P-40 turn rate/Flight model check

[Crump]

 

 

Yes, exactly. That is why I'd wager that you can, in fact, compare indicated speeds in-game because to model each ASI differently would be a large investment in person-hours with negligible return.

 

A 20% error is not negligible return.  In fact some of the VVS designs PEC curves are unusual and would return results that are complete nonsense in the context of relative performance. 

 

 

For example, comparing the P-51C to the La-7 at 400 kph we have introduced a 20 KPH airspeed error in terms of relative performance right from the beginning.  That is a huge error in terms of aerodynamic coefficients.

[Farky]

Because the relative performance is the most important performance in the game.  For example, if you just use IAS to determine stall speed performance between an FW-190A3 and a Spitfire Mk V you will introduce ~20% error in their relative performance.  That is a huge error and greatly effects the type of fight the FM's are capable of doing.

 

 

You don't get my point, this is not about relative performance between two airplanes. Not yet anyway, since you are testing if game matches real data for P-40E (same for Bf 109) right now.

 

First thing you need to do - check stall speeds in IAS in game against stall speeds in IAS in manuals for both (all) airplanes and be sure that they are in match with manuals. Or this is done?

 

Then we can start talking about position error, relative performance between airplanes (both in game and IRL) and other things.

 

P.S. - what document do you use for P-40E data?

[Crump]

 

 

You don't get my point, this is not about relative performance between two airplanes. Not yet anyway, since you are testing if game matches real data for P-40E (same for Bf 109) right now.   First thing you need to do - check stall speeds in IAS in game against stall speeds in IAS in manuals for both (all) airplanes and be sure that they are in match with manuals. Or this is done?   Then we can start talking about position error, relative performance between airplanes (both in game and IRL) and other things.   P.S. - what document do you use for P-40E data?

 

Yes, that is kind of the point of the thread and preliminary testing done.

 

As for speed conversions...that is also done as it is a very relevant and important part of aircraft performance.

 

I would be glad to add you to the PM thread and move forward with this instead of spending pages justifying normal aircraft performance convention. 

[ACG_KaiLae]

There are flying P-40E in the world today, so I can't believe that the real aircraft's clmax is an unknown. There's a test, somewhere. What document do we need to get?

[unreasonable]

There are flying P-40E in the world today, so I can't believe that the real aircraft's clmax is an unknown. There's a test, somewhere. What document do we need to get?

 

You need a RL stall speed test  provided that it gives a very accurate speed reading, plus corrections as discussed above to determine the TAS, plus the atmospheric conditions, plus the weight and wing area. (Or EAS if you are confident that this has incorporated the atmospheric conditions correctly). Calculate CLmax from that.

 

CLmax Calculator.zip

 

If the speed (TAS) is a few % out, the CLmax will be out by much more, which is why Crump is saying that IAS comparison is not so useful, and I agree with him in this case because any calculation of CLmax is more sensitive to changes in the speed number than to anything else.

 

In effect you are comparing two aircraft: in-game and RL P-40E, but we do not know if the TAS-IAS conversion is the same in each case, since we do not know how IL-2 handles this: generically or by aircraft.

 

We can see if the in-game IAS matches report/handbook IAS, but unless we can convert both to TAS, whether they do match or not, this does not tell us that the in-game CLmax is the same as the RL CLmax and hence whether other aspects of performance affected by CLmax also match. 

Edited December 3, 2016 by unreasonable

[ACG_KaiLae]

It wouldn't be in a wind tunnel or flight test?

[unreasonable]

At risk of being corrected by an engineer, I would just say that a wind tunnel test is basically a flight test, just with the air moving rather than the plane moving.

 

To determine CLmax you still have to see what happens in each case, and AFAIK seeing when the plane stalls at Vmin is the best (only?) way to get the data to calculate CLmax for a whole aeroplane.  You can do this in a wind tunnel or with a flight test. Wind tunnel has more controlled conditions, hence results likely to be more accurate, but experiments sometimes miss real factors that are only discovered with real flight testing, so ideally you would have both.

