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SJ_Butcher

Is acceleration performance in game wrong?

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13 minutes ago, SJ_Butcher said:

 

Could you share your code? 

 

It's over 9000 lines of code and I have spent years putting it together and I plan to use the results in a book I'm writing so no, I'm not going to make it public. I'm assuming you want to validate it and my answer to that is that you have to judge it in the same way you judge BoX: You look at the results it provides and base your assessment on that. The developers of this simulation are not going to make their code public and neither will I. I have been posting results on-line for years and you can look at these and make up your own mind if you think it’s reliable or not. However, it seems to me that the problem is that you simply don’t like the results I have provided and prefer the ones you posted in the OP so I’m not gonna hold my breath. ;)

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Just now, Holtzauge said:

 

It's over 9000 lines of code and I have spent years putting it together and I plan to use the results in a book I'm writing so no, I'm not going to make it public. I'm assuming you want to validate it and my answer to that is that you have to judge it in the same way you judge BoX: You look at the results it provides and base your assessment on that. The developers of this simulation are not going to make their code public and neither will I. I have been posting results on-line for years and you can look at these and make up your own mind if you think it’s reliable or not. However, it seems to me that the problem is that you simply don’t like the results I have provided and prefer the ones you posted in the OP so I’m not gonna hold my breath. ;)

 

 

Lol, this is not about if I like or not, but there is no evidence that the result you posted are right, you questioned my source too, so Why I should believe your or the devs? When they don't provide information or data or test or a book as source. Sadly ww2 performance planes are a mystery and I only want to know the truth about it, because all the data are over the place.

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13 minutes ago, 216th_Nocke said:

just curious: is it really drag force, or drag coefficient thats plotted here? Is it possible that drag forces decreases with speed, at least in a certain speed range?

 

It really is drag force. Lift induced drag goes down as speed goes up, just as shown in the graph. This is the drag that comes only from the lift your plane creates. To make this easier to understand, while not 100% correct - if you fly the aircraft very slowly, you need to fly at a very high angle of attack, with the nose up high in the air. If you fly slightly faster, you can already lower the nose quite a bit, and drag will go down.

 

As you may know, aircraft have best climb speeds, for WW2 fighters typically in the range 250-300km/h. At these speeds, drag is minimum, if you go faster or slower, your climb rate goes down, because drag goes up. You can try that in game.

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20 minutes ago, SJ_Butcher said:

 

Lol, this is not about if I like or not, but there is no evidence that the result you posted are right, you questioned my source too, so Why I should believe your or the devs? When they don't provide information or data or test or a book as source. Sadly ww2 performance planes are a mystery and I only want to know the truth about it, because all the data are over the place.

 

OK since you seem to be missing the point I will spell it out to you in the clear: You will have to make up your mind by looking at the RESULTS that come out of the simulations and compare that to IRL DATA. Again, I have been posting results for years on-line so all you have to do is look at the results posted and make up your mind.

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1 minute ago, Holtzauge said:

 

OK since you seem to be missing the point I will spell it out to you in the clear: You will have to make up your mind by looking at the RESULTS that come out of the simulations and compare that to IRL DATA. Again, I have been posting results for years on-line so all you have to do is look at the results posted and make up your mind.

How can I compare the acceleration data if don't exist! 

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2 minutes ago, SJ_Butcher said:

How can I compare the acceleration data if don't exist! 

 

When I said compare data I meant other data as well: Speed, climb and turn rate etc. If the model has a good overlap with IRL data for certain data points it will most likely provide good data for other unknown data points as well and since the model basically assesses the forces acting on a body you can by simple mathematical integration work out many things including acceleration if you model is any good. So you don't specifically need acceleration data to do a good model that can provide such data as output.

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5 minutes ago, VO101Kurfurst said:

 

Oh, you are not the only one who has asked HZ for any sort of source or reasoning in the past decade, but its always the same smoke and mirrors answer with some accusation of bias. HZ has been paddling his so-called calculations on various flight sim boards and developer for decades now (albeit without success :D ) and trust me, we have seen it in all forms and shapes, and you will never get a straight answer from him.  I guess the reason is simply that he simply fears anyone could cross check his numbers, as there is hardly any secrecy in how to calculate aircraft performance and they were hardly ever close enough to real test results to have any kind of monetary or scientific value to anyone, expect perhaps him.

 

And so there is this cloud of mystery and there is never any more specific answer than ‘I am an engineer you know’ , or ‘calculations show’ and/or some passive/aggressive retort. Its essentially cheap rhetoric, the kind you see in the circus. 

