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FatCat_99
07-30-2008, 06:22 AM
Hi,

I would like to know properties of standard atmosphere used by major WWII participants.

I'm interested to know are performance charts standardized by same method.

All I know for sure is that NACA used temp. 15degC, pressure 760mmHg and density 0,002378 slugs/ft^3 at 0m as standard. What about the others?

Any info appreciated.

FC

FatCat_99
07-30-2008, 06:22 AM
Hi,

I would like to know properties of standard atmosphere used by major WWII participants.

I'm interested to know are performance charts standardized by same method.

All I know for sure is that NACA used temp. 15degC, pressure 760mmHg and density 0,002378 slugs/ft^3 at 0m as standard. What about the others?

Any info appreciated.

FC

Bremspropeller
07-30-2008, 06:47 AM
ICAO:

Temp 15?C

Density 1.225 kg/m³

Pressure 1,013.25 mbar or 29.92 inch/Hg

M1.0 340 m/s or 1225 km/h

FatCat_99
07-30-2008, 07:18 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Bremspropeller:
ICAO:

Temp 15?C

Density 1.225 kg/m³

Pressure 1,013.25 mbar or 29.92 inch/Hg

M1.0 340 m/s or 1225 km/h </div></BLOCKQUOTE>

Thx, that's what NACA was using but I would like to see is that's what others were using too.

I know that USN or USAF had few types of standards, something like standard day, standard hot day etc.

I saw that somewhere but can't find that info again. So question is what type of standard was used when charts were made.

To make things more interesting we always had to make tests in Il2 on Crimea map which is:
25degC
745mmHg

which results with lower density, so planes on Crimea are faster and should climb and turn worser than on ICAO standard day.

FC

KrashanTopolova
07-31-2008, 07:41 PM
Is this the reason why the in-game P-40 in the Pacific is so...?

Down in the equatorial tropics with those hot and humid thermals whipping up, the P-40 was much different to the way it is portrayed in -game, Even in the African Western Desert it performed very well (No3 Squadron RAAF shot down well over 100 planes for the loss of 16 P-40's).

A question I have is whether standard atmosphere data is vital to pilot procedure since the aircraft normally had altimeter setting (height above aerodrome) no matter where it was operating... and did some also have QNH setting? Neither of these settings are modelled in il-2. I hope they include them in BOB/SOW.

Kettenhunde
07-31-2008, 09:07 PM
There was no standard atmosphere back then. There really isn't one today either.

Instead we have quite a few "standard" models. If you are an AIAA member go to the library and you can purchase a copy. It runs ~70 USD.

http://img378.imageshack.us/img378/9991/standardreferneceatmospju0.jpg (http://imageshack.us)
http://img378.imageshack.us/img378/9991/standardreferneceatmospju0.d6eb920dc6.jpg (http://g.imageshack.us/g.php?h=378&i=standardreferneceatmospju0.jpg)

Drop me a PM if I can help.

All the best,

Crumpp

Viper2005_
07-31-2008, 10:14 PM
Evolution of a Standard Atmosphere:
http://naca.central.cranfield.ac.uk/reports/1923/naca-report-147.pdf
http://naca.central.cranfield.ac.uk/reports/1926/naca-report-218.pdf
http://naca.central.cranfield.ac.uk/reports/1954/naca-tn-3182.pdf
http://naca.central.cranfield.ac.uk/reports/1955/naca-report-1235.pdf

&lt;Missing US 1962, ICAO 1964, ISO 1975&gt;

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19...09539_1977009539.pdf (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf)

You will note from the above that not much has changed in what one might describe as the WWII altitude range (&lt;&lt;20 km). This is largely because change would necessitate repetition of a whole raft of performance calculations, and possibly make a fair few aeroplanes illegal unless regulations moved in step.

Given that the modern standard atmosphere really dates from the 1920s (before the first report in my list, NACA assumed the atmosphere to be isothermal at 10ºC for the purposes of altimeter calibration and appears to have considered this to be "good enough for government work"), it is likely that almost everybody would have ended up singing from much the same hymn-sheet (since AFAIK nobody else had any useful budget), especially given that NACA helpfully worked in what was then "SI".

M_Gunz
08-01-2008, 02:15 AM
An old quote:
"That's the problem with standards, there's so many of them!"

Kettenhunde
08-01-2008, 08:51 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">You will note from the above that not much has changed in what one might describe as the WWII altitude range (&lt;&lt;20 km). This is largely because change would necessitate repetition of a whole raft of performance calculations, and possibly make a fair few aeroplanes illegal unless regulations moved in step. </div></BLOCKQUOTE>

It does not have to change if you know the limitations of the model used to derive the data. If you do not then you are "****ing up a rope".

Most folks wouldn't know these limitations and even knowing the general limitations is of little use unless we know the specfic values to convert from one to other.

For example, even in the same model, data converted to a "standard day" in Berlin Germany in December will have different results from a "standard day" measured in Baha California in July.

http://img84.imageshack.us/img84/2517/isoatmosphereiq8.jpg (http://imageshack.us)
http://img84.imageshack.us/img84/2517/isoatmosphereiq8.767bc7f799.jpg (http://g.imageshack.us/g.php?h=84&i=isoatmosphereiq8.jpg)

All the best,

Crumpp

FatCat_99
08-02-2008, 02:36 AM
Hi,
thanks for answers.

Crumpp, in that part you marked it seems to me that they only say that real values of atmosphere properties could and will be different than those in standard model.

But that's what is expected. After all that's why we need standard model to have reference when we are comparing data.

And data comparison is what really interest me here. On most of WWII performance charts there is no notes about weather conditions so that mean that some sort of standard was in use.

It doesn't have to be single standard, as far as I'm concerned every factory and test department can use their standards but if we want to compare plane performance than we need to know for which atmosphere conditions these data in charts are corrected.

So my question is if plane X have top speed 600kmh on British chart what will be it's speed on German chart, same or different?

BTW Crumpp, I'll PM you in CWOS.

FC

Kettenhunde
08-02-2008, 08:24 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Crumpp, in that part you marked it seems to me that they only say that real values of atmosphere properties could and will be different than those in standard model.
</div></BLOCKQUOTE>

It is letting you know that model approximates the atmosphere at 45 degrees North on a "standard day".

http://img99.imageshack.us/img99/1626/45degreenorthqu1.jpg (http://imageshack.us)
http://img99.imageshack.us/img99/1626/45degreenorthqu1.b9bf7ee8b9.jpg (http://g.imageshack.us/g.php?h=99&i=45degreenorthqu1.jpg)

The farther we are from those conditions, the larger our errors are going to be when we convert measured data to the standard model.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">So my question is if plane X have top speed 600kmh on British chart what will be it's speed on German chart, same or different? </div></BLOCKQUOTE>

Most likely it is different. It just depends on the conditions the data was gathered under and the conversions used. I personally just eliminate all these errors when I do a performance analysis by converting IAS to EAS myself so that I estabilish the conditions.

Sure there is some slight error remaining in the PEC curve determination differences but it is better than piling on multiple errors IMHO.

Ok on the PM.

All the best,

Crumpp