 

CLmax is a ratio - you cannot measure it directly.

Edited December 3, 2016 by unreasonable

[Holtzauge]

You need a RL stall speed test  provided that it gives a very accurate speed reading, plus corrections as discussed above to determine the TAS, plus the atmospheric conditions, plus the weight and wing area. (Or EAS if you are confident that this has incorporated the atmospheric conditions correctly). Calculate CLmax from that.

 

CLmax Calculator.zip

 

If the speed (TAS) is a few % out, the CLmax will be out by much more, which is why Crump is saying that IAS comparison is not so useful, and I agree with him in this case because any calculation of CLmax is more sensitive to changes in the speed number than to anything else.

 

In effect you are comparing two aircraft: in-game and RL P-40E, but we do not know if the TAS-IAS conversion is the same in each case, since we do not know how IL-2 handles this: generically or by aircraft.

 

We can see if the in-game IAS matches report/handbook IAS, but unless we can convert both to TAS, whether they do match or not, this does not tell us that the in-game CLmax is the same as the RL CLmax and hence whether other aspects of performance affected by CLmax also match. 

 

Yes, how to measure an accurate speed to determine the Clmax is as you say key but is unfortunately also a bit of a problem: However, there are ways to do this accurately and for example, the British RAE used something called a trailing pitot which is basically a pitot based measuring device that you can wind out after taking off so it trails some multiples of 10 m behind and below the aircraft. This essentially eliminates position errors since the pitot is out in the so-called far field flow and consequently you get a very accurate IAS reading. The RAE used this very method in flight trials to determine the Spitfire and Me-109 low Mach Clmax to 1.36 and 1.4 respectively. So whenever you see an IAS figure, you have to try to decipher how it has been determined and what corrections have been applied.

 

At risk of being corrected by an engineer, I would just say that a wind tunnel test is basically a flight test, just with the air moving rather than the plane moving.

 

To determine CLmax you still have to see what happens in each case, and AFAIK seeing when the plane stalls at Vmin is the best (only?) way to get the data to calculate CLmax for a whole aeroplane.  You can do this in a wind tunnel or with a flight test. Wind tunnel has more controlled conditions, hence results likely to be more accurate, but experiments sometimes miss real factors that are only discovered with real flight testing, so ideally you would have both.

 

CLmax is a ratio - you cannot measure it directly.

 

As you pointed out, ideally you have both wind tunnel and flight tests data to base the Clmax on but if you only have wind tunnel data this can be tricky to use: In theory a wind tunnel test is as you say just reversing the reference system with the plane stationary and the air moving but since the wind tunnel has to be finite this results in a number of problems such as blockage, i.e. the test object speeding up the flow locally and mirroring effects in the tunnel walls. In addition, if you have to use a lower wind tunnel speed or scale models you have Reynolds number, Mach and surface finish effects as well to take into account. All this results in the need to introduce correction factors which are difficult to do accurately which in turn means that wind tunnel data has to be interpreted to make the correct deductions which is difficult to do even for professionals.

[Crump]

 

 

All this results in the need to introduce correction factors which are difficult to do accurately which in turn means that wind tunnel data has to be interpreted to make the correct deductions which is difficult to do even for professionals.

 

Corrections are not difficult and are quite accurate as long as the input data is correct.

 

You are correct in that wind tunnels are a tool and have varying degrees of accuracy depending on the question we are looking to answer.

 

Clmax measurement is one area that wind tunnels are far more accurate than flight or mathematical analysis. 

 

 

However, there are ways to do this accurately and for example, the British RAE used something called a trailing pitot which is basically a pitot based measuring device that you can wind out after taking off so it trails some multiples of 10 m behind and below the aircraft. This essentially eliminates position errors since the pitot is out in the so-called far field flow and consequently you get a very accurate IAS reading. The RAE used this very method in flight trials to determine the Spitfire and Me-109 low Mach Clmax to 1.36 and 1.4 respectively. So whenever you see an IAS figure, you have to try to decipher how it has been determined and what corrections have been applied

 

Everybody used a trailing rake system at one time or another.  It has varying degrees of accuracy depending on what portion of flight you wish to measure.   

