Q about magnetic compass'

[MarkColeman]

You know those questions in general nav and instruments about accellerating and decellerating in n/s hemispheres? Where you get a turn to the north or south etc.

Anyone have a good way to remember these? Would be appreciated!

[mcgoo]

ANDS = Accelerate North Decelerate South
SAND = South Accelerate North Decelerate


UNOS = Undershoot North Overshoot South
ONUS = Overshoot North Undershoot South

Top lines = Northern Hemisphere
Bottom = Southern Hemisphere

[MarkColeman]

that looks good, im a bit confused though, can it be applied to the following question:

Q: When accelerating on an easterly heading in the Northern hemisphere, the compass card of a direct reading magnetic compass will turn:

A: Clockwise giving an apparant turn towards the north

Accellerate north, undershoot north right? So on an easterly heading if it undershoots it would indicate a turn north i can see that, but would it not be anticlockwise?

[dumdidum]

How about figuring out first WHY the compass acts as it does and then deriving the correct answer from there. No need to memorize anything.

Start from the weight that needs to be added to the compass, why that weight is needed(magnetix flux, there you can derive where the weight needs to be when used in northern/southern hemisphere) and then remember the energy conservation law... and there you go.

[THRILLSEEKER]

The compass card turns clockwise:

If you imagne the compass card in your head, say 090 as the selected heading, therefore to the left of 090 would be 089 and to the right 091. If you accelerate in the NH then the card shows a turn to the North. To do this the card must turn clockwise to bring 089,088,087 etc... to the selected heading.

To hopefully hammer this home, imagne a standard compass you used when young. If you accelerate in the NH on a headng of 090 the needle would move to the left to indcate a turn to the North, the standard compas has a non moving card as the needle moves. A compass in an a/c has a moving card and therefore to show a neelde turn to the left the card must turn to the right.


Another way to remember which way the neelde would move is thus:

An acceleration shows a turn to the nearer pole
A decelleration shows a turn to the opposite pole

Ie. In the SH an acceleration shows a turn to south and decelleration a turn to North

Hope this helps


Thrillseeker :p

[llanfairpg]

SD NI

Southerly decrease

Northerly increase

[MarkColeman]

thanks guys thats great help