Compass trouble

I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

On Fri, 11 Apr 2008 19:45:50 -0700, Road Dog
wrote:

I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.

Stealth Pilot wrote:

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.

So he claims but what would this be that wasn't there
when the plane left the factory ? Without any new
equipment, how could it get so bad that it throws the
compass off more than 10 degrees through mu shield ?

In any case, thanks for the reply.

On Apr 12, 10:07 am, Road Dog wrote:
Stealth Pilot wrote:

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.

So he claims but what would this be that wasn't there
when the plane left the factory ? Without any new
equipment, how could it get so bad that it throws the
compass off more than 10 degrees through mu shield ?

In any case, thanks for the reply.

Pipers sometimes suffer from magnetized engine mounts. I think
it might have to do with the alternator ground cable terminals getting
corroded so that the alternator ground current runs throught the mount
tubing instead, magnetizing it and screwing up the compass.

Dan

It's possible that something got magnetized during a lightening
strike. Happens
in Mooneys where that 4130 chromealloy tube runs down the center of
the
windshield.

You should check it on cardinal headings with the compensator magnets
completely removed. Should not be off more than about 15 degrees.

I've heard that stronger compensation magnets are available. I think
it would
be better to find the source of interference, as tweeking it that far
will cause
errors on some headings.

BTW, a great way to compensate compasses: On a large part of a ramp,
taxiing
with everything running... Use the track info on the GPS--which is
calibrated in
magnetic heading--to line up on a cardinal heading. Taxi on the
cardinal heading
and smoothly come to a stop without changing the heading -- which can
be
verified by the DG. Much more accurate than lining up on a compass
rose.
Best done with someone along who can make sure you don't run into
anything!!
Best done on some ramp that isn't loaded with steel.

Bill Hale BPPP instructor a&p


On Apr 12, 8:22*am, Stealth Pilot
wrote:
On Fri, 11 Apr 2008 19:45:50 -0700, Road Dog
wrote:





I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.- Hide quoted text -

- Show quoted text -

On Sat, 12 Apr 2008 22:22:43 +0800, Stealth Pilot
wrote:

On Fri, 11 Apr 2008 19:45:50 -0700, Road Dog
wrote:

I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.

Swinging a compass in 15 minutes may be possible if no corrections are
needed but to create a new card properly requires 8 points instead of
just 4. chasing stray magnetism can take up a lot of time. Unless you
have other reasons to believe that your mechanic is incompetent or
trying to screw you then I'd be inclinded to trust him.

On Sat, 12 Apr 2008 16:11:59 GMT, (Drew
Dalgleish) wrote:

On Sat, 12 Apr 2008 22:22:43 +0800, Stealth Pilot
wrote:

On Fri, 11 Apr 2008 19:45:50 -0700, Road Dog
wrote:

I took my Piper Warrior in for its annual and the mechanic
said that the compass card was missing and that he'd have
to swing the plane to generate a new one.

After swinging it, he claimed that he couldn't get the
E-W deviation within the minimum. So he suggested we
try "mu" shield (or something) to block the source of
magnetism which he claims is coming from one of the
instruments. (He says the compass works fine outside
the plane.)

Note: The instruments are all original, stock. Nothing
has been changed (except a radio was added which he says
is not the source.)

The mu shield fails too. He says the next thing to try is
to move the compass up to between the visors.

He says he has spent 3 hours on this so far. I'm beginning to
wonder, shouldn't a mechanic be able calibrate a compass
in a stock Piper after 3 hours ? Is he incompetent ?
Padding the bill ? Or does this really take this long ?

He has inspected and fixed everything else. Do you think
its reasonable at this time to ask him to sign off
everything else, and take the plane somewhere else where,
presumably, they know how to calibrate a compass ?

the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.

Swinging a compass in 15 minutes may be possible if no corrections are
needed but to create a new card properly requires 8 points instead of
just 4. chasing stray magnetism can take up a lot of time. Unless you
have other reasons to believe that your mechanic is incompetent or
trying to screw you then I'd be inclinded to trust him.

If you look at a deviation card, I think you'll find it takes 12
points -- every 30 degrees, not every 45 degrees.
--
Jay (remove dashes for legal email address)

On Sat, 12 Apr 2008 22:15:41 -0400, Jay Somerset
wrote:

On Sat, 12 Apr 2008 16:11:59 GMT, (Drew

Swinging a compass in 15 minutes may be possible if no corrections are
needed but to create a new card properly requires 8 points instead of
just 4. chasing stray magnetism can take up a lot of time. Unless you
have other reasons to believe that your mechanic is incompetent or
trying to screw you then I'd be inclinded to trust him.

