Great circles route?
 

Can anyone explain in plain english the concept of the great circle routes? :confused:

Shortest distance between two points on a flat 2D surface = straight line

Shortest distance between two points on a spheric 2D surface = curve

If in doubt about the latter, get an apple & a rubber band. If you wrap the rubber band around the apple, you will see it describing an a curve on the surface.

Thus: rhumb line = constant true track - great circle = changing true track.

These are the very basics - but hope it helps :8

Cheers,
Empty

more on this in tech log under isoganals and great circles

I had some better graphics to help get my kids' heads around this, but can't seem to find them (the graphics, not the kids' heads). This'll have to do... ( I didn't have an apple or a rubber band, so I had to opt for this approach.)

Imagine Cathay Pacific is enroute from Los Angeles to Hong Kong. On a Mercator projection (flat map) the route might look curved, like this:

http://www.atcmuseum.org/cathay2.gif

However, if you were to look at that same route plotted on a globe, it might look more like a straight line, like this:

http://www.atcmuseum.org/cathay1.gif

Same route, different view.

I, for one, think it is magic.

Dave

great graphics and explanation Av8boy:ok:

This is an excellent thingy to play with...

Great Circle Mapper

av8boy

Nice one:ok:

And when you've got it, you'll be able to answer:

When does a Rhumb line = a Great Circle? :E

thank you for the replies

The Equator? :confused:

Or along any meridian of longitude, i.e. tracking 000T or 180T!

Hes a witch!!!!!!

If there was a VOR at the magnetic pole which radial would you be on if you were at the true North Pole?

The 361 radial

Burn him!

I'd say you are on radial 360, since your VOR at MNPole would have to use TN as a reference to avoid a singularity...

cheers

But in practice, to avoid the need to constantly change heading, the actual route flown is more likely to be a composite great circle route, which is a tad longer but makes navigation easier by flying series of small GC's between lines of longitude which closely follow the true GC arc, usually at around 10degree increments. The heading between the waypoints being averaged out to a single course.

Radial 180!!!

DOH! :D