Vertical Card Compass Mis-reading

[lsearcy]

I have a vertical card compass in my J. Picture attached.  We did some recent panel work and the glare shield was removed.  After picking the plane up we noticed that the compass did not read correctly. Presumably the displacement was caused when the compass was hit when removing the glare shield.  

 

I know the little white balls on each side help "balance" the compass because of the amount of metal int he Mooney, but I am not sure exactly how to re-calibrate the compass.  There are two small screws in the bottom of the compass card that I assume are used to re-calibrate.  Is this something I can do or do I need a mechanic.  If I can do it, any helpful hints, youtube video of this being done or other suggestions are welcome.  

[mooniac15u]

One or both balls probably got rotated. The orientation of the balls is important.

[mooniac15u]

Do you have an older picture of your interior where you might be able to see the orientation of the red and green dots on the balls?

[kortopates]

Check to see if the compass is still level - it may have been pushed up from R&R'ing the glare shield. But no, re-swinging the compass is not on the owner approved list of maintenance items.

[carusoam]

Those darn things have a name...

Chris, with the big GFs, has written about them.

Unfortunately my memory is not cooperating enough today to help.

Best regards,

-a-

Try this for more....

http://mooneyspace.com/topic/7927-compass/?hl=%2Bcalibration+%2Bballs#entry82752

[mooniac15u]

Those darn things have a name...

Chris, with the big GFs, has written about them.

Unfortunately my memory is not cooperating enough today to help.

Best regards,

-a-

Try this for more....

http://mooneyspace.com/topic/7927-compass/?hl=%2Bcalibration+%2Bballs#entry82752

They're called a "compass compensator". They provide a localized magnetic field to compensate for magnetic fields in the aircraft from avionics or magnetized steel frames that can occur in our Mooneys. The localized magnetic field comes from small magnets in the balls. Like any magnet they have poles and the compensating magnetic field is "tuned" by adjusting the orientation and distance of the magnets from the compass. If the balls are bumped the alignment of the magnetic field can change which will throw off your compass.

[Marauder]

Those darn things have a name...

Chris, with the big GFs, has written about them.

Unfortunately my memory is not cooperating enough today to help.

Best regards,

-a-

Try this for more....

http://mooneyspace.com/topic/7927-compass/?hl=%2Bcalibration+%2Bballs#entry82752

Mooniac is using a politically correct nomenclature. Everyone else calls them balancing balls:

http://www.chiefaircraft.com/pcn-pbb475.html

http://www.skygeek.com/precision-aviation-pbb-475-balancing-ball-kit.html

http://www.aircraftspruce.eu/balancing-ball-set--pbb-475.htm

Sent from my iPad using Tapatalk

[Vance Harral]

The legal answer is no, an aircraft owner/operator can not swing the compass on a certified airplane.  It's not listed in the "preventive maintenance" definition of FAR 43 Appendix A.  In fact, asking who is legally authorized to do this tends to ignite debate: it's not clear an ordinary A&P can legally perform the procedure.  Some interpret the regulations to say only an authorized repair station can do so.

 

That said, if you just want to learn what's involved in the procedure, the official reference is AC 43.13 Section 3.  There are other techniques employed by homebuilders, but that's the FAA way.  How you use that information is, of course, entirely up to you.

 

Factoid of the day: did you know you're supposed to recalibrate your compass any time the aircraft is "subject to a shock; for example, after a hard landing or turbulence"?  I'd bet that puts 99.9% of all certified airplanes out of compliance.

[Marauder]

I have a vertical card compass in my J. Picture attached. We did some recent panel work and the glare shield was removed. After picking the plane up we noticed that the compass did not read correctly. Presumably the displacement was caused when the compass was hit when removing the glare shield.

I know the little white balls on each side help "balance" the compass because of the amount of metal int he Mooney, but I am not sure exactly how to re-calibrate the compass. There are two small screws in the bottom of the compass card that I assume are used to re-calibrate. Is this something I can do or do I need a mechanic. If I can do it, any helpful hints, youtube video of this being done or other suggestions are welcome.

I think your balls got moved. I think they should have been glued in place.

Swinging your compass while balancing your balls requires a mechanic to help you.

Here are the instructions including how to use the balancing balls: https://www.cumulus-soaring.com/precision/Bulletin_IC-102.pdf

Sent from my iPad using Tapatalk

[lsearcy]

Thank you for the responses.  Since Vance said I cannot do it myself and Marauder gave me the instructions, I will do exactly what the FAA requires while also making the compass work correctly.  I appreciate all of the help and answers.  I'm not completely sure Marauder was still referring to my compass.

[HRM]

Hangar elves do a great job getting a compass to read near perfect. I hear they use a GPS.

[Mooney Flyer]

I am a long time C model owner with a PAI Vertical Card Compass.  Over the years I have done the compensation a number of times.  Having read the thread I thought I would post the procedures using the balancing balls and also a compensation routine sheet for the steps and data collection.  Remember, when adjusting the screws in the unit start with the little dots in the 9 o'clock position and do not rotate them more to more than the 3 o'clock position or damage to compensator mechanism will occur.  I hope this is helpful.

 

 

PAI-700 Vertical Card Magnetic Balls Compensation.pdf PAI Compass Adjustment Routine..docx

[DXB]

On 6/9/2015 at 5:29 PM, lsearcy said:

I have a vertical card compass in my J. Picture attached.  We did some recent panel work and the glare shield was removed.  After picking the plane up we noticed that the compass did not read correctly. Presumably the displacement was caused when the compass was hit when removing the glare shield.  

 

I know the little white balls on each side help "balance" the compass because of the amount of metal int he Mooney, but I am not sure exactly how to re-calibrate the compass.  There are two small screws in the bottom of the compass card that I assume are used to re-calibrate.  Is this something I can do or do I need a mechanic.  If I can do it, any helpful hints, youtube video of this being done or other suggestions are welcome.  

I have some mostly unpleasant experience here.

STEP 1:  Take the compass outside your plane, remove balls (the compass', not yours), and make sure it can be made to read roughly correctly using the compensation procedure - this should be pretty easy outside the plane.  Your Iphone can give you a pretty good heading reference.  If it doesn't read right outside the airplane, send it back to the company for overhaul or place in trash receptacle (probably the more economical option). Get a new compass. Consider a SIRS, which is less finicky. 

Skipping step 1 wasted a huge amount of time for me.  In addition to heavily magnetizing my airframe during install of a windshield, a  shop must have given my vertical card a big whack at some point, rendering it permanently inop.

If the compass is fine outside the plane, go through the procedures in the aircraft.  You can do it. It's easy if you have a magnetometer -referenced heading in your panel so you don't have to find a compass rose.  Technically your mechanic has to sign off but I didn't bother - there is zero magic here. If it doesn't work out, your steel cage and or/engine mount are magnetized.  Good luck finding a shop that wants to help you with this - I couldn't - it is a bit of a PITA.  I ended up accomplishing it with my CFII after multiple failed attempts.  My CFII happens to be an electrical engineer (probably would have electrocuted myself on my own).  

See my prior thread: