How best to deal with malfunctioning vertical card compass

[DXB]

So I have a Precision Vertical Card Compass that is showing very large deviations on certain headings not accounted for by the compass deviation card. It agrees with the card on other headings. I need to get a working compass before my IR check ride so I can practice compass turns.  I think the unit is around 7 years old and  predates my purchase of the aircraft but it was calibrated ~2 years ago when my panel was redone.  It was true to the deviation card at that time, and it has the correction balls permanently glued in position.  I'm not sure when or why it started malfunctioning, but I wonder if it's wear in the unit itself given that nothing else has changed in the past two years.  Which of the below options would you suggest:

1. Attempt to recalibrate the existing vertical card compass before deciding to overhaul or replace. Maybe install a new set of balls.  

2. Overhaul or replace the vertical card compass, get new balls, calibrate.

3. Junk the vertical card compass, install a S.I.R.S. compass which is harder to read but should be more bulletproof?  I hate wasting time on these recurring maintenance minutiae.

I don't want to waste A&P hours trying to get a compass to work that may need replacement anyway.  What's the likelihood of getting it to work?  Do these vertical compasses tend to wear out and fail?  If I'm replacing should I go with the simpler option even if harder to read?  Appreciate any experience and insight in this area. Thanks!!

[Mooneymite]

I'd suggest taking the compass out of the plane to determine if it is a compass problem, or a compass deviation problem caused by magnetic interference in the cockpit.

Mooneys are famous for magnetized structural tubing.

As has been mentioned many times before, compass compensating balls from Aircraft Sruce is the easy solution.

[DXB]

1 minute ago, Mooneymite said:

I'd suggest taking the compass out of the plane to determine if it is a compass problem, or a compass deviation problem caused by magnetic interference in the cockpit.

Mooneys are famous for magnetized structural tubing.

As has been mentioned many times before, compass compensating balls from Aircraft Sruce is the easy solution.

Embarrassed to admit I haven't checked outside the aircraft - an obvious diagnostic maneuver.  Will do.  It already has the balls installed.

[Bolter]

If you decide that it is a worn out compass, PAI will give you an offer to repair or trade-up.  At the time, it was $260 plus the old broken unit to get a new unit, tax and delivery included. Repairs were only a little less costly.  I went with the fire and forget option.  

[takair]

Likely a calibration issue.  Mooney's can tend to cause drift over time or with new avionics.  I think you have had recent work done.  Did the avionics shop do a compass swing after?  That would be standard practice.  Can usually get them to within the required 10° with patience.  If you are up this way, contact me and I can give you a hand...15 to 30 minutes and you would know if it's good or bad.

[Guest]

The vertical card compass has to rank among the worst inventions in aviation.

Clarence

[DXB]

29 minutes ago, M20Doc said:

The vertical card compass has to rank among the worst inventions in aviation.

Clarence

Experienced folks with strong opinions are always worth hearing - can I persuade you to elaborate?

[DXB]

41 minutes ago, takair said:

Likely a calibration issue.  Mooney's can tend to cause drift over time or with new avionics.  I think you have had recent work done.  Did the avionics shop do a compass swing after?  That would be standard practice.  Can usually get them to within the required 10° with patience.  If you are up this way, contact me and I can give you a hand...15 to 30 minutes and you would know if it's good or bad.

Engine work and new nav strobe lights but nothing major in proximity since the last time it was calibrated.  Let me see - I may take you up on the offer.

[kortopates]

The Vertical card compass is a big plus for instrument students because it doesn't turn the opposite direction like the Whiskey compasses.

But they are notorious for being difficult to calibrate, hence the balls and sometimes magnetism of the steel cage makes it impossible. But there is a solution for this too using a growler.

You're probably going to have to try re-calibrating the compass to find if it can be successful - or just send it back for inspection and repair/OH.

The good news is, after you learn how to do compass turns you won't actually need to rely on in partial panel flying as long as you have a WAAS GPS in the panel. Instead you'll use that and discover partial panel is easy to do even to ATP standards with the GPS TRK/DTK info. Which is another reason why a IFR GPS is so vital in these days. 

Edited February 6, 2018 by kortopates

[N201MKTurbo]

The earth's magnetic field just doesn't produce much torque. With a whiskey compass that torque has to overcome the friction of one needlepoint bearing with a few micro grams of force on it.

A vertical card compass has a megnetic disk held between two jeweled bearings, a gear to change the motion from horizontal to a vertical card on ball bearings I believe. Not to mention the magnetic dip puts sideloads on the bearings.

Thats a lot of mechanism to drive with the earths magnetic field.   

