Convergency question
 

Has anyone got any rules of thumb or methods which help working out if the angle is plus or minus when you come to apply it at the other end of a great circle depending on the hemisphere etc.

Some how this afternoon i have managed to beat proberbility and get it wrong at least 75% of the time. Right numbers but applied in the wrong direction.

Anyway back to Airlaw to see if i can beat my previous record of 45mins study without losing the will to live and falling asleep.

MJ

The way I was shown was to make a little sketch,not to scale.Start with a horizontal line,this represents the GC track.If track is generally easterly then start point is on the left going to the right.If track is generally westerly then you start on the right and go left.Now draw in two vertical lines to represent the meridians,slightly converging if in the northern hemishere and diverging if in the southern hemishere.Work out your convergency....look at the diagram if the final angle is larger than the start angle add the convergency,if it is smaller then subtract it.Hope that makes sense.
That`s how the great god Alex W. advises to do them and certainly helps a thickie like me.Good luck. :)

M_J
Tried to email you but it was returned. Count me in for the room re: Gatwick seminar (pending selection of course). Having a bit of trouble with convergency myself.

Cheers

Flying Kiwi

As Delta Wun Wun ppointed it out. Do it the Alex W way. You can't go wrong. The sketch hasn't got to be to scale or indeed exact angles, but it gives you the answer every time. :D

I agree with D11 - this is how I teach my students to do this. Any more questions, email - I am a nav groundschool instructor, and happy to help!

Thanks people, give me a couple of day to play with it. Send clowns thanks with your offer i will take you up on it if i hit the stops again.

I find that the more effort i put into working it through my mind the more conceptal understanding i have. Which means it is with me for life instead of just for the exam.

thanks again

MJ

don't remember any convergency problems during my ppl, more an atpl theory problem

Nunos and whats your point?

if i had my bloody books i'd have trouble i wish i was a prepubescent oats pilot

Yep,Alex's method works. In case Delta Wun Wun's explanation isn't completely clear - your two vertical lines need to converge towards the pole. And it may help to put in your rhumb line track as a curve on the equator side of the great circle (hint from Baz, Alex's right hand man: "rum comes from hot countries, ie near the equator"!). Then you have the whole picture and it should be obvious whether to add or subtract; hope so anyway, but if this just confuses the issue then ignore it.