[Holtzauge]

Corrections are not difficult and are quite accurate as long as the input data is correct.

 

You are correct in that wind tunnels are a tool and have varying degrees of accuracy depending on the question we are looking to answer.

 

Clmax measurement is one area that wind tunnels are far more accurate than flight or mathematical analysis. 

 

Everybody used a trailing rake system at one time or another.  It has varying degrees of accuracy depending on what portion of flight you wish to measure.

Sorry Crump but you are wrong:

 

First of all wind tunnel corrections are not easy to do and I think you will find it very difficult to find an aerodynamicist who agrees with you.

 

Secondly, your statement "Clmax measurement is one area that wind tunnels are far more accurate than flight" is not correct: Flight measurements are much more accurate since they incorporate all the gaps, surface imperfections, gun ports, joints and need no Reynolds number or tunnel corrections etc.

 

Thirdly, a rake is something completely different from a trailing pitot: A rake is used to measure momentum losses and can be used to gauge drag while a trailing pitot is a device suspended sufficiently far from the aircraft get an accurate airspeed measurement.

[Crump]

hirdly, a rake is something completely different from a trailing pitot:

 

I know that.  Rakes and trailing pitot systems have been used since the dawn of aviation.  Typing too fast and not proof reading.

 

 

 

 

Everybody used a trailing pitot and rake system at one time or another.  It has varying degrees of accuracy depending on what portion of flight you wish to measure.   

 

 

 

Wow guy...you just want to argue to argue.

 

 

 

First of all wind tunnel corrections are not easy to do and I think you will find it very difficult to find an aerodynamicist who agrees with you.

 

Ever wonder why wind tunnels have the industry standard since the Wright Brothers?    Nobody said they were "easy to do".  What I said was they are not difficult and if the designers pay attention to the required details then the data is very accurate.  It is not some impossible task to get accurate wind tunnel data.  That is why they are so useful and popular in aeronautical engineering circles

 

If the results are not in agreement, then it is time to examine the process.  In fact, that is exactly what you see Focke Wulf do at Chalais Meudon.

 

 

 

Secondly, your statement "Clmax measurement is one area that wind tunnels are far more accurate than flight" is not correct: Flight measurements are much more accurate since they incorporate all the gaps, surface imperfections, gun ports, joints and need no Reynolds number or tunnel corrections etc.

 

 

No, your problems are different in flight than in a wind tunnel but the measurement is not more accurate.   In fact the less controlled environment introduces problems which you nicely point out and is the result of most of the disagreements with tunnel data with the exception of gun port design as most manufacturers paid no small amount of attention to it in the design phase.  

 

Problem is you're thinking that surface imperfections, joints, and ........why would you think there is no Reynolds Number in flight?  Is there like a Reynolds number generator included in wind tunnels on your planet? (Sucks when people do this kind of stuff doesn't it?)  Perhaps you just meant something else?

 

Reynolds Number is a property of the atmosphere and sizing of the object.  It very much exists in flight and if it did not...well there would be no point at all to wind tunnels.

 

You do however seem to have a very unrealistic expectation of exactly what these parameters actually mean.  "Surface imperfections" means smoother than 320 grit sandpaper, seals, gaps, requirements are not that stringent.  These are not hyper, super, or even transonic aircraft designs.  They NEVER had the sealing caulk that is required on panels in those airspeed realm designs.

 

All the World War II piston engine fighters are subsonic aircraft designs and have a completely different set of rules because of that fact.

 

Here is what a surface finish of 800 grit and surface gap tolerance means in practical terms for a subsonic aircraft, Holtzauge:

 

This gap is out of tolerance and requires a fairing.  

 

 

You can see the sanding marks:

 

 

A little paint and you will never know those sanding scratches existed.  That is far finer than the 320 grit standard.  

[Crump]

Let's eliminate this line of thinking that any inflight airspeed measurement is more accurate than the controlled environment of a wind tunnel.

