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PakoAry
03-29-2009, 12:47 AM
A question I also have no answer is posted in another forum.
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Does anyone know the formula used by IL-2 to calculate TAS from IAS? (not real life)

I'm aware that we have some spreadsheets, good software such as bombsighttable2, reference tables, rules of thumb and spreadsheets... I also know what a E6B is and that TAS is affected by many other variables such as air density, temperature, moisture and etc... bear in mind that I'm not looking for a good method or solution to calculate my TAS in the game.

We could also take educated guesses on how the programmers, to compensate the lack of density and temperature modeling, could have linked a variance to one of the other factors to alter the ADAF - Air Density Adjustment Factor, so it loses the linear characteristics the absent variables confer to it. However, before we do that, let's not loose the original question:

Does anyone know the formula used by IL-2 to calculate TAS from IAS? once again, not real life, guys.
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PakoAry
03-29-2009, 12:47 AM
A question I also have no answer is posted in another forum.
-----
Does anyone know the formula used by IL-2 to calculate TAS from IAS? (not real life)

I'm aware that we have some spreadsheets, good software such as bombsighttable2, reference tables, rules of thumb and spreadsheets... I also know what a E6B is and that TAS is affected by many other variables such as air density, temperature, moisture and etc... bear in mind that I'm not looking for a good method or solution to calculate my TAS in the game.

We could also take educated guesses on how the programmers, to compensate the lack of density and temperature modeling, could have linked a variance to one of the other factors to alter the ADAF - Air Density Adjustment Factor, so it loses the linear characteristics the absent variables confer to it. However, before we do that, let's not loose the original question:

Does anyone know the formula used by IL-2 to calculate TAS from IAS? once again, not real life, guys.
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Viper2005_
03-29-2009, 01:06 AM
I don't know, but if I really wanted to know then I'd plot a graph of speedbar speed v/s wonderwoman view TAS, tell excel to plot a best-fit curve and then ask it to tell me the formula of that best-fit curve.

M_Gunz
03-29-2009, 04:17 AM
We were given a table with the game (as opposed to 3rd party) but no formula.

FatCat_99
03-29-2009, 07:11 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PakoAry:
A question I also have no answer is posted in another forum.
-----
Does anyone know the formula used by IL-2 to calculate TAS from IAS? (not real life)

I'm aware that we have some spreadsheets, good software such as bombsighttable2, reference tables, rules of thumb and spreadsheets... I also know what a E6B is and that TAS is affected by many other variables such as air density, temperature, moisture and etc... bear in mind that I'm not looking for a good method or solution to calculate my TAS in the game.

We could also take educated guesses on how the programmers, to compensate the lack of density and temperature modeling, could have linked a variance to one of the other factors to alter the ADAF - Air Density Adjustment Factor, so it loses the linear characteristics the absent variables confer to it. However, before we do that, let's not loose the original question:

Does anyone know the formula used by IL-2 to calculate TAS from IAS? once again, not real life, guys.
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IAS = TAS* SQRT(Density / 1.225) [m/s]

What made you think that Temperature and Density are not modeled?

FC

Wurkeri
03-29-2009, 08:56 AM
The formula is the one given by FatCat. However, the problem is to get correct atmosphere parameters which vary depending on map. Some Il-2 apps, like UdpGraph2, contain built in formulas for IAS/TAS conversion, you just give the sealevel parameters and the app does the work with good accuracy.

ElAurens
03-29-2009, 09:43 AM
Temperature is modeled in the game, but only one aircraft, the He 111 has a gauge that allows actually viewing it. However the gauge is not finely calibrated so accurate measurements are not really possible, even if you zoom in to it with TIR.

Also pressure is modeled as well, but unless you open map files in the modded game you have no way of knowing what it is.

One more thing, the Crimea map is often said to be modeled to "Standard day" atmospheric conditions. This isn't exactly true. It's barometric pressure is indeed spot on, but the sea level temperature is 10 degree C. to high. And because we have no accurate way to measure temp delta with altitude change, computing TAS is just going to be hit or miss.

It also makes accurate aircraft performance testing in the game rather hit or miss as well.

FatCat_99
03-29-2009, 09:58 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ElAurens:
Temperature is modeled in the game, but only one aircraft, the He 111 has a gauge that allows actually viewing it. However the gauge is not finely calibrated so accurate measurements are not really possible, even if you zoom in to it with TIR.

Also pressure is modeled as well, but unless you open map files in the modded game you have no way of knowing what it is.

One more thing, the Crimea map is often said to be modeled to "Standard day" atmospheric conditions. This isn't exactly true. It's barometric pressure is indeed spot on, but the sea level temperature is 10 degree C. to high. And because we have no accurate way to measure temp delta with altitude change, computing TAS is just going to be hit or miss.

It also makes accurate aircraft performance testing in the game rather hit or miss as well. </div></BLOCKQUOTE>
IIRC Crimea is 25deg C and 745 mmHg, if I'm not mistaken standard is 15deg C and 760 mmHg.

Pressure,Temperature and Density are polynomials in game but for TAS calculation it's enough to use temperature and pressure from map files and standard temperature laps rate of -6,5deg C/km

Error is just a few Kmh at certain altitudes.

For testing you can modify Crimea or any other maps to standard conditions, of course, there are some other ways of precise FM testing but that's not something to discuss in forums.

FC

PakoAry
03-29-2009, 12:31 PM
First of all, thanks for the fast replies. I've found many, many posts asking the formula, but the only answers were regarding the "real-life" formula. That may or may not be the one used in the game.

I didn't know until FatCat and Wurkeri confirmed the game is using equivalent air speed.

Good to know you could provide the game one, FC.
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">IAS = TAS* SQRT(Density / 1.225) [m/s]

What made you think that Temperature and Density are not modeled? </div></BLOCKQUOTE>

In fact that "not modeled" could have been clearer written.

I believe the game doesn't model different air masses for the same map and that the mass is static. Therefore, I inferred that it would be cost-effective in terms of processing to get the polynomials out of the way and derive density from altitude using the same lapse rate wherever the planes are. They could seed a sea level temperature and pressure per map and, from there, get the adjustment factor simply from altitude.

the problem is this same question has been asked in different ways and forms without getting a proper answer. It started flame wars, received tons of "I don't know"s, you don't need to know the formula, just use this software, table, spreadsheet and what not...

You guys were the first ones to be able to confirm the formula used for by the game.

Thanks.

ElAurens
03-29-2009, 05:07 PM
More testing needs t be done, but I would not be surprised it the standard lapse rate is not modeled either.

Wurkeri
03-30-2009, 07:25 AM
The standard lapse rate is not far off in the game but not precise either (at least up to 11km). As FatCat noted, there are more precise methods but that is whole another story.