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Protecting the compass from interference

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longg(at)pjm.com
Guest

Posted: Mon Aug 31, 2009 8:53 am Post subject: Protecting the compass from interference

Is there anything I use as a shield to protect my compass (panel

mounted) from interference with surrounding neighbors? I was thinking

about dipping it in lead. Perhaps I could wrap it in tin foil?



Thanks,

Glenn

Sam

Joined: 18 May 2008
Posts: 135

Posted: Mon Aug 31, 2009 9:24 am Post subject: Protecting the compass from interference

So, you want to prevent the compass from receiving magnetic influences?  If you do that, it may not work so well.



You are going to have to eliminate the outside influences or move the compass.  You might possibly gain something by wrapping the sources with a ferrous material, but that sounds like a loser too.

 

Sam

 	  Quote: 	
		  	




On Mon, Aug 31, 2009 at 11:46 AM,  <longg(at)pjm.com (longg(at)pjm.com)> wrote:

 [quote]--> AeroElectric-List message posted by: <longg(at)pjm.com (longg(at)pjm.com)>

  

 Is there anything I use as a shield to protect my compass (panel

 mounted) from interference with surrounding neighbors? I was thinking

 about dipping it in lead. Perhaps I could wrap it in tin foil?

 

 Thanks,

 Glenn

 

 

 

 

 

 

 

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_________________
Sam Hoskins
www.samhoskins.blogspot.com

longg(at)pjm.com
Guest

Posted: Mon Aug 31, 2009 11:17 am Post subject: Protecting the compass from interference

Correct, thanks Sam. Looks like there may be a move scheduled for the compass.  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Sam Hoskins

 Sent: Monday, August 31, 2009 1:19 PM

 To: aeroelectric-list(at)matronics.com

 Subject: Re: Protecting the compass from interference  

So, you want to prevent the compass from receiving magnetic influences?  If you do that, it may not work so well.

 You are going to have to eliminate the outside influences or move the compass.  You might possibly gain something by wrapping the sources with a ferrous material, but that sounds like a loser too.

 Sam  

On Mon, Aug 31, 2009 at 11:46 AM, <longg(at)pjm.com (longg(at)pjm.com)> wrote:  

--> AeroElectric-List message posted by: <longg(at)pjm.com (longg(at)pjm.com)>

 Is there anything I use as a shield to protect my compass (panel

 mounted) from interference with surrounding neighbors? I was thinking

 about dipping it in lead. Perhaps I could wrap it in tin foil?

 Thanks,

 Glenn

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 http://forums.matronics.com

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 ="_blank">http://www.matronics.com/contribution

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khorton01(at)rogers.com
Guest

Posted: Mon Aug 31, 2009 11:19 am Post subject: Protecting the compass from interference

Supposedly, some magnetic interference issues can be solved by  

wrapping the source of the interfering magnetism in mu-metal, a nickel- 

iron alloy with very high magnetic permeability.



Kevin Horton



On 31-Aug-09, at 13:18 , Sam Hoskins wrote:



 	  Quote: 	
		   So, you want to prevent the compass from receiving magnetic  

 influences?  If you do that, it may not work so well.



 You are going to have to eliminate the outside influences or move  

 the compass.  You might possibly gain something by wrapping the  

 sources with a ferrous material, but that sounds like a loser too.



 Sam

 On Mon, Aug 31, 2009 at 11:46 AM, <longg(at)pjm.com> wrote:

 



 Is there anything I use as a shield to protect my compass (panel

 mounted) from interference with surrounding neighbors? I was thinking

 about dipping it in lead. Perhaps I could wrap it in tin foil?



 Thanks,

 Glenn

ivanjackie(at)hotmail.com
Guest

Posted: Mon Aug 31, 2009 2:48 pm Post subject: Protecting the compass from interference

There is something called mu metal available a Aircraft  Spruce. I know of some who used it that had a similar problem and it  worked.

 No guarantees.

 Ivan Carlson

  



  From: longg(at)pjm.com (longg(at)pjm.com) 

 Sent: Monday, August 31, 2009 1:53 PM

 To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)  

 Subject: RE: Protecting the compass from  interference

 



  

Correct,  thanks Sam. Looks like there may be a move scheduled for the  compass. 

   

From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Sam  Hoskins

Sent: Monday, August 31, 2009 1:19 PM

To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)

Subject:  Re: Protecting the compass from  interference

 

  

So, you want to prevent the compass from receiving magnetic  influences?  If you do that, it may not work so well.



You are going  to have to eliminate the outside influences or move the compass.  You might  possibly gain something by wrapping the sources with a ferrous material, but  that sounds like a loser too.