 

These are just measurement errors.  It is not including, wind, gusting, turbulence, temperature gradients, RAM heating, altitude changes, etc...ALL of which introduce significant errors into airspeed measurement with any system.

 

Here is the range of typical error associated with a fixed pitot tube installation:

 

 

So we are typically looking at ~5 to 15% measurement error at our most accurate!

 

A trailing head pitot system does eliminate some of this error taking our measurement error down to ~3%.

 

Now that is assuming a total lack of static pressure and altimeter measurement error.

 

Of course that is just not realistic either as both have their own margin of error.

 

At its most accurate, a bourdon tube altimeter is going to have a ~3% margin of measurement error.  At 3000 feet that equals 90 feet altimetry error which results in ~24% error in static pressure measurement.

 

 

http://www.ohio.edu/people/uijtdeha/naca-tn-616.pdf

 

Airspeed measurement being nothing more than the ratio of measured dynamic pressure (which has its own error) to static pressure (which also has its own error).

 

This was extremely accurate measurement.....for 1940...

 

Unfortunately things have not gotten much better and most agree that a well done speed course is the best measurement of airspeed.

 

Because velocity is squared a small error in velocity equates to a large change in the aerodynamic coefficients.

[Crump]

 

 

Farky, on 02 Dec 2016

 

Do you want to be added to the PM on the P-40 before this thread get dragged any further off topic? 

[Venturi]

Don't forget to mention the engine.

[Farky]

Do you want to be added to the PM on the P-40 before this thread get dragged any further off topic? 

 

Yes

[Holtzauge]

I know that. Rakes and trailing pitot systems have been used since the dawn of aviation. Typing too fast and not proof reading.

 

Well a mistake like that can happen to anybody!

 

Wow guy...you just want to argue to argue.

 

Sorry but that is wrong: If you go back you will see that I answered a post by unreasonable (to his satisfaction it seems since he upvoted it). You then intervened in the discussion and all I have done is to point out the errors in your post.

 

No, your problems are different in flight than in a wind tunnel but the measurement is not more accurate. In fact the less controlled environment introduces problems which you nicely point out and is the result of most of the disagreements with tunnel data with the exception of gun port design as most manufacturers paid no small amount of attention to it in the design phase.

Problem is you're thinking that surface imperfections, joints, and ........why would you think there is no Reynolds Number in flight? Is there like a Reynolds number generator included in wind tunnels on your planet? (Sucks when people do this kind of stuff doesn't it?) Perhaps you just meant something else?

Reynolds Number is a property of the atmosphere and sizing of the object. It very much exists in flight and if it did not...well there would be no point at all to wind tunnels.

 

Sorry but I think you are confused: Wind tunnel measurements can never be as accurate as flight testing. If you spend some time Googling comparisons of flight trials and wind tunnel model results you will see what I mean.

Maybe you don’t understand because you misunderstood what I wrote? I suspect this since you are saying that you think that I was saying that there is no Reynolds number in flight. What I said is that you in general need to do corrections for Reynolds number if you do wind tunnel tests which you don’t need to do for flight tests. You understand what I mean now?

 

Let's eliminate this line of thinking that any inflight airspeed measurement is more accurate than the controlled environment of a wind tunnel.

 

Sorry if you misunderstood: I did not say that that measurement of speed was better IRL than in a wind tunnel. I said that assessment of flight characteristics was better to do based on flight trials than on wind tunnel measurements. Is it clearer to you now?

[Crump]

 

 

I said that assessment of flight characteristics

 

You realize you are changing the subject here.  Flight characteristics or otherwise known as flying qualities is not the topic of discussion.   The topic is the determination of the coefficient of lift.  Wind tunnels can do that very well.  

 

http://encyclopedia2.thefreedictionary.com/flight+characteristic

 

I agree that the accuracy of wind tunnel data is very much dependant upon the question being asked.

 

The determination of the aerodynamic coefficient of lift is the topic of this thread.  Now, there are problems in our ability to express in the physics what happens and the effects in the expression of boundary layer mechanics.  We are not going to solve those issues here.  

