View Full Version : Compass

05-13-2016, 12:21 AM
Just bought a Tri-Pacer. It had an aftermarket vert. card compass, previous owner said it would wander off unreliably. I had it exchanged for a whiskey glass compass. On inaugural flight home, it swung wildly so as to be useless, as if it was poorly dampered. When I checked it on a compass rose, the compass was WILDLY off as well. I wonder if the problem is brought on by the risers behind the windshield, and if the problem is common to the type, or if I just had the bad luck to run on to two faulty compasses.

Fred Mayes
05-13-2016, 11:23 AM
Soquetero, I don't know what you mean by risers behind windshield. It is not normal to have this problem. Did you have an IPad or anything else near that would affect the compass?

Homer Landreth
05-14-2016, 02:25 AM
I am assuming that by being "wildly off" to mean it is swings unstable, back and forth. Again I assume you mean it is doing that with the engine running . I am also assuming that the compass is mounted on the top of the instrument panel. If that is the case, you probably have the compass mounted where it is affected by the engine tach. Tell us if the compass is stable with the engine not running. Also, can you adjust the compass to be on heading with the plane sitting still and engine and all power off ? If so, then start the plane up and see if the compass oscillates back and forth. IF it does, then the tach is probably the source of interference. If it doesn't then start turning your radios and electrical equipment on and see which one makes the Compass go off heading. Post your information from this activity, if it doesn't identify the problem we will at least nave a little more to go on for further troubleshooting.

Tom Anderson
05-14-2016, 11:56 AM
I agree with Homer in that your compass is probably being affected by electrical interference. His suggestion for checking with all power off including the engine and then turning on each item starting with the generator / alternator is well founded. It could be caused by lack of grounding, improper shielding, or electrical wiring or antennas to close to the compass. One other possibility is a magnetized fuselage or portion thereof. For a discussion on this subject try this thread http://forum.shortwingpiperclub.org/showthread.php?p=7685#poststop.

Tom Anderson

05-14-2016, 03:28 PM
Thank you for the reply. Your Assumptions are in the ballpark. The compass is mounted dead center on top of the glare shield. Voila, the taco-meter (ok, tachometer) is just below it, offset to the right a bit. Studying a photo in the P.O.H., the plane was probably delivered osolongago with the compass located atop the glareshield, but directly in front of left-seat pilot...it's a poor picture, but the compass is recognizable (as are the A.I. and D.G. directly below it...) The "wildly off" was on the ground over a compass rose, engine on. The compass was reasonably steady, but the headings were crazy. 045 for North, 150 for South, & such). I did not check the compass engine-off. The "swinging" was in the air; The air was a bit rough, but the oscillation, as you put it, was ridiculous. Interestingly, the D.G. was steady as no D.G. I've seen before;. The movement matched the heading changes of the plane, but the D.G. needed almost no adjustment during the two hour legs.... How I ended up navigating home was, match the D.G. to the predicted course line on Fore-flight. And pilotage.....

05-14-2016, 06:32 PM
..,the compass is located directly above the radio stack