity of the airplane, which you could derive from Vsg1 (1g stall speed) using your formula.

 

This change in regulations of what must be in the manual came much later. I suggest you read page 106 of this:

https://www.faa.gov/documentlibrary/media/advisory_circular/ac25-7a.pdf

Edited January 30, 2017 by Cpt_Branko

[unreasonable]

That is a possible mechanism that might account for discrepancies, I agree, but would it be large enough?  The 109 and Spitfire cases suggest the IAS is showing about 20% below the TAS.

 

Personally I am convinced that the change in projected area at high AoA is behind it, as described in the report on measurement systems Holtzauge posted earlier. I have found another more up to date NACA paper on the same topic - plus another paper with an interesting graph showing a U shaped PEC (upside down, but the principle is the same). From USNTPS-FTM-C2.pdf 

 

Edited January 30, 2017 by unreasonable

[Cpt_Branko]

Sorry, I edited a bit to further explain.

 

Anyway, it's entirely possible to account for discrepancies this way - there is no telling what the load factor is when the pilot is only commited to decelerating at 1 knot per second.

 

To quote the problem with old regulations (I gave the link above) - "he regulatory requirements of § 25.201(d) define the stalled condition as occurring when the airplane has reached an angle of attack measurably greater than that for maximum lift. The related stall speed has been defined as the minimum speed obtained in the stalling maneuver (VS , also referred to as VMIN). This VS MIN definition has led to stall speeds sometimes being defined at excessively low load factors, with pilot objectivity and flying technique having considerable influence over the results. The subsequent effect on operating speeds can then lead to inconsistencies between similarly configured airplane designs and result in inadequate maneuver margins."

 

However, if stall speeds in manuals of the day do not necessarily represent Vsg1 - stall speed at 1g, but rather minimum controllable airspeed at constant rate of deceleration, the manual speeds are basically useless for Clmax calculation, and can be correct only by chance.

 

To make matters worse, during the time of WW2, regulations of different countries were substantially different, making comparisons between how country A tested something and how country B tested something very difficult.

 

Anyway, yes, on the Spitfire and Bf-109 which have similar installations and similar overall error curve, they have a similar error. It's likely that other aircraft with a similar installation exhibit similar error, maybe shifted left or right overall, depending how exactly the tube is positioned and at what angle it is set and so on. This however doesn't fix the problem of manual speed and ordinary flight tests (not those aimed at discovering the CLmax of the airplane) not being necessarily at 1G.

Edited January 30, 2017 by Cpt_Branko

[ACG_KaiLae]

Thanks - more data is always good.

 

Using Clmax= W/(0.5* S*rho*Vmin^2), it comes out to 1.98 with a 84mph stall speed at those weights. Someone else please check my workings.

 

To get a speed correction to make it 1.4 you have to add 16 mph. Ie the TAS must be ~100 mph.

 

In other words, the IAS is under-measuring speed at stall. 16/84 = 19% ie this is not a +/- variation issue.

 

Then there is the question of why manual stall IAS is 90 compared to 84 here: are they different marks? What report are we looking at?  Is the "stall speed" F+G up or down?

 

Where does the 1.4 come from? It is not in the report - at least the posted pages.

1.4 is what crump lists in his email to me. Quoting:

 

"The stalling speed of the aircraft is listed as 84 mph power off stall in clean configuration at sea level (Equivilent Airspeed or True Airspeed Only at Sea Level). The official weight used in all the performance estimates is 8439lbs.

 

That makes our power off CLmax:

 

In the British Gravitational System....

 

84mph EAS * .869 = 72.9 KEAS

 

72.9^2 / 295 = 18.01494915psf

 

Coefficient of Lift = 8439lbs / (18.01494915psf * 335ft^2) = 1.4

 

The design Coefficient of Lift is 1.4"

 

I did not check his math, it was late for me. Also there were issues where some AC were delivered at above design weight because the subcontractors did not produce components at the specified weight which caused quality control issues. This was later corrected but could explain some of the different values we have seen.

[Farky]

 

Then there is the question of why manual stall IAS is 90 compared to 84 here: are they different marks? What report are we looking at?  Is the "stall speed" F+G up or down?

 

Well, USAAF manual states POWER ON stalling speed for flaps and landing gear up 85 mph, pretty close. We don't know if stall speed in document is for power off stall, just saying.

[unreasonable]

1.4 is what crump lists in his email to me. Quoting:

 

"The stalling speed of the aircraft is listed as 84 mph power off stall in clean configuration at sea level (Equivilent Airspeed or True Airspeed Only at Sea Level). The official weight used in all the performance estimates is 8439lbs.

 

That makes our power off CLmax:

 

In the British Gravitational System....

