Crazy compass

[John Welna]

I've got the original 3 1/8" compass in my Champ, centered in the panel. I've taken the plane out to the compass rose at the airport and "swung" it to read correctly. When I fly, it just goes around in a circle. I have no electrical system and my handheld radio is way over on the left side. Does anyone have any suggestions?

[joea]

Check for any new instruments added or even metal screws in the area of the compass. You might have to move it to the top of the dash and get it away from the rest of the instruments for it to be accurate. This is where they were usually from the factory.

[John Welna]

Thanks for the reply. My instrument screws are all brass. I'm not sure but I think Champ compasses were in the dash. The fact that my compass is accurate with the engine off sort of tells me that there may be some electrical interference with the ignition. Any one else know about this?

[Paul Agaliotis]

John,
It sounds like it's out of fluid.
Paul

[Mark Julicher]

Does it change the direction or speed of rotation with RPM? If so it may me vibration induced. Some interesting antique toys worked that way - look up whimmydiddle.

[vintageair]

Mine did the same thing when I picked up my Champ. Like Paul said, it was out of fluid. Rock the plane on the ground, if the compass bounces around alot it's empty.

[John Welna]

Thanks for the suggestions, boys. My compass has fluid but it's not totally full. I'll have to check about the RPM. Someone told me that an airframe can become magnetized which can cause problems. I hear there is a procedure to demagnetize called "degaussing". I don't think that's my problem since it's OK when the engine isn't running.

[shorty]

One can only properly swing a compass with the engine running at higher rpm than idle, and with all (if any) electrics turned on.

Compass swing procedures for non-electrical compass systems (systems that require no electrical power to operate and/or indicate) are in Advisory Circulars 43.13-1B CHANGE 1 and 150/5300-13 Appendix 4 Paragraph 3.

[shorty]

Better yet here it is:

SECTION 3. GROUND OPERATIONAL CHECKS FOR AVIONICS EQUIPMENT
(NON ELECTRICAL)
12-37. COMPASS SWING must be performed
whenever any ferrous component of
the system (i.e. flux valve compensator, or
Standby Compass) is installed, removed, repaired,
or a new compass is installed. The
magnetic compass can be checked for accuracy
by using a compass rose located on an airport.
The compass swing is normally effected by
placing the aircraft on various magnetic headings
and comparing the deviations with those
on the deviation cards. Refer to CFR14,
23.1327, 14 CFR 23.1547, and the equipment
or aircraft manufacturer's manual.
a. A compass swing must be performed on
the following occasions:
(1) When the accuracy of the compass
is suspected.
(2) After any cockpit modification or
major replacement involving ferrous metal.
(3) Whenever a compass has been subjected
to a shock; for example, after a hard
landing or turbulence.
(4) After aircraft has passed through a
severe electrical storm.
(5) After lighting strike.
(6) Whenever a change is made to the
electrical system.
(7) Whenever a change of cargo is
likely to affect the compass.
(8) When an aircraft operation is
changed to a different geographic location with
a major change in magnetic deviation. (e.g.,
from Miami, Florida to Fairbanks, Alaska.)
(9) After aircraft has been parked on
one heading for over a year.
(10) When flux valves are replaced.
b. Precautions.
(1) The magnetic compass must be
checked for accuracy in a location free of steel
structures, underground pipes or cables, or
equipment that produces magnetic fields.
(2) Personnel engaged in the compensation
of the compass shall remove all magnetic
or ferrous material from their possession.
(3) Use only nonmagnetic tools when
adjusting the compass.
(4) Position the aircraft at least 100
yards from any metal object.
(5) All equipment in the aircraft having
any magnetic effect on the compass must be
secured in the position occupied in normal
flight.
c. Compass Swing Procedures.
(1) Have the aircraft taxied to the
NORTH (0°) radial on the Compass Rose. Use
a hairline sight compass (a reverse reading
compass with a gun sight arrangement
mounted on top of it) to place the aircraft in
the general vicinity. With the aircraft facing
North and the person in the cockpit running
the engine(s) at 1000 rpm, a mechanic, standing
approximately 30 feet in front of the aircraft
and facing South, “shoots” or aligns the
master compass with the aircraft center line.
Using hand signals, the mechanic signals the
person in the cockpit to make additional adjustments
to align the aircraft with the master
AC 43.13-1B CHG 1 9/27/01
Page 12-14 Par 12-37
compass. Once aligned on the heading, the
person in the cockpit runs the engine(s) to approximately
1,700 rpm to duplicate the aircraft’s
magnetic field and then the person reads
the compass.
NOTE: (1) For conventional gear aircraft,
the mechanic will have to position
the magnetic compass in the
straight and level position or mount
the tail of the aircraft on a moveable
dolly to simulate a straight and level
cruise configuration. (2) Remember
the hairline sight compass is only intended
to be used as a general piece of
test equipment.
(2) If the aircraft compass is not in
alignment with the magnetic North of the
master compass, correct the error by making
small adjustments to the North-South brass
adjustment screw with a nonmetallic screw
driver (made out of brass stock, or stainless
steel welding rod). Adjust the N-S compensator
screw until the compass reads North (0°).
Turn the aircraft until it is aligned with the
East-West, pointing East. Adjust the E-W
compensator screw until it reads 90°. Continue
by turning the aircraft South 180° and
adjust the N-S screw to remove one-half of the
South’s heading error. This will throw the
North off, but the total North-South should be
divided equally between the two headings.
Turn the aircraft until it is heading West 270°,
and adjust the E-W screw on the compensator
to remove one-half of the West error. This
should divide equally the total E-W error. The
engine(s) should be running.
(3) With the aircraft heading West, start
your calibration card here and record the magnetic
heading of 270° and the compass reading
with the avionics/electrical systems on then
off. Turn the aircraft to align with each of the
lines on the compass rose and record the com
pass reading every 30°. There should be not
more than a plus or minus 10° difference between
any of the compass’ heading and the
magnetic heading of the aircraft.
(4) If the compass cannot be adjusted to
meet the requirements, install another one.
NOTE: A common error that affects
the compass’ accuracy is the mounting
of a compass or instruments on or in
the instrument panel using steel machine
screws/nuts rather than brass
hardware, magnetized control yoke,
structural tubing, and improperly
routed electrical wiring, which can
cause unreasonable compass error.
(5) If the aircraft has an electrical system,
two complete compass checks should be
performed, one with minimum electrical
equipment operating and the other with all
electrical accessories on (e.g. radios, navigation,
radar, and lights). If the compass readings
are not identical, the mechanic should
make up two separate compass correction
cards, one with all the equipment on and one
with the equipment off.
(6) When the compass is satisfactorily
swung, fill out the calibration card properly
and put it in the holder in full view for the pilot’s
reference.
d. Standby (wet) Compass. Adjustment
and compensation of the Standby Compass
may also be accomplished by using the “compass
swing” method.

[John Welna]

Thanks, Shorty. I'll get on it. It's so danged cold here in Minnesota that I'll have to wait untill the snow and ice is gone so I can see the compass rose.