Compass trouble

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

Might it be possible to kludge a degausser? I'm looking for a
volunteer to try this scheme:

1) Get a 500 ft length of 4 conductor (3 conductor plus ground) # 14
AWG Romex still in the box coil.

2) Configure/connect the ends to make it a 2000' long single wire
bundle of about 400 turns.

3) There should then be enough resistance in the wire to plug it into
the 110 V 60 Hz line for short periods.

4) Remove the compass. With the power on, sweep the airplane
anywhere there is steel, and then step back several feet before
turning power off. Reinstall the compass.

No warranty. Don't wear any watches. Remove all credit cards etc
from your billfold..........

If nothing else, a gun type soldering iron puts out a pretty strong
field above the transformer, but of course it is small and will soon
get hot.

"nrp" wrote

Might it be possible to kludge a degausser? I'm looking for a
volunteer to try this scheme:
No warranty. Don't wear any watches. Remove all credit cards etc
from your billfold..........

I wonder about the possibility of it working without some type of iron core,
to form and concentrate the field.

Seems to me, that there have been articles about degaussing done with a
welder connected through the frame, slowly ramped up, then down.

Anyone remember something like this?
--
Jim in NC

The iron core is the steel in your airplane. Even with no iron, the
coil would current limit however by just the sheer length of 2000 ft
of number 14 wire.

Is there an electrical engineer out there?

In article nrp writes:
Might it be possible to kludge a degausser? I'm looking for a
volunteer to try this scheme:

1) Get a 500 ft length of 4 conductor (3 conductor plus ground) # 14
AWG Romex still in the box coil.

2) Configure/connect the ends to make it a 2000' long single wire
bundle of about 400 turns.

3) There should then be enough resistance in the wire to plug it into
the 110 V 60 Hz line for short periods.


With a bit over 23 amps from the resistance (5.05 ohms), you will need to
hope the inductance will limit the current, or the breaker on any normal
120 volt AC source will trip pretty quickly.

A bit over 2700 watts will warm it up pretty quickly, too.


4) Remove the compass. With the power on, sweep the airplane
anywhere there is steel, and then step back several feet before
turning power off. Reinstall the compass.


You might want to remove the magneto as well. There are almost certainly
other magnetic parts in the instruments that you want out of there first --
no sense destroying the instruments in the panel. Any permanent magnet motors
will not appreciate it. In fact, anything with a coil to pick up energy from
that field could well be damaged. The alternator and connected parts may
not like this.


As with old shadow mask color TV degaussing, do it fairly slowly, and
step back fairly slowly. Turn the coil horizontal then turn it off.


No warranty. Don't wear any watches. Remove all credit cards etc
from your billfold..........

You should expect this to break something expensive.


Alan

On Apr 13, 7:20*pm, Ron Wanttaja wrote:
On Sun, 13 Apr 2008 15:38:49 -0700 (PDT), John wrote:
I had a similar tough time swinging a compass in a Commander 114 which
has a large steel support bar just above the compass. *Couldn't find a
degaussing devise but was able to get more powerful compensating
magnets which took care of the problem but virtually every point had 2
to 8 points of variation....

Damn...Do you realize that a "point" on a compass is a bit over 11 degrees? *So
your compass was 22 to 88 degrees off...should we start calling you "Wrong Way
Dupre'"? :-)

(or maybe we'll just assume you meant 'degrees')

My own compass-swinging adventure is at:

http://www.bowersflybaby.com/tech/hillbilly.html

There are certain advantages of Experimental category.....

Ron Wanttaja

Remind me not to tell you about my first long solo cross country
flight.....

John Dupre'

nrp wrote:
Might it be possible to kludge a degausser? I'm looking for a
volunteer to try this scheme:

1) Get a 500 ft length of 4 conductor (3 conductor plus ground) # 14
AWG Romex still in the box coil.

2) Configure/connect the ends to make it a 2000' long single wire
bundle of about 400 turns.

3) There should then be enough resistance in the wire to plug it into
the 110 V 60 Hz line for short periods.

4) Remove the compass. With the power on, sweep the airplane
anywhere there is steel, and then step back several feet before
turning power off. Reinstall the compass.

No warranty. Don't wear any watches. Remove all credit cards etc
from your billfold..........

If nothing else, a gun type soldering iron puts out a pretty strong
field above the transformer, but of course it is small and will soon
get hot.
Radio Shack used to sell big degaussing coils as "bulk tape erasers".
Their only drawback was that it had a thermal overload switch that would
shut it off after about a minute.
Bypassing the switch let you keep it on until it was too hot to hold,
but it worked great on Mooneys and Navions. Never tried mine on a Piper.

Rip

You should expect this to break something expensive.

Alan

I agree you are very possibly right.

However, I don't think an alternator would be bothered in that it
doesn't need any magnetism to start. Magnetoes might be another story
& would require an experiment. Obviously remove all radios as a
precaution too.

Do you have any feeling as to just how powerful a degausser this might
be? If it is too powerful, operating it more remotely would allow a
more general degaussing. How close to a 4130 steel tube would it have
to be to demagnetize for example? Another experiment......

At least the wire coil could be reused to wire a house or hangar etc
as long as it isn't allowed to get too hot. A ballast such as a
toaster/iron or other high current device is series could limit the
current and degaussing power.

This is not rocket science.. A 120 volt solenoid can be used as a
degausser, as can the ones used for TV's... Even small ac motors will
have a pretty good induction field - esp. if you can open the metal
case up... The way to test is to magnetize a screw driver and then
use your degausser to demagnetize it... If it will do that it will do
the airframe...

Start with it right against the metal and run it back and forth across
the surface gradually increasing the distance away from the metal
until you are at least a foot away...

denny

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