What's the customary technique for adjusting the magnetic compass

[dov_elyada]

My magnetic compass was way off. I found the screw that adjusts it. I took the compass off and adjusted it away from the aircraft and from interfering steel structures and objects. This I did using lines-of-sight to geographic references for which I knew the bearings. But how can I be sure that the adjustment remains valid once I put the compass back in place?

I realize that I may have been "re-inventing the wheel." So how experienced pilots do it?

Thanks for your advice
Dov

[Zack Baughman]

Not sure how accurate these are, but here are some links with some advice:

http://www.cfisher.com/compass.htm

http://www.aviationpros.com/article/...-compass-swing

http://www.bellanca.us/compass.pdf

http://www.bowersflybaby.com/tech/hillbilly.html

[martymayes]

My magnetic compass was way off. I found the screw that adjusts it. I took the compass off and adjusted it away from the aircraft and from interfering steel structures and objects. This I did using lines-of-sight to geographic references for which I knew the bearings. But how can I be sure that the adjustment remains valid once I put the compass back in place?

I realize that I may have been "re-inventing the wheel." So how experienced pilots do it?

Thanks for your advise
Dov

The compass has to be installed in the aircraft. Compass swinging procedures are outlined in AC 43.13-1B Ch. 12. I usually follow that to the letter.

[Tom Downey]

My magnetic compass was way off. I found the screw that adjusts it. I took the compass off and adjusted it away from the aircraft and from interfering steel structures and objects. This I did using lines-of-sight to geographic references for which I knew the bearings. But how can I be sure that the adjustment remains valid once I put the compass back in place?

I realize that I may have been "re-inventing the wheel." So how experienced pilots do it?

Thanks for your advise
Dov

Compasses need to be swung in the environment they operate in, IOWs they need to be installed to be adjusted properly.

[Eric Marsh]

I installed another compass a while back and adjusted it by pulling my airplane onto a compass rose, taking the reading with my radio on, moving it 180 degrees, averaging the readings and adjusting the compass. Then I did it on the perpendicular headings, back to the original headings until everything was as close as I could get it. Then I went to the minor compass points and took readings and used them on my deviation card.

[dov_elyada]

AC 43.13-1B Ch. 12 Sec. 3 Par. 12-37 relates to "real" aircraft that operate from "real" airports, for which the compass is a critical navigation equipment. It requires using a compass rose, probably available only at such airports. But I fly a basic LSA with no aviation electronic navigation equipment, operate from a "bush" unpaved airstrip, navigate by landmarks and car GPS, and use the compass only as an accessory. (That's why I ventured to do the adjustment myself in the first place.)

So the techniques I can use should not require dedicated facilities, on the one hand, and on the other hand not be expected to result in any great precision.

[WLIU]

Well just because you operate away from a "real" airport does not mean that you can't go find an airport with a compass rose and do your adjustments. Or if you know the true bearings of prominent landmarks from a spot on the location that you fly from, and you can beg, borrow, or rent an inexpensive surveyor's transit, you can draw your own compass rose. The transit will have a 360 degree protractor as part of its base. You point the transit's telescope at your known landmark and turn the base until the known bearing number matches the direction the transit is pointing. Then you rotate the optics to each of the cardinal points listed on your compass card and have a buddy stand out there with stick and mark or stake that spot. Once you have all of the stakes in place, you tow or taxi your airplane to put the on board compass over the spot that the transit was at, and you follow the procedure in AC43-13.

If you bring some beer for your friends and helpers and invite some other airplane owners to swing their compasses too, you can make a party out of it and everyone's navigation might get a little better too.

You could also invent a procedure where you fly a series of GPS courses and write down the deviations as you fly, and then guess the adjustments when you are back on the ground, but that juggling is likely more difficult to do.

As you note, compasses are important. You haven't lived until you have been out in strange mountains, with nothing but a compass and a sectional chart and your wrist watch, in a bare VFR equipped airplane, with weather coming down, following that compass to a strange airport.

Best of luck,

Wes
N78PS

[dov_elyada]

Thanks, Wes, for your advice. It certainly helped delineate my options.

Let me summarize the options you propose: 1) Fly to an airport that has a compass rose and do it there. 2) Create a makeshift compass rose at my home airstrip. 3) Use in-flight GPS courses as references to adjust by.

Of these, Solution 1 is impractical, because in my country "real" airports with compass roses do not let lowlife "ultralights" in. Solution 3 works only in cases where the crosswind is assuredly insignificant and the ball is not only perfectly centered throughout the pass but also sensitive enough to detect a sideslip of the order of 1 degree. I'm left with Solution 2 -- not easy or immediate, but can be done using landmarks and with the help of such wonders as Google Earth.

As to your suggestion of a Beer & Swing party, I would add that invitees should bring along sleeping bags and other camping equipment to let the beer wear off before they can legally depart.

Dov

[rwanttaja]

Thanks, Wes, for your advice. It certainly helped delineate my options.

Let me summarize the options you propose: 1) Fly to an airport that has a compass rose and do it there. 2) Create a makeshift compass rose at my home airstrip. 3) Use in-flight GPS courses as references to adjust by.

Of these, Solution 1 is impractical, because in my country "real" airports with compass roses do not let lowlife "ultralights" in. Solution 3 works only in cases where the crosswind is assuredly insignificant and the ball is not only perfectly centered throughout the pass but also sensitive enough to detect a sideslip of the order of 1 degree. I'm left with Solution 2 -- not easy or immediate, but can be done using landmarks and with the help of such wonders as Google Earth.

As to your suggestion of a Beer & Swing party, I should add that invitees should bring along sleeping bags and other camping equipment to let the beer wear off before they can legally depart.

Dov

Zack posted the link to my "Hillbilly Swing" article...it sounds like it might be closer to what you need.

http://www.bowersflybaby.com/tech/hillbilly.html

Ron Wanttaja

[dov_elyada]

Yes, Ron, I've seen your Hillbilly post; it's nice and contains a lot of good stuff I might adopt. I'm now working on a variation of my own. When done and successfully applied, I'll let the community know.