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How best to deal with malfunctioning vertical card compass


DXB

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2 hours ago, Marauder said:

 


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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Even with my 1 magnetometer, this compass trouble makes me skeptical that keeping my compass accurate over time will be worth the effort required.  I did some partial panel practice with my instructor this past weekend.  With both the Aspen and my vac AI covered, I found control and navigation with simply the track vector on the GTN650 map, the turn and bank indicator on my STEC30, and the altimeter to be not so challenging. I was quite surprised that I pulled off three practice non-precision approaches that way with minimal difficulty.  If I lost the whole electrical system, then I would certainly look to Foreflight my Ipad linked to the Stratus receiver plus the backup AI without ever glancing at the compass. I just need the dang thing to work and some practice doing turns with it before  the checkride!

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  • 3 weeks later...

Our painful compass compensation saga continues!  I got a new SIRS compass, which compensates fine E/W but is 30 degrees off N/S.  We are doing the compensation procedure correctly.  The problem is same with avionics on or off,  in flight or on ground, engine running or not running.  The '67 and later Mooneys have the austenitic steel center post, so that is not the problem.  My CFII fortuitously is a retired electrical engineer and put together a strong degaussing coil.  We followed the SB on Mooney degaussing meticulously.  Now it's improved but still off 15-20 degrees on some northerly and southerly headings.  Any further advice is appreciated.  I need to get this PITA addressed so I can do compass turns on my IR checkride!!

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Have you gone down the degaussing route? Even though the center post may not be ferromagnetic the rest of the cage can account for your error.  I have read that folks have had issues after things like running an electric motor within the cage enough to magnetize it    

I am happily blissfully ignorant of where my whiskey compass stands.  Feel for you re the checkride though.  

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11 minutes ago, DXB said:

Our painful compass compensation saga continues!  I got a new SIRS compass, which compensates fine E/W but is 30 degrees off N/S.  We are doing the compensation procedure correctly.  The problem is same with avionics on or off,  in flight or on ground, engine running or not running.  The '67 and later Mooneys have the austenitic steel center post, so that is not the problem.  My CFII fortuitously is a retired electrical engineer and put together a strong degaussing coil.  We followed the SB on Mooney degaussing meticulously.  Now it's improved but still off 15-20 degrees on some northerly and southerly headings.  Any further advice is appreciated.  I need to get this PITA addressed so I can do compass turns on my IR checkride!!

Dev - did you forget the exorcism chant as you were doing the degaussing? How did you attach the compass to the stainless steel center post? Brass screws? When the steel cage gets magnetized, it usually is because power leads are running around or across it. I would make sure that any wires are away from the cage. Or as Brad mentioned, running an electric device in the plane and running power lines across the frame.

Another thing to look for is what is directly below or near the compass? What is under the glareshield in that location? You may have something that is producing magnetic interference under it. Try using an orienteering compass and look for any deflections in the area. It doesn't need power applied to it to make it interfere.

One of the reasons I like the vertical compass was that I could always adjust the interference out. 

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This is where my first attempt at IR training came to a hault, un ceremoniously...

1965M20C...

The compass would run into a shadow and stop turning... the plane kept turning at a standard rate...

The compass would break free of the shadow, and accelerate as it was catching up... Replaced the compass, kept the problem...

my CFII wouldn’t skip this step to move on...

 

See if you can get an automotive compass that vacuum sticks to the windshield... this will give you an idea if the problem is plane related or if it more Center post related...

More modern Mooneys have the compass on top of the instrument panel.  The center post is SS ? of some form... the rest of the IP is the same tubular structure as all other Mooneys...

In real life... Dev’s chances of needing to navigate by solely using a compass are about a billion to one... and getting slimmer by the year...

There might be an MSC kind of tribal knowledge to this metal tube / compass interference challenge...

We have a guy...   @M20Doc might Be familiar with how to take care of this challenge?

Best regards,

-a-

 

 

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23 hours ago, DXB said:

Our painful compass compensation saga continues!  I got a new SIRS compass, which compensates fine E/W but is 30 degrees off N/S.  We are doing the compensation procedure correctly.

Start with your new compass outside (far away from interfering objects) and make sure the compass is good.

Then move it to various locations in and around the aircraft.  See if it can be corrected when not close to the instrument panel.  That might give you an idea of the source of interference/deviancy.

Obviously metal hangars, lawn tractors, etc. can also be causing problems on the ground.  In flight, it may be UFO's, or hangar elves.....

Perhaps @Marauder will share his secret incantation, but I wouldn't count on it.