 

You can most certainly determine Reynolds number in flight but you are correct that you do not have too.  It can be thought of as a ratio of laminar to turbulent flow.  The airfoil will find that same ratio on its own in the context of the actual atmospheric conditions.

 

As flawed as it is...the controlled environment of a wind tunnel is the most accurate methodology we have available for measuring aerodynamic coefficients.  That is why measured data is relied upon over any method of calculation.  Only the latest CFD analysis has been found to be as accurate.  Like anything though it is only as accurate as the operator makes it.  That is why design teams do multiple measurements instead of a single study and done with it.  That is why Focke Wulf and Grumman did comparative studies on their wing designs.

 

That is also why Grumman did not just measure airspeed and work the lift formula when they determined the CLmax in flight of their aircraft.  

 

They measured the change in acceleration to determine the normal force coefficients which are roughly comparable to the actual lift coefficient.

 

 

 

I did not say that that measurement of speed was better IRL than in a wind tunnel.

 

Without an accurate velocity measurement you cannot have accurate aerodynamic coefficients of lift.  

 

Simply put, velocity measurement is more accurate in a windtunnel.  We do not have altimetry errors that affect our static pressure measurement nor do we have the movement errors that affect our dynamic pressure measurements.

 

Yes there are different errors a tunnel can introduce.  There are measurements that are taken and corrections.  Properly accounted for the margins of error are smaller than in flight in terms of the determination of aerodynamic coefficients of lift.

 

That is why wind tunnels are used today.....

 

 

 

Followed by a very important caveat:

 

 

The accuracy to which the corrections must be determined and the time to be spent in calibrating the tunnel must ultimately be decided by the tunnel operator from considerations of the purpose for which the tests are being conducted, the precision required in the final results, and the time available for determining and applying the corrections.

 

 http://www.dtic.mil/dtic/tr/fulltext/u2/a801310.pdf

[Crump]

Finding the P-40's design CLmax would be holy grail in terms of modeling the aircraft.

[Holtzauge]

You realize you are changing the subject here. Flight characteristics or otherwise known as flying qualities is not the topic of discussion. The topic is the determination of the coefficient of lift.

 

No I’m not changing the subject to flying qualities. If you go back you will see that I answered unreasonable about determining Clmax, i.e. determining the coefficient of lift.

 

As flawed as it is...the controlled environment of a wind tunnel is the most accurate methodology we have available for measuring aerodynamic coefficients.

 

This is where we have to agree to disagree: Flight testing is simply a better method than wind tunnel tests or CFD calculations to determine a Clmax. Frankly I can’t understand why you persist in arguing that a model, be it in a wind tunnel or a CFD simulation can be better than measuring on the real thing and that determining a correct IAS in flight trials would be a bigger problem than correcting wind tunnel results for Reynolds number, Mach, trim effects, surface conditions, tunnel blockage, wall mirroring, supporting struts etc. However, if you want to continue to believe that wind tunnel data is better than flight testing then by all means do so but for me this conversation is pretty much concluded.

 

Summing up it looks like we have very different opinions on this and during my more than 10 years in the Swedish aeronautical defence industry working for SAAB and Ericsson Defence I never came across anyone who worked with the flight trials or with aerodynamics who shared your opinion that wind tunnel testing trumps flight tests. But hey, I was only working on the JAS39 Gripen which lacks a propeller so what would I know………

[Crump]

This is where we have to agree to disagree: Flight testing is simply a better method than wind tunnel tests or CFD calculations to determine a Clmax. Frankly I can’t understand why you persist in arguing that a model, be it in a wind tunnel or a CFD simulation can be better than measuring on the real thing and that determining a correct IAS in flight trials would be a bigger problem than correcting wind tunnel results for Reynolds number, Mach, trim effects, surface conditions, tunnel blockage, wall mirroring, supporting struts etc. However, if you want to continue to believe that wind tunnel data is better than flight testing then by all means do so but for me this conversation is pretty much concluded.

 

 

 

The maximum coefficient of lift is more accurate derived in a wind tunnel than any inflight testing in the 1940's.