 

Thing is, most of the (known) single data points can be reached by tinkering with the drag, thrust, lift or other factor, and its not too complicated you can even do it an excell table. Essentially this is the only thing he does, he picks a known data point (like turn time from a tests), tinkers with the lift and drag until he gets a close enough to already known numvers and tries to sell it as evidence of how ‘accurate’ his estimations are. And if he cannot get it anywhere close, he claims the real world results are wrong, his calculations are correct. :)


And on the other hand if the simulations would proof OPs doubts then OP would clap his hands. Would say "I knew it". And no further questions would be asked. "Must be right cause it proofs my point".

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19 minutes ago, VO101Kurfurst said:

 

Oh, you are not the only one who has asked HZ for any sort of source or reasoning in the past decade, but its always the same smoke and mirrors answer with some accusation of bias. HZ has been paddling his so-called calculations on various flight sim boards and developer for decades now (albeit without success :D ) and trust me, we have seen it in all forms and shapes, and you will never get a straight answer from him.  I guess the reason is simply that he simply fears anyone could cross check his numbers, as there is hardly any secrecy in how to calculate aircraft performance and they were hardly ever close enough to real test results to have any kind of monetary or scientific value to anyone, expect perhaps him.

 

And so there is this cloud of mystery and there is never any more specific answer than ‘I am an engineer you know’ , or ‘calculations show’ and/or some passive/aggressive retort. Its essentially cheap rhetoric, the kind you see in the circus. 

 

Thing is, most of the (known) single data points can be reached by tinkering with the drag, thrust, lift or other factor, and its not too complicated you can even do it an excell table. Essentially this is the only thing he does, he picks a known data point (like turn time from a tests), tinkers with the lift and drag until he gets a close enough to already known numbers and tries to sell it as evidence of how ‘accurate’ his estimations are. And if he cannot get it anywhere close, he claims the real world results are wrong, his calculations are correct. :)

 

Exactly my thoughts, thats why I asked for the formula, because as much as I searched I couldn't find anything in Internet that determine the acceleration of a plane, but he still negate my source that use a formula too, both are not accepted by the aerodynamic but still claim he is correct, I don't get it

 

11 minutes ago, DerSheriff said:


And on the other hand if the simulations would proof OPs doubts then OP would clap his hands. Would say "I knew it". And no further questions would be asked. "Must be right cause it proofs my point".

 

I don't get what this is supposed to mean, I'm just asking for sources, test, or whatever that proves I am wrong with the exception of own calculations, now If you have a formula that proves your point and is widely know that the formula is 100% correct I don't have problems to admit my mistake, but I need answers and nobody can refute my source yet

Edited by SJ_Butcher

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...nobody can refute my source yet.

 

The developers have repeatedly made it clear that they require actual performance data before considering changes to FMs. 'Extrapolations' based on unspecified formulae that even the author admits aren't part of accepted aerodynamic theory aren't 'sources' at all as far as BoX development is concerned.

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Some food for thought - no formula, but plausibility check: Climb rate is excess thrust, as is acceleration. If you see a slower climbing plane out-accelerating a faster climbing plane, something is fishy. The informations doesn't necessarily have to be wrong, but you'll be at least be missing some parts of the puzzle.

 

WRT the Fw190, an acceleration of ~12km/h/s at a speed of around 270km/h equals a power excess of about 1000kW. This would be near 100% the power of the BMW801 with a prop efficiency of 85% (typical for prop of the time), meaning the Fw190 would be flying drag free, or, if tested at combat power, it would create energy from nothing or maybe dark matter and thereby at least destroy the known universe. :o: This is even more true if figures of 50mph in 5s were to be taken seriously. 1000kW excess power also translate to 25+m/s climb rate, which the Fw190A-3 didn't have. So the data listed fails two simple plausibility checks.

 

The ~2.3m/s² posted by Holtzauge pass these checks - not saying that they are exactly right, but at least they aren't obviously wrong. Hope that helps.

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19 minutes ago, SJ_Butcher said:

 

Exactly my thoughts, thats why I asked for the formula, because as much as I searched I couldn't find anything in Internet that determine the acceleration of a plane, but he still negate my source that use a formula too, both are not accepted by the aerodynamic but still claim he is correct, I don't get it

 

Roughly estimating the acceleration of a plane at a given speed, for example climb speed isn't very hard. Planes require roughly 8 times the power to reach twice the speed (i.e. power requirements increase with the cube), and from that correlation and from the power required for max speed you can easily estimate the power required from a given speed, and what is left is the excess power available for accelerating the plane from that speed.

