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peteohms
Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX
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 Posted: Thu Sep 25, 2008 1:05 pm Post subject: Altimeter Question |
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When I fly my Kitfox III with the vents open, I get about a 200' error in altitude reading compared to my GPS reading. I suppose this is common when the static pickup is inside the cabin. I set my altimeter to the GPS reading and forget it. Any problems with this solution?
Pete
Hell Paso, TX
III SN1000
912
[quote][b]
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Pete
Leander, TX
Kitfox III, 912ul, Grove |
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Michel
Joined: 10 Jan 2006
Posts: 966
Location: Norway
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| Posted: Thu Sep 25, 2008 1:34 pm Post subject: Altimeter Question |
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| Quote: | From: Pete Christensen [apeterchristensen(at)sbcglobal.net]
When I fly my Kitfox III with the vents open, I get about a 200' error in altitude
reading compared to my GPS reading.
|
Oops! First, yes Pete, the pressure inside the cockpit varies a lot. A static port going aft of the fuselage is best. Secondly, the GPS altitude reading is seldom accurate to 200 ft. If you think of the geometry of the GPS satellites; the angle between them and then their relatively low altitude (angle) in relation to you, you understand that the Y axis (altitude) is less accurate than the X,Z (latitude, longitude) axis. I contribute to PocketFMS, a GPS based moving map and flight planner software and e.g. an ILS function is out of question: a glide slope to some accuracy can't be assessed.
Incidentally, when I installed a Jabiru, instead of the old 582 on my model 3, I saw such a lower pressure in the cockpit that I was forced to install a static port. I am not sure why but it looks like the vacuum chamber I created under the cowling was affecting the cockpit too.
Cheers,
Michel Verheughe
Norway
Kitfox 3 - Jabiru 2200 ... flying as a PAX
<pre><b><font size color="#000000" face="courier new,courier">
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pwmac(at)sisna.com
Guest
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| Posted: Thu Sep 25, 2008 2:12 pm Post subject: Altimeter Question |
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Not really. The best air speed would result from a properly designed
piton- static device. The only disadvantage is one has to run two
lines to the panel. Anybody who still had the wings uncovered should
give this method strong consideration. Error on a pitot static is the
lowest of any compared to any other method.
Not as sensitive to yaw or pitch within reason.
Paul
====================
At 03:31 PM 9/25/2008, you wrote:
| Quote: | > From: Pete Christensen [apeterchristensen(at)sbcglobal.net]
> When I fly my Kitfox III with the vents open, I get about a 200'
error in altitude
> reading compared to my GPS reading.
Oops! First, yes Pete, the pressure inside the cockpit varies a lot.
A static port going aft of the fuselage is best. Secondly, the GPS
altitude reading is seldom accurate to 200 ft. If you think of the
geometry of the GPS satellites; the angle between them and then
their relatively low altitude (angle) in relation to you, you
understand that the Y axis (altitude) is less accurate than the X,Z
(latitude, longitude) axis. I contribute to PocketFMS, a GPS based
moving map and flight planner software and e.g. an ILS function is
out of question: a glide slope to some accuracy can't be assessed.
Incidentally, when I installed a Jabiru, instead of the old 582 on
my model 3, I saw such a lower pressure in the cockpit that I was
forced to install a static port. I am not sure why but it looks like
the vacuum chamber I created under the cowling was affecting the cockpit too.
Cheers,
Michel Verheughe
Norway
Kitfox 3 - Jabiru 2200 ... flying as a PAX
<pre><b><font size color="#000000" face="courier new,courier">
href="http://www.matronics.com/Navigator?Kitfox-List">http://www.matronics.com/Navigator?Kitfox-List</a>
href="http://forums.matronics.com">http://forums.matronics.com</a>
href="http://www.matronics.com/contribution">http://www.matronics.com/contribution</a>
</b></font></pre>
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Tom Jones
Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA
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| Posted: Thu Sep 25, 2008 3:03 pm Post subject: Re: Altimeter Question |
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[quote="peteohms"]When I fly my Kitfox III with the vents open, I get about a 200' error in altitude reading compared to my GPS reading. I suppose this is common when the static pickup is inside the cabin. I set my altimeter to the GPS reading and forget it. Any problems with this solution?
Pete
Hell Paso, TX
III SN1000
912
[quote][b][/quote
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Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA
Last edited by Tom Jones on Fri Sep 26, 2008 4:18 am; edited 1 time in total |
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peteohms
Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX
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| Posted: Thu Sep 25, 2008 4:59 pm Post subject: Altimeter Question |
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Tom,
It'll soon be winter and I can keep the vents closed and have an accurate
altimeter. Never let it be said that I fly in violation of Sec. 91.121 -
Altimeter settings out in the middle of the desert SW.
Pete
do not archive
---
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Pete
Leander, TX
Kitfox III, 912ul, Grove |
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mikeperkins
Joined: 22 May 2007
Posts: 123
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| Posted: Fri Sep 26, 2008 10:33 am Post subject: Altimeter Question |
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Ditto on the inaccuracy of GPS altitude. Ditto on the addition of a static port. My port is about 24” behind the passenger door and about even with the height of the seat cushion. I chose that location because it doesn’t get beat by the prop wash as much as the other side.
Test flights at 50 feet above a runway indicated that this location produced no more than 20 feet of altitude difference between Vway-slow and Vway-fast in my Model I at varying throttle settings.
Mike Perkins
[quote][b]
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Mon Sep 29, 2008 4:54 am Post subject: Altimeter Question |
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I live at sea level + 20 ft. My GPS will show an altitude here of anywhere from -2 to +20 meters. Check the barometric pressure at your closest airport or believe it or not high school and use the to set your altimeter. I say high school because they often have true mercury barometers in the physics lab.
If you are in the area of a GPS correction service and subscribe to it then you can depend on the altitude reading.
[img]cid:image001.jpg(at)01C9221D.730D0980[/img]
Noel Loveys
Campbellton, NL, Canada
CDN AME intern, PP-Rec
C-FINB, Kitfox III-A
582 B box, Ivo IFA, Aerocet 1100 floats
[url=noelloveys(at)yahoo.ca]noelloveys(at)yahoo.ca[/url]
From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Pete Christensen
Sent: Thursday, September 25, 2008 6:34 PM
To: kitfox-list(at)matronics.com
Subject: Altimeter Question
When I fly my Kitfox III with the vents open, I get about a 200' error in altitude reading compared to my GPS reading. I suppose this is common when the static pickup is inside the cabin. I set my altimeter to the GPS reading and forget it. Any problems with this solution?
Pete
Hell Paso, TX
III SN1000
912
| Quote: | | http://www.matronics.com/Navigator?Kitfox-List |
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Noel Loveys
Kitfox III-A
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