 

Summing it up I know from my education and experience that the ability to control conditions gives you more accurate information.  That is why wind tunnels are used and exactly why Grumman did not use a simplistic lift formula analysis when determining the IN FLIGHT CLMAX of their design.

 

You even agree!

 

 

I did not say that that measurement of speed was better IRL than in a wind tunnel.

 

The measurement of airspeed in flight does have a much higher margin of error than airspeed measured in a wind tunnel. 

 

 

Simply explain to all of us why Grumman did not simply use the lift formula to determine the IN FLIGHT CLmax of their design?

 

 

Why do you think they went to all that trouble if airspeed measurement did not have such a large margin of error?  

 

Grumman simply knew that in fight airspeed measurement has a large margin of error and a small change in velocity represents a large change in coefficient of lift.....

[Holtzauge]

The maximum coefficient of lift is more accurate derived in a wind tunnel than any inflight testing in the 1940's.

 

Summing it up I know from my education and experience that the ability to control conditions gives you more accurate information.  That is why wind tunnels are used and exactly why Grumman did not use a simplistic lift formula analysis when determining the IN FLIGHT CLMAX of their design.

 

You even agree!

Sorry but I do not agree: I suggest you go back and re-read my posts. Start with my reply to unreasonable and you will better understand what I mean.

[Crump]

Simply explain to all of us why Grumman did not simply use the lift formula to determine the IN FLIGHT CLmax of their design?

 

Thanks!

 

Edited December 4, 2016 by Crump

[ACG_KaiLae]

Back to the point of the thread...which is the performance of the P-40. Specifically, checking the flight model and if found to be in need of correction writing up a package to get that done. In summary of the previous discussions, there are 2 specific areas so far with the P-40 that possibly may be incorrect. The aircraft maneuverability and the engine performance both seem to be possibly underperforming. Starting with the aircraft maneuverability, there have been 2 possible hypothesis listed:

 

1. The aircraft coefficient of lift is incorrect in the sim.

2. The aircraft aerodynamics are incorrect in the sim.

 

For the determination of (1), stall testing was performed to attempt to collect data to learn what the clmax of the sim P-40 is. Rather obviously it would need to be right in the sim in order for the plane to behave correctly. Now that we've done that - and it would seem (I don't think we need to do it again, correct?) that the data is good, what are the next steps to determine the value that the game has? Please keep in mind that I don't have a background in aerodynamics so I will need it explained in at least some detail so I have a basic understanding of what would be required. It would seem that the final result would be deriving an accurate game clmax, and then comparing it against whatever the clmax on the real aircraft is. I would assume that the clmax of the P-40E is a known value that would have been calculated during flight testing of the actual aircraft during the 1930's, so after we get a clmax of the aircraft in the sim, it should be a simple thing to compare against RL data and see if there is an error. Have I missed something here? If not, what documentation, data or other information do we not now possess that we would need to aquire to do this comparison?

 

As for the check of (2), a few people have brought this up, but not listed any means I'm aware of of testing to determine if there's an issue or not. How would we go about checking this, if we desired?

 

I'd like to thank everyone for their assistance here however. I strongly believe that an accurate game is a better game, and that's what we are all working towards, both with the Fw-190, here, and beyond. 

Edited December 4, 2016 by Kai_Lae

[Crump]

Thank you Kai-Lai.  We have taken up enough off topic space in this thread.

 

 

 

I would assume that the clmax of the P-40E is a known value

 

Yes, the Curtiss design team had a design CLmax they would have achieved in order for the airplane to be a P-40 and do what they intended.  Screwing that up means the aircraft will not do what it was intended to do in the first place.  It speaks to load configuration, stability and control, landing/take off performance, control surface design and a plethora of other issues.  That is why getting the wing right and conducting comparative studies to ensure achievement of the design Clmax are the norm even today. 

 

That information is somewhere in an archive and it would be nice to find it. 

 

 

 

(I don't think we need to do it again, correct?)

 

No I think it is close enough and we need to concentrate on comparative performance with an aircraft we do know the aerodynamic and relative performance details.  