[Mooneymite]

When I bought my plane, I inherited a vertical card compass built by a company that (apparently) was out of business.  The compass pointed in no particular direction, but it was decorative.

I tried to get an avionics shop to take a look at it, but because they didn't have any manuals on it and (apparently) couldn't get them, they politely refused.

One night, long after I was asleep, the hangar elves decided to take a look at it.  Figuring it was "broke beyond repair", they completely disassembled it, cleaned it and not knowing any better, re-assembled it without benefit of books.

When I awoke and went out to the hangar, it worked perfectly outside of the plane; a set of balancing balls got it pointing perfectly when it was (temporarily, of course) installed in the plane.  I still can't find any paperwork on it.

 

[DonMuncy]

18 minutes ago, Mooneymite said:

When I bought my plane, I inherited a vertical card compass built by a company that (apparently) was out of business.  The compass pointed in no particular direction, but it was decorative.

I tried to get an avionics shop to take a look at it, but because they didn't have any manuals on it and (apparently) couldn't get them, they politely refused.

One night, long after I was asleep, the hangar elves decided to take a look at it.  Figuring it was "broke beyond repair", they completely disassembled it, cleaned it and not knowing any better, re-assembled it without benefit of books.

When I awoke and went out to the hangar, it worked perfectly outside of the plane; a set of balancing balls got it pointing perfectly when it was (temporarily, of course) installed in the plane.  I still can't find any paperwork on it.

 

Leave out extra milk and cookies for the hangar elves. They earned them. And it would take a really sharp IA or FAA inspector to notice that there is no paper work for the compass.

[DXB]

3 hours ago, kortopates said:

The good news is, after you learn how to do compass turns you won't actually need to rely on in partial panel flying as long as you have a WAAS GPS in the panel. Instead you'll use that and discover partial panel is easy to do even to ATP standards with the GPS TRK/DTK info. Which is another reason why a IFR GPS is so vital in these days. 

Ha - yes we just practiced last weekend.  Aspen pfd off, vac driven AI covered, use turn coordinator, altimeter and adjust TRK to DTK on the GPS using shallow banks.  Surprisingly I was able to manage and did not perish in a graveyard spiral.  

If my panel GPS and PFD perished simultaneously, I would still look at my Ipad (supported by the Stratus GPS and AHRS) before it would occur to me to squint at the compass.  

[Guest]

5 hours ago, DXB said:

Experienced folks with strong opinions are always worth hearing - can I persuade you to elaborate?

They are generally a pain in the butt to swing with any degree of accuracy.  I’ve seen little difference in steel tube airframes or all aluminum airframes.

I certainly would waste my time or money installing one in my own airplane.

Clarence

[lamont337]

Does your C have the old split windshield? We ended up finding the wrong fasteners going up the divider on mine. Can probably check with a magnet.

[Raptor05121]

I put one in my plane. N/S its dead on. E/W, its up to 20 degrees off. And thats WITH the correction balls.

[DXB]

6 hours ago, Raptor05121 said:

I put one in my plane. N/S its dead on. E/W, its up to 20 degrees off. And thats WITH the correction balls.

Yup  that’s exactly how mine was when it was working at its best, including balls, now E/W deviations are more like 40, which makes it useless.

 

13 hours ago, lamont337 said:

Does your C have the old split windshield? We ended up finding the wrong fasteners going up the divider on mine. Can probably check with a magnet.

 single piece 201 style windshield

[DXB]

On 2/6/2018 at 12:20 PM, takair said:

Likely a calibration issue.  Mooney's can tend to cause drift over time or with new avionics.  I think you have had recent work done.  Did the avionics shop do a compass swing after?  That would be standard practice.  Can usually get them to within the required 10° with patience.  If you are up this way, contact me and I can give you a hand...15 to 30 minutes and you would know if it's good or bad.

 

On 2/6/2018 at 11:58 AM, Mooneymite said:

I'd suggest taking the compass out of the plane to determine if it is a compass problem, or a compass deviation problem caused by magnetic interference in the cockpit.

Mooneys are famous for magnetized structural tubing.

As has been mentioned many times before, compass compensating balls from Aircraft Sruce is the easy solution.

So I finally had a chance to check compass outside the plane.  It performed terribly! it  reads accurately only facing magnetic east, seems to get "hung up" turning to any other cardinal direction. I realize it may be a bit flawed outside the plane because of the previous compensation settings used to calibrate inside the plane, but I can't imagine it would be this bad?  I suspect it is an issue intrinsic to the compass.  It's frustrating given it worked nearly perfectly 2 years ago after my panel redo.  Come to think of it, the only change since then has been the 201 windshield.  I guess it might have gotten jostled and damaged  during that process?  I'm sure they must have unmounted it at that time.  