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What would it take to delete the whisky compass altogether?  

Can the G500 with its magnetic heading sensor plus the ESI500 with its own separate magnetometer and battery backup replace the old floating compass?  

In fact I have not used the whiskey compass in years. 

 

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On 4/2/2018 at 2:31 PM, DXB said:

I just need the dang thing to work and some practice doing turns with it before  the checkride!

Even a working compass is full of errors :P ANDS and UNOS? Something like that...

There were no compass turns during my check ride in September. If there were, I would have had to remove my foggles to see the compass way up on the center post which seems to defeat the purpose. I would have resorted to using either GPS track or timing during standard or 1/2 standard rate turns.

Consider why we do compass turns in the first place: in case we lose heading info due to a vacuum failure. In the age of CRM, even as a single pilot, use everything at your disposal to get yourself on the ground. This includes anything else still functional in your panel as well as ATC. Have you tried a practice PAR or SAR approach? Cool stuff.

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Not sure - my CFII says to expect to do them as part of partial panel with the DPE that he likes to use.  He's a seasoned guy so I'm trusting him on this one.  We're giving it one more shot with degaussing the plane this weekend.  The consensus after further investigation seems to be that it's the engine mount that's likely magnetized.

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After endless frustration, I finally got the plane degaussed adequately this weekend to compensate the SIRS compass to within 10 degrees on all headings. We used the degaussing coil ripped out of an old cathode ray tube TV and coiled it tighter to a diameter of about 7"  before securing the loops together with zip ties.  The coil was put in series with a light bulb socket with a 660W cone heater element in it  (https://www.lightbulbdepot.com/products/details/di/660w-120-volt-cone-heater-heat-element-not-bulb/29036a/) to provide a ton of current.  One must be very cautious not to burn oneself on the heater element and also to hold the coil outside the plane when turning off the power so as not to remagnetize stuff.  We ran it over the front half of the steel cage , which helped but it was not enough. The engine mount was also heavily magnetized and we had to run the coil over that as well, and then it fully fixed the problem.  

BTW My CFII is a retired electrical engineer and did all the hard work. I certainly would have electrocuted myself on my own, but we have some Mooney degaussing expertise now. Three shops including an MSC declined to help along the way, but we got it done.   If I had put that time into studying for the IR oral exam I'd be completely ready by now - I only need about 3 more hours.  

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Great report on degaussing, Dev!

I remember seeing some old CRT monitors with a degaussing button... those were expensive Cad/cam monitors...

Check your grounds to see if current is being run through the engine mount...  you may have to degauss again over time if it is...

Best regards,

-a-

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  • 2 years later...

Our M20J has had the same issue, the magnetic compass and the subsequent vertical card compass that replaced it both were always difficult to swing. Our VCC was previously mounted on the original mag compass bracket, but it was installed before PAI had the Mooney-specific bracket available:

1535019077_PAIMooneymount.gif.b42b4f39dbc91d057010024f172d449e.gif

This is available here: https://www.aircraftspruce.com/catalog/inpages/pacmovmn.php

While removing the old mount to put on this new one, I noticed the screws and nuts holding the old bracket on were plain cadmium-plated steel (#6 machine screws). In examining the removable u-channel the screws went through, I noticed it had been repainted with a brush and there was some small areas of rust visible.

Ruh-roh.

The center windshield post is a stainless steel tube 3/4" in diameter and is non magnetic. But the U-channel I removed was regular steel. I decided to check the bracket components against a new military grade lensatic survival compass. And the results were astonishing, to say the least:

IMG_0577.thumb.jpeg.d1596c60009cf272a290166c0a5e433d.jpeg

IMG_0578.thumb.jpeg.d9d7cc5e6e3fa4e58e6f6cee50722b2b.jpeg

IMG_0579.thumb.jpeg.d0e5c39e171079a88e75ff48d76cbaab.jpeg

As you can see, the OEM bracket has been strongly magnetized. It's off the airplane now and I am going to do a new swing on this PAI VCC this weekend, on the brand new compass rose at Arlington airport (KAWO). And I will report on the results.

 

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  • 4 months later...

Seems I forgot to report on the results as I said I would earlier. Bottom line is I was able to get the VCC within 4 degrees or less on all 12 headings on the compass correction card. The interesting thing now is to watch it swing during an engine start. That #2 battery cable runs from left to right under the instrument panel to the starter contactor, then thru the firewall and back right to left along the engine mount to the starter. Lots of current, lots of steel, magnetar!!

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