Hi all,

Is there an easy way to determine if my airframe has become magnetized? My compass is absolute garbage (1955 Tri-Pacer), off by 30-40 degrees on some headings. Was going to buy a new compass for it, but guessing there's not much point if the airframe is magnetized and causing the issue? From what I understand, deguassing the airframe would need to be done uncovered? So if it is magnetized, guess I'm stuck with a compass being useless.

It is possible to degauss an airframe, at least partially. The bad news is, it will likely re-magnetize over time.

But, the keys to getting a compass to work in a steel frame is location, location, location…..and the right compass.

For example, many Piper aircraft came from the factory with the compass mounted in the panel…..really bad location, considering all the wiring and electrons that are floating around behind most panels….

Many were mounted on TOP of the glareshield….see above, electrons just below the compass.

S, the key is to mount the compass as far from electronics AND that magnetized airframe as practical, while still viewable. That means somewhere close to the top of the windshield.

If your compass is already mounted there, an inexpensive test would be to add a set of “compensator balls” as sold by Spruce, to that compass, then see if you can adjust as much error out as practical.

Failing that, a Hamilton vertical card compass, with compensators, mounted high in the windscreen MAY work.

But, my favorite solution is the S.I.R.S. Compass, again mounted high in the windshield. I’ve seen those installed in a number of problematic planes with good success.

And, you’ll hear from folks saying there’s no need for an accurate compass, just use your GPS. Unfortunately, that technology does fail occassionally….and a whiskey compass can save the day.

Secondly, every airliner comes equipped with….a compass.

Finally, my philosophy is this: A compass is required equipment. If it’s going to reside in my plane, I want it to function as intended.

I’d order a SIRS compass with windshield mount. And remember, EVERY compass must be placed on a compass rise and adjusted.

MTV

When I was in high school my father had a customer with the same problem in a PA-14. He removed the compass and took his DC magneto magnet charger and put it on all the tubes under the panel he could get too. Then did the same through the fabric on the out side and motor mount. It would stick to the tubes and had to be aggressively pulled away. Then moved the charger away before shutting it off. This worked at least for the short term. You can use a paper clip on a thread to test to see if tubes are magnetized. Paper clip will pull toward tube if it is magnetized. There is also a meter for this purpose and I think moving a compass around the plane would also indicate a problem.

There is a submarine degaussing range near Whidbey Island. Of course, you’d have to be submerged to make that work…..

MTV

My 180 had a panel mounted compass, when I redid my panel I put a SIRS on the windshield. Even with fly wires it required almost no adjustment. I like the unit very much, easy to read, lighted, and seems to be more stable than other compasses.

I'm struggling to remember the last time I looked at the Olde Whiskey Compass. All my VFR fun flying is more of a "connect the dots" style of navigation. I try to stay over landable terrain; usually lakes, I'm either on floats or skis depending on the season.

Just put a vertical card in

Not many use the compass, tons of time in the soup on many a dark stormy night, that thing was right up there in importance as the “panel mounted clock”


Especially in the day and age of solid state drop in AHRSs, they also seem to be less prone to issues as the temperamental old school whiskey compass


Side note, plane I’m training in right now, man…tech I go two ways, one is give me the level of tech where I have something smooth and detailed, like a GNS or better, Honeywell ACE, etc, or give me a 46 champ and a chart or just a AAA road map

We’ll this thing, it’s the annoying level of tech, lots of buttons but not much function, as in it doesn’t even have a MAP point for the missed, I had to time a missed approach point…and this thing doesn’t have props, oy vey I don’t get why this thing can’t have a extra 2kb of data per approach to just have a lat/lon for that critical point

I digress

We had a 185 that the boss really wanted a vertical card compass in. Long story short, the only thing I found that helped much was "Mu-Metal" around the wiring harnesses and avionics. Still, it wasn't satisfactory.
Then I stuck a SIRS compass in on top of the glare shield and as far as I know, it's still there, doing a great job! Since then, I've installed probably a dozen of them in Stinsons, Maules, Cessnas Grummans and a few others, and every time, the customer is happy.
John

I trusted a post MTV made years ago about this issue and he is correct!! SIRS is the answer!! It took a bit of work moving it around but I found a spot on my cub (lower Right windscreen) it works great. DENNY

mtv wrote:There is a submarine degaussing range near Whidbey Island. Of course, you’d have to be submerged to make that work…..

MTV

Wonder how that works

NineThreeKilo wrote:

mtv wrote:There is a submarine degaussing range near Whidbey Island. Of course, you’d have to be submerged to make that work…..

MTV

Wonder how that works

Beats the hey outta me, but apparently, I was at least a couple times many years ago, thoroughly degaussed.

MTV

I have a [maybe stupid] question: how do airframes get magnetized??

Zzz wrote:I have a [maybe stupid] question: how do airframes get magnetized??

Friction. Ever scoot yer feet across a carpet in winter, then just almost touch that cute girl Suzy’s earlobe, thus jumping a spark from your fingertip to that ear lobe?

Same concept….airframe moves through the air, causing friction, and developing a charge on the airframe. Rubber tires insulate the frame.

A helicopter doing long line work….you touch that load before the pilot puts it on the ground, and it’ll knock you flat….better hope your ticker is solid…..

Submarine moves through water, causing surface friction….. The airborne submarine hunters have MAD gear…..the long probe sticking out the back of the P-3 Orion. Theoretically, it detects magnetic anomalies in the ocean….like a magnetized submarine.

Etc. No way to avoid it, though most IFR aircraft have “static wicks” on control surfaces to try to dissipate some of the static generated by flying through clouds/moisture. Too much static buildup can interfere with comm and nav equipment.

MTV

I seem to remember that just whacking sharply with a hammer will magnetise an iron bar that is oriented a certain way (N-S?). Some of my landings…..

Also welding.

Also large electrical currents running through airframe. This includes battery back in tail being grounded to airframe.

Awesome y'all, thanks! SIRS compass looks cheap enough to give one a try. How are you mounting it to the windshield - are you drilling & screwing it through the lexan, or just using strong double-sided tape?

I wouldn’t drill a windshield, especially for a compass

CT_Pilot wrote:Awesome y'all, thanks! SIRS compass looks cheap enough to give one a try. How are you mounting it to the windshield - are you drilling & screwing it through the lexan, or just using strong double-sided tape?

SIRs compass comes with an adhesive strip adhering to a windscreen.

Years ago a 185 customer we had was complaining about his compass adhesive failing. We took a block of thicker Lexan, drilled and tapped for the screw spacing on the compass and then adhered the block to the windscreen with CA glue. That proved to be a pretty bomb-proof installation.

Order the SIRS compass that attaches to windshield. Follow the installation instructions to the letter. Those things REALLY stick, done right.

MTV

My PA-12 airframe had become magnetized and the compass wasn’t worth a lick. Found a rental degaussing ring and that fixed the problem. That was a long time ago, and SuperCubMD (from the sc.org site) did the degaussing for me during an annual: he might remember where we found the ring.