Magnetic Compass

Notatestpilot said:
My compass has some how stopped spinning when I cruise at 4500 feet. Can altitude affect the compass?
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Not that I'm aware of. But it might be related to the time it takes for you to get to 4500 or some other repeatable task. Perhaps check flight times, etc. for when the compass is 30 deg off and when not?
 
Exactly what kind of compass? A standard whisky compass (filled with kerosene) should not be affected by altitude. But there are other kinds of compasses.
 
There is a rubber diaphragm inside the compass to compensate for pressure changes. If the compass isn't completely full with fluid, whether due to a leak or not being properly filled, the diaphragm can distort enough to contact the moving parts and affect its motion.
 
I went for flight yesterday.The compass was just spinning like a top through cruise climb and while I leveled at 2500’ MSL for about 15 minutes. Once I cleared the bravo airspace I climbed to 4500’ MSL. The compass held a heading that was only 15 degrees difference from GPS, just gentle slow changes like normal while I banked left & right. I will take video the next time I fly…
 
Notatestpilot said:
The compass was just spinning like a top through cruise climb
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This is different than what you mentioned in the OP of only being off 30 degs? A spinning compass is different and needs a stronger external alternating or rotating mag field or there is an internal issue.

But since it steadies out after a spell and is only 15 degs (?) off now my 1st guess is something external. Do you have any DC motors behind your panel? Electric DG? Did you notice if your battery was still charging while it was spinning?

Maybe get a handheld compass and place it near your existing one without affecting it and see if it spins.
 
Bell206 said:
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But since it steadies out after a spell and is only 15 degs (?) off now my 1st guess is something external. Do you have any DC motors behind your panel? Electric DG? Did you notice if your battery was still charging while it was spinning?
Maybe get a handheld compass and place it near your existing one without affecting it and see if it spins.
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Good suggestions. Another: while flying VFR in an airspace / area that doesn't require radios, mode C xponder or ADS-B out (> 30 nm from class B, etc.), turn off the airplane electrical system both battery & master.Then see how the compass responds.

This is assuming you have a conventional magneto fired engine so that will keep running. Because the regulations require ADS-B out to be on, if you are so equipped, even when not flying in areas where ADS-B is required, I'll add that this is just for purposes of troubleshooting, will only take a few minutes. Then you can turn it all back on.
 
Here’s the latest from today’s flight…
The compass goes nuts (spinning like crazy) when my engine rpm is above 2500.
I brought along a separate compass and nothing happens to this portable compass while I’m running 2500 rpm.
At 2400 rpm, the compass is steady and normal.
 
That sounds like EMI from magnetos or spark plugs. Another test you can do is listen to static noise on a radio while you operate the engine below and above 2500 RPM. Can you hear a difference in the radio noise? Yet if so, one would think EMI would affect both compasses. Maybe it is mechanical vibration, but that seems like a long shot.

I would also suggest turning off the alternator while leaving the battery on, but if the alternator were the source of the EMI, it would not change with engine RPM.
 
MRC01 said:
That sounds like EMI from magnetos or spark plugs. Another test you can do is listen to static noise on a radio while you operate the engine below and above 2500 RPM. Can you hear a difference in the radio noise? Yet if so, one would think EMI would affect both compasses. Maybe it is mechanical vibration, but that seems like a long shot.

I would also suggest turning off the alternator while leaving the battery on, but if the alternator were the source of the EMI, it would not change with engine RPM.
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…but the handheld compass remain steady/normal indication while engine rpm was at 2500.
 
Notatestpilot said:
I brought along a separate compass and nothing happens to this portable compass while I’m running 2500 rpm.
At 2400 rpm, the compass is steady and normal.
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How is the compass mounted in the cockpit?
And the compass is serviced to the proper level and with the proper fluid?
 
A toy from a simpler age, made from an ice cream stick, with a hole thru the center, mounted on a nail thru a dowel, with notches on the side of the dowel. Rub another stick along the notches, and the propeller spins.

