The Mercator Chart

Question 1

On a mercator chart, a rhumb line appears as a -

Answer 1

straight line

Question 2

On a mercator chart, convergency at the poles =

Answer 2

zero. There is no convergency on a mercator chart

Question 3

Meridians on a mercator chart is -

Answer 3

parallel straight lines

Question 4

The scale of a mercator chart is only correct at the -

Answer 4

equator

Question 5

On a mercator chart, great circles are -

Answer 5

curved towards the poles

Question 6

The mercator latitude limits are -

Answer 6

75 N and 75 S

Question 7

Scale calculation:

Latitude = 60 N
scale at the equator = 1:1 000 000

Answer 7

1 000 000 x cos 60 = 500 000

The scale increases towards the poles

Question 8

Scale calculation:

The scale at 30 S is 1: 1 000 000

What is the scale at the equator?

Answer 8

The scale decreases towards the equator:

1 000 000 / cos 30 = 1 154 701

Question 9

In order to convert a great circle bearing(radio bearing) to rhumb line bearings, what must be applied to the great circle bearing?

Answer 9

Conversion angle

Question 10

Radio bearings on a mercator is a -

Answer 10

great circle track which is curved(towards the poles)

Question 11

Before applying the relative bearing, magnetic heading or compass heading must first be converted to -

Answer 11

True.

Question 12

When the scale increases, the value?

Answer 12

reduces

Question 13

When the scale decreases, the value?

Answer 13

Increases

Question 14

On a mercator, the scale increases towards the?

Which means the value?

Answer 14

poles

Decreases

Question 15

On a mercator, the scale decreases towards the?

Which means the value?

Answer 15

Equator

Increases

Question 16

when a problem includes longitude difference, what formula should be considered?

Answer 16

Departure formula

Question 17

How to calculate:

Determine the distance in cm between meridians 1 degree apart on a chart the scale of which is 1:2 000 000 at 40 N

Answer 17

60( the distance) x 185 300cm x cos 40 / 2 000 000

Question 18

How to calculate:

On a Mercator chart the distance between meridians 173 W and 177 E is 33cm. The latitude at which the scale is 1: 3 000 000 is?

Answer 18

1. First find the difference in longitude:

Remember that whenever you add longitude, and it results in a value, you must subtract 360.

177 + 173 = 350

350 - 360 = 10

2. Find the corresponding distance of 10 degrees and the scale:

10 x 60 = 600nm

Which means 33cm = 600nm.

600 x 185 300cm = 111 180 000cm

now 33cm = 111 180 000cm

111 180 000cm / 33 = 3 369 090cm

the scale is 1:3 369 090

2. Use the ABBA formula:

Denom A x cos B = Denom B x cos A

= 3 369 090 x cos B = 3 000 000 x cos A

Thus, 3 000 000 / 3 369 090 = cos 0.89

Inverse of cos 0.89 = 27 degrees.

Question 19

Which trig function should be utilised with mercator scale problems -

Answer 19

cos of latitude

Question 20

All charts used for navigation must be -

Answer 20

orthomorphic/conformal (plotted bearings are correct)

Question 21

How to solve.:

An aircraft in the southern hemisphere obtains an RMI bearing from a VOR station of 058°. Station variation is 22° E, variation at the aircraft is 19° E. The deviation is 2° W and the conversion angle between the aircraft and the VOR is 4°. On a mercator chart the bearing to plot from the station is:

Answer 21

First of all, only the conversion angle and the VOR variation apply. The bearing obtained need to be converted to true, since all maps are true and not magnetic.

The aircraft heading is irrelevant, since we do not need the aircraft’s heading in order to plot QTE from the station. Thus, compass deviation is also irrelevant.

The received bearing = 058° + 22 = 080. Therefor relative to the beacon the aircraft is roughly to the west(080 + 180). Draw a diagram with straight meridians.

On the mercator chart, a rhumb line will be straight, which is also the required track in this question.

The great circle track will be a curved line bias to the poles, draw it.

Now we can apply the conversion angle.

first take

Question 22

will the change of long of two points on the same parallel differ with latitude on the mercator?

Answer 22

No, since the meridians parallel. No convergency with latitude.

Question 23

How to solve:

An aircraft flying due east along the 20°N parallel covers a distance of 14cm in 27 minutes on a Mercator chart, The scale of the chart is 1: 1 000 000 at 35°N. the aircraft’s ground speed is:

Answer 23

the corresponding earth distance of 14cm at 20°N, 35°N and at the equator, without multiplying or dividing by the cos(lat), differ significantly (scale not constant). The reason we use the scale formula is to find the actual scale at a given latitude, I.E the cosine of lat rectifies the scale error, and thus provides the actual corresponding earth distance.

First find the equator scale:

Remember that scale decreases towards the equator(value increases) and increases towards the poles (value decreases).

scale at the equator = 1 000 000 / cos 35° = 1 220 774

scale at 20°N = 1 220 774 x cos 20° = 1 147 152.

scale at 20°N = 1: 1 147 152

14cm = 16 060 140

14cm = 86.67nm

86. 67 / 27min = 3.2nm per minute
87. 2 x 60 = 192nm per hour.

= 192knots.

Question 24

For mercator radio bearings, always apply convergency & variation where -

Answer 24

the bearing is measured

Question 25

For mercator radio bearings problems:

VOR & VDF:

Should the convergency and variation be applied at the VOR or aircraft?

Answer 25

The VOR, since that is where the bearing is measured from.

Question 26

For mercator radio bearings problems:

For relative bearing problems only, the order of operation is -

Only the reciprocal is valid of a?

Answer 26

True heading + RB = GC QUJ +/- CA = RL QUJ +/- 180 = RL QTE

RL

Question 27

For mercator radio bearings problems:

NDB:

Should the convergency and variation be applied at the NDB or aircraft?

And the reciprocal should only be applied to the -

Answer 27

The aircraft, since that is where the bearing is measured from.

RL

Question 28

What should be applied to an RMI NDB bearing in order to find the QUJ?

Answer 28

Deviation and variation, relative bearing is already applied.

Question 29

The difference between an RMI NDB bearing and ADF bearing?

Answer 29

The RMI bearing is QDM, the ADF bearing is a relative bearing i.e aircraft heading should be applied in order to find the QDM.

For the RMI, we still need to apply deviation and/or variation at the aircraft(always at the aircraft for an NDB)

Question 30

Should deviation and variation be applied to an RMI NDB bearing in order to find QUJ?

Answer 30

Yes.

Question 31

When doing mercator radio bearing problems:

In order to plot a radio bearing, do we require a GC or RL?

Answer 31

A RL(straight line)