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View Full Version : TAS...IAS, whats modeled, whats not?



FBXtremeAddict
07-26-2004, 11:19 PM
OK, with all this discussion that goes on with FMs etc ESPECIALLY the P47 just what does the sim model in terms of environment-eg we know that TAS (true airspeed) is a function of calibrated airspeed, Altitude, Altimeter setting and outside temp-can TAS be computed? I note that wind is not present, so dont have to worry about that if you want to plan your flights, use DR etc..

Thanks

FBXtremeAddict
07-26-2004, 11:19 PM
OK, with all this discussion that goes on with FMs etc ESPECIALLY the P47 just what does the sim model in terms of environment-eg we know that TAS (true airspeed) is a function of calibrated airspeed, Altitude, Altimeter setting and outside temp-can TAS be computed? I note that wind is not present, so dont have to worry about that if you want to plan your flights, use DR etc..

Thanks

WTE_Galway
07-26-2004, 11:37 PM
IAS in the cockpit

not sure about speedbar I always turn it off

there is a pdf on one of the original Forgotten Battles install disks with a TAS to IAS convertor

the maps have two scales the grid is either 10km or 1km its usally pretty obvious which scale the grid is at

i tend to navigate with a rough rule of thumb:

"at 300kmh indicated in cockpit a 10km map square takes 2 minutes to fly across"

its not very precise but its good enough to get you in visual of the correct target

El Turo
07-27-2004, 12:43 AM
Airspeed indicator is.. well.. Indicated Airspeed.

If you need just a rough approximation of your True Airspeed which for all intents and purposes in this game is the same as your ground speed, you take your IAS and multiply it by your altitude in KM x 7%

So, at 4km, you would add right about 28% to your IAS to get your approximated TAS.. let's say you're going 400kph. 400 x 1.28 ~ 500kph or so.

If you have the "no cockpit" option available, I believe the speedbar in no-cockpit mode reads as TAS instead of IAS as well.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

BennyMoore
07-27-2004, 01:00 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by El Turo:
If you need just a rough approximation of your True Airspeed which for all intents and purposes in this game is the same as your ground speed, you take your IAS and multiply it by your altitude in KM x 7%<HR></BLOCKQUOTE>

That's [(IAS x altitude) / 100] x 7? Or is it IAS x [(altitude / 100) x 7]?

I hate mathematics with a passion.

FC_KPAX
07-27-2004, 01:10 AM
Hello,

Some time ago I found this formula on a board. I can't remember where.

TAS = [ 1 + (ALT/15250) ] * IAS

Only valid under 10000 meters (I am not sure of this restriction).

Example : 3000m and 300km/h

TAS = [ 1 + (3000/15250) ] * 300 = 359.016

TAS is 359km/h at 3000m with 300km/h as IAS

Have fun

diomedes33
07-27-2004, 01:12 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BennyMoore:
That's [(IAS x altitude) / 100] x 7? Or is it IAS x [(altitude / 100) x 7]?

I hate mathematics with a passion.<HR></BLOCKQUOTE>

lol, short answer ... yes.

They're both right, forgot which law it is, communicative or something like that.


aka 3./JG51_Specter
http://www.public.asu.edu/~guthriec/ubi_sig.jpg

El Turo
07-27-2004, 01:22 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BennyMoore:
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by El Turo:
If you need just a rough approximation of your True Airspeed which for all intents and purposes in this game is the same as your ground speed, you take your IAS and multiply it by your altitude in KM x 7%<HR></BLOCKQUOTE>

That's [(IAS x altitude) / 100] x 7? Or is it IAS x [(altitude / 100) x 7]?

I hate mathematics with a passion.<HR></BLOCKQUOTE>


It's real easy and you can do it in your head:

Altitude in KM x 7 = modifier
IAS x modifier ~ TAS

So, at 4km, your modifier (error) is 4 x 7 = 28

IAS assumed at 400kph
400kph plus 28% OF 400kph added back in = 1.28

400kph x 1.28 is appx 500kph

Roughly a quarter of 400kph is about 100kph, added back to 400kph equals 500kph.

400 x 1.28 ~ 500kph



In feet, it is about 2% for every thousand feet of altitude. So, technically, it's somewhere between 6 and 7 percent per KM.. but close enough for estimation in any case.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,
reloading my rifle.

~V.

WTE_Galway
07-27-2004, 01:33 AM
pretty sure the cockpit off is TAS


TAS is needed for level bombing as well as navigation

FBXtremeAddict
07-27-2004, 03:06 PM
Thanks fellas, now hands up who would like to see dyamic weather, ie wind etc moddelled as well??