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Magnetic shielding



 
 
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  #1  
Old July 20th 09, 02:41 AM posted to rec.aviation.soaring
Steve Freeman
external usenet poster
 
Posts: 44
Default Magnetic shielding

I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.
  #2  
Old July 20th 09, 03:19 AM posted to rec.aviation.soaring
[email protected][_2_]
external usenet poster
 
Posts: 65
Default Magnetic shielding

On Jul 19, 6:41*pm, Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.


Not trying to be a smart ass, but why are you worried about mag
interference? I mount my little PZL mag compass right next to my
electric varios, PDA power supplies, GPS antennas and when I swung the
compass, the error was within my need to hold a heading in a glider...

This may be considered heresy, but with GPS, the old magnetic compass
should be relegated to emergency status, at best - better (and
considerable less expensive, to boot) to carry a cheap handheld GPS in
the cockpit, along with some spare batteries.

Unless this is an EASA (or FAA) thing, of course...

Just curious.

Cheers,

Kirk
66
  #3  
Old July 20th 09, 02:51 PM posted to rec.aviation.soaring
Steve Freeman
external usenet poster
 
Posts: 44
Default Magnetic shielding

On Jul 19, 9:19*pm, "
wrote:
On Jul 19, 6:41*pm, Steve Freeman wrote:

I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.


Not trying to be a smart ass, but why are you worried about mag
interference? *I mount my little PZL mag compass right next to my
electric varios, PDA power supplies, GPS antennas and when I swung the
compass, the error was within my need to hold a heading in a glider...

This may be considered heresy, but with GPS, the old magnetic compass
should be relegated to emergency status, at best - better (and
considerable less expensive, to boot) to carry a cheap handheld GPS in
the cockpit, along with some spare batteries.

Unless this is an EASA (or FAA) thing, of course...

Just curious.

Cheers,

Kirk
66


I am worried about interference because no matter what direction I am
flying, the compass only points to within about 15 degrees of south.
Not much use in an emergency. I do carry a GPS PDA and have an LNAV/
GPSNAV in the panel but would like to have an operational compass.
Also not sure if FAA item or not but would guess that it is.
  #4  
Old July 20th 09, 03:29 PM posted to rec.aviation.soaring
[email protected][_2_]
external usenet poster
 
Posts: 65
Default Magnetic shielding

On Jul 20, 6:51*am, Steve Freeman wrote:

I am worried about interference because no matter what direction I am
flying, the compass only points to within about 15 degrees of south.
Not much use in an emergency. I do carry a GPS PDA and have an LNAV/
GPSNAV in the panel but would like to have an operational compass.
Also not sure if FAA item or not but would guess that it is.


Understood, I have one too - for FAA (sigh) and nostalgic reasons.

Sounds like something is seriously magnetized in your instrument panel
- do you have a big radio or vario speaker nearby? And have you been
able to place the compass anywhere in your cockpit and get correct
readings? It could be a bad compass...I've seen whiskey compasses
stuck in all sorts of improbable places and work OK!

Kirk
66
  #5  
Old July 20th 09, 06:25 PM posted to rec.aviation.soaring
Brian Whatcott
external usenet poster
 
Posts: 915
Default Magnetic shielding

Steve Freeman wrote:
On Jul 19, 9:19 pm, "
wrote:
On Jul 19, 6:41 pm, Steve Freeman wrote:

I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.

Not trying to be a smart ass, but why are you worried about mag
interference? I mount my little PZL mag compass right next to my
electric varios, PDA power supplies, GPS antennas and when I swung the
compass, the error was within my need to hold a heading in a glider...

This may be considered heresy, but with GPS, the old magnetic compass
should be relegated to emergency status, at best - better (and
considerable less expensive, to boot) to carry a cheap handheld GPS in
the cockpit, along with some spare batteries.

Unless this is an EASA (or FAA) thing, of course...

Just curious.