You have a variation of this, the bearings of your compass are vibrating, and the shaft is spinning.

Symptom of a bad dynamic balance of the engine and propeller.

That is shaking everything in your plane apart, slowly. Search this site for dynamic balancing, and learn all about it.

www.pilotsofamerica.com

Dynamic Balancing in FL/Southern GA

Looking for recommendations for a Dynamic Balance in the South East. My on field AP doesn't do it and I've had a tough time finding someone good to do it. One thing I'm looking for is using the holes in the Lycoming flywheel for the weights vs drilling into the spinner backplate. I had a...
www.pilotsofamerica.com www.pilotsofamerica.com

In addition, the clear kerosene may have leaked out, removing the damping that concealed the effects of vibration on the compass.
 
Uh oh!
Compass is not a concern now...I'll need to look into this engine/prop imbalance.
Thanks for the good info.
 
tsts4 said:
91.205 requires...
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91.205?

"Come on and join the **103s**, and get your flying pay.
You never have to work at all, just fly around all day.
While others toil and study hard, and soon grow old and blind,
We'll take the air without a care, and you will never mind."

(Okay... It really says Air Force... But they don't have Mustangs any more...)
 
geezer said:
A toy from a simpler age, made from an ice cream stick, with a hole thru the center, mounted on a nail thru a dowel, with notches on the side of the dowel. Rub another stick along the notches, and the propeller spins.

You have a variation of this, the bearings of your compass are vibrating, and the shaft is spinning.

...

In addition, the clear kerosene may have leaked out, removing the damping that concealed the effects of vibration on the compass.
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I suspect you've hit the nail on the head, and it's almost certain the compass is no longer fluid filled. A full compass can't really "spin"; it turns fairly slowly.
Notatestpilot said:
Uh oh!
Compass is not a concern now...I'll need to look into this engine/prop imbalance.
Thanks for the good info.
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The compass is probably in need of attention also. Quite likely it's empty. The seals only last so long, then the fluid leaks out and evaporates. Aircraft Spruce sells repair kits, with or without compass fluid - which is basically mineral oil. I just got done rebuilding an Airpath that needed new gaskets, diaphragm, light (I upgraded it to an LED lamp), and fluid. It took less than half a pint of fluid to fill it. Now my $40 eBay purchase is like brand new. Properly filled, the compass card will turn fairly slowly.
 
Notatestpilot said:
while engine rpm was at 2500
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I've only heard of it happening one time, but the next time you fly at 2500 rpm and the compass spins, grab the compass housing and see if the spin changes. Or install a thin piece of rubber between the compass mount and airframe and see if it changes spin 2500. That one time the spin was caused by a vibration harmonic in a helicopter when in flight only.
 
Bell206 said:
I've only heard of it happening one time, but the next time you fly at 2500 rpm and the compass spins, grab the compass housing and see if the spin changes. Or install a thin piece of rubber between the compass mount and airframe and see if it changes spin 2500. That one time the spin was caused by a vibration harmonic in a helicopter when in flight only.
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I flew yesterday, but will check on the compass with your suggestions on my next flight.
I've had this compass for about 20 years now. So I'm starting to believe the fluids are dry and most likely needs servicing.
I'll report back in a few weeks.
Thanks!
 
The key to a refill is to read the directions with the kit and not try to unscrew the big obvious screw on the top of the compass. But your A&P knows that.
(Posted Just In Case Of Someones Being As Dumb As I Am. :) )
 
Capt. Geoffrey Thorpe said:
The key to a refill is to read the directions with the kit and not try to unscrew the big obvious screw on the top of the compass. But your A&P knows that.
(Posted Just In Case Of Someones Being As Dumb As I Am. :) )
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You can fill it that way, but it's fussy. I did it yesterday. It takes a little technique and some patience, I was just seeing if I could do it before submerging it.
 