[ACG_KaiLae]

All right, next obvious step is we need to figure out where clmax information would be stored and obtain it. I'll admit to having no idea exactly how to do that, Curtiss being basically put out of business by mismanagement over the SB2C program after world war 2. Anyone got any ideas on where to look? What report would have that information? Obviously knowing in what report it is in would be key so I can know what to look for.

[Holtzauge]

Simply explain to all of us why Grumman did not simply use the lift formula to determine the IN FLIGHT CLmax of their design?

 

Thanks!

 

 

In order for you to understand this better I suggest you read the paragraph that is written above what you have underlined in red in NACA's summary which details the "unusual corrections" that were needed to the wind tunnel results which is really a case in point for what I have been saying all along.

 

But this is getting off topic and if you have any more questions about aerodynamics and flight mechanics you can PM me.

Edited December 4, 2016 by Holtzauge

[ACG_KaiLae]

Were we looking for position error correction information?

 

http://web.archive.org/web/20160302132936/http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/avia/AVIA_734_Report_783__Part_08.pdf

[unreasonable]

Back to the point of the thread...which is the performance of the P-40. Specifically, checking the flight model and if found to be in need of correction writing up a package to get that done. In summary of the previous discussions, there are 2 specific areas so far with the P-40 that possibly may be incorrect. The aircraft maneuverability and the engine performance both seem to be possibly underperforming. Starting with the aircraft maneuverability, there have been 2 possible hypothesis listed:

 

1. The aircraft coefficient of lift is incorrect in the sim.

2. The aircraft aerodynamics are incorrect in the sim.

 

For the determination of (1), stall testing was performed to attempt to collect data to learn what the clmax of the sim P-40 is. Rather obviously it would need to be right in the sim in order for the plane to behave correctly. Now that we've done that - and it would seem (I don't think we need to do it again, correct?) that the data is good, what are the next steps to determine the value that the game has? Please keep in mind that I don't have a background in aerodynamics so I will need it explained in at least some detail so I have a basic understanding of what would be required. It would seem that the final result would be deriving an accurate game clmax, and then comparing it against whatever the clmax on the real aircraft is.

 

Yes: but you need to know what, if any, PEC is included for the in game P-40 too.  At the moment, you can measure the IAS stall speed, or take the developers' robot measurements that are also given in IAS. But unless you know what the PEC is you do not know the TAS of the game stall.  Same with the real thing from the manual data. It is the comparison between the game and RL, it is TAS stall speeds that are important, since the CLmax calculation from the lift formula requires TAS.

 

It may well be the case that the PEC is sufficiently similar in each case that it makes little difference, but given the sensitivity to speed, this is worth finding out.

[ACG_KaiLae]

Who can we get this from? I assume something similar was needed for the Fw-190 checks. RL PEC is shown in the previously linked document I believe.

Edited December 5, 2016 by Kai_Lae

[unreasonable]

Either stick a question in the "questions to developers" thread, or PM directly. In the latter case, it may be best to get someone who has been in regular recent contact to do it - Opcode? JtD?.

 

 

edit: I see Opcode already asked "How are pitot-static systems modeled in the game? Are they modeled individually per aircraft or is the pitot-static system in, say, the Bf-109 the same as that in the He-111?"

 

so this might get you what you want to know once Han gets out the next batch of answers. 

 

Edited December 5, 2016 by unreasonable

[ACG_KaiLae]

Wish I had known this on Saturday I would of just asked them lol

[JG13_opcode]

 

Either stick a question in the "questions to developers" thread, or PM directly. In the latter case, it may be best to get someone who has been in regular recent contact to do it - Opcode? JtD?.

 

 

edit: I see Opcode already asked "How are pitot-static systems modeled in the game? Are they modeled individually per aircraft or is the pitot-static system in, say, the Bf-109 the same as that in the He-111?"

 

so this might get you what you want to know once Han gets out the next batch of answers. 

