Compass woes...

[Shadrach]

I recently replaced my leaky old airpath compass with a new S.I.R.S unit. I swung it with an A&P on the field. I've spent a lot of time lining the plane up on the compass rose and then starting it to make the adjustments... It has been most disappointing. While the old airpath was at most 3 degrees out on a few cardinal headings it was shaky and required time to stabilize, the new S.I.R.S is very stable yet horribly uncorrectable. many of the headings are off by the maximum allowable 10 degrees. Do I need to degauss???...buy some mumetal? If so, why was the old airpath fine? When I move my head with my bose X headsets, the compass follows. So far I'm less than impressed with the "best whiskey compass" money can buy...

[Piloto]

The problem you are experiencing is due to the compass magnets strength. The stonger the magnets the more stable the compass would be but more prone to be affected by surrounding magnetic material. I switched mine for a vertical compass card and I am really happy with it. Very stable, accurate and easy to calibrate. Have not seen it sensitive to magenetic materials unless you set the headsets next to it.

José

 

[richardheitzman]

Getting a compass calibration done is very time consuming. First is your compass rose a "calibrated" compass rose? If so and you take a look at the N/S deviation and the E/W deviation and you cannot bring it below 2 degrees then you have other issues. First I would suggest that you look at the hardware that is used in installing the compass and anything near to the compass. Non Magnetic is the only hardware that can be used. If you dont have any issues there then you should have the tubular structure degaussed. Then if your headset is moving the compass as you move your head then you have too much metal in your head and that will cause issues with swinging the compass and using the compass in flight, although I have never seen that happen before. How close are you sitting to the compass? Take the compass out of the aircraft and make sure you do not have any metal on you and go out to the compass rose and "walk it around" to make sure you compass itself is not bad.

That should put you on the right track. Make sure you are doing your calculations for the error adjustment correctly.

Let me know how it goes.

[Shadrach]

Quote: richardheitzman

Getting a compass calibration done is very time consuming. First is your compass rose a "calibrated" compass rose? If so and you take a look at the N/S deviation and the E/W deviation and you cannot bring it below 2 degrees then you have other issues. First I would suggest that you look at the hardware that is used in installing the compass and anything near to the compass. Non Magnetic is the only hardware that can be used. If you dont have any issues there then you should have the tubular structure degaussed. Then if your headset is moving the compass as you move your head then you have too much metal in your head and that will cause issues with swinging the compass and using the compass in flight, although I have never seen that happen before. How close are you sitting to the compass? Take the compass out of the aircraft and make sure you do not have any metal on you and go out to the compass rose and "walk it around" to make sure you compass itself is not bad.

That should put you on the right track. Make sure you are doing your calculations for the error adjustment correctly.

Let me know how it goes.

[richardheitzman]

whew I have never built one. The method is explained in the S&M manual but from what I remember doing is

1. take the compass out and any other items that might be damaged from strong magnetic fields

2. gain access to the entire upper tubular structure (drop the overhead panels)

3. with the degausser off, place it next to the tubular structure, turn it on and in a continous and smooth motion run the degauserr down the tube and then pull it away from the tube when you reach the end of the tube then turn it off.

4. Check with a compass to determine if any residual magnetic field is still there. If it is, then do it again, and again, and again till it is gone.

 

[meddesign]

If you had an Airpath or if your  current one takes an Airpath correction module, you can get a set of "high Power" cobalt magnets from Airpath. it will correct to up to 45 degrees.  Also I found it easier to drive around with the GPS on to adjust the swing.

[takair]

Quote: Shadrach

 Thanks! the compass was properly installed using the included hardware and tools. The compass rose is well maimntained. It was freshly painted a year ago and was used by the avionics shop for years. I spent at least 2 hours hand aligning (plumb bob on the tail). My Bose X are about 2 feet from the compass when in use.

I will try all of the above mentioned recomendations.  Can anyone point me to a link that explains the Mooney degaussing process and how to build a degausser???

[meddesign]

Quote: takair

 Fairly long discussion including link to MOoney SB on degaussing:    http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=2&threadid=1725

[skyking]

I had the same problem and the Mooney dealer in Calgary ( Calavlier Aviation)charged me $200 bucks to degausse the frame. Solved all my woes!

There is a complete procedure issued by Mooney on this. I may have a copy around. if i do i will scan it for you.

[Shadrach]

Quote: skyking

I had the same problem and the Mooney dealer in Calgary ( Calavlier Aviation)charged me $200 bucks to degausse the frame. Solved all my woes!

There is a complete procedure issued by Mooney on this. I may have a copy around. if i do i will scan it for you.

[skyking]

no problem. It may be a few days as i dont get home until thursday.