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John Bolding
Joined: 23 May 2006
Posts: 281
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 Posted: Tue Jun 19, 2007 5:14 am Post subject: Swinging the compass |
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Never thought of the fact that all those compass rose's I've seen in the last 50 yrs were placed over sections of the runway that didn't have any rebar in them. I learn something every day. :>)
LOW&SLO John
[quote]
The process is called swinging the compass. You
need to find an airport with a compass rose. Or you could lay one out.
Don't lay one out on rebar reinforced concrete or near metal
buildings. > jeff
[b]
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klaus(at)utdallas.edu
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| Posted: Tue Jun 19, 2007 2:41 pm Post subject: Swinging the compass |
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Hi John,
There is an alternate method for getting correct directions when
swinging the compass.
You turn on the GPS unit and let the plane roll forward a small
distance, say 15 ft.
If it is a good GPS unit, it will tell you the direction with utter
precision.
BTW, this is a quick way to recheck the compass periodically.
Happy flying,
Klaus
--
Klaus Truemper
Professor Emeritus of Computer Science
University of Texas at Dallas
Erik Jonsson School of Engineering and
Computer Science EC31
P.O. Box 830688
Richardson, TX 75083-0688
(972) 883-2712
klaus(at)utdallas.edu
www.utdallas.edu/~klaus
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tshankland(at)sbcglobal.n
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| Posted: Tue Jun 19, 2007 6:44 pm Post subject: Swinging the compass |
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I think there may be a problem with this method, a GPS will give you
true North not local magnetic north, which is what a compass does. In
the eastern and midwest USA there isn't much difference but in the west
is about 18 degrees declination.
Tim Shankland
Klaus Truemper wrote:
| Quote: |
Hi John,
There is an alternate method for getting correct directions when
swinging the compass.
You turn on the GPS unit and let the plane roll forward a small
distance, say 15 ft.
If it is a good GPS unit, it will tell you the direction with utter
precision.
BTW, this is a quick way to recheck the compass periodically.
Happy flying,
Klaus
|
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craig(at)craigandjean.com
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| Posted: Tue Jun 19, 2007 8:38 pm Post subject: Swinging the compass |
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My Garmin GPSMAP 296 can be set to display magnetic or true.
-- Craig
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rroberts
Joined: 04 Sep 2006
Posts: 50
Location: Birmingham, AL USA
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| Posted: Wed Jun 20, 2007 2:49 am Post subject: Re: Swinging the compass |
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Guys,
True is usually printed WX, etc, or when you get so close to the poles... If it comes from a cockpit it should be Magnetic. The variation does fluxuate across the country/globe...check your Jep plates or Sec chart..
I will use a hand held compass and get out on the field between the taxiway and the apron here at KCCO and lay my headings out. If they'll let you out on the rwy be careful.
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_________________
Low & Slow
Rick
www.n701rr.com
www.ricksplace.info |
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klaus(at)utdallas.edu
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| Posted: Wed Jun 20, 2007 10:24 am Post subject: Swinging the compass |
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The default on my Garmin is magnetic. It should be, too, since then
GPS, compass, DG agree in no-wind condition. In fact, there is a nifty
formula to estimate crosswind, using the difference between GPS and compass.
For aircraft doing around 100 kts,
take the difference between compass and GPS (in deg), multiply by 2,
and you get approximately the crosswind in kts. For example, if
the GPS shows 125 deg, the compass 128 deg, then the crosswind is
approximately 2(128-125) = 6kts. Inverting the formula gives the crosswind
course correction needed for a given crosswind.
--Klaus
--
Klaus Truemper
Professor Emeritus of Computer Science
University of Texas at Dallas
Erik Jonsson School of Engineering and
Computer Science EC31
P.O. Box 830688
Richardson, TX 75083-0688
(972) 883-2712
klaus(at)utdallas.edu
www.utdallas.edu/~klaus
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