 

84mph EAS * .869 = 72.9 KEAS

 

72.9^2 / 295 = 18.01494915psf

 

Coefficient of Lift = 8439lbs / (18.01494915psf * 335ft^2) = 1.4

 

The design Coefficient of Lift is 1.4"

 

I did not check his math, it was late for me. Also there were issues where some AC were delivered at above design weight because the subcontractors did not produce components at the specified weight which caused quality control issues. This was later corrected but could explain some of the different values we have seen.

 

Well to start with he has a wing area of 335ft^2

 

I have a figure of 21.92 m^2 taken from Wiki, so I am not vouching for it, also it is the figure in the Il-2 Tech Specs.

 

21.92m^2 = 236ft^2

 

Replace his 335 with 236 and you get...... 1.98

 

335ft^2  ~ 31.1m^2 ie about the same as a Stuka. 

 

Always check Crump's maths, both data and workings.

Edited January 30, 2017 by unreasonable

[ZachariasX]

 

 

335ft^2 ~ 31.1m^2 ie about the same as a Stuka

 

British feet?

[JG13_opcode]

1.98 seems awfully high for power-off stall.

[ACG_KaiLae]

FYI Crump says he used the wrong wing area, so 1.98 is the value that comes out with the correct values. At any rate, I'm trying to get access to all the papers he has. There are something like 250 pages of it, so it might take some time. 

[Cpt_Branko]

If he's got airfoil data that'd probably be useful for the developers.

 

Sister airfoil to the 2215, the 2212, has a CLmax of around 1.6 and critical AoA of 16 and something degrees, but the test is very old (1932, I think) and with little detail, and of course, not exactly the same airfoil.

[unreasonable]

1.98 seems awfully high for power-off stall.

 

That has been what the last x pages have been about.  

 

In case you have missed them, I am arguing that the IAS near the stall is badly under-measured by the plane's instruments, taking the RAE tests on Bf109E and Spitfire as analogies, where this phenomenon is experimentally tested.

 

Not everyone is convinced - but so far the only other explanation offered is that the P-40 has (rather a lot of) net lift from the horizontal stab and other surfaces, which has it's own problems.  

[JG13_opcode]

Isn't the Clmax for the A6M Zero something like 1.4? I highly, highly doubt that the P-40 achieved 1.98, power off/clean.

Edited January 31, 2017 by JG13_opcode

[unreasonable]

Isn't the Clmax for the A6M Zero something like 1.4? I highly, highly doubt that the P-40 achieved 1.98, power off/clean.

 

You are not alone in that doubt. I want to say "of course it did not"....

 

So if the equation is right, the test is adjusted for sea level, the wing area is correct and the weight is right - then it must be a speed measurement problem. And we know speed measurement is a problem in general at very low speeds and high AoA.

 

The same issue crops up with every aircraft for which I have found a handbook stall speed number.

[ACG_KaiLae]

Pic of the pile o'docs:

 

[ZachariasX]

Pic of the pile o'docs:]

Wow... someone has been busy. Will be interessting what can be learned from that. Whatever it is, I suspect we are looking at a phenomenon that is occurring on all planes to some extent and maybe some some show the effect in a more pronounced way than others.

 

One effect being the increased reading error of the speedometer, the other being the lift drag relatinship of a full aircraft at very low airspeeds, depending on its properties and configuration.

 

Low speed performance of simulated aircraft is a tricky thing. Just talking from personal impression, many aircraft (be it Cessna or other GA type) seem to have exessive lift to make them match low speed performance figures. RoF planes, also for another reason, "suffer" from that to different extents as well IMHO. If you don't give them that extra lift, they underperform. Without constant cross check with the real aircraft, this error seems hard to remove.

 

I mean if Curtiss guaranties certain speeds, they must be somewhat right... There is something we're not seeing yet.

[=362nd_FS=Hiromachi]

Is this all from NASM Kai_Lae ?

[Cpt_Branko]

You are not alone in that doubt. I want to say "of course it did not"....

 

So if the equation is right, the test is adjusted for sea level, the wing area is correct and the weight is right - then it must be a speed measurement problem. And we know speed measurement is a problem in general at very low speeds and high AoA.

 

The same issue crops up with every aircraft for which I have found a handbook stall speed number.

 

Well, let's look if it crops up with every aircraft.

 

Let's take a look at a fighter for which we have instrumented flight test, the P-39D1. Tests were done in early 1943, so the airframe was somewhat aged at the time (so we can surmise the Clmax obtained will be a bit on the low side, but probably not very much).

