Max Drift
Max Drift
Join Date: Oct 2001
Location: United Kingdom
Posts: 16
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If you multiply the forcast wind by 60 then divide this by your T.A.S the answer will be your MAX DRIFT. i.e. 20kts x 60 = 1200 / 120kts T.A.S. =10 degrees max drift. You can then use the watch analogy to determine how this will effect you in flight.If the wind is at ninety degrees to your longitudinal axis you will have full drift. You can expect full drift down to an angle of 60 degrees. This is where the watch comes in. 45minuits is 3/4 way round your watch,if you have a wind angle of 45 degrees then use 3/4 of the MAX DRIFT. For a wind angle of 30 degrees you would use 1/2 the MAX DRIFT etc. Hope this helps. 
W/V divided by TAS (in miles per minute) = Max drift. So at 90 KTAS with a 30 knot wind, max drift is 30/1.5 = 20 deg. Now apply the relevant 'clock factor' to your track; if the wind is 15 deg off, use 1/4 of max drift, if it's 30 deg off use 1/2 max drift, if it's 45 deg off use 3/4 of it and if it's 60 deg or more, use all of it. Thus if you're on a track of 360 at 90 KTAS and the W/V is 330/30, your max drift is 20 deg. The wind is 30 off, so use half of max drift and make your heading 350 deg.
Similarly, your groundspeed is affected by a wind at 90-