Author Topic: margin  (Read 263 times)

S6

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margin
« on: September 21, 2019, 07:24:50 PM »
I have a safety margin set at 1000 feet in my CNv.
But the real number I get when flying is 400 feet lower.
Check everything on the ground and all is ok.
What can be done to correct this?
Thank you
Gilles

Evan Ludeman / T8

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Re: margin
« Reply #1 on: September 23, 2019, 12:10:27 PM »
There's simply not enough information here to go on. 

Things to check:  waypoint database, altimeter setting, various other settings, units, polar...

It used to work correctly, yes?  Figure out what changed.

Evan Ludeman / T8

S6

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Re: margin
« Reply #2 on: September 24, 2019, 06:25:22 AM »
Check every setting, nothing has changed

When my Oudie show 1000 feet above glide
CNv show 600 feet.
I do not use Oudie for final glide
I prefer the CNv.

Also.
Relating to a previous post about my screen flicking it is getting worst.

Gilles

carbonprop

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Re: margin
« Reply #3 on: September 24, 2019, 07:37:13 AM »
Could it be that the conditions are causing you to arrive lower?  More sink than expected?

Evan Ludeman / T8

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Re: margin
« Reply #4 on: September 24, 2019, 08:43:13 AM »
With glider at rest on your home airport and altimeter properly adjusted, what is the arrival altitude and distance CNv reports to your home field?  The arrival altitude should be roughly -200 feet less any reserve (i.e. -1200' for a 1000' reserve).

Let's keep the topics organized... updates to other topics should be posted in the appropriate thread.
Evan Ludeman / T8

S6

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Re: margin
« Reply #5 on: September 25, 2019, 09:28:48 AM »
I am not arriving lower.
The number on my display are wrong by 400 feet.
When I am at 1000 feet altitude the Oudie altimeter and the mechanical altimeter display are at 1ooo feet, the CNv is at 600 feet.
Setting for the vario and the Oudie for that parameter are the same.
One month ago I did not have this problem.

Evan Ludeman / T8

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Re: margin
« Reply #6 on: September 25, 2019, 09:48:47 AM »
Check the basics:  database has correct airport elevation, CNv set to correct altimeter setting.

If you are at your destination, at your margin height, CNv should read ZERO.  Likewise, if you are precisely on final glide to your margin height, the instrument reads ZERO. 

If it isn't working the same as one month ago, something changed.

If you want help with this, you'll need to provide more information. 
Evan Ludeman / T8

S6

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Re: margin
« Reply #7 on: September 26, 2019, 04:13:25 AM »
On the ground vario indicate -1200 feet as it should, because I am below margin height and I fly QNH 170 feet.
What other info do you need?
Gilles

Evan Ludeman / T8

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Re: margin
« Reply #8 on: September 26, 2019, 07:49:07 AM »
-1200 vs final glide with glider at rest at your destination field with 1000' margin is correct and indicates that altimeter, database and margin are either correct or have offsetting errors (unlikely).

Check that the polar is correct and that TAS & IAS as reported by CNv make sense (http://clearnav.net/main/cn-vario-manual.html#IAS).

Why do you think your Oudie is correct and CNv is wrong?  Is the discrepancy independent of distance and altitude?   Are the MC settings the same, and in same units?

For high speed, high MC final glides, the polar, ballast and bugs settings are quite important, however the spread between devices will in general be distance dependent. 
Evan Ludeman / T8

S6

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Re: margin
« Reply #9 on: September 26, 2019, 09:43:21 AM »
All setting have been check and they are ok in both instrument.
The Oudie is correct because when I am at 1000 feet margin is 0. CNv show -400 feet.

Evan Ludeman / T8

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Re: margin
« Reply #10 on: September 30, 2019, 04:53:15 AM »
How do the two devices compare ten miles out? 

Evan Ludeman / T8

S6

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Re: margin
« Reply #11 on: September 30, 2019, 12:15:55 PM »
Same difference. CNv indicate I will be home about 400 feet lower than real altitude.

Evan Ludeman / T8

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Re: margin
« Reply #12 on: October 01, 2019, 06:18:10 PM »
I still think that the overwhelming likelihood is some combination of user setup and database.  If it were hardware, there would be other issues.  I think you need another set of eyes on your setup.  If you have a CN knowledgeable guy at your home field, use him.  If not... I suppose you could give us a tour of all the settings / etc. via a cell phone video or something (youtube). 
Evan Ludeman / T8

jr970

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Re: margin
« Reply #13 on: October 15, 2019, 09:04:44 AM »
Also worth checking that CNV and Oudie are using the same wind, so is CnV seeing more headwind component ?