G Nav Questions - 2

[ABO944]

Hi

Need help on these questions please ...

On a Mercator chart a straight line is drawn between point A (34 23'S 007 00'W) and point B (34 23'S 009 00'E). Use this info to answer following...

The chart distance of the line is 83cm. The scale of the chart at 34 23'S is:-

a) 1:954,000
b) 1:1,772,000
c) 1:1,160,000
d) 1:2,150,000

--------------------

The scale of the chart at the equator is:-


a) 1:954,000
b) 1:1,772,000
c) 1:1,160,000
d) 1:2,150,000

-------------------

The rhumb line track from A to B is:-

a) 090 T
b) 090 M
c) 270 T
d) 270 M

-------------------

The great circle track from A to B measured at A is:-

a) 086T
b) 090T
c) 094T
d) 099T


Any help will be greatly appreciated !

Best regards,

Seabass

[Send Clowns]

Scale = Chart length / Earth Length

Chart length = 83 cm
Earth length is departure = ch. long (minutes) x cos lat = 16 x 60 x cos 34°23' = 792 nm

change to centmetres : 792 x 1852 x 100 = 146,728,000 cm

Scale is 83 : 146,728,000 however should be expressed as 1 : something so divide both sides by 83. Scale is then 1 : 1,768,000.

----------------------

For scale at the equator divide the denominator of the scale (the "1,768,000" bit) by cos of the latitude.

1,768,000 / cos 34°23' = 2,142,000. Scale is 1: 2,142,000

---------------------

They are at the same latitude, rhumb-line track must be 090° or 270°. B is further East so track is 090°.

--------------------

The rhumb-line track is 090°. If you draw a diagram the great-circle track at A is greater than the rhumb-line track. The difference is conversion angle.

C.A. = 0.5 x ch.long x sin mean lat = 0.5 x 16° x sin 34°23' = 4.5°

90° + 4.5° = 94.5°

Any better answer requires diagrams, so you should contact your training povider. Best of luck!

Send Clowns
Gen Nav instructor, BCFT

[Hulk]

here my answers:

departure: 16 degrees*60miles*cos 34=794 miles
794miles*1.852=1470 km
1470000m:0.83=1772000

answer B.
-------------------------------------------------------


then the scale contract at the equator(biger) and expand away from equator
1772000 : cos 34=2137418

answer D

--------------------------------------------------------
rhumb line 090T

answer A

----------------------------------------
last question: we are in the south!!!

16 degree * sin34=9 degrees
9:2=4.5 degree
090+4.5=94.5 degree

[Alex Whittingham]

Just a small point ABO, you're meant to be doing these progress tests yourself!

[Hulk]

Well, It is written nowhere you have to do the progress tests by yourself. So ABO is in his right to post his homework, and it is good for us , it makes us safer, exactly what the CAA/JAA wants...;)

[TurboJ]

Full marks for initiative ..............