IAS -> TAS air density model

[Alberich]

Hello,
this is my first posting here and I hope this is the right place to post and the subject was not discussed already. Searching the forums did not help me finding the desired information though.

I am interested in how IL2 1946 models the atmosphere, especially how the game derives TAS. Is, for example, air temperature (and its effect on air density) taken into consideration?

Right now I use the '2%-rule of thumb' to derive my TAS (from IAS and altitude above sealevel) which says that TAS increases by 2% every 300 meters of altitude. Well, that is just a rule of thumb...
When dropping bombs with the Pe-2 (OPB-1 bombsight, no bombsight automation) it looks like the error made by this rule of thumb leads to quite incorrect bombsight-angles.
Some information on this topic would be greatly appreciated!

Alberich

[Letum]

If temperature does change air density, then the effect is simplified.
Air density should decrease more slowly at high altitude in hot areas, but this is not modelled in IL2.

[JtD]

Actually not true, density decreases less at altitude on warm maps. At least up to 10000m we have a linear reduction of temperature. I've tested Crimea and OnlineMT once, and while Crimea had higher pressure at sea level, it was pretty much the same at 10000m.

I guess the problems with the inaccuracy of high altitude level bombing stems from the fact that the atmospheres are not standard and thus sea level pressure doesn't give you IAS = TAS. You can get the correct TAS from the yellow gauges in the cockpit off view, if you want to do your bombing accurate down to the last km/h, you should memorise the speeds you attain with certain power settings on certain maps at certain altitudes.

[Alberich]

Thanks a lot for the quick answers!

Originally Posted by JtD

[...]the atmospheres are not standard and thus sea level pressure doesn't give you IAS = TAS.[...]

Now that is strange...
The 'wonder-woman-view' (no cockpit-view ) shows TAS, very interesting, I never used ww-view. I'll do some testing on this, outcome should be that IAS and TAS are the same at sealevel... very interesting and new information, thanks!
This should at least tell me if the TAS derived by IL2 differs from the TAS I derive.

Originally Posted by KG26_Alpha

Don't forget unless you are level bombing at sea level you will have to +/- the targets terrain altitude from the bombsite altimeter setting, unless your using the Norden sight.

Not sure what you mean with "unless your using the Norden sight". The target-altitude must not be subtracted from the bombers altitude when using this bombsight?

Thanks a lot for the TAS-charts! And also the smartphone-utility is very interesting, although I do not have such a new mobile phone.

In fact I made such a utility for the X52pro display myself, here are some pictures:













This little application does all the mathematics 'behind the scenes' and computes the bombsight-angle, also wind and the resulting side-slip (bombsight correction left/right) is taken care of.
The angles derived by this tool are quite accurate, I am just wondering if the formula (2% every 300m or 1000ft) I use to derive TAS (speed over ground in fact regarding wind) is 'good enough' for airspeed is the most critical parameter here. That is why I posted my question here, I thought that maybe someone with a deeper insight into the games functions could tell me how IL2 actually derives TAS...

Again, thanks a lot for your answers!
Alberich

[WTE_Galway]

Slightly off topic but a really interesting read ....

[K_Freddie]

This is engineering for you !!

[too-cool]

Originally Posted by Alberich

Thanks a lot for the quick answers!

Now that is strange...
The 'wonder-woman-view' (no cockpit-view ) shows TAS, very interesting, I never used ww-view. I'll do some testing on this, outcome should be that IAS and TAS are the same at sealevel... very interesting and new information, thanks!
This should at least tell me if the TAS derived by IL2 differs from the TAS I derive.

Not sure what you mean with "unless your using the Norden sight". The target-altitude must not be subtracted from the bombers altitude when using this bombsight?

Thanks a lot for the TAS-charts! And also the smartphone-utility is very interesting, although I do not have such a new mobile phone.

In fact I made such a utility for the X52pro display myself, here are some pictures:













This little application does all the mathematics 'behind the scenes' and computes the bombsight-angle, also wind and the resulting side-slip (bombsight correction left/right) is taken care of.
The angles derived by this tool are quite accurate, I am just wondering if the formula (2% every 300m or 1000ft) I use to derive TAS (speed over ground in fact regarding wind) is 'good enough' for airspeed is the most critical parameter here. That is why I posted my question here, I thought that maybe someone with a deeper insight into the games functions could tell me how IL2 actually derives TAS...

Again, thanks a lot for your answers!
Alberich

How about sharing that utility along with the instructions for it's install and use? TC

[KG26_Alpha]

Originally Posted by Alberich

Thanks a lot for the quick answers!


Not sure what you mean with "unless your using the Norden sight". The target-altitude must not be subtracted from the bombers altitude when using this bombsight?

Alberich

The Norden Sight calculates TAS for you.
You don't need to =/- target altitude in the bombsite altitude setting.

Lofte 3D operation

http://translate.google.co.uk/transl...26prmd%3Dimvns



Theres plenty of videos out there for Allied's and Axis sights on google.






.

[Alberich]

Thats indeed some nice reading Galway, thanks for posting!

How about sharing that utility along with the instructions for it's install and use? TC

Right now I am making the application ready for 4.11m (three new flyable bombers) and UP3 RC4. I am also working on a detailed manual on how to use the tool and a translation to english language, should be done in a few days and I will upload it as soon as possible.

The Norden Sight calculates TAS for you.

If I am right TAS (speed over ground in fact) is obtained with the norden sight by synchronizing the bombsight-automation with the target in the crosshair.

You don't need to =/- target altitude in the bombsite altitude setting.

From the sturmowiki-article you posted:
Original language: Dazu muss von der abgelesenen Höhe (Höhe über NN) die Höhe des Ziels abgezogen werden.
Translation: This must be subtracted from the read height (height above sea level) the level of the target.

I love google-tranlations
OK, just as I thought. Target-altitude is, more or less, important for precise bombing and should be subtracted from own altitude.

Thanks you for helping!
Alberich

[swiss]

Originally Posted by Alberich

In fact I made such a utility for the X52pro display myself, here are some pictures:

Care to to share?