Sam 

   

On Mon, Aug 31, 2009 at 11:46 AM, <longg(at)pjm.com (longg(at)pjm.com)> wrote: 

--> AeroElectric-List message  posted by: <longg(at)pjm.com (longg(at)pjm.com)>



Is  there anything I use as a shield to protect my compass (panel

mounted) from  interference with surrounding neighbors? I was thinking

about dipping it in  lead. Perhaps I could wrap it in tin  foil?



Thanks,

Glenn



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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 31, 2009 6:43 pm Post subject: Protecting the compass from interference

At 11:46 AM 8/31/2009, you wrote:

 	  Quote: 	
		  



Is there anything I use as a shield to protect my compass (panel

mounted) from interference with surrounding neighbors? I was thinking

about dipping it in lead. Perhaps I could wrap it in tin foil?



Thanks,

Glenn


	


   The magnetic compass is intended to deduce alignment of

   the earth's magnetic field (on the order of 500 milliGauss)

   and produce a useful navigation display based thereon.



   Your query doesn't give us a good sense of any problems

   you may be having. ALL compasses installed on ALL vehicles

   are subject to external influences that tend to distort

   the field of interest. This is why the compass is "swung" or

   calibrated at the compass rose after installation. Further,

   swinging the compass is done with a known condition for

   certain electrical system components being ON or OFF.



   There is no value in attempting to isolate surrounding

   effects with special shielding. If there is some accessory

   that causes a major swing in compass reading, then you

   increase the separation between compass and antagonist.



   The last compass issue I worked was on the Bonanza after

   the B&C standby alternator was installed. Magnetic leakage

   from the alternator on the back of the engine produced

   an unacceptable deviation to the compass reading when mounted

   on the glare shield.  Moving the compass to a previously

   qualified location higher on the windshield fixed the problem.



   The BEST compasses are remotely sensed with the transducer

   in the tailcone or out on wing.



   But your panel mounted GPS should be backed up with

   a hand held GPS . . . the compass has become a historical

   curiosity of limited usefulness.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

longg(at)pjm.com
Guest

Posted: Tue Sep 01, 2009 6:10 am Post subject: Protecting the compass from interference

Thanks Bob,



Based on your last comment I've thought seriously of just removing it. I

have 2 Dynon AHRS remotes in the wings and 2 Garmin GPS units (panel)

and 1 handheld unit on board. If all of that goes to hell, I'll just

land in a field and ask directions.



While building my panel I did notice specifically when or what caused

the interference, it just developed over the process. First I should

probably remove the compass to be sure it is in itself accurate simply

standing outside.



I have a small military compass from LL Bean which I carry and may do in

a pinch. Cheaper too.



Glenn



--

echristley(at)nc.rr.com
Guest

Posted: Tue Sep 01, 2009 6:43 am Post subject: Protecting the compass from interference

longg(at)pjm.com wrote:

 	  Quote: 	
		   



 Thanks Bob,



 Based on your last comment I've thought seriously of just removing it. I

 have 2 Dynon AHRS remotes in the wings and 2 Garmin GPS units (panel)

 and 1 handheld unit on board. If all of that goes to hell, I'll just

 land in a field and ask directions.



Regardless of that, you will need to please the bureaucrats.  The regs 
	


say you need a compass.  Come hell or high-water, you don't have an 

airplane until you have a compass.



I got a cheap, light plastic thingy from Advance Auto.  A 1" hole in the 

dash, and I have it front and center, but low enough that it can be 

safely ignored (ie, it doesn't interfere with the all important view of 

the runway 8*).

junk(at)jaredyates.com
Guest

Posted: Tue Sep 01, 2009 8:42 am Post subject: Protecting the compass from interference

If you are thinking of 14CFR part 91.205 b.3, I think it says that you are

required to have a magnetic direction indicator, not a compass.  Doesn't a

Dynon satisfy this requirement, since it derives its heading from a

magnetic-field based sensor?



--

larry(at)macsmachine.com
Guest

Posted: Tue Sep 01, 2009 1:22 pm Post subject: Protecting the compass from interference

Hi guys,

The compass does seem an excess item until you’ve left the GPS home or 

the replacement batteries don’t seem to be working. I’ve been only 

30-miles out when the snow and visibility had me “temporarily” dependent 

on the GPS and it quit. I knew the last GPS heading and followed it back 

via that “worthless compass” until the white on white of the airport was 

back in view. I’d give the Compass more respect, as it’s probably the 

only thing that works when all else has dumped out on you. I’m 

constantly comparing my compass heading with what’s on the GPS.

http://www.macsmachine.com/images/flightviews/full/Seaton(4).gif

Larry McFarland 601HDS at www.macsmachine.com

Ernest Christley wrote:

 	  Quote: 	

 <echristley(at)nc.rr.com>

 longg(at)pjm.com wrote:

> 

>

> Thanks Bob,

>

> Based on your last comment I've thought seriously of just removing it. I

> have 2 Dynon AHRS remotes in the wings and 2 Garmin GPS units (panel)

> and 1 handheld unit on board. If all of that goes to hell, I'll just

> land in a field and ask directions.