Given that I'm not into recurring expenses, I'm going with a SIRS compass, which seems more durable, unless anyone still thinks this particular vertical card is worth trying to save.

[Marauder]

33 minutes ago, DXB said:

 

So I finally had a chance to check compass outside the plane.  It performed terribly! it  reads accurately only facing magnetic east, seems to get "hung up" turning to any other cardinal direction. I realize it may be a bit flawed outside the plane because of the previous compensation settings used to calibrate inside the plane, but I can't imagine it would be this bad?  I suspect it is an issue intrinsic to the compass.  It's frustrating given it worked nearly perfectly 2 years ago after my panel redo.  Come to think of it, the only change since then has been the 201 windshield.  I guess it might have gotten jostled and damaged  during that process?  I'm sure they must have unmounted it at that time.  

Given that I'm not into recurring expenses, I'm going with a SIRS compass, which seems more durable, unless anyone still thinks this particular vertical card is worth trying to save.

ANY compass subjected to jarring will result in a potential problem being created. It is likely that it was hit a number of times during the install. Especially if Pete did your installation.

[Piloto]

I have the vertical card compass on my 1982 M20J and it is right-on on runway headings. Very happy with it. However the VCC will not work properly on the older Mooneys with steel center post tubing. Later Mooneys have non-magnetic center post.  

José

[ragedracer1977]

50 minutes ago, Piloto said:

I have the vertical card compass on my 1982 M20J and it is right-on on runway headings. Very happy with it. However the VCC will not work properly on the older Mooneys with steel center post tubing. Later Mooneys have non-magnetic center post.  

José

My VCC works very very well.  Mounted on a steel post and all

[Piloto]

10 hours ago, ragedracer1977 said:

My VCC works very very well.  Mounted on a steel post and all

Yours was probably gas welded. Electric welding leaves a high magnetic residue.

José

[DXB]

Updating this thread.  I gave up on my vertical card compass w/  balls because it didn't rotate freely even outside the plane and would get stuck.  Rather than fix or replace, I bought a cheaper new SIRS compass figuring it would be a piece of cake to set up.  Nope.  E/W is easy but  N/W is off  by 30 degrees.  I have to slide it all the way up the center post before the errors become acceptable, but that's too far out of the line of sight.  The center post on '67 Mooneys and later is austenitic stainless steel, so that post itself being magnetized should not be a big factor for my '68C. Turning off the avionics master does improve the situation slightly, so I ordered this shielding material from Spruce to put between the center stack and the glare shield:  

http://www.aircraftspruce.com/catalog/inpages/magneticcompassshield.php

I'm not sure what I'll do if that doesn't work.  Degaussing the whole plane seems like a tricky affair that is way too much work just so I can have an accurate compass for an upcoming IR check ride.  Any ideas??

 

[Marauder]

Updating this thread.  I gave up on my vertical card compass w/  balls because it didn't rotate freely even outside the plane and would get stuck.  Rather than fix or replace, I bought a cheaper new SIRS compass figuring it would be a piece of cake to set up.  Nope.  E/W is easy but  N/W is off  by 30 degrees.  I have to slide it all the way up the center post before the errors become acceptable, but that's too far out of the line of sight.  The center post on '67 Mooneys and later is austenitic stainless steel, so that post itself being magnetized should not be a big factor for my '68C. Turning off the avionics master does improve the situation slightly, so I ordered this shielding material from Spruce to put between the center stack and the glare shield:  
http://www.aircraftspruce.com/catalog/inpages/magneticcompassshield.php
I'm not sure what I'll do if that doesn't work.  Degaussing the whole plane seems like a tricky affair that is way too much work just so I can have an accurate compass for an upcoming IR check ride.  Any ideas??
 

Someone could make a career of swinging compasses in a Mooney. The challenge is that if the error is due to the plane being magnetized (caused by avionic power wiring draped over the roll cage or running electrical equipment inside of the cockpit, ex, using a vacuum), you can be degaussing and swinging on a regular basis.

I’m fortunate that I have multiple magnometers in my plane and the cross check with the magnetic compass becomes more of a symbolic exercise. Don’t get me wrong, I check the magnetic compass for accuracy, but keeping it accurate can be a bit of a challenge.


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[thinwing]

On 2/6/2018 at 9:30 AM, M20Doc said:

The vertical card compass has to rank among the worst inventions in aviation.

Clarence

Mine lasted 2 years I think in a Baron...they are easy to read but won't last like a whiskey compass