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Compass Errors

Hedge

By Hedge
in General Mooney Talk

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Hedge

Posted
Posted

My old compass was having some troubles (so I thought) and I couldn't trust it especially in IMC.  So I had it replaced with a vertical card compass.  When trying to calibrate the new compass, it was off by 20 degrees to the east no matter if the radios were on or off.  It is the old steel bar down the windshield, and I believe the plane has a magnetic charge.  Anyone else have this problem and if you did, what did you do.  Degaussing the airplane is the only thing I can think to do, but not sure how it would be done.

 

Thanks

Hedge Collaborator

Hedge

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The problem with the compensation is it is -6 at 60 deg and +9 at 90 deg.  It just stops and I don't have a clue what to trust when it starts bouncing around.  I trust my DG more than the compass.

sleepingsquirrel Mentor

sleepingsquirrel

Posted
Posted
  1. Every old crt monitor has a degaussing coil at the front of the screen. I made mine with a momentary switch, just plug it into ac power and  activate by pressing the button. Be SURE to remove the COMPASS first!  This thing can and will heat up while you are holding it waving it around in a circular motion!
  2. You may hear the mags vibrating ,you are too close to them!!  Keep it high and start  close to the windshield bar. Push the button as you slowly circle the coil and back away from it without coming closer to  any other steel then release the button. It is not hard but requires some knowledge of the magic of fields, you can make it worse! You can make it better, it may require several attempts degaussing then  at swinging the compass. There is an order of cardinal points to swing as well. 
  3. Theory is that the rapidly alternating current in the degaussing tool  magnetizes steel one way then the other.  As you back away the magnetization gets weaker and weaker in the metal you are degaussing.
  4. I had to exchange the compensator in my compass because someone had stripped the gear trying to compensate for the magnetized window steel  tubing. Mine was about 20 degrees off and I flew it for a couple of years that way just applying a deviation card of my own (mentally)
  5. My mechanic thought I was surely  going to get lost! 
  6. disclaimer: I'm not an A&P , I'll not be responsible for beating you with a stick to make you let go of a live circuit. I can't possibly know how talented you are with electricity , or building something from salvage parts. I don't even know if you can use a screwdriver so good luck!
  7. Get a flying buddy to let you practice on his airplane first!

compensator.JPG

Guest

Guest

Posted
Posted

It makes you wonder how a compass on a steel ship works?  Any Navy guy with an answer?

Clarence

Piloto Grand Master

Piloto

Posted
Posted
5 minutes ago, M20Doc said:

It makes you wonder how a compass on a steel ship works?  Any Navy guy with an answer?

Clarence

That is why they have big balls. The balls compensate for the hull magnetization that changes at different headings.

José

sleepingsquirrel Mentor

sleepingsquirrel

Posted
Posted
1 hour ago, M20Doc said:

It makes you wonder how a compass on a steel ship works?  Any Navy guy with an answer?

Clarence

Do iron ships pose particular problems for magnetic compasses?

Yes. The magnetic field of the iron body of the ship itself affects the reading on the compass.

When iron and steel ships became common, many scientists studied the problem. One of the earliest was the Astronomer Royal, Sir G.B. Airy, who in 1838 used the iron steamer Rainbow for his experiments. Airy thought of a method of neutralizing a ship's magnetism by placing magnets and pieces of unmagnetized iron near the compass.

 

Modern ships and submarines have huge cables running around the longitudinal axis of the vessel which can be energized with AC power to degauss while underway. This helps resist setting off magnetic mines,or having a magnetic signature which the enemy can target.

big balls.jpg

  • Like 1
carusoam Grand Master

carusoam

Posted
Posted

You are not really using the compass in IMC are you?

That is why....

- Garmin has sold so many of those portable GPS devices.

- Modern Mooneys don't mount the compass on the steel tube.

- Really modern Mooneys have a stainless tube for that vertical piece.

How many GPS(s) does your ship have on board?

- panel mount, one or two?

- iPads, one or two?

- iPhones, one or two?

- Garmin Wristwatch?

The modern HSI is connected to a compass electronically.  Sure, it gets compared to the compass on the flight on a schedule...

We have come a long way in a decade.

This was a problem for my M20C that I had training for IFR. Part of the training is navigating with minimal tools, compass and wind up clock.  The compass would get hung up during 360° turns. Not just be off by a few degrees.

The degaussing and balancing balls are the best technology available to improve the unpowered equipment.

the IFR system isn't that flexible anymore. Real life back-up systems include portable radios with an ILS, GPS, and personal locator beacons.

Thoughts that come to mind...

Good luck getting over this hurdle.

Best regards,

-a-

Marauder Grand Master

Marauder

Posted
Posted
27 minutes ago, Hedge said:

They installed these after they installed the compass and it still wouldn't work.

The compensating balls will work if the magnetism isn't too great -- or if the magnetism isn't reintroduced. I would look for power lines from your avionics being tied wrapped to the tubular structure. Also check under the glare shield to make sure there are no power lines run near the compass. I had a lot of wires draped over the tubular structure that needed to be moved before I degaussed. Even after degaussing, I still needed the compensator balls to offset the remaining magnetic interference. 

Also, as Robert mentions, running power lines for a vacuum, trouble shooting light,portable heater, etc, will potentially re-magnetize the tubular structure. 

Hedge Collaborator

Hedge

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I have the GPS, but I am trying to get my IFR cert. and trying to do an ILS using no gps and partial panel makes it nearly impossible and it stops processing.  I totally agree that having all the modern equipment is great, but it does fail.

 

I just had a 650 GTN and I didn't even get it home and it doesn't work.  I have to take it back to get it replaced.  So even though i have all the technology, I would like it to be working better than it currently does.  Thanks for all of this advice.  And yes I have vacuumed out my plane with the motor inside.  I also have a heater that I blow warm air in my engine during the winter. 

DonMuncy Grand Master

DonMuncy

Posted
Posted
Just now, RobertGary1 said:

By chance have you ever vacuumed the plane with the motor inside the plane? :) I've always been careful to use a long hose and keep the vacuum away from the airplane. 

-Robert

I have read this before. Can someone explain to me how an alternating current can magnetize anything.

Hedge Collaborator

Hedge

Posted
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5 hours ago, OR75 said:

are you sure it is not coming from a headset or an iPad sitting on or near the dash ?

 

There wasn't anything near it.  The avionics shop that installed it also put in the new vertical compass and couldn't get it calibrated.

sleepingsquirrel Mentor

sleepingsquirrel

Posted
Posted
1 hour ago, don.muncy said:

I have read this before. Can someone explain to me how an alternating current can magnetize anything.

Good question! The degaussing coil which uses AC can magnetize or demagnetize .

Voltage in the coil is creating field lines that reverse N/S slightly out of phase with the voltage. Current lags voltage. Current in a conductor creates a magnetic field. As long as the field is rapidly changing as it is distanced from the steel tube the steel tube it is likely to retain a small / insignificant (0) residual magnetism. If the current is stopped while the coil is close to the steel tube it can remain  magnetized in the polarity of the last cycle as voltage/current decays to zero in the coil. Ideally you would want to stop the dergaussing tool when  the AC voltage reaches zero, the current has stopped and  the  magnetic field around the coil has collapsed, hard to measure  even harder to do . After the AC is turned off the  collapsing field around the degaussing tool  creates current in the tool and power supply wires until the field is completely collapsed. This current in the coil and conductors in close proximity to ferrous material can magnetize.

The SB mentions that this can happen with the growler (  shop tool for testing motor armatures for shorts)

I also forgot to mention that degaussing requires the swinging  of a dead cat above your head while fervently repeating the Lord's Prayer backwards to be completely effective.

I reserve the right to defend myself when the EEs weigh in. 

  • Like 1
Andy95W Grand Master

Andy95W

Posted
Posted

So, you're saying I should vacuum my airplane with the shop vac in the plane, and then slowly take it out of the plane while it's running to successfully degauss my steel roll cage.

  • Like 1
sleepingsquirrel Mentor

sleepingsquirrel

Posted
Posted
9 minutes ago, N1395W said:

So, you're saying I should vacuum my airplane with the shop vac in the plane, and then slowly take it out of the plane while it's running to successfully degauss my steel roll cage.

It's entirely freaking possible! but how you gonna do that while swinging the dead cat?

  • Like 2
Hedge Collaborator

Hedge

Posted
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Posted
9 hours ago, sleepingsquirrel said:

degaussing-coil-magnetic-fields-sign-s-7

Please be careful ! Under no circumstances let the degaussing coil come near the Mooney's flux capacitor , because where we are going when that happens , we don't need no stinking compass!  

Pretty funny.  Ok, I have the cat.  do you swing it clockwise or counterclockwise.  Or does it have to be relative the voltage current?  Would it be best to use an oscilloscope while spinning the cat?

cnoe Mentor

cnoe

Posted
Posted

Does the cat REALLY need to be DEAD?

If PETA sees this thread we're ALL gonna be in trouble.

I'm going to try it with a live cat and report back with the results.

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