thanks for all answers. I cannot believe one PPL Nav question can get so many different replies!
Anyway I have learned the wind down method up to now for all the other types of calculations so would like to stick to this method rather than mixing and matching.
So am I right in adapting whoswho's method as someone pointed out it was wrong and do it the following way:-
1. Spin the rotating part (inner scale) so index points to 90 (wind direction)
2. Set the centre blue dot (wind index) over the 100 speed arc.
3. Mark (down the way) the wind speed in at 80 (80 because 100-20(wind speed) = 80)
4. Rotate the inner scale to set the true track, 180 (180 under index)
5. Move the vertical rectangle part down (in this case) until the mark you made sits on the 80 line. (80 because that's the groundspeed that you need to maintain)
6. Now you need to apply the drift, in this case it is right drift by 14 so rotate inner scale right by 14. Index now is 166. (you could've just done 180-14 also). The drift is shown as that's where your put the mark (step 3)
7. True heading is 166
8. NOW MOVE THE CARD UNTIL YOUR WIND DOT (THE MARK YOU MADE WITH YOUR MAGIC MARKER) UNTIL IT IS BACK OVER THE GS OF 80KTS, THIS WILL REVEAL YOUR TAS OF 83KTS.]
So will this "wind down" method work for any calculations of this type, i.e find TAS and true heading whilst maintaining a particular groudnspeed taking into account a specfic wind...
?