Magnetic shielding

[Steve Freeman]

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.

[[email protected][_2_]]

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

[Steve Koerner]

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

[Brian Whatcott]

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

[James D'Andrea[_2_]]

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

[James D'Andrea[_2_]]

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

[James D'Andrea[_2_]]

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.

[Leroy Tire]

Search the Web on Mu-Metal. It can provide some improvement. Won't
necessarily remove all interference, but may be enough to swing the
compass. We had to do this in one of our powered aircraft.
Leroy

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.

[Steve Freeman]

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.

[Steve Koerner]

And Leroy, where are you suggesting that Mr Freeman put this mu-
metal? If you put it anywhere near the compass you will significantly
alter the compass readings. If it happens that he has a speaker on
his panel (or an instrument that has a speaker built-in) then it is
concievable that encompassing the speaker in mu-metal could be helpful
but that is the only scenario I could see for mu-metal. If he does
have a loudspeaker on the panel, a better solution would be to remote
it.

Brian W is correct that if he happens to have power wiring running
near the compass, then get it away from the compass and twist it with
the return.

Alas, why bother? Compasses are relics with all sorts of annoying
foibles.

Steve

[[email protected][_2_]]

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

[Brian Whatcott]

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

[Wayne Aspland]

At 14:22 20 July 2009, Steve Koerner wrote:
>And Leroy, where are you suggesting that Mr Freeman put this mu-
>metal? If you put it anywhere near the compass you will significantly
>alter the compass readings. If it happens that he has a speaker on
>his panel (or an instrument that has a speaker built-in) then it is
>concievable that encompassing the speaker in mu-metal could be helpful
>but that is the only scenario I could see for mu-metal. If he does
>have a loudspeaker on the panel, a better solution would be to remote
>it.
>
>Brian W is correct that if he happens to have power wiring running
>near the compass, then get it away from the compass and twist it with
>the return.
>
>Alas, why bother? Compasses are relics with all sorts of annoying
>foibles.
>
>Steve
>
Most pure gliders don't require a compass under EASA, (look in the
equipment list in the type certificate) If you feel you need one just in
case all the GPS kit gives up at the same time, buy one from halfords,
keep it it the pocket and stick it on the canopy when required, well away
from all those nasty (none working) sources of magnetism. More than good
enough to get you home.

Wayne

[Brian Whatcott]

Steve Koerner wrote:
> And Leroy, where are you suggesting that Mr Freeman put this mu-
> metal? If you put it anywhere near the compass you will significantly
> alter the compass readings. If it happens that he has a speaker on
> his panel (or an instrument that has a speaker built-in) then it is
> concievable that encompassing the speaker in mu-metal could be helpful
> but that is the only scenario I could see for mu-metal. If he does
> have a loudspeaker on the panel, a better solution would be to remote
> it.
>
> Brian W is correct that if he happens to have power wiring running
> near the compass, then get it away from the compass and twist it with
> the return.
>
> Alas, why bother? Compasses are relics with all sorts of annoying
> foibles.
>
> Steve

For powered aircraft in particular (including all civil aircraft) a
magnetic compass is mandatory equipment.

Brian W