Compass Dip

[Fabulous]

Something I came across when buying new gear.

Compass Dip is an issue if you travel between northern and southern hemispheres.

Have you experienced this problem?

 

[jpcpat]

In a Scuba context, not an issue. Outside Scuba, a very small issue.

 

[AggieDad]

Wow! Let me see if I can remember this stuff from 30 plus years ago. First. It is not a problem at all for scuba. 2nd. It is not a problem for pilots either. Without having to dig out my books to give you page numbers in them..imagine the magnetic lines of flux that are around the world from the poles. As your compass (remember now this explanation is EXTREMELY simplfied on a subject that is not complex to begin with) travels on one of these lines of flux it will dip towards the pole. At the equator these lines of flux are at the highest above the earth but there is a smaller dip there. That is where they are probably talking about compass dip. The only thing that would make sense about a compass dip there would be the reversal of the direction of the dip. Now pilots have to deal with accleration and deceleration errors but to be noticeable under water would probably require a scooter and then it corrects itself after a speed equlibrium is attained.
You have magnetic course and a magnetic heading difference due to variation of the magnetic poles vs. the true poles. But today! With GPS nav, internal reference nav etc. we look at the mag compass to make sure that the airplane is headed in the correct direction before takeoff and otherwise I never look at it again. In fact on my airplane it is folded out of view.
Buy your equipment and don't worry about it. If you can stay underwater long enough to have it affect you then you are in a submarine anyway.

Shoot! Now I am sitting here trying to remember the ditties. Lead from east to north lag from east to south????? May have it backwards.

 

[The Kraken]

Boy, that does bring back some memories, AggieDad !!!

the K-opter Pilot

 

[cerich]

actually guys compasses for scuba are made for northern or southern hemispheres.

The both work in the other but they are not as accurate.

AggieDad, in the northern hemispher entering aturn from a north heading the compass shows a turn in the opposit direction, from a south heading compass turns in proper direction but leads the turn until on a heading ofeast or west.
Acceleration in the northern hemisphere the compass swings towards the north and south on decel. Greatest error on east-west headings, least on north south. Acronym ANDS (accelerate north, decelerate south) In the southern hemisphere it is opposit.

 

[AggieDad]

I remember that now. The solution is to always have lots of gas to find yourself after you get lost.

I was not aware of the compasses built for different hemispheres. Learn something every day. Thanks.

Now, I will just return to programming my Inertial Nav System and turning on the autopilot for the next 11 hour flight. The real fun flight though is a map, a wet compass and a watch.

 

[AggieDad]

Boy, that does bring back some memories, AggieDad !!!

the K-opter Pilot

I always just averaged the swings and used the TLAR method of navigation.
That looks about right.

 

[cerich]

A little more research and I remeber the exact variations...

Why compasses are different in the different hemispheres has to do with spherical geometry. In the Northern Hemisphere, a small counterweight is placed on the north seeking end of the compass needle such that the needle will be parallel to the earths surface and perpendicular to a line drawn from the centre of the earth to the position of the observer on the earths surface. In the Southern hemispere the converse applies and a counterweight is positioned on the south seeking end of the needle. That is why they only work in one hemisphere.

Our avaition compasses are all built to work in both.

 

[cerich]

I remember that now. The solution is to always have lots of gas to find yourself after you get lost.

I was not aware of the compasses built for different hemispheres. Learn something every day. Thanks.

Now, I will just return to programming my Inertial Nav System and turning on the autopilot for the next 11 hour flight. The real fun flight though is a map, a wet compass and a watch.

cool toys...

Todays real world GA instrument flying in "steam" gauge aircraft, make sure aircraft has passed IFR recert in last two years, verify all steam gauges work properly, make sure the cigarette lighter outlet works for yoke mount GPS and you have plenty of spare batteries and fresh ones in the unit. Get very confused if GPS breaks.:huh:

Thats why GA pilots just seem to love the cirrus, let it fly for you, if the glass stops working just pull the chute! Then again that may be why so many are killing themself flying the Cirrus....

 

[The Kraken]

For us it was "needle, ball, airspeed and "Hey, didn't we fly over that crater a little while ago?""

the K