Tuesday, 26 August 2008

PPL: Ex 18 (i): NAVIGATION: The Dalton "Dead Reckoning Computer" OR Wizz Wheel Ex 18

I am often asked the question, "Should I use the 'wind UP' or the 'wind DOWN' method when solving the problem of finding Heading and Groundspeed on the "Dalton" navigation computer? Personally I use a Jeppesen CR-5 Computer which solves the wind triangle trigonometrically and you can put the CR5 in your shirt pocket. I also have a beautiful AristoAviat 617 which has a rotary indicator for the wind. Both of these instruments are EXCELLENT for accuracy. I am attaching the R.A.F. teaching (at least it was the teaching when I was in the air force a long time ago) which should clarify any queries you may have. Nothing has changed since then, but do also study the USER MANUAL that comes with your flight navigation computer. The important facts to remember are: HEADING (HDG) is on the same vector as TRUE AIRSPEED (TAS) and TRACK (TRK) is on the same vector as GROUNDSPEED (GS). Like oil and water, they do not mix. The conventional PPL navigation problem is to find HEADING and GROUNDSPEED. You have measured the TRACK and you have downloaded the WINDS for your planned flight from the Met Office (Click here for the Met Office weather & winds). So you know the track and you know the wind. We will have to assume that you also know the True Airspeed. TAS will be addressed later (see Ex 18 (v)). Paragraph 12 of the R.A.F. Notes addresses the problem of finding the HEADING and the GROUNDSPEED neatly (although you will note the TAS is 350kts - those were the days!! not a mere 90!!), but please read everything up to, and including Paragraph 12. Click on any image to ENLARGE.

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