Compass Errors

[uwochris]

Hey guys,

Can someone please explain "why:"

1. The acceleration/deceleration errors are zero when on a heading of North or South.
2. The turning errors are not a factor when on a heading on East or West.

I know the errors associated with the compass, but I do not understand "why." Since I will probably be teaching this stuff soon, I hope someone can pass along their knowledge.

Thanks in advance,

Chris.

 

[Snakum]

1. It doesn't occur when flying exactly North or South because the magnet weight in the compass is in line with the line of flight.

2. There actually is an error turning from East or West, also related to magnetic dip. You get an increasing lag/lead error as the turn completes.

Minh

(I been stud'n )

 

[mar]

More on the dip

Maybe you already know this:

Magnetic dip is when the compass magnet tries to align itself with the Earth's magnetic lines. Briefly, they're mostly parallel to the surface of the earth near the equator but angle quite sharply near the poles.

Imagine a drawing of the earth with a magnet through it representing the poles and the magnetic lines drawn from pole to pole.

I bet if you do a search on the internet you'll find better stuff than I'm spewing here.

Gotta run.

 

[siucavflight]

If you are already on north and accelerate the airplane how can the compass turn north? It cant.

 

[Mmmmmm Burritos]

The effect of the compass weight is still there, but it doesnt cause the compass to change heading. If you are on a north or south heading and accelerate or decelerate, it will cause the compass card to move up/dowm slightly. But it doesnt change heading since the magnet and weight are in line with the airplane's heading.

 

[uwochris]

Thanks for the responses.

I am still a little confused when you mention the compass "weight." Is this synonomous with the compass's CG, which is offset to prevent dip?

 

[MarineGrunt]

Thanks for the responses.

I am still a little confused when you mention the compass "weight." Is this synonomous with the compass's CG, which is offset to prevent dip?

Correct. The compass has a small weight on the "south" side to offset some of the dip error. When an airplane accelerates/decelerates, the magnet's inertia will cause the compass to move.

Note: This is for magnetic compasses made for the northern hemisphere. Ones made for the southern hemisphere have the weight on the north side, so it's effects will be the opposite.

 

[Snakum]

Note: This is for magnetic compasses made for the northern hemisphere. Ones made for the southern hemisphere have the weight on the north side, so it's effects will be the opposite.

Wow ... now that's something I didn't know. I guess I never really thought the process thru, because now that question is obvious.

Thanks, from me, too.

Minh

 

[ROB-x38]

When remembering where the CoG is in relation to the pivot point you can either picture the magnetic field lines curving into the magnetic poles, and therefore which way the compass will dip

or

just remember the CoG is always displaced towards the equator