I read somewhere that an A&P cannot legally refill or service your compass, because it is a flight instrument.
However, the compass fairy has been known to visit airplanes while sitting overnight in the shop.
 
MRC01 said:
I read somewhere that an A&P cannot legally refill or service your compass, because it is a flight instrument.
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FYI: Servicing falls under maintenance so an A&P can perform it on a compass. But repairing or altering a compass is not permitted. However, servicing a mag compass overnight without making a mx record entry is not legal.;)
 
Dana said:
Yes. A compass isn't required for EAB, so you can do anything you want to it.
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Even if it was, and I know you know but for other folk’s benefit, anyone can conduct any level of maintenance on an E-AB aircraft and its systems/components. Not saying that’s safe, but it’s legal.
 
tsts4 said:
anyone can conduct any level of maintenance on an E-AB aircraft and its systems/components.
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I thought there still were some exceptions like the transponder 411/413 checks or IFR pitot/static checks. Has this changed?
 
Bell206 said:
I thought there still were some exceptions like the transponder 411/413 checks or IFR pitot/static checks. Has this changed?
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No that hasn’t changed to the best of my knowledge but I don’t consider either of those things to be maintenance per se and I suppose if one has the requisite test equipment theoretically I guess you could do it yourself unless there’s a FAR other than part 91 that governs this. And there very well may be as I’m not particularly knowledgeable on the FARs that govern maintenance outside of part 91. Obviously if there’s an issue with the transponder or any LRU you’re gonna R&R it. But fixing any plumbing or wiring issues can be done by anyone.
 
The person using the equipment or the shop has to be certificated.
 
tsts4 said:
I suppose if one has the requisite test equipment theoretically I guess you could do it yourself unless there’s a FAR other than part 91 that governs this.
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If it hasnt changed then only certain people can perform those tests. Part 91 actually lists who can perform those tests regardless class of aircraft.
 
Bell206 said:
I've only heard of it happening one time, but the next time you fly at 2500 rpm and the compass spins, grab the compass housing and see if the spin changes. Or install a thin piece of rubber between the compass mount and airframe and see if it changes spin 2500. That one time the spin was caused by a vibration harmonic in a helicopter when in flight only.
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Here’s an update:
While flying yesterday at 2500RPM, the compass start spinning wildly. I grabbed with my free hand and it stopped spinning!
 
Guaranteed it's empty. You may need the prop balanced, but you definitely need your compass serviced.
 
DaleB said:
Guaranteed it's empty. You may need the prop balanced, but you definitely need your compass serviced.
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I’m reluctant to prop balance.
Before the last two flights, I did remove and reinstall the prop 180 degree from last position. Also I have a chopper production and Mx background, I’m not too worried nor a big believer in dynamic balance ‘airplane props’.
I’m likely to buy a new compass for 50 bucks from Amazon.
 
Here’s a photo from my recent flight.
It’s mounted nearly center line on top of my RV6 dash.
 

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Notatestpilot said:
I grabbed with my free hand and it stopped spinning!
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Maybe alter the compass mounting by adding a rubber pad or adding a thick doubler and see if the spin changes? Or move it to a different location?
 
Wagondriver said:
Unless things have changed, a compass is required. The pc12 ngx I flew had one, very frequently grossly off, but it had one.
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I fly PC-12 NGs (older plane for those not aware). Some have a compass, some do not.

All you have to do to screw up a compass is put any of the following in top of the panel:
iPad
Phone
Headset
 
Different physics models best illustrate the different ways noise couples from one device to another. Magnetic fields are generally formed by sending significant current through a conductor. Something with an moving iron core could affect a compass by re-directing existing magnetic fields. I expect spark plug noise involves very little current. A spark is generally broad band noise that would probably contribute to RF noise but, I wouldn't expect to drive a compass. My first thought is maybe the primary electrical circuit in a mag or maybe the field current in an alternator. I expect an alternator trying to charge a nearly dead battery probably has a pretty good rotating magnetic field.
 
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