Compass Swing Procedure

About to swing the whiskey compass in my recently completed RV-8. 43.13-1B CHG 1 says to do it with engine at 1700 rpm & electrics on and in cruise attitude.

Getting the tail up and moving it for alignment is bad enough, but with the engine running - look out.

How have other tail dragger RVs done it?

the ugly truth

ok, I'll bite.

from talking to many EAB flyers; the straw poll looks like this.....

1. don't even bother
2. do it in flight
3. do it on a compass rose, with everything off.....then compare to GPS in flight, calm day, fly over known surface grid

if it ain't broke, don't fix it.

sadly, one of the compass rose's within 100 miles had a fuel tank put almost on top of it. probly no effect tho', right?

ever read the specs for an engineered 'rose'?
brass rebar, buried in the concrete slab, 400 yards from the nearest electric conduit or metallic object, radio source, or Tim Hortons?

sorry, was that helpful? I don't mean to say I take it lightly....just.....well......

I've done mine on the ramp with a good compass taped to the wing, and a plumb-bob water bottle dangling from the tailhook, really helps the alignment picture.
I put tape on the ground when oriented N S E W, and then checked on repetitive rotations.
then checked on the compass rose
then in flight

absolutely, positively, nailed it accurately, + or - the mandated 10 degrees, every time.

http://www.faa-aircraft-certification.com/compass-swing-requirements.html

sorry, unable to find the same thing on the Transport Canada site after searching for an hour!

I've done it in my production taildragger without lifting the tail and with the engine running and the electrical system all active. The results appeared to be accurate in flight.

The main thing, I think, to be sure of is that the compass card is free to swivel in the 3-point attitude.

All of my experience doing this has been with the older style compasses. I don't know if this works with the newer vertical card ones.

Dave

Swinging the ole Whiskey Compass

Had instructions, compass rose-nicely painted, brass screw driver, and myself....with a Dynon d100.......dang..hot summer day, and thank goodness for an air/water cooled Rotax....Lyc and Con would have been hot with all the pirouetting I did...Well I got close kinda sorta, felt like with all that going for me and some simple instructions I would have nailed it and went on to something more exciting like chasing sparks.....after about 20 evolutions or would that be revolutions around that **** thing...I called it quits....went out and bought a plane without one....there...."where there's a will there's a way".........I Trumped it!

I do mine in the air using the GPS and the Autopilot. Just be sure to use Heading, not Track.

Seems to me to be more accurate than using a compass rose that was put in place many decades ago - the deviation since then makes it quite inaccurate to start with. I don't cruise at 1700 RPM so if that makes a difference it would add more error, and obviously I am in the proper flight attitude when I check it.

SMO said:

I do mine in the air using the GPS and the Autopilot. Just be sure to use Heading, not Track.

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Mark - just curious, how do you determine the heading without a calibrated compass?

Roads

I think most roads run true north and south, and due east and west. Why can't you fly along the road (same heading, not same track) and add magnetic deviation?

PilotjohnS said:

I think most roads run true north and south, and due east and west. Why can't you fly along the road (same heading, not same track) and add magnetic deviation?

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That makes sense, at least in places where roads are laid out on a grid. You could measure the road orientation on a topographic map to be sure.

Alan Carroll said:

Mark - just curious, how do you determine the heading without a calibrated compass?

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I have a Garmin G3X with a magnetometer. It requires a one time calibration, and the only requirement in order to calibrate it is to have a place devoid of magnetic interference, and to know where north is within 5*. I believe this is the same or similar requirement for other magnetometers.

Given that has been done, I can set my autopilot to fly the various headings required to calibrate my compass, which has to be checked for compliance annually in Canada.

So, I guess my magnetometer is my "calibrated compass".

What I did

Many airports have a compass rose painted on the ground..ours does. Its a good way to get a fairly accurate setting. As others said, engine running, everything in flight mode. In m y -4, I never got mine to work well, so my final "swing" was overhand, into the woods...I never looked back and don't miss it a bit.

SMO said:

I have a Garmin G3X with a magnetometer. It requires a one time calibration, and the only requirement in order to calibrate it is to have a place devoid of magnetic interference, and to know where north is within 5*. I believe this is the same or similar requirement for other magnetometers.

Given that has been done, I can set my autopilot to fly the various headings required to calibrate my compass, which has to be checked for compliance annually in Canada.

So, I guess my magnetometer is my "calibrated compass".

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Now I get it. I'd guess that since the magnetometer doesn't have a moving magnet its lets sensitive to position-based errors during calibration (for example tail up vs. down).

Use your flight supplement and a runway.

Champ said:

About to swing the whiskey compass in my recently completed RV-8. 43.13-1B CHG 1 says to do it with engine at 1700 rpm & electrics on and in cruise attitude.

Getting the tail up and moving it for alignment is bad enough, but with the engine running - look out.

How have other tail dragger RVs done it?

Click to expand...

Providing you have a wiskeycompass that is free to pivot with the tail down,just make a slow taxi down your runway centerline. Your current flight sup will tell you to the nearest degree, what the mag heading of the centerline is .