Hi guys I have stumbled on question 51 page 6.7 in the VFR study guide trying to determine the heading and grounspeed to be flown!! I have just completed most of the questions on page 3.3.8 exercise 9 to find its pretty straight forward using the CR-3 calculator but for some reason can't work out how to crack question 51

Any help will be much appreciated

Cheers

There is no Question 51 in that exercise. Can you check it out and indicate which one you are referring to?

Hi bob the question I am stuck on is on page 6.7 question 51, I was referring to exercise 9 as they are the same question and seem to have gotten exercise 9 correct but have stumbled on question 51.

So my question is can you explain how to work out question 51

Kind regards

Since you were getting other problems correct, maybe there is just one of those hard to spot silly mistakes in your working of this problem somewhere.

Things to check: the Wind information given is from an ARFOR so it is in degrees true and the required track is also given in degrees true. The answer however is asking for your heading in degrees magnetic. Make sure you work with wind and track in true and convert the answer (the heading) into magnetic by applying the 10 degrees of variation correctly.

When I do this problem I get the answer (a). What answer are you getting with your working? If you haven't spotted the problem yet, we can step through the process for you...

Cheers,

Rich

Hi Richard thanks so much for your reply, if its ok can you do an example using the CR-3 for me using that same example as Q51 as I keep getting the incorrect answer!!

Kind Regards

Mark

Richard I'm pretty sure I have worked it out, again just another silly mistake using true instead of magnetic!!!

Thanks heaps Richard

Richard just for curiosity did you get a GS of 130 knots as the book says 123 knots

Hi Mark,

I got 123 kts as in the book.

You have the following information:
W/V = 150/45 (in degrees True)
TR(T) = 080 Deg ,
Variation = 10 Deg E,
TAS = 145kts.

1) Set up the TAS:
Align 145 with the TAS indicator arrow. This sets you up for your TAS of 145 kt.

2) Set up the True Course
Align the inner disc so the true track of 080 is lined up with the "TC" marker.

3) Find the Headwind and Crosswind Components
Find 150 on the angular scale, follow the radial line inwards until it intersects the 45 kt arc (which you read from the vertical scale). Read off a headwind component of about 15kt and a crosswind component of about 42kt.

5) Find the drfit correction for the Crosswind
Go to the outside scale and find 42kt and read off the required correction angle of about 17 degrees.

Here comes the step you are forgetting:

6) Find Effective TAS
Because we have such a large correction angle (17 degrees) we need to adjust the TAS and use what's called the "Effective TAS". Next to the TAS indicator on the outer scale, you'll see some degrees marked in white on black. This shows how much adjustment to the TAS you need to make to compensate for the extreme heading correction.

17 degrees correction at a TAS of 145kt means your effective TAS is actually only 138kt.

7) Find GS
Subtract the headwind component of 15kt from your effective TAS: 138-15 = 123kt.

8) Find HDG
You apply the 17 degrees correction for the right crosswind to get a true HDG of 080+17 = 097.
Convert that to magnetic using the variation: 097-10E = 087 degrees Magnetic.

Answer: HDG: 087 degrees magnetic with a GS of 123 kt

You had simply forgotten to do the TAS adjustment for large drift corrections and apply your headwind to the effective TAS.

Cheers,

Rich

Uh Huh thank you so much Richard, another silly mistake

Cheers

Mark

Happens to all of us. Don't stress it

Cheers,

Rich