Compass Correction/Deviation Card

NordicDave said:
It's very difficult to know the 1-4º of variation that needs to be documented on the compass card from a painted marking.
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FYI: if talking about your mag compass it's +/- 10 degrees error allowed to be documented on the correction card.
NordicDave said:
from a painted marking.
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One of the tricks to using a compass rose is to line up the main wheels on the opposite cardinal heading paint lines. Once you have your N/S-E/W magnets set then use a ground spotter to put your nose on the remaining compass points.
 
bnt83 said:
I don't see how any tool could be used to calibrate a compass.
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There's some equipment out there that generates its own calibrated magnetic field to test aircraft systems. But I've been using a master sight compass for years. I find it much easier. But your correct you have to understand the magnetic signature of area you're using, however, there's some tricks to check the area. To use the sight compass, we would either use an un-calibrated compass rose area or fly to a grass strip or if possible taxi onto a grass area at an airport...with permission of course. Some airports have dedicated "non-magnetic" areas but no compass rose due to the cost of maintaining it.
 
Bell206 said:
That's the point. He's not duplicating the card as he doesn't have the original heading compensation values.
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With out an old card, how would you know if he was duplicating or not? prove the new card ain't just like the old one.
 
Bell206 said:
One of the tricks to using a compass rose is to line up the main wheels on the opposite cardinal heading paint lines. Once you have your N/S-E/W magnets set then use a ground spotter to put your nose on the remaining compass points.
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Another trick is to use a 2x4 laid across the desired heading +/- 90° and let the tires just kiss the edge of the 2x4 to line up nearly perfectly.

Jim
 
Bell206 said:
One of the tricks to using a compass rose is to line up the main wheels on the opposite cardinal heading paint lines. Once you have your N/S-E/W magnets set then use a ground spotter to put your nose on the remaining compass points.
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Any reference against a set of painted lines is difficult. A fraction of an inch off the line is an error in establishing the deviation for a particular compass. Only a magnetometer can provide single degree accuracy. Who even knows the painted rose is within 1%?

Compass roses are great for a pilot to see if they have a significant issue or pointing in the general direction to set-up the magnetometer.

-David
 
one of the few times I totally agree with tom.i find this happening more often as of late.my head is full of f..k.
 
bnt83 said:
Each mark being 5 degrees, its easy enough to get under 4 via eyeballs. Drive around the compass rose again and its easy to see that it is repeatable. It can be a lot easier with a tech outside helping the driver get lined up, (second tech is SOP where I work)

Did the same after calibrating a G5 HSI, compass rose works well.

Without someone actually coming out and testing an area for magnetic disturbances on schedule, I don't see how any tool could be used to calibrate a compass.
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That's why a calibrated magnetometer is needed. A decent avionics shops will provide very accurate deviations. Some of my major cardinal coordinates are 4% off. Even with a compass with 5º increments this is important. In my opinion with a 4º deviation, shouldn't you want to know what side to the marking is accurate?
 
Heck, I just used a prismatic compass taped to the turtledeck. Helps to have a wood airplane...and an experimental certificate.
swing.jpg

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

Ron Wanttaja
 
Bell206 said:
FYI: if talking about your mag compass it's +/- 10 degrees error allowed to be documented on the correction card.
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A 10º documented deviation allowance, is not 10º of slop allowed. For me, If a compass has a heading on it the plane should fly in the direction it is pointing after compensating for magnetic variation and compass deviation. 10º of slop after an hour of flying and the plane is way off course.
 
By the time you do all the above...........inaccurate, time consuming, right out of the 1940's methods..........you could make compass correction cards for 10 airplanes using a GPS. Sheesh!!!
 
wanttaja said:
Heck, I just used a prismatic compass taped to the turtledeck. Helps to have a wood airplane...and an experimental certificate.
swing.jpg

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

Ron Wanttaja
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The prism compass is better than lining up on painted lines, however magnetic deviation differences between the ship compass and the prism compass compound the actual deviation error of the ship board unit. e.g. prism compass off +3º north and ship compass also +3º ends up with +6º error rate rather than 3% a magnetometer would have indicated.

I fully realize I'm pushing a rock up a hill with a wet noodle concerning DIY deviation measurements having a high error rate. I get it. There are a number of pilots who just don't care. I get that too.

For those who want an accurate compass card, a magnetometer measurement by an Avionics shop is needed. For me the $80-100 is well spent to have a proper log entry and factual deviation card.
 
Tom-D said:
prove the new card ain't just like the old one.
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Not my concern. The OP asked and I gave him the guidance as I would have given any one else who asked. Whether they follow it is up to them. There is guidance that is technically acceptable and guidance that is not. It's not rocket science.
 
So just call an avionics shop? $80-$100 don't sound bad. I can't hardly read mine, I'm thinking it too may be 72 years old! It's my only built in navigation tool, and seriously been thinking of scrapping foreflight and get pencil and sectional out. I enjoy the "classicness" or her, and her simplicity- kinda always seems like cheating when I pull the iphone out and follow the magenta line. Come on, they paint town names on water towers for a reason1 :)
 
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