Quick G Nav Q

[wbryce]

Hello,

I got a loan of some ATPL notes and i'm just trying to understand the concepts of great circle v rhumb line tracks etc.

When you have your Initial track and you use the formula (change of long X sin mean lat) to find convergency, the part thats failing me is the understanding on whether to add the convergency to the initial track to find the final track or subtract convergency to find the final track....

Have i missed something?

Thanks in advance,

[Send Clowns]

Draw a diagram. The bearing must be measured clockwise from a meridian, as true north is taken by reference to the local meridian. Draw a simple graticule, I always use 2 meridians and 2 parallels. Of course the meridians should converge towards the nearer pole, the parallels be curved concave to that pole. Draw a straight line to represent your great circle. You can then see that at one end its bearing is greater than the other. In the northern hemisphere it should be greater to the east, in the southern hemisphere to the west.

This can be summarised by the politically incorrect mnemonic "DI Is Dead". Draw a circle, run a line across the middle to represent the equator. Write D at teh top left, I at the top right, I at the bottom left and D the bottom right. This shows whether the great-circle bearing (or straight line bearing on most charts) is increasing or decreasing in a westerly or easterly direction.

[wbryce]

Thanks SC,

I put a bit more thought into my diagrams, I was drawing them incorrectly. Now I'm able to draw them correctly; it becomes more clearer.

Thanks for your help, lets hope this stays in the ole matter between the ears.

[Send Clowns]

Anytime. Glad it helped

[wessexairways]

SC Knows his stuff........just got me through Gen Nav really well

Cheeeeeeeeeers SC


WA

[Jinkster]

Yer he aint too bad!

[Send Clowns]

I'll not be able to walk through the door if my head gets too big

Pleasure, Wessex, Jinks.