If you look at a deviation card, I think you'll find it takes 12
points -- every 30 degrees, not every 45 degrees.
--
Jay (remove dashes for legal email address)

You're right Jay I was thinking 8 extra but that's obviously not what
I wrote.

On Sat, 12 Apr 2008 16:11:59 GMT, (Drew
Dalgleish) wrote:


the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.

Swinging a compass in 15 minutes may be possible if no corrections are
needed but to create a new card properly requires 8 points instead of
just 4. chasing stray magnetism can take up a lot of time. Unless you
have other reasons to believe that your mechanic is incompetent or
trying to screw you then I'd be inclinded to trust him.

your first one will take lots longer.
you need two people.
one pilot in the aircraft another outside with an accurate land
compass.

in a location well away from metal objects like hangars line up the
aircraft with magnetic north using the land compass to align.
(in my tailwind I just lift the tailwheel to reposition so I suppose
that would be a sizeable time aid)
take the cover off the compass front. usually just one screw is
removed, the other loosened and the cover swings away.
under the cover are two screws. one labeled NS the other EW.
with the engine running at idle, all electrics turned on, you adjust
the NS screw with a bronze or austinitic stainless screwdriver, until
the card is reading N. (both screwdrivers mentioned are non magnetic)

turn the aircraft and line it up to magnetic east using the land
compass. adjust the EW screw until the compass reads E.

using the land compass to align, turn the aircraft to face due
magnetic south.
here is the important bit. using the NS screw, adjust out *HALF* the
error.

turn the aircraft to face west using the land compass (and standing
well back from the aircraft)
here is the other important bit. using the EW screw, adjust out *HALF*
the error.

now turn the aircraft back to mag north using the land compass to
align. record on the chart the error seen on the aircraft compass.
turn to 30 degrees magnetic aligning with the land compass. again
record the error on the correction chart.
repeat this for every 30 degree increment around the compass card.

now provided that all your corrections are under 5 degrees you have a
newly swung and adjusted compass.
lifting the tailwheel to position it all takes me 15 minutes.

at the end of it all the engine (idling all this time) and oil are
quite hot so that is the time to drain the oil for the oil change.

Stealth Pilot

On Tue, 15 Apr 2008 21:53:31 +0800, Stealth Pilot
wrote:

On Sat, 12 Apr 2008 16:11:59 GMT, (Drew
Dalgleish) wrote:


the problem doesnt seem to be the compass but some stray magnetism in
the aircraft.
swinging a compass takes about 15 minutes.

Swinging a compass in 15 minutes may be possible if no corrections are
needed but to create a new card properly requires 8 points instead of
just 4. chasing stray magnetism can take up a lot of time. Unless you
have other reasons to believe that your mechanic is incompetent or
trying to screw you then I'd be inclinded to trust him.

your first one will take lots longer.
you need two people.
one pilot in the aircraft another outside with an accurate land
compass.

in a location well away from metal objects like hangars line up the
aircraft with magnetic north using the land compass to align.
(in my tailwind I just lift the tailwheel to reposition so I suppose
that would be a sizeable time aid)
take the cover off the compass front. usually just one screw is
removed, the other loosened and the cover swings away.
under the cover are two screws. one labeled NS the other EW.
with the engine running at idle, all electrics turned on, you adjust
the NS screw with a bronze or austinitic stainless screwdriver, until
the card is reading N. (both screwdrivers mentioned are non magnetic)

turn the aircraft and line it up to magnetic east using the land
compass. adjust the EW screw until the compass reads E.

using the land compass to align, turn the aircraft to face due
magnetic south.
here is the important bit. using the NS screw, adjust out *HALF* the
error.

turn the aircraft to face west using the land compass (and standing
well back from the aircraft)
here is the other important bit. using the EW screw, adjust out *HALF*
the error.

now turn the aircraft back to mag north using the land compass to
align. record on the chart the error seen on the aircraft compass.
turn to 30 degrees magnetic aligning with the land compass. again
record the error on the correction chart.
repeat this for every 30 degree increment around the compass card.

now provided that all your corrections are under 5 degrees you have a
newly swung and adjusted compass.
lifting the tailwheel to position it all takes me 15 minutes.

at the end of it all the engine (idling all this time) and oil are
quite hot so that is the time to drain the oil for the oil change.

Stealth Pilot



My home airport has a compass rose and I use that. Taxiing aroud and
getting lined up on each heading takes me quite a bit longer than
that. Having a helper would speed things I'm sure but if we consider
man hours since the OP was about mechanics time then double your
15minutes. I was going to ask how do you know if it's an accurate land
compass but it occurs to me that a GPS would do the job and then you
could do it by yourself . I still don't think I could do it as fast as
you can though. It takes me that long to find my brass screwdriver.