Compass trouble

Gordon Misch said:

Actually, I gave that considerable thought as I was wiring the plane. I bundled wires that were anywhere close to the compass behind the panel such that their magnetic field vector would be vertical in the vicinity of the compass. The intent was to not interfere with the horizontal component of the earth's field. At first, it was great, but like I said, gradually degraded and was independent of radio, lights, etc being on or off. I don't know why. Maybe high current fore/aft wiring, like for starter or alternator had an influence on the frame even though at a distance from the compass. I considered degaussing, but decided against that effort because whatever caused the problem would undoubtedly reassert itself.

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One of the problems with compasses in aircraft is that an airframe actually becomes more magnetized as it moves through the air. Friction is a powerful force.

Consider the submarine. All US submarines go through degaussing periodically to reduce their own magnetic field. The "stinger" you see on the tail of an anti submarine aircraft like the P-3 Orion is a "Magnetic Anomaly Detector", or MAD system. It can actually detect disturbances in the Earth's magnetic field, including a submarine, which is a pretty big chunk of metal. But, by degaussing the submarine periodically, that disturbance is minimized.

In my experience, the Vertical Card compasses, and the SIRS compasses both can work when hung somewhere high in the windshield, as Gordon describes. In a couple of cases, I found that the Vertical card compasses also required installation of compensator balls, which are available for them.

Look at the large compass on many ships....surrounded by huge quantities of steel. Many if not most of those compasses have some sort of compensators installed as well.
That said, I've had SIRS compasses in two airplanes that I couldn't get a standard compass to work in, and the SIRS worked very well in both with no compensators.

MTV

I don't know what has happened in the last 40 years but in my first life flying from 1971 to 1986 flying several certified and E-AB's all I had, again ALL I had was a whiskey compass, chart and clock. I managed to fly all over the eastern part of the country many times in 3-5 mile soup and never had an issue. When I bought my Pitts Special we took it to the compass rose at APG and updated the compass card, swinging it with the engine running. It was accurate with-in 3 degrees when finished and remained so even after aerobatics...

Maybe the guvmint is screwing with the earth. Maybe make tinfoil hats for the compasses?

Fast forward, both of my current planes are magnetized, both homebuilts. Got one close enough to not get lost but I don't go anywhere anyway. If I was going to do any x-c I'd get the compass within 7-8 degrees & fill out the card just in case and buy a GPS.

Oh well.

Jack