Originally Posted by captaa
Q2(Just wanted to check answer for this one mine is D)
What is the chart distance between longitudes 179°E and 175°W on a direct Mercator chart with a scale of 1:5 000 000 at the equator?
A) 106 mm B) 167 mm C) 72 mm D) 133 mm
Earth distance at equator between A(179°E) and B(175°W)
dLong = 6°E = 6 x 60' = 360'
Departure at equator = dLong in mins = 360NM
Now, scale is 1:5 000 000 at the equator. i.e. 1mm on chart at equator equates to 5 000 000 mm on real earth.
So, we need to find out how many mm on chart is 360NM.
1/5,000,000 = cd/360x1852x1000
cd= 360x1852x1000/5,000,000 = 36x1852/500 = 9x1852/125 =
133mm
Same question solved for 30°N; Unrequired; For practice calculations
Earth distance at 30°N between A(179°E) and B(175°W)
Departure=dLong x cos (Lat) = 360 x cos30 = 311.77NM
Scale at Latitude= Scale at Equator x Secant(Lat)
cd/311.77x1852x1000=1/5,000,000 x cos30
cd=311.77x1852x1000/5,000,000xcos30=577398/4330.1=133.3mm