SIMUFLY.COM Discussion Forums - Different values after alignment

toelg

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Different values after alignment
Sep 4^th, 2007, 9:19pm

Hi INS-friends,

last time, I often notice this at my DF 727 - INS :

After the alingment is finished (at NAV), the values at "POS" and "WayPT" have other values as I have typed into INS for alignment.

For example :

I type in for alignment: N 51.16.8 E 006.45.8 (as it is written at the Fs9 (Shift/Z).

After the alignment (at NAV) I found at POS and WayPT 0 : N 51.16.7 E 006.45.6 (sometime it differs between POS and WayPT 0 too).

Although the difference is not high, but this causes a permanent deviation from the flight-track.
I would this assume, all values must be the same actually ?

Best regards
Dietmar

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skipper Forum Member Offline I am an Australian living in Hungary Posts: 14 Hungary Gender:	Re: Different values after alignment Reply #1 - Sep 5^th, 2007, 11:01am I have similar problems too. My problem is, after a couple of hours of flying, my position differs by as much as 30-40 minutes in longitude from the position that is displayed when using Shift Z. Would anyone have an idea? Thanks and regards, Nick Cserny
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Marco Ravanello Forum Administrator Offline Posts: 309 Gender:	Re: Different values after alignment Reply #2 - Sep 5^th, 2007, 2:35pm > Would anyone have an idea? That is due to INS drifting, if you don't perform any DME Update you'll lose navigation precision. Regards Marco
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skipper Forum Member Offline I am an Australian living in Hungary Posts: 14 Hungary Gender:	Re: Different values after alignment Reply #3 - Sep 5^th, 2007, 2:48pm Thank you Marco. I guess, I am still thinking AN/ASN42 system, your answer makes a lot of sense. Regards, Nick
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toelg Forum Member Offline Posts: 14	Re: Different values after alignment Reply #4 - Sep 6^th, 2007, 9:11am Hi Marco, ok, that explains the behaviour during flight well. But in my case this happens at the gate just after the alignment, before any movement of the aircraft. Best regards Dietmar
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Gianfranco Corrias

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Re: Different values after alignment
Reply #5 - Sep 7^th, 2007, 3:36pm

Did you align the INSs with the engines running?
The coordinates indicated in the position zero are always the plane present position and it's normal,at ramp, that the ramp position you inserted coincides with the waypoint position zero.
About the cordinates changing if you align the INSs with the engines running even with parking brake set the plane moves slowly due at a FS9 bug as written in the Doc.
Gianfranco

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« Last Edit: Sep 7^th, 2007, 3:48pm by Gianfranco Corrias »

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toelg

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Re: Different values after alignment
Reply #6 - Sep 8^th, 2007, 4:32pm

Hi again,

sorry, no engine running, parking brake is set. Only running APU (hope this causes no crawling).

I just tried it again :

The exact position at Fs9 (Shift/Z) is : N 51.16.82 E 006.16.82

I put at POS the values : N 51.16.8 E 006.16.8

After switching to NAV : the same values , ok ! But after about 15 minutes (no engines, only APU running) aperar the following values:

POS : N 51.17.1 E 006.16.2
WayPT 0: N 51.16.8 E 006.16.8

Is the drifting also on ground without movement (no engines, only APU running) ?
And if it is due to drift, is it really so heavy ?

Have a nice weekend !
Dietmar

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Gianfranco Corrias Member Offline Posts: 261 Gender:	Re: Different values after alignment Reply #7 - Sep 8^th, 2007, 5:14pm confirm please that you remained 15 min at ramp with parking brake set after having posed the MSU switch to NAV. Gianfranco
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toelg Forum Member Offline Posts: 14	Re: Different values after alignment Reply #8 - Sep 8^th, 2007, 10:34pm Hi Gianfranco, yes, I always switch to NAV-Position just after coming the green light, when alignment is finished. (Hope that's right) Regards Dietmar
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Gianfranco Corrias

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Re: Different values after alignment
Reply #9 - Sep 9^th, 2007, 11:01am

Hi,
I just finish to try to reproduce this issue and the result of my checks is:
With Shift+Z pushed to watch also at FS9 position,Parking brake set, I aligned the INS posing the MSU selectors on ALIGN position.
I made the complete Alignment till to API zero and after 16 mins the Positions of FS9,INS and WPT 0 remained the same.
The problem arose only with the INS (not with FS9) when NAV was selected on the MSU panels.
After about 10 mins the position changed from:
N41*47.8 E 12*15.0 to N41*47.8 E12*14.9 and the API from API1 to API2 without any aicraft movement.
I suspect that it's do to the wind effect but I'm not sure and Marco and me we'll investigate about this issue.
Anyway a not surely complete tenth of minute is a distance not important for a plane Flying at Mach 0.84.
Your way to operate isn't wrong but is out Standard.Please from now on until this issue will be solved, pose the MSU selector to NAV at "BEFORE START CHECK LIST" in this manner the time from the INS navigation status and the aircraft movement will be short and any further little position changing cannot be noticed.Moreover the API cannot increase again and you can leave the ramp at the best Alignment status.
Thanks for your information
Gianfranco

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« Last Edit: Sep 9^th, 2007, 11:26am by Gianfranco Corrias »

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toelg Forum Member Offline Posts: 14	Re: Different values after alignment Reply #10 - Sep 9^th, 2007, 12:51pm Hi Gianfranco, thanks for Your investigations ! . I also would be interested in knowing what the reason for it was. So it would be kind to get further information, if You have found the cause. Have nice Sunday ! Dietmar
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