Cheers,

Kirk
66


I am worried about interference because no matter what direction I am
flying, the compass only points to within about 15 degrees of south.
Not much use in an emergency. I do carry a GPS PDA and have an LNAV/
GPSNAV in the panel but would like to have an operational compass.
Also not sure if FAA item or not but would guess that it is.



I just have to ask: have you swung the airframe with all power switched
off? You could be seeing the effects of some magnetized metal.

Brian W
  #6  
Old July 20th 09, 03:23 AM posted to rec.aviation.soaring
Steve Koerner
external usenet poster
 
Posts: 430
Default Magnetic shielding

I believe there is not a practical way to use shielding against DC
magnetic interference as the shielding material itself will interfere
with the compass. Here is a web reference that says as much and
provides some instruction on compensating and swinging a compass.

http://www.bellanca.us/compass.pdf

These days many of us rely entirely on GPS and don't even bother
installing a compass.

Steve Koerner
  #7  
Old July 20th 09, 04:00 AM posted to rec.aviation.soaring
Brian Whatcott
external usenet poster
 
Posts: 915
Default Magnetic shielding

Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.


Here's one approach you could consider. Most deviation arises from wires
within 3 inches of the compass.
If wires cannot be routed further than 3 inches away, and every inch
counts, most deviation can be squashed by providing closely twisted
pairs for current carrying wires.
They don't even have to have the same twist over the whole length, so
if done judiciously, a pair of wires could be twisted with a tourniquet
and secured with this twist. Placing the tourniquest as far from the
compass as possible will improve things best.

Brian W
  #8  
Old July 20th 09, 05:05 AM posted to rec.aviation.soaring
James D'Andrea[_2_]
external usenet poster
 
Posts: 5
Default Magnetic shielding

On Jul 19, 8:00*pm, brian whatcott wrote:
Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.


Here's one approach you could consider. Most deviation arises from wires
within 3 inches of the compass.
If wires cannot be routed further than 3 inches away, and every inch
counts, most deviation can be squashed by providing closely twisted
pairs for current carrying wires.
* They don't even have to have the same twist over the whole length, so
if done judiciously, a pair of wires could be twisted with a tourniquet
and secured with this twist. Placing the tourniquest as far from the
compass as possible will improve things best.

Brian W


  #9  
Old July 20th 09, 05:06 AM posted to rec.aviation.soaring
James D'Andrea[_2_]
external usenet poster
 
Posts: 5
Default Magnetic shielding

On Jul 19, 8:00*pm, brian whatcott wrote:
Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass. Anyone know anything about the various forms of
magnetic shielding available now. On one site alone they sell over 5
different types of material. A compass manufacturer once recommended
this as an easy solution to interference in a power plane but it was a
few years ago and I do not remember the material we used.


Here's one approach you could consider. Most deviation arises from wires
within 3 inches of the compass.
If wires cannot be routed further than 3 inches away, and every inch
counts, most deviation can be squashed by providing closely twisted
pairs for current carrying wires.
* They don't even have to have the same twist over the whole length, so
if done judiciously, a pair of wires could be twisted with a tourniquet
and secured with this twist. Placing the tourniquest as far from the
compass as possible will improve things best.

Brian W


  #10  
Old July 20th 09, 05:12 AM posted to rec.aviation.soaring
James D'Andrea[_2_]
external usenet poster
 
Posts: 5
Default Magnetic shielding

On Jul 19, 8:00*pm, brian whatcott wrote:
Steve Freeman wrote:
I need to mount a compass on the instrument panel glare shield. There
is magnetic interference in most all of the areas that are best for
viewing the compass.


There is a very good and experienced pilot at our field who went to
the local auto parts store and bought a "glass marble" type compass
that he uses in his glider. It's a compas contained in plastic sphere
about 1" in diameter. I guess he paid no more than $5 for it. He
made a small mount for it and velcro'd it on the inside of the canopy
in the same spot where his yaw string is attached. Pretty neat setup
and very inexpensive. Also solves the problem of being far enough
away from the panel where potential magentic fields exist.
 




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