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Compass Requirements in Experimental Aircraft (updated)

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echristley(at)nc.rr.com
Guest

Posted: Wed Dec 26, 2007 10:14 pm Post subject: Compass Requirements in Experimental Aircraft (updated)

Eric Newton wrote:

 	  Quote: 	
		   So problem solved.  

   

Good for you, Eric.
	




During the discussion, I promised to take a few pictures of my $9, 

"ornamental"  compass.  I had taken the pictures, but never posted the 

links.  It turned out even better than I'd hoped.

http://ernest.isa-geek.org/Delta/Pictures/Compass.jpg

http://ernest.isa-geek.org/Delta/Pictures/CockpitFrontLeft.jpg

http://ernest.isa-geek.org/Delta/Pictures/CockpitFrontRight.jpg

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Tim Olson

Joined: 25 Jan 2007
Posts: 2881

Posted: Thu Dec 27, 2007 10:13 am Post subject: Compass Requirements in Experimental Aircraft (updated)

So one of the morals to the story is that magnetic base antennas

have no place in an airplane.  They won't just screw with your

nearby compass but can screw with your much more sensitive EFIS

magnetometer as well.  Any antenna with a magnet should be cut

apart and have it's magnet yanked...if you're going to use it

in the plane.



Tim Olson - RV-10 N104CD - Flying

do not archive

Eric Newton wrote:

 	  Quote: 	
		   Hi All,

  

 Well its been kind of slow so I thought I would give a little update 

 regarding my research into whether or not a "wet" compass is required if 

 you have a EFIS with a remote external compass feeding a heading to it. 

 After much research and searching archives of all of the various 

 airplane groups that I belong to, I finally decided to just mount an 

 airpath compass on my glareshield and be done with it.  I said to myself 

 -  "no sense getting into a pissing match with the DAR over a $160 

 instrument, just put it in and forget it".

  

 So I purchased the Airpath C2400 lighted compass.  It arrived sometime 

 last week and over Christmas vacation, I finally got out to the airport 

 to see how it would work with my Bearhawk.  I had heard that some people 

 were having as much as 30 degrees of installation errors in a Bearhawk 

 with a glareshield mounted compass.

  

 So there I was standing beside my airplane which was pointed in a 

 generally northward direction.  I held the compass out in front of me 

 and it read 358 degrees. I then reached inside and sat it on the 

 glareshield centered and as far back from the "V" tubes as I could.  It 

 read "N" 360 degrees. PERFECT, only about 2 degrees off right??? WRONG!!!

  

 I then grabbed the tail and swung it around to point the nose in a 

 generally south direction.  Poked my head inside for a look at the 

 compass and  . . . What's this???? It still says "N" 360 degrees!!!  I 

 grabbed the compass out of the airplane and once again stood next to the 

 airplane and sure enough the compass now read 178 degrees.  Put back on 

 the glare shield and  . . . "N" 360 degrees.

  

 So there I stood, scratching my head, thinking about what I had done to 

 cause what Erbman would call a "Gross Buffoonery".  As I was standing 

 looking at things, I saw the problem.  My lightening fast brain finally 

 figured out what I had done.  When I mounted my XM satellite radio, I 

 didn't want to run the external antenna all the way outside so I had 

 simply mounted it up near the windshield right between the "V" braces.  

 The antenna has a strong magnet built in to allow it to stick to the 

 roof of your car.  Of course it didn't stick to my aluminum boot cowl so 

 I had just double stick velcroed it in place.

  

 The wire running from the antenna to the Xm radio on the right side of 

 the instrument panel was included in the main wiring harness and is well 

 wrapped within the bundle of wires running from the comm and intercom 

 system.  Removing and replacing the XM satellite antenna would take a 

 long time laying on my back under the instrument panel cutting every tie 

 wrap I made. 

  

 So I decided to do what I should have done in the first place.  I called 

 my DAR to ask him his opinion on the magnetic direction indicator in the 

 Dynon.  I described the Dynon D100 EFIS with its remote magnetic compass 

 feeding heading information to the Dynon D100.  He asked me again what I 

 was building.  I said a Bearhawk.  He said "That's Experimental right?" 

  I said "yes it is".  He said "Well then, it falls under FAR part 91.205 

 which specifically says "Magnetic direction indicator" . He said as long 

 as the Dynon receives, and displays, a heading based on the Earth's 

 magnetic field, then it qualifies as a "magnetic heading indicator" as 

 required in Part 91.205  and he doesn't see why I would need an old 

 whiskey compass littering up my glareshield. 

