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Brian

Magnetic compass

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Didn't know what forum was best for this so I will post it here. I have a new magnetic compass installed. I need to do a calibration/compass card for it. Where can one find a list of airports that have an accurate compass rose? I've looked in the AFD; there is no list in the back of the book (at least the one I have) like the listing for VOR check points. I have looked at specific airports that I seem to remember having a compass rose a decade ago but they don't have any indication of having one now. Either they no longer have one or the AFD doesn't list it.

 

So, how can one find a compass rose?

 

Thanks for your help.

 

Brian

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Most people make their own compass roses now with chalk and your own compass. Laser lines work even better if you want to tech up :P

 

It's not recommended to use a compass near the aircraft while setting it up because electrical systems can skew it. I'm not kidding. We did a demonstration at A&P school and it knocked a compass off a few degrees, and even being near the building did it too.

 

Don't forget to make adjustments to the compensators. Use a brass screwdriver to turn the screws.

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Corey,

 

Thank you for responding. I may be especially thick today but how would that help? Unless my own compass has been certified as accurate at that location, how can I lay out an accurate rose? I'm not a surveyor nor do I have certified equipment. Using my own compass from the camping department would be no more accurate then using the aviation compass out of the box without compensation or a compass card. And, yes, I know about using a brass screwdriver and having everything in the plane running so it is as much like flying as possible. I've been flying for almost 50 years and I've adjusted compasses before but I've always had an airport compass rose available which takes into account buildings and other local magnetic anomalies.

 

Brian

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I made the windsock at Copperhill a GPS waypoint.

 

I then walked a couple hundred feet directly south per the GPS and drew a line on the ramp pointing to it, establishing N/S.

 

Then drew an E/W line perpendicular.

 

My vertical card compass was virtually useless before. After swinging it with that, it seems to at least roughly coincide with the real world!

 

Certainly good enough for government work!

 

Caveat - may or may not be legal for a standard or SLSA. For Experimental, I think it would fly.

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If you know your magnetic deviation you could adjust off a GPS track by taxiing the airplane on all the headings you want to adjust for. Just work backwards from the true course provided by the GPS.

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Corey,

 

Thank you for responding. I may be especially thick today but how would that help? Unless my own compass has been certified as accurate at that location, how can I lay out an accurate rose? I'm not a surveyor nor do I have certified equipment. Using my own compass from the camping department would be no more accurate then using the aviation compass out of the box without compensation or a compass card. And, yes, I know about using a brass screwdriver and having everything in the plane running so it is as much like flying as possible. I've been flying for almost 50 years and I've adjusted compasses before but I've always had an airport compass rose available which takes into account buildings and other local magnetic anomalies.

 

Brian

 

 

If you want to split hairs, many airport compass roses are not surveyed either. If the whiskey compass was a new invention these days, it probably would have required a repair station to do the adjustments too, but the general consensus on this ancient instrument is that any A&P can do it on an approximately true compass using equivalent techniques.

 

To be honest, whiskey compasses are not a precision navigation instrument. Trying to line the plane up correctly on the compass rose exactly in itself is extremely difficult. Even being on the ground will alter the readings.

 

There are self calibrating digital compasses out there that have a number of validity tests and are extremely accurate. I'd personally use one of those.

 

If you do really want to split hairs, one would have a very strong argument that only a mechanic or repair station can swing a compass anyways (I'm not sure if you are either, just stating from 43 App A). It's up to you how far you want to take it.

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It was a simple question.  If I were the OP, Eddie and Tom's posts would have made me glad that I had come to ctflier for information.   

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I don't think there is any problem with Eddie's technique.  The regs specify that you have to have a correction card for your mag compass, IIRC there is no specified procedure for determining the values on the card.

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We used to have one that a local fellow used survey equipment to make, but it is long gone. Like I said above I use the GPS in the airplane and taxi around the ramp. I have done this calibrating the Dynon compass, and it should work for a regular compass too. If you are set on using a compass rose look for an airport with a avionics shop. I would think they would have one.

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