>

 Regardless of that, you will need to please the bureaucrats. The regs 

 say you need a compass. Come hell or high-water, you don't have an 

 airplane until you have a compass.

 I got a cheap, light plastic thingy from Advance Auto. A 1" hole in 

 the dash, and I have it front and center, but low enough that it can 

 be safely ignored (ie, it doesn't interfere with the all important 

 view of the runway 8*).

r.r.hall(at)cox.net
Guest

Posted: Tue Sep 01, 2009 6:42 pm Post subject: Protecting the compass from interference

You might want to be careful abouting getting rid of the compass. FARs require a Magnetic direction indicator. If you ditch the compass what do you have that will meet that requirement? A GPS won't meet it as its not magnetic.

Rodney

---- LarryMcFarland <larry(at)macsmachine.com> wrote: 

 	  Quote: 	

 Hi guys,

 The compass does seem an excess item until youâ€™ve left the GPS home or 

 the replacement batteries donâ€™t seem to be working. Iâ€™ve been only 

 30-miles out when the snow and visibility had me â€œtemporarilyâ€ dependent 

 on the GPS and it quit. I knew the last GPS heading and followed it back 

 via that â€œworthless compassâ€ until the white on white of the airport was 

 back in view. Iâ€™d give the Compass more respect, as itâ€™s probably the 

 only thing that works when all else has dumped out on you. Iâ€™m 

 constantly comparing my compass heading with whatâ€™s on the GPS.

 http://www.macsmachine.com/images/flightviews/full/Seaton(4).gif

 Larry McFarland 601HDS at www.macsmachine.com

 Ernest Christley wrote:

 > 

 > <echristley(at)nc.rr.com>

 >

 > longg(at)pjm.com wrote:

 >> 

 >>

 >> Thanks Bob,

 >>

 >> Based on your last comment I've thought seriously of just removing it. I

 >> have 2 Dynon AHRS remotes in the wings and 2 Garmin GPS units (panel)

 >> and 1 handheld unit on board. If all of that goes to hell, I'll just

 >> land in a field and ask directions.

 >>

 > Regardless of that, you will need to please the bureaucrats. The regs 

 > say you need a compass. Come hell or high-water, you don't have an 

 > airplane until you have a compass.

 >

 > I got a cheap, light plastic thingy from Advance Auto. A 1" hole in 

 > the dash, and I have it front and center, but low enough that it can 

 > be safely ignored (ie, it doesn't interfere with the all important 

 > view of the runway 8*).

 >

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Sep 02, 2009 5:01 am Post subject: Protecting the compass from interference

At 03:13 PM 9/1/2009, you wrote:




Hi guys,



The compass does seem an excess item until you've left the GPS home 

or the replacement batteries don't seem to be working. I've been only 

30-miles out when the snow and visibility had me "temporarily" 

dependent on the GPS and it quit. I knew the last GPS heading and 

followed it back via that "worthless compass" until the white on 

white of the airport was back in view. I'd give the Compass more 

respect, as it's probably the only thing that works when all else has 

dumped out on you. I'm constantly comparing my compass heading with 

what's on the GPS.



   Don't think anyone is 'dissing' the compass . . .

   only suggesting that there are alternatives for

   navigation that are equally if not more useful.

   But like preventative maintenance on your

   ship's battery, the batteries in your "plan-b"

   back-ups are worthy of still more attention.



   This was the thrust of my article some years ago

   that explored the value of el-cheapo alkaline

   cells.



   http://www.aeroelectric.com/articles/AA_Bat_Test.pdf



   The outcome of that study suggested that

   my plan-b devices could get a brand new set of

   cells before leaving home base of every trip.

   The cost of such cells was insignificant compared

   to other costs for making the trip. But the

   availability of those plan-b devices was never

   in doubt. This is why to this day I prefer

   the lowly alkaline to any form of rechargeable

   battery whether replaceable or built in.



   This goes beyond a bureaucratic/regulatory

   mandate to have any particular piece of equipment

   aboard. According to a particularly lucid B/R type

   who attended one of my seminars a few years ago, an

   electronic compass with failure resistant power paths

   (like an e-bus or second battery) was an acceptable

   substitute for the liquid compass. In fact

   preferable if the sensor was out in the wing.

