CRP 5 correct to 1 kt

[bultaco]

Should an instrument be read to a greater accuracy than the smallest
graduation on its scale ?

I reckon, for the pooleys CRP 5, maybe half a graduation is ok, but the ATPL questions take the biscuit.

For example, take the following sample navigation feedback question
(Italian feedback).

14) Given:
True HDG = 233°,
TAS = 480 kt,
Track (T) = 240°,
GS = 523 kt.
Calculate the W/V?

A 110/75kt
B 115/70kt
C 110/80kt
D 105/75kt

They give you TAS 233 Kts and GS 523 !!!
And then they have the cheek to present possible answers within very
close values.

For this question I got out my CRP 5 and a pencil. I sharpened the
pencil lead down so it's diameter was ~ 1 micron.
I proceeded to do the question as accurately as possible under a x50 microscope. I still did not get an answer that matched the possible answers.

Do they expect you to use a laser to etch the wind dot on the Perspex
face of the CRP 5 ?

[High Wing Drifter]

Dust the device down with talculm power, makes the mechanism super smooth and so precise setting is much easier to achieve.

[-IBLB-]

what's the answer supposed to be? A?

14) Given:
True HDG = 233°,
TAS = 480 kt,
Track (T) = 240°,

....

They give you TAS 233 Kts and GS 523 !!!
Also, be careful, and doublecheck, these little mistakes can screw you up.

[bultaco]

Yes, A is supposed to be the correct answer but I got closer to B on the wind direction

[bultaco]

Yeah that was just a typing mistake...I worked it out with the correct values

True HDG = 233°,
GS = 523 kt.

[-IBLB-]

Yes, A is supposed to be the correct answer but I got closer to B on the wind direction
I get A exactly if i do it on my CRP5...granted i have a windarm one, it's a little easier to read.
480 under the grommet, 233 on top. Mark 7 degrees right, on the 523 line. draw line from windmark -> grommet -> edge of scale, or rotate the mark to be in the middle, reads 110 for me.

[bultaco]

Hi IBLB,

I don't see how you can get the exact heading since the difference in a couple of degrees is almost impossible to determine. However, when you already know the answer it's easy to position the marker and say it fits.

[-IBLB-]

I don't see how you can get the exact heading since the difference in a couple of degrees is almost impossible to determine. However, when you already know the answer it's easy to position the marker and say it fits.
Like i said, i think the CRP5 with the windarm is actually a little easier for this kind of questions. But i really do get exactly 110/75 out of it, not even 111 or 109, sorry. Also make sure you start with the true hdg on top, and the GS under the grommet. You can do it another way, but it will give you a slightly different answer.

Like you said, if you really don't know the answer, you can always reverse the question and begin with the answers, but you will need to have some spare time.

[bultaco]

I entered the values into the fields of the following online flight computer, and it displays an answer of 111 so I guess it's closer to the correct answer than I got. But my point is that the difference of 1kt on the analogue flight computer is probably of the same order as the thickness of the scale lines.

http://www.csgnetwork.com/e6bcalc.html

[LeFreak]

this is funny .. i did my jar-atpl navigation exam yesterday and i got the exact same question .. i'm using the Pooleys Aviat 617 which is probably similar or the same as the crp-5 .. i also got an answer somewhat close to the options given, so i decided to make a drawing and just measure the wind vector .. in the end i just had to guess the closest answer

don't know if i got it right but i passed the exam with 88.6% so i don't really care anymore if i got it right or wrong :O

[-IBLB-]

I entered the values into the fields of the following online flight computer, and it displays an answer of 111 so I guess it's closer to the correct answer than I got. But my point is that the difference of 1kt on the analogue flight computer is probably of the same order as the thickness of the scale lines.


Sure, one knot difference is almost a given when you use a crp of some sort. i got 110, and it is 111, there is your one knot. but if you look at the answers, 1 knot, or even 2 knots should still bring you to answer A. So, just take whichever one is closest.

[-IBLB-]

don't know if i got it right but i passed the exam with 88.6% so i don't really care anymore if i got it right or wrong :O
Congratulations! i am glad i passed that one long time ago...

[bultaco]

I get A exactly if i do it on my CRP5...granted i have a windarm one, it's a little easier to read.
480 under the grommet, 233 on top. Mark 7 degrees right, on the 523 line. draw line from windmark -> grommet -> edge of scale, or rotate the mark to be in the middle, reads 110 for me.

Where is the 523 line ? you mean 3/10 of the 1mm between the 520 and 530 line ?....You must have great eyes.

[-IBLB-]

Where is the 523 line ? you mean 3/10 of the 1mm between the 520 and 530 line ?....You must have great eyes.
Allright, the IMAGINARY 523 line. But yeah, i do have great eyes.