Bearings etc.

#1
I have been scouring the internet for hours and still haven't found a suitable method for figuring out what I am about to ask, without a pen and paper or calculator.

When I was doing my FATS, there were a number of questions which went something like this;

You are at an army base and travel NW for 15km, then SE for 25km, until you arrive at a helipad, you then travel NE for 3 kms.

How far from the army base are you?

So that is an entirely made up question, the numbers are maybe terrible for an example and same with the directions. What I wanted to know was, how do you figure out your distance from your original starting point?

There is the possibility that I am missing some vital piece of information (my brain being somewhat exhausted after the FATS), but I don't think there is.

I have a feeling trig maybe involved, but I can't find anything which helps. Is there anyone with a better grounding in maths and navigation than me, that could help?

cheers
 

GuyC

Badgeman
#2
Don't know if I'm missing something, but that seems a very easy equation.
7km from base, correct?
After you're first point, you walk past your original start position by 10km, then 3k back towards it again.

That's all mental arithmetic.
 
#4
NW to NE is 90 degrees. Therefore you have a right angled triangle with sides of 10 and 3 km.
Join up the dots! Pythagoras will give you the answer.

2BM
 

GuyC

Badgeman
#5
Ah, my bad - I did miss something! DOH! Must read questions properly. Sorry.

You need to use Pythagoras' Theorem.

I worked out from those figures you'll be 10.4km from your start location.
 
#8
littleshinydemon said:
I have been scouring the internet for hours and still haven't found a suitable method for figuring out what I am about to ask, without a pen and paper or calculator.

When I was doing my FATS, there were a number of questions which went something like this;

You are at an army base and travel NW for 15km, then SE for 25km, until you arrive at a helipad, you then travel NE for 3 kms.

How far from the army base are you?


cheers
In this particular question as NE / NW / SE / SW are at right angles to each other then Pythagoras' Theorem will give you the answer if you draw it out (google it if not familiar). As I don't have anything better to do I have drawn it out on a ppt slide and inserted below. If you had other directions / bearings then I would suggest drawing it out to get a visual idea of the problem and then you would have to use trigonometry to find the length of the missing side. I hope this helps.



PS: tinypic.com seems to be a great way of quickly uploading pics to embed in replies without having to open an account anywhere.
 
#10
Hey thanks everyone for your quick replies, that was really helpful. Especially Sep86 for doing a drawing and everything!

I hadn't even tried this question, as I just made it up as I was writing out the post:) I see exactly where you are all coming from.

To throw a spanner in the works though, what would you do if the directions didn't automatically make up a right angle triangle?

for example;

You are at an army base and travel NW for 15km, then SE for 25km, until you arrive at a helipad, you then travel NE for 3 kms then S for 5km.

The reason I am asking all this after passing my FATS is because I have my AIB coming up, and I know that bearings etc. make up part of one of the papers and you can't use paper or pen (or at least I was led to believe this), so I wanted to make sure I was a bit better prepared. Would the above type of question be possible in your head? Or do they not ask questions as challenging as that?

My apologies for my complete ignorance, but would rather make a fool of myself on here than fail my AIB:)

cheers
 
#11
To be honest, the AIB isn't there to catch you out, so I doubt the questions will be unsolvable. I would hazard a guess that they will neatly resolve themselves to a series of triangles - I certainly remember using my fingers to plot out the course, and did fairly well in that section....
 
#13
This time you are given the Hyp and Base, find Perp

Square of Hyp = 25, square of Base = 9 therefore, 25 - 9 = 16...Perp = square root of 16 = 4.

Ans 4km


Ordnance Survey was carried out using Triangulation, doubtless they will need batteries these days. ( there may be a pun in there)
 
#15
Kilometers? I thought we still used (Nautical) miles! o_O

All you need is a good mapping GPS with inbuilt measuring software. Garmin GPSMAP series are very good....
 
#17
As it is now sunday afternoon and I would rather go and eat my roast dinner than draw trig out on powerpoint slides ...

To answer the more complex questions, break them down into steps, see which side lengths and which angles you have and work out the missing ones using trig. If you have 2 sides, you are most likely going to use the cosine rule for finding the opposite side. This site has some video lessons and looks interesting. Good luck.

http://www.graspr.com/videos/Sine-and-Cosine-rule-lesson-2-1
 
#18
And I thought all you young stars of tomorrow left education the most highly qualified in decades. Or have the BBC news reporters got it wrong?

Sorry, having a bad day!!!!! :?
 
#20
Thanks everyone by the way, for contributing to this thread. I hope that figuring out sine and cose in your head isn't covered in the AIB, but at least now I have the basics for doing it in my head.

Somehow I managed to pass the FATS and apparently did not bad in the navigation section, which I hope will be similar to the AIB questions, but I wanted to just clarify the basics.

Anyway thanks guys, now to study:)
 
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