 

I did get added to a groupchat with the FM programmers but I'd rather not pester them with more PMs... they're busy folks and can answer it on their own time in the normal fashion like the host of other questions in that big thread.  I'm sure they get PMs all the time from hundreds of people.

[Farky]

Were we looking for position error correction information?

 

http://web.archive.org/web/20160302132936/http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/avia/AVIA_734_Report_783__Part_08.pdf

 

This figures are from report you linked -

 

 

 

As always, there is a issue - data are for RAF style pitot tube (cranked pitot tube). For American style pitot tube, we can use this -

 

NOTE - this PEC is ASSUMED.

 

or this (data for "short tail" P-40F, wing and pitot tube position is the same as for P-40E)

 

 

 

Question is, what type of pitot tube is in game. I know what is used for external model (US type), but what type is actually simulated i don't know. No clue how PEC is simulated in game.

 

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

 

Here is a interesting document, RAAF Attitude trials of Kittyhawk. Is it P-40N-20, not P-40E, but still pretty interesting. And before you ask - no, I do not have better copy of it.

 

[NZTyphoon]

This figures are from report you linked -

 

position error1.JPG

 

position error2.JPG

 

As always, there is a issue - data are for RAF style pitot tube (cranked pitot tube). For American style pitot tube, we can use this -

 

position error3.JPG

NOTE - this PEC is ASSUMED.

 

or this (data for "short tail" P-40F, wing and pitot tube position is the same as for P-40E)

 

position error4.JPG

 

position error5.JPG

 

Question is, what type of pitot tube is in game. I know what is used for external model (US type), but what type is actually simulated i don't know. No clue how PEC is simulated in game.

 

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

 

Here is a interesting document, RAAF Attitude trials of Kittyhawk. Is it P-40N-20, not P-40E, but still pretty interesting. And before you ask - no, I do not have better copy of it.

 

 

Thanks Farky: I downloaded the P-40N report some time ago and made it into a pdf file: page 4 has been rendered marginally more readable:

 

P-40N_high_altitude_performance_RAAF.pdf

[ACG_KaiLae]

I did get added to a groupchat with the FM programmers but I'd rather not pester them with more PMs... they're busy folks and can answer it on their own time in the normal fashion like the host of other questions in that big thread.  I'm sure they get PMs all the time from hundreds of people.

I don't want to aggravate anyone. Waiting for them to answer in that thread is the best way to proceed then? Is there any other data that we should look for in the meantime?

[JG13_opcode]

 

 

Waiting for them to answer in that thread is the best way to proceed then?

 

Could be.

 

If you have a report detailing what is wrong, with sources, PM it to Han in a polite fashion.  Otherwise probably just best to proceed in a different area. 

[ACG_KaiLae]

The problem seems to be that we need to know what PEC info they use for the FM, so we can calculate what the clmax is for the P-40 in game and compare it to what sources list. Unless there's another way you can think of? Because to get started we need to compare in game to RL clmax to see if there is a variance as suspected.

Edited December 6, 2016 by Kai_Lae

[JtD]

You can check PEC with in game tests, TAS, CAS and IAS are all possible to measure separately.

[ACG_KaiLae]

Oh really?

 

Edited December 6, 2016 by Kai_Lae

[JG13_opcode]

Oh really?

 

IMG_0029.JPG

Yes, he's right.

 

I'm not sure how you'd measure CAS directly in-game but it can be easily calculated from EAS.  

 

There are a few ways to do it but the simplest I can think of offhand would be to fly a measured course with wind disabled in the options, on the Autumn map which apparently is standard conditions. The distance/time formula gives you your true airspeed and you can use the map editor to position objects allowing for precise distance measurements and the pause/slow-motion feature of the replay to accurately measure time. If we assume the game does not model instrument errors (and if not then you can do another test to determine the error and subtract it) then your altimeter gives you accurate pressure altitude readings and you can look up the density in the standard atmosphere chart.

 

From there that gives you EAS, and you can subtract the compressibility correction to get CAS.

 

edit:  here is a compressibility correction chart from the US Navy flight test manual.

Edited December 6, 2016 by JG13_opcode