Gen Nav Chart Q`s

[Lewy Boy]

Got some feedback questions for you Gen Nav fans to have a look at:


On a Mercator chart 47 cm represents 247 nm at 35°S. The scale of the chart is:
Correct answer : 1:1,200,000 at the Equator



An aircraft is at 75°N 140°W steering 330°T. For a grid aligned with the Prime meridian the grid track on a polar stereographic chart will be:
Correct answer : 110°



The rhumb line distance of the 53°N parallel of latitude is measured on a Mercator chart as 133 cm; what is the scale of the chart at 30°S ?
Correct answer : 1:25 000 000

[Send Clowns]

Scale = Chart Distance / Earth Distance

Both have to be in the same unit, so scale at 35°S is

47 / 247 x 1852 x 100 = 47 / 45,744,400 = 1 / 973,285

This is not a common way to express scale so if we divide both top and bottom by 47.

47 / 45,744,400 = 1 / 973,285

There are various ways of changing the Mercator scale, so I won't show you any particular one - refer to your notes. To change the scale to that at equator the denominator (973,285) must be divided by cos 35° to give a scale of 1 : 1,188,161.

Have to work now, but will answer the rest tomorrow if no-one beats me to it. One point: which notes are you using? These should be covered in the notes, and if you ask your instructors they should take you through the techniques.

Send Clowns
Gen Nav instructor, BCFT