  

 We talked a bit about redundency and when I told him about my battery 

 backup of the Dynon as well as a GPS with battery backup as well as a 

 handheld radio with a VOR indicator, he was more than satisfied.

  

 So problem solved.  I called Aircraft Spruce for an RMA number and as of 

 this morning, the compass is on its way back to Corona, CA and I'll have 

 a credit for it.  Guess I could have saved some shipping $ by simply 

 calling the DAR first.

  

 Lesson learned and shared.

  

 Eric Newton - Long Beach, MS

 BH #682- Mississippi Mudbug

 BEARHAWK BUILDER'S MANUALS

 http://mybearhawk.com

 

 *

 

 

 *

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MauleDriver(at)nc.rr.com
Guest

Posted: Wed Jan 02, 2008 5:44 pm Post subject: Compass Requirements in Experimental Aircraft (updated)

Robert Feldtman wrote:

  	  Quote: 	
		     Secondly - most of us use our GPS to set our DG anyway - not the compass.

 Is that true?  I am under the impression that it continues to be necessary to set the DG relative to magnetic north in order to correctly respond to vectors.

 I believe that ATC gives only magnetic heading vectors (though it seems that it's time to go to true headings).  It's an important issue in IFR ops but still relevant in VFR.  Usually it doesn't make much of a difference but I just did 400 miles in 45knot winds at 8,000 and below it really did make a difference.  (BTW, it was a glorious tailwind!)

 Do many of you use the GPS to set your DG?  I navigate with by GPS, follow vectors using my DG, use my compass to set my DG, and constantly try to discern the meaning of the difference between the two.  

 Perhaps I can simplify things a bit.  Thinking it through, I could easily keep my DG set to my desired GPS course.  But I would then have to remember to reset it or at least check it when getting vectors.  I usually only get vectors at the beginning and end of flights.  But I guess I've just learned to use my GPS as primary during point to point navigation and use my DG as primary during vectors and put up with the difference between the two.

 Bill "can't wait to get that 45 knots all the time when I move to an RV10" Watson

 [quote]   

   On 12/28/07, Tim Olson <Tim(at)myrv10.com (Tim(at)myrv10.com)> wrote:    	  Quote: 	
		  --> AeroElectric-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com) >

 Another builder asked me to forward this because he's on

 vacation, but wanted to join in the thread:

 "But another very important issue regarding magnetism is that the steel

 parts in the plane can pick up residual magnetism from permanent magnets     

 and it can be a real problem to sniff out and get rid of with a

 magnaflux (I think he means degaussing -Tim) tool.   I believe a I made

 a complete posting regarding this in the RV10-list archive.  But even

 the helical steel coil in scat tubing is capable of causing totally     

 eronous compass readings.   I had this occur when we re-did  the

 instrument panel in our glastar.   I even avoid using magnetic tip tools

 now that I've seen how difficult it can be to solve the residual

 magnetism problem.     

 -bob newman

 Tim Olson wrote:

 > --> AeroElectric-List message posted by: Tim Olson <Tim(at)MyRV10.com (Tim(at)MyRV10.com)>

 >

 > So one of the morals to the story is that magnetic base antennas     

 > have no place in an airplane.  They won't just screw with your

 > nearby compass but can screw with your much more sensitive EFIS

 > magnetometer as well.  Any antenna with a magnet should be cut

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Jim Baker

Joined: 30 Mar 2006
Posts: 181
Location: Sayre, PA

Posted: Wed Jan 02, 2008 7:13 pm Post subject: Compass Requirements in Experimental Aircraft (updated)

X-SpamReason %%SpamReason%%: 



 	  Quote: 	
		   I believe that ATC gives only magnetic heading vectors (though it seems that it's time to go to 

 true headings).


	


I'll second that. My current job is a contract procedures 

development specialist for the FAA and the things we see with 

facility Mag Var issues would make most folks cry.



A lot of the facility Mag Vars go back to the 60s, 70s and 80s. 

Consider what happens when you have an NDB with a 60s Mag 

Var, a nearby VORTAC with a 70s Mag Var, and an ILS with an 

80s Mag Var.



ZZV  ZANESVILLE VOR/DME  Variation: 06W (1990)

TVT  TIVERTON VOR/DME  Variation: 03W (1965)



Only 32 miles from each other. If you saw how much havoc 

changing just one Mag Var causes, which you really can't do 

efficiently because of the ripple effect....change one, you'd better 

be prepared to change a lot of them. That's why Mag Vars don't 

get changed often.



Personally, I'm hoping for the pole reversal........

Jim Baker

580.788.2779

Elmore City, OK

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