Sunday evening trivia question

[StuartUK]

Currently revising for my navigation question but keep getting this question wrong and I have no idea how the correct answer is actually correct.

Given Hdg of 138T, a track of 141T, a TAS of 122kts and a G/S of 101kt, what is the W/V?
a) 136/26
b) 120/21
c) 141/19
d) 131/21

I come up with ~125/22 (which isn't one of the options!) but the actual answer is D (131/21). All of the other W/V questions I've attempted I've managed to get right but it's just this little fella that has me stumped. I'm about to chuck either the computer or CRP (or both) out of the window.

Can someone explain how to get the right answer?

Thanks

[2close]

I'm in agreement with you - I'm also getting between 124/22 and 125/22 on three different whizz-wheels.

Hope that helps.

:)

[foxmoth]

First make sure the rotating section is properly centred and all the screws on the CRP are done up tight, not doing this it is easy to end up with big errors and the biggest cause of wrong answers.
Hopefully I do not need to explain how to do it, but just in case - heading at the top and TAS under the centre circle - use a SHARP pencil and draw a line on the drift and another round the Groundspeed. Rotate until the cross so formed is immediately below the centre - read off wind direction at the top and speed as the difference between the centre and the cross.

[jjones666]

showing 124/021 on an electronic "whizz"

[chrisN]

Using: whiz wheel calculator (http://www.pilotfriend.com/calcs/calculators/whizz.htm)

124/22

Chris N

[StuartUK]

Thanks for confirming guys.

[2close]

And agreed on electronic WW - 124/22

:)

[24Carrot]

The correction angle is small, so you can do it fairly accurately with an ordinary calculator:

The headwind is 122-101 = 21 kts, so let's use that as the wind speed.

3 degrees wind correction angle at 122kts = D degrees wind angle at 21 kts.

D = 3 x (122/21) = -17.5

141 - 17.5 = 123.5

so roughly 124/21.

[piperarcher]

What test prep source did the question come from?

[phiggsbroadband]

Hi, using trigonometry (sine rule and pythagarous.) I get...

Direction = 123.962 degrees T.
Windspeed = 21.789 knots

My bet is that there is an typo error in the given numbers in the question, it happens.

[StuartUK]

This question came from the usually spot on pplcruiser.co.uk.

[Whopity]

Using the traditional method, Douglas protractor, pencil and ruler 126/21.5