Gen Nav Question Help

[Phenom100]

Hi Guys (& Girls)

I Need help on the following question:

The Great Circle distance from A at 57'00N 012'30W to B 57'00N 167'30E is

A: 1980nm
B: 6840nm
C: 5882nm
D: 3960nm

I work it out to be 5882nm, but the answer is given as 3960nm????

012'030 + 167'30 = 180'00
180 x 60= 10800
10800 x cos 57 = 5882.10nm

is 5882 the Rumb line distance?

Any help would be much appreciated

Cheers
Danny C

[Sharky12t]

Hi Danny,

Seen a lot of these questions lately:

Trick is you're not going East/West but North over the pole, your two Latitudes are exactly 180deg apart.

(55N to 90N) up to the pole then (90N to 55N) down again gives 66deg

66x60' is 3960nm.

The way you calculated is the rumb line distance.

Hope this makes sense, it's difficult enough to explain in person.

Good luck,

Sharky

[Phenom100]

Hey thanks Sharky,

It makes sense now, this is my first week at Nav and i'm pulling my hair out over it.

Your a star, i have a few other's which l may need help on. so keep a look out.

Thanks once again

Danny

[BlueRobin]

Draw the longitudes out on a circle with the prime meridian at the bottom. You can then work out which is the shortest way. Otherwise if using mental gymnastics and doing it your head, you may find that when stressed the mind will fail.

[Sharky12t]

Glad to be of help bud,

As BlueRobin says, diagrams are always the best way to go unless you're really good at visualising the earth. Be careful when in the Southern Hemisphere or round the back of the world though (apologies to any antipodeans or people in the Pacific region) I find even the diagrams get tricky to draw in these areas.

I'm in week 11 now so if you've any questions I'll hopefully be able to lend a hand, where are you studying?

Sharky

[Stumpyotoole]

Gen nav is never as bad as you think - you just have to draw the f-ing diagram!!