 

Gliding Clmax was measured to be on average 1.35, 1.77 at cruise power and 1.97 at normal rated power (in climbing condition). You can see in gliding condition it's at about 100 mph CAS when it can't do no more, looks like 101-102 mph.

 

So:

102 mph * 0.869 = 88,638 knots

From same report, 213,2 sq ft of wing area, 7847 lb gross weight

 

(88,638*88,638) / 295 = 26,632865 psf

7847 / ( 26,632865 *  213,2) = 1,38 (likely they corrected for minor weight difference for takeoff and all)

 

Fine, okay, let's see British handling test, done without special instrumentation. Stalling speed is listed as 105 mph, weight unknown - it was compiled after a few hours of flying on the type. PEC curve is not provided, but linear extrapolation from other tests suggests -2 around 100 mph (PEC curve is of same shape as P-40 one, by the way). Really, for a preliminary handling trials this is uncannily good match. 

 

Manual listed? 105 mph, also! Subtract 2 mph, and we also get a surprisingly good match. 

 

So, why does it work out for P-39 and not for many other planes, P-40 included? Well, one possible explanation which I think you would be partial to is that it's indicated airspeed meter was of different mounting than on Spitfire and Bf109, so the error was much smaller on the P-39 and in a different direction. This is totally true, actually - the installation was indeed different. The thing is, though, it's much closer to the P-40 installation with which it has an otherwise similar curve also, but then why does P-40 show totally abnormal values, which can't possibly be correct?

 

I find it most likely explanation to be that the P-39 (unlike many other aircraft) departed from controlled flight pretty sharply. If you look at time history of the stall you see that even though load dropped below 1G, the plane was not very effectively controlled. So the listed stall speed for this airplane is the actual 1G stall speed and hence the results match. For other planes with more gentle stall characteristics, the manual speed isn't really the 1G stall speed (definition of the time only included constant 1 knot per second rate of deceleration, it was revised much later), and hence it is pretty useless for calculation of Clmax.

 

But anyway, I'm thrilled someone dug up data on the P-40! The documentation on it which is publicly available right now is rather scant.

Edited January 31, 2017 by Cpt_Branko

[ACG_KaiLae]

Is this all from NASM Kai_Lae ?

That is my understanding. He expressed an intention also for getting more relating to the engine as well, though it might take a bit to get access to them. The large number of pages makes scanning them a PITA, and our archive diver is apparently very busy.

[=362nd_FS=Hiromachi]

I never got so much materials despite two years of "relationship". Maybe I should buy them cookies or something. 

[ZachariasX]

I never got so much materials despite two years of "relationship". Maybe I should buy them cookies or something. 

Maybe they are receptive to Crumps charm....

[=362nd_FS=Hiromachi]

I am charming ... sometimes. But hey, I enhance that charm with $$$. 

 

Anyway, so now proper question is what can be done with all this data to change current state of things. Following 190 pattern is the reasonable way to approach this.  

[Kurfurst]

Sharing so many papers and doing the research work is extremely generous of Crumpp, great job! 

[unreasonable]

I am charming ... sometimes. But hey, I enhance that charm with $$$. 

 

Anyway, so now proper question is what can be done with all this data to change current state of things. Following 190 pattern is the reasonable way to approach this.  

 

That actually is not the proper question because nothing we have yet found suggests that the P-40 actually needs any changes.  

 

The Fw190 pattern was different: after the revisions the Clmax was lowered to 1.15-1.20, depending on what weight speed combinations you pick from the Tech Specs. This was a mistake, according to the team, so we expect the new revision to come in around 1.30-1.35

 

The P-40 in game is already at 1.32-1.35 very much in line with all the other single seaters: so in terms of aiming off from the airfoil/wing number there is no obvious issue.

[unreasonable]

Well, let's look if it crops up with every aircraft.

 

 

 

 

That is interesting: I agree those P-39 figures seem to work out in reasonable conformity with the manual. What does that mean for the P-40, however?   

 

My simple minded way would be to assume that the airfoils are not that much different, (and that therefore the CLmax is about the same) but the P-40 is 27% heavier than the P-39, while having a wing area only 11% larger. In which case it seems very strange that the P-40 should have a stall speed - according to the manual - 12% lower, when it ought to have a stall speed about 7% higher! 

 

(Checking the assumption about the wing runs into the same issue with both - the NACA report I have lists values for the one next to the one we want in the relevant series.)

Edited January 31, 2017 by unreasonable

[ZachariasX]

That actually is not the proper question because nothing we have yet found suggests that the P-40 actually needs any changes.

Yes, so far.

 

While the P-40 is certainly consistent based on current understanding, I think there is maybe something to be learned from those documents. We can take it from there then. This much less so to raise an issue with current things, but to get a better understanding in general.

