General Navigation question 1

[gphillips134]

a lambert conformal conic chart has a constant of the cone 0.80.
A straight line course drawn on this chart from A (53N 004W) to B is 080 at A, course at B is 092 T.
What is longitude of B?

explaination please

[Aim High]

The formula for Chart Convergency (CC) on a Lambert conformal conic chart is:

CC = dlong x sin P of O

Constant of the Cone is sin P of O calculated for you

Straight lines on Lamberts approximate to Great Circles (GC), so you are looking at a GC. If Initial GC is 080 and Final GC is 092 the convergency is the difference between the two = 12 degrees

Going back to your formula for CC

CC = dlong x sin P of O
12 = dlong x 0.8
dlong = 15 degrees

From 004W you end up at 011E

[Send Clowns]

Aim High's answer is correct, theory is almost right. Sorry to be a pedant!

Chart convergence represents the change in bearing of a straight line drawn on that chart. Earth convergence gives change of great-circle bearing. The question gives the straight line bearings, from which we can work out the change, 12°. This is itself, therefore, chart convergence. The proximity of the straight line to a great circle is not required.

The formula AH used was for chart convergence, so the exact change of longitude is 15° as correctly calculated.