 

From that you can roughly estimate the excess thrust (most estimates use about 80% propeller thrust), and from there on its a simply matter of F = m * a -> a= F/m formulae. If you want to do it all the way through, you can just make an excel table that keeps calculating acceleration vs time and speed.  From what was seen those sekrit C++/iamanengineer tables hardly do anything more serious than that.

 

Of course all this is just quick and dirty estimate may give you reasonably close estimates (at least between planes relative to each other), but they are fundamentally not very accurate because of the cumulative effect if small deviations in real life from the assumed / guessed base values

 

If the real plane having a 83% propeller efficacy at the given speed and flight condition, which shall also vary with speed, blade angle and altitude, and, for example, if  you used an assumption of 'flat' 80% propeller efficiency curve all the way long, you have already underestimated the available trust, and probably overestimated the drag, which will add up as the timescale moves forward (all errors will accumulate) and will deviate even further if the propeller efficiency changes with that speed as well. Thus the calculation may be reasonably accurate at one point but results that are built on that 'good' data are likely further to further from the real values.

 

As the uncertainty of the base data also extends to lift curves, drag curves, Oswald efficiency factor and so on,  there is about an infinite number of possible variations - planes with high propeller efficiency and poor drag curves and so on - and the margin of error will be increasing the further you get from the last known historic data point. 

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1 minute ago, Holtzauge said:

 

As usual I think your post actually says more about you than me Kurfurst and I have reported it as it deserves. You know I really feel sorry for you: You must live a really miserable life seeing all the vitriol you spread about you. Anyway, now it's time for some dinner: Moose steak with wine so I'll leave all the sour grapes to you. Cheers! ;)

 

wow you guys love each other, but please keep the discussion civilized, I don't want the thread got locked

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A formula is a very simple mathematical expression. When things get to complicated you use what is called a model. A model is more or less like collection of formulas. When a model is to complex to be solved analytically or if certain parameters have to be simplified a lot  it is often called a simulation. You can of course use excel or anything you want, but that doesn’t mean it will not be less sophisticated than using other methods.

 

So when you look for a formula to get your results on the internet you will probably not find anything, because it is not as simple as that.

 

I can understand if people do not want to publish their work on the internet. It is work, nonetheless even if it is just a model. Demanding some sort of academic peer review before excepting calculation results posted on a flight sim forum is simply ridiculous.

 

Ultimately you should really just du some basic plausibility checks for the data you provided. Even though there may be no final proof, if it looks like fish and smells like fish well then...

Edited by =EXPEND=SchwarzeDreizehn

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It is, in itself, a plausibility check for the Il-2 flight model. A very good one if you ask me. If two independently developed algorithms agree on the result, it's a good sign. If not, well, it's good to take another look. So it does help improving the quality of Il-2. It just shouldn't be taken as the truth, which imho doesn't exist anyway.

Edited by JtD
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11 minutes ago, Pupo said:

 

 

The FM discussion  is currently dominated by from a non-validated, non-reviewed, non-state-of-the-art program, which will not help in any way improving the quality of Il-2.

 

Which is perfectly fine as far as I am concerned.

I think you are exaggerating when you say it is dominated by it. It gives a second educated guess to double check things.

you are making it sound like the whole forum is viewing it as some truth machine, which Inthinknit really isn’t regarded as at all.

It is a ball park checker.

 

If you think the forum can create a stand alone second model that improves on their professionally produced flight model, which IL2 essentially is, you are demanding too much

 

Oh JtD just Beat me 20 seconds:biggrin: to it :wacko:

Edited by =EXPEND=SchwarzeDreizehn
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1 minute ago, Pupo said:

The problem is  that some users are now holding Holtzauge simulations as the ultimate truth on how the FM should be adjusted...

 

What 'some users' are doing is beside the point, since the developers aren't going to change anything resulting from simulations based on unspecified formulae. I know some people dedicate a great deal of effort to 'proving' each other wrong on this forum, but none of it has any bearing on actual development without verifiable data.

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Wow, I really had to look at the topic again to make sure I was in the correct thread.

So this really is the one where the figures from a 1944 Fw190 written by an author who says that they are probably not accurate estimates are presented as evidence.

Holtzauge does a plausibility check and says, well the numbers look off. IL2 is probably a better estimate...

A 2 Page bash feast of his model

follows.

Seriously, what is your problem people? Really? :lol:

Edited by =EXPEND=SchwarzeDreizehn
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Locking

 

Look by now we all know the drill. 

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I have cleaned up and unlocked this thread...  Let's keep it on topic and non personal shall we. 

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