   These things provided much more stable and useable data

   for navigation. But HE too carried a stand-alone,

   hand-held GPS in his flight bag and never

   expected to be dependant upon the liquid compass

   in his airplane either.

   Bob . . .

phillip.johnson(at)lmco.c
Guest

Posted: Wed Sep 02, 2009 5:54 am Post subject: Protecting the compass from interference

Interesting comment about the compass being mandatory in the  USA.  In the Great White North and according to our inspection agency MDRA  it is permissible to have an electronic compass providing it is backed up by a  battery see item 2 under Cabin/cockpit, page 4 of 11 in http://www.md-ra.com/pdfs/what_inspectors_ck.PDF.   Notice it says battery backup.  Our regulations say :Magnetic compass  and page 307 of the Aeronautical Information Manual http://www.tc.gc.ca/publications/en/tp14371/pdf/hr/tp14371e.pdf says:

  

  

Power-driven Aircraft – day VFR  

605.14   

No person shall conduct  a takeoff in a power-driven aircraft for the purpose of day VFR flight unless it  is equipped with    

(a) where the aircraft  is operated in uncontrolled airspace, an altimeter;  

(b) where the aircraft  is operated in controlled airspace, a sensitive altimeter adjustable for  barometric pressure;  

(c) an airspeed  indicator;  

(d) a magnetic compass  or a magnetic direction indicator that operates independently of the  aircraft electrical generating system;   

(e) a tachometer  for each engine and .......................................................... 

So I  guess that since I have dual AHRS and it is also backed up by a secondary  battery I don't need a whisky compass.  (My friend has one in his RV and it  swings 90 degrees when the landing lights go on but it is  legal.) 

It may  be prudent to search the US regulations and confirm the situation down there as  most of our regulations are based on the US regulations with a few  exceptions.  Maybe this is one of those  exceptions.

  

  Phillip  Johnson

longg(at)pjm.com
Guest

Posted: Wed Sep 02, 2009 7:16 am Post subject: Protecting the compass from interference

I see Aircraft Spruce sells a magnetic compass shield specifically for

the PAI-700 that is 80% nickel. Supposedly this is used to absorb the

offending magnetism.



Glenn



--

Bruce(at)glasair.org
Guest

Posted: Wed Sep 02, 2009 7:47 am Post subject: Protecting the compass from interference

But how does it let the earths magnetic field lines into the compass?



Bruce

www.Glasair.org 



--

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Sep 02, 2009 8:05 am Post subject: Protecting the compass from interference

At 10:45 AM 9/2/2009, you wrote:

 	  Quote: 	
		  



But how does it let the earths magnetic field lines into the compass?


	




   EXACTLY!  The preferred technique for dealing with

   on-board, magnetic interference issues is to first

   craft your system to minimize such risks. This

   includes keeping alternator b-leads out of the cockpit

   and keeping other fat-wires as low as practical and/or

   forward of the firewall.



   Now, go swing your compass and TEST AT ALL 4 cardinal

   orientations for the effects of turning things ON and

   OFF. If any combination of switch operations causes more than

   a couple degrees of variation, you have some choices for

   either KNOWING what those variations are and accommodating

   them on your compass calibration card -OR- take steps

   to reduce the effects to acceptable levels. You do this

   by (1) increasing the distance between compass and the

   offending field generator or as a last resort, (2)adding

   some form of shielding between the compass and the

   interfering field source.  I mean last resort.

   I'm aware of NO instance in a TC aircraft where the

   problem was fixed by added shielding.



   In fact, for black boxes tested to DO160 there may

   have been an investigation into Magnetic Effects

   of any black box upon the panel mounted liquid

   compass. These effects must be very small or the

   device is not qualified for installation on the

   aircraft. What we cannot control by DO160 pre-tests

   are the effects of wire routing and those of

   devices with LARGE magnetic fields like starters,

   alternators, PM motors, etc. etc.



   Even in the instance where a B&C standby alternator

   mounted on the engine accessory case upset a cowl

   mounted compass, we MOVED the compass. Adding weight

   and $cost$ of ownership by shielding is a repugnant

   solution that we'll go to some effort to avoid.



   Wrapping the compass itself in a shield will indeed

   make it immune to the effects of on-board interference

   while making it useless as an aid to navigation.



   Bob . . .

rv(at)thelefflers.com
Guest

Posted: Wed Sep 02, 2009 8:43 am Post subject: Protecting the compass from interference

Sort of......   It's really a 5" x 12" strip of mu metal that you'll have to

fabricate into the appropriate form to shield the PAI-700.



--

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