Nav Question

[YYZ]

Hey All
This may seem a bit easy for some but I need a pointer, as I have never studied trigonometry.


Convergency Formula?

Q. Find the Convergency between 40 N 025 W & 60 N 060 E

Apparently this is done by:
Change of long x sin mean lat
= 85 x sin 50
= 85 x 0.7660
=65

My question is how did this calculate .7660? I am missing the mathematical calculation of sin?

Same for this one as well.

Departure Formula

Find the departure between 47S 113 E & 47S 172 W

I can calculate the first part fine.

EG 113+172=285
Higher that 180 so 360 -285=75
75x60=4500

This is the bit I cannot get
CHANGE OF LONGITUDE X COS LAT?
=4500 X COS 47
= 3069 nm?

How do you get 3069?

Im sure its easy when you know how. (Scientific calculator is not the answer, as you cannot take these into the exams)

Any pointers

Cheers
YYZ
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[fly-dj]

You dont need to understand trig. You know the formula

Earth Convergence = Change in Long x Sin Mean Lat

to work out the .7660 from your example get your calculator press the sin button then enter 50 and press equals and you should get 0.766044443119. Put this figure back into your formula and you get your answer.

NOTE : If you type this in and get another number check that your calculator is in the deg mode and not rad or grad mode.


The second problem is solved in the same way but use the cos button.

If you can remember the formula and use the calculator you can get the answer every time.

[YYZ]

Two things...

1. I do not have a scientific calculator to hand

2. Your not allowed one in the exam so I need to know how to work it out on a normal calculator.

I know it can be done easily with the right tool but I need to know the easiest method using a normal calculator?

Thanks for the reply so far but not what im after.

YYZ
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[fly-dj]

Thats not correct. You can take a Scientific calculator in to the exam. You are not allowed programable calculators, not the same thing. But if you really want to make life hard for yourself on your desk in the exam hall will be a page of trig tables. Basically its a long list of numbers and their SIN, COS and TAN values. An understanding of the maths involved in working out trig is not required to pass the exam, I have know idea how SIN values are arrived at and with the aid of my sharp EL-531VH scientific calculator I have just passed Nav at the first atempt with 84%.

[High Wing Drifter]

YYZ,

You will notice in the Bristol notes, that they provide a table of values for the various angles in the progress tests. If you use those then you will always get the same answer as those listed, else you may need to do a bit of rounding.

Correct me if I am wrong somebody but...

...As for how this Sin, Cos and Tan numbers are calculated. They are the various ratios of the opposite, adjacent and hypotenuse (spelling?).

Sin A = Opp/Hyp
Cos A = Adj/Hyp
Tan A = Opp/Adj

Just remeber SOHCAHTOA.

Also:

Tan A = Sin A / Cos A (and the transpositions thereof)

So...

If in the northen hemisphere you were to choose a point along the GC track and then draw line perpendicular to it to intersect with a line drawn along the Rhumb line track and measure the distance from the start point to the right angle and from the start point to the point of intersection, divide those distances (the GC track is the Opp and the RL track is the Hyp) you would get the Sin of the angle of convergence. Obviously this is utterly impractical so they porivide the tables or you provide the calculator with the right buttons.

Or something like that!!

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[YYZ]

Cheers guys

I though i must be wrong somewhere?
Will be going to argos today to buy a new calculator, was a bit worried about having to calculate everything myself!


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