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