Gen Mutley's Gen Nav Questions
 

I have a couple of questions but will start with this one -

What is the final position after the following rhumb line tracks and distances have been followed from position 60degrees 00minutes N 030degrees 00minutes W
South for 3600nm
East for 3600nm
North for 3600nm
West for 3600nm

Answer - 60degrees 00minutes N 090degrees 99minutes W

Could someone explain simply how this answer is reached - thanks.


Question 2!!

The rhumb line track between 45degrees 00 minutes N, 010 degrees 00 minutes W and 48degrees 30 minutes N, 015degrees 00minutes W is approximately -

Answer - 315degrees.

A simple explanation would be much appreciated.

Thankyou all :ugh:

The first answer is the departure formula , a quick look shows that it puts you down on the equator where as you travel east and then back up the meridian you wouldnt use departure (ch long x cos lat) BUT as you come back west you would then use the departure formula and so you will not end up where you started due to the earths spherical shape (hence using departure)

The second question i remember ( and had on my exam in March) but cant recall the answer , Bristol do have the full explaination on the databank tho , it just involves you drawing it out , the other 3 answers are obviously wrong when you draw it.

Hope this isnt too garbled im having 2 mins from Met and Instruments but both explanations are on the DB :bored:

DW

Thanks for taking time to reply. Im trying to decipher the depature formula etc but it really isnt too clear to me!!!!
thanks again

Rhumbline question
 

Sorry to ask you all again but....

Given -
A is 55degrees N 000 degrees
B is 54degrees N 010 degrees E
The average true course of the great circle is 100 degrees. The true course of the rhumbline is....?

Answer - 104 degrees.

Can anyone explain what I am supposed to do please?

Thankyou :{

Yes, the second question just needs a simple diagram. Don't think too deeply!

The first:

S for 3600 nm takes you to the Equator
E For 3600 nm takes u to 30E
N for 3600 nm takes u back to 60N
W for 3600 nm at .5 (cosine 60 degs) is twice the number of degs, or 90W

Phil

BTW - that was all in the notes ;)

question 2 is sorted, question 1 has me stumped!!!

Again, draw a diagram. You can eliminate 2 answers from the choices see below) without working anything out due to the relative positions of great circles and rhumb lines. For the audience, the choices are:

107
100
096
104

phil

Working back dont forget to rearrange the formula..........

3600 divide by 60 = 60 divide by cos 60 = 120

30 degrees east travelling west for 120 degrees = 90 west

When you have the departure distance you have to divide , i really dont know how i passed with 86% but i did , make sure you nail the crp-5 tho that will get you over 50% of the marks !

hope this helps

A long time ago, in a galaxy far, far away...
 

You go south to the equator from 60 degrees north (3600/60 = 60 degrees; on a meridian, so no complications).
you go east by another 60 degrees (3600/60 = 60 degrees; on a horizontal meridian, the equator, so no complications).
you go north by 60 degrees (3600/60 = 60 degrees; on a meridian, so no complications).

If you draw this (just rough, nothing exact) you will see that you are on the same latitude as the start point, but 60 degrees to the east of your original longitude, ie 30 east.

Head west 3600 nm at 60 degrees north? You are looking for the change of longitude, so apply departure: (3600/60)/(cos60) = 60/0.5 = 120 degrees west from 30 degrees east = 90 degrees west.

I hope.

Thankyou all. I can do this now - .
Cheers for your help :ok:

Good Gen Nav book???
 

Can anyone recommend a good, plain english ATPL gen nav book. I see oxford do one as do CAT but would be interested in your thoughts.
Thankyou:)

No picture needed and the answer based on your wording is actually 100.
The question is basically testing your definition knowledge.

The question states AVERAGE GC = 100 this means half way which is exactly the same as the rhumb line. Remember a rhumb line is constant bearing and is also the same as average great circle.

IF the question had stated INITIAL GC tk 100 then 104 would be correct.

Is there anyone out there who can explain this to me in really 'Simple' terms please. I know this must be easy once you know what is going on but at the moment I dont!!!lol

Try this:-
On your North Atlantic Plotting Chart 27th.
Draw a straight line (great circle as it's a Lamberts) from
Tiree N56:30 W007 to Oystr N54 W055

Now measure the INITIAL GC at Tiree - should get 284
Now measure the FINAL GC at Oyster (might have to extend line)
should get 245
Maths average = 245 + 284 /2 = 264

Now measure the AVERAGE GC exactly half-way along track you should get 264. So your rhumb line/constant direction/average GC between Tiree & Oystr is 264.

Please PM me for any further assistance.

RichardH summed it up beautifully; 100 degrees true.

The following link is an interesting history which I found useful for context; a few terrifying looking equations at the end which can be ignored!

http://www.cwru.edu/artsci/math/alex...mag349-356.pdf

In order to picture a rhumb line, try this, courtesy of Wikipedia...

http://upload.wikimedia.org/wikipedi...oxodrome-1.gif

Quote 'The question states AVERAGE GC = 100 this means half way which is exactly the same as the rhumb line. Remember a rhumb line is constant bearing and is also the same as average great circle.' This is true however....

From the answers given on the original question the wording is incorrect? , there is a question on the DB that gives those answers but it lists co-ordinates , its been a few months so i cant recall. Il see if i can find it.

Richard what are you like with Met and Instruments :}

thanks for all your time :ok:

I sympathise with your plight, but the best books for nav. are the one's issued for your groundschool.

Personally I found that Gen. Nav. and Meteorology were the type of subjects that you need to play with concepts and one day it just, well, clicks.

I am sure that you could waste a whole load of dosh on extra books, but plug away at the examples and it will come good, I promise!

I struggle with certain things. I tend to need things explained simply first then working fully through examples using layman terms!. Found the oxford cd made a massive difference for the met exam.

Go with what you know
 

I found the OAT Met. cd worked for me. If there is a Gen. Nav. equivalent, go with that, then.

Thrash through your groundschool examples, however, and it will come good; I would suggest that you hit the BGS database, but only do so when you understand the concepts. I found that helps you to eliminate the two nonsense answers immediately and gives a grace period for working out the two likely candidates with reason rather than hope.