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Acars Atis and Taxi question
http://www.ocs-support.co.uk/forums/viewtopic.php?t=1981		 Page 3 of 3
Author:  Chrash65 [ Wed Apr 27, 2016 12:17 am ]
Post subject:  Re: Acars Atis and Taxi question
Hi Ralf,

if the METAR Data is delivered to PF3 not by any Wather Engine direct but through FSUPIC, why is there a QNH-Difference of -1 between the Weather Engine and PF3?

I switch radio for ATIS on:

my Weather Engine OPUS shows me QNH 1015 in the running green line on the top of the screen
In the same time I hear and see PF3-ATIS Message in the FSUPIC-Window: QNH 1014

I think, I should use the OPUS item, sholdn't I? But, why are they not the same?

By the way, I stay on the ground in EDDL, not airborne, not 100 nm away ...

Regards

Alexej
Author:  RALF9636 [ Wed Apr 27, 2016 6:57 am ]
Post subject:  Re: Acars Atis and Taxi question
Chrash65 wrote:
Hi Ralf,

if the METAR Data is delivered to PF3 not by any Wather Engine direct but through FSUPIC, why is there a QNH-Difference of -1 between the Weather Engine and PF3?

I switch radio for ATIS on:

my Weather Engine OPUS shows me QNH 1015 in the running green line on the top of the screen
In the same time I hear and see PF3-ATIS Message in the FSUPIC-Window: QNH 1014

I think, I should use the OPUS item, sholdn't I? But, why are they not the same?

By the way, I stay on the ground in EDDL, not airborne, not 100 nm away ...

Regards

Alexej
Good question Alexej. I also use Opus and experience the same.
I guess it is because the sim isn't able to produce the exact weather injected by Opus even close by. You also have a wind difference sometimes, e.g. 227 at 9 instead of 230 at 10.
I'm not bothering with it any more and just imagine the weather has changed since the last ATIS update...
I tend to use the the ATIS value as that seems more realistic. And remember 1 mb only makes a difference of about 30 ft.

You might want to ask this question at the Opus forum though. They are very helpful there too.

Regards
Ralf
Author:  ThomasAH [ Wed Apr 27, 2016 8:20 am ]
Post subject:  Re: Acars Atis and Taxi question
I think I have noticed this without an external weather engine, too, but have not verified it further.
Now I'm using FSXWX and notice the same, so I assume it is not related to Opus.

Maybe one of us should check the behaviour with inHG to compare?

It could be repeatedly converting from one to the other with always rounding down (truncating):
29.92 inHg -> 1013.2075 mb (rounded down: 1013 mb)
1013 mb -> 29.91387 inHg (rounded down: 29.91 inHg)
29.91 inHg -> 1012.8689 mb (rounded down: 1012 mb)

Or something completely different :)
Author:  helix1250 [ Wed Apr 27, 2016 8:23 am ]
Post subject:  Re: Acars Atis and Taxi question
Just to add my tuppence worth, I have seen this behaviour as well, I'm using ASN. So it's defiantly not just Opus!

I go by ASN and just use Atis for the active runway.

Rob
Author:  vololiberista [ Wed Apr 27, 2016 9:05 am ]
Post subject:  Re: Acars Atis and Taxi question
I think this is down to how the weather engine one uses converts pressure in comparison to how the sim converts pressure. Each weather engine has anomalies. For example FSMetar also has a bug whereby the reported temperature in the sim differs by 2 degrees. FSRealWX, I have to manually send global data to the sim otherwise the reported QNH at the destination is always standard.
All the sims FS9, FSX and P3D calculate millibars as 29.54545 feet per millibar. If your weather engine uses a different formula which is quite likely then a rounding difference will appear from time to time. Also a discrepancy can occur if your a/c instruments use their own variables instead of the sim variables.
At the end of the day though PF3 only does what it is told! Only the final step as it were will be reported to PF3 by FSUIPC. FSUIPC itself can have an effect too if you have made any weather tweaks to it.
Author:  ThomasAH [ Wed Apr 27, 2016 9:38 am ]
Post subject:  Re: Acars Atis and Taxi question
vololiberista wrote:
I think this is down to how the weather engine one uses converts pressure in comparison to how the sim converts pressure.
...
At the end of the day though PF3 only does what it is told!
Or PF3 converts too often and always rounds down, just checked an older log:
Code: Select all
16/03/2016 18:59:12: 870 - Transcript: 'Schiphol Airport Information Sierra Weather at 1845 Zulu winds 80 at 12 visibility greater than 20 miles.
   Sky condition 4 thousand 7 hundred Few 7 thousand 8 hundred Few . Temperature 9 . Dewpoint minus 1 . Altimeter 1028 . [...]
16/03/2016 18:59:57: 760 - Baro=30.38401  CompensatedAlt=-475
16/03/2016 19:26:24: 310 - Transcript: 'Roger J-Bird 1608 Radar contact QNH 1028  '
30.39323 inHgh = 1029.2328962 mb
1029 mb = 30.38635 inHg
30.38 inHg = 1028.7849 mb
1028.7849 mb incorrectly rounded down (truncated) = 1028 mb = 30.35682 inHg
(conversions done via google search, e.g. "1028 mb in inHg")

If PF3 reads QNH 1028 instead of Altimeter/inHg 30.38401 via FSUIPC at some point, it does not log it.
Author:  Dave March [ Wed Apr 27, 2016 10:34 am ]
Post subject:  Re: Acars Atis and Taxi question
There was no rounding at all. This has now been corrected.

Well spotted
Author:  Chrash65 [ Thu Apr 28, 2016 8:26 pm ]
Post subject:  Re: Acars Atis and Taxi question
Hallo Dave,

should I understand yours "This has now been corrected." as -- there is (soon available) a next version of PF3, which hasn't 1mb difference in PF3-ATIS-Message?

Alexej
Author:  Dave March [ Thu Apr 28, 2016 8:43 pm ]
Post subject:  Re: Acars Atis and Taxi question
Well hopefully the figures will be better and yes, there will be an update very soon

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