[ACG_KaiLae]

I never got so much materials despite two years of "relationship". Maybe I should buy them cookies or something.

I doubt you ever got the chance to go there in person, which always is more effective.

[Cpt_Branko]

Really, since you're going to have huge trouble finding representative tests (those specifically geared at finding out Clmax), and even those have a margin of error (consider they were done on one aircraft, and sometimes only once), you could either calculate it using 2d airfoil data or use CFD modelling for better results, which is the best bet at making accurate flight models of airplanes which don't exist anymore.

 

I don't really know about the inner workings of the flight engine, how much data the FM team has, their standards, etc, so there's no telling what they'll do - but I reckon information will be useful for them.

 

Really, I'd expect for most WW2 fighters would come out as some 1.4 +- 0.5. Most have root airfoils which give you around 1.5-1.6 Clmax at Re number which fits their size, stall speed and sea level conditions, so you subtract 10% off that and you're roughly there.

Edited January 31, 2017 by Cpt_Branko

[JG13_opcode]

I have results for the speed testing. Using a mission made by KG200_Volker, who set the test range up so that at 1000m it would have sea level conditions, I was able to run and record the course for analysis. The mission contains 2 floating fires slightly offset to the aircraft's flight path 5km apart. The mission can be downloaded here:

 

https://www.dropbox.com/s/vv5pqxx8dujb96q/P%2040%20Test%202.7z?dl=0

 

The recorded track can be downloaded for analysis here:

 

https://www.dropbox.com/s/dljspmh8q436t3p/Tracks.rar?dl=0

 

Conditions for the analysis; I started the course and let the aircraft stabilize out at 198 MPH IAS with the autolevel on the whole time . This was the displayed speed on the HUD, which seemed to match exactly what was displayed on the speedometer in the dash. To answer a question therefore from before by JTD it therefore seems that the HUD display and the dash display are the same (I verified this several times in different conditions). I set the time to be 1/32 so for every 32 seconds of game (for highest accuracy of start/stop times), one second would pass. From arrival at the first fire, to arrival at the second fire, an elapsed time of 1804.63 seconds was recorded. Dividing that by 32 gets us 56.3945875 seconds of elapsed game time. This then equates to .01566519 hours of game time, which when divided by 5km resolves to:

 

TAS=319.17902 KPH (198.328648195 MPH).

 

I don't believe that the start and stop timing positions are incorrect, so the elapsed total time should be good. The only issue is that it is impossible to determine what the exact speed of the plane is with total certainty, only that it was between 198 MPH and 198.5 MPH.

 

Let me know if there's anything else I should do with regards to this to advance the FM check further. I know Crump is interested in also doing the F4 109, which I will do at a later date.

Were you able to get this mission working? I put it in data/Missions and it won't show up in my game.

[ACG_KaiLae]

I was, though not that version I think. It's not compatible after a patch. I could see about having it redone?

[303_Kwiatek]

That actually is not the proper question because nothing we have yet found suggests that the P-40 actually needs any changes.  

 

The Fw190 pattern was different: after the revisions the Clmax was lowered to 1.15-1.20, depending on what weight speed combinations you pick from the Tech Specs. This was a mistake, according to the team, so we expect the new revision to come in around 1.30-1.35

 

The P-40 in game is already at 1.32-1.35 very much in line with all the other single seaters: so in terms of aiming off from the airfoil/wing number there is no obvious issue.

What about critiacl angle of attack? With these Clmax BOS P-40 looks like  very low critical angle of attack - 14 degree?  I expect rather something about 16 degree at least? Actually P-40 got the lower CAoA from all other fighters in BOS

[unreasonable]

What about critiacl angle of attack? With these Clmax BOS P-40 looks like  very low critical angle of attack - 14 degree?  I expect rather something about 16 degree at least? Actually P-40 got the lower CAoA from all other fighters in BOS

 

That is true, it was mentioned earlier in the thread, (by me as it happens )  and I have no idea why the critical AoA is so very low. And it is: every other fighter is above 17 degrees.

 

If it was in this normal range everyone would certainly find it easier to fly even if the CLmax were unchanged.  

 

But if you just extended the line up to 16 degrees (on the graph of CL/AoA, assuming straight line through the origin at the same slope)  you would get a CLmax of 1.52 - still below the wing, we think, but way higher than any other single-seater.

 

Unfortunately no-one seems to have any additional information on this except there has been mention that the AoA in three point configuration was below the critical AoA (F+G down, presumably) so the developers may have used this as a limit. But perhaps it was not actually stalling in this configuration, just having some other issue giving it "stally" behaviour. 

 

Perhaps Kai_Lai's data trove will yield something relevant.