Drift and transport wander

[Staaf25]

Hello all,

For my study had to investigate the basic six instruments. I had to find out what a gyroscope is and what the properties are.

I know what drift and transport wander is but the thing that is not clear to me is to what sort of gyroscope the 2 properties relate, horizontal gyroscopes or vertical gyroscopes.
Second thing that is not clear to me are the terms "local north" "local vertical" and "local east". Maybe someone has a site with an animation or clear figures.

Thanks in advance:ok:

Lars

[rudderrudderrat]

Hi Lars,

If you look at a globe of the Earth and if you have 3 gyros set with their axis at right angles to each other (X,Y,Z) and spin them to speed at some moment on on the equator, then if X is aligned towards the North Pole Star, Y is pointing East and Z is aligned vertically to earth, then you have your described your "Local" axis.

6 hours later, when the Earth has rotated through 90 degs, relative to an observer on Earth, your original original North axis (X) is still pointing North, your original East axis (Y) is now pointing vertically and your original vertical axis (Z) is now pointing West.

I could try a similar one at the North Pole and at mid Latitudes on the Earth - but my brain hurts.

[Staaf25]

So the term "local" is just the term used for the position of the rings at a certain point of the earth? For instance if i set up a gyro here, and let the spinaxis pointing to the north, that is called the local north position of the gyro?

Do u happen to know to which type of gyro transport wander relates to?

Thanks so far!

[rudderrudderrat]

Hi Lars,

Have a look at :

Transport Wander of a Gyroscope (http://www.sphaera.co.uk/transport_wander.htm)

As far as I understand it, "Local" will have to be defined as position and time on the Earth (because it's rotating).

Good Luck.

[Staaf25]

I'm familiar with that site, and that brings up another question: Why does transport wander only effects when gyros are transported E-W or W-E?

[davecfm56]

How about getting a globe and some pencils and lable the pencils N-S E-W and UP-DOWN hold them fixed in space and move them around the globe/ball/friends head.

Might be better to see it like that rather than an animation?

Just an idea.

[rudderrudderrat]

Hi Lars,

It's because of the shape of the Lines of Longitude as you approach the Poles.

At the Equator, Longitude lines are parallel to each other and at right angles to the Equator (Latitude Zero). So there is no transport wander.

Now imagine a flat map of the North Pole looking like a dart board (a Polar Projection, with the bull representing the N Pole). Keep your pencil pointing to some distant point and move N - S over the dart board. No change in heading apart from flipping due South as you cross the Pole. Now move E - W, you'll see big changes in heading (with ref to the Longitude Lines).

[Microburst2002]

Hi

A gyro has an axis which maintains its direction in space constant. As if it was pointing at a star (we can consider the fixed in space) all the time, regardless of the motion of the gyro.

So if the earth rotates, the gyro apparently wanders because it will keep pointing the "moving" star.
Similarly, if you move from point A to B, the path is curved because the earth surface is curved, so the gyro will apparently move, always pointing its beloved star.