Vertical card compass

[cdlapadula]

I have noticed huge errors in indicated bearings with my vertical card compass PAI-700 (Aircraft Spruce).
Can anybody suggest me how to compensate and/or calibrate it using the two little screws mounted in the compass base?
Thanks.

[rleffler]

You may need to try something like this:

http://www.aircraftspruce.com/catalo...ompensator.php

Here's Spruce's description:

The vertical card compass is very sensitive to stray magnetic fields within the aircraft. If the compensators of the compass will not bring the compass within tolerances, it will be necessary to install the HBB47S compensator ("balanced balls"). These balls contain magnets which permit the compass to be properly compensated. Instructions furnished

[Jim Percy]

Depending on how much error you have the balls and/or shielding MAY not be enough. The screws are good for about 25-30 degrees I think, when I spoke to the guy at Precision he said the balls may add another 5-10 (it's been a while, I don't remember for exactly). I had my compass very close to the turn coordinator (45-50 degrees of error) and ended up moving it to the other side of the panel where it works fine.

[Guy Prevost]

This only applies if your error is caused by magnetized steel in your cockpit.

I had a 60 degree error in my VCC when I first installed it. I checked and my roll bar was highly magnitized. I removed my compass, and degaussed the roll bar and associated hardware with an automotive growler. Although I haven't fine tuned it yet, my VCC is now matches a handheld compass outside of the airplane quite closely.

A growler is a device used to excite armatures for testing. Search Ebay for "growler" or "armature tester". Or see if you can borrow one from your local automotive electrics shop. You don't need any of the test functions, just the big coil with a notch in the field guides (iron plates the coil is wrapped around).

Guy

[N916K]

I purchased one of the cheap Falcon VC compasses, it worked very well for a while, then one day it took a dump. After quite a bit of testing we found that by removing the compensator all together, the compass works quite well. It was as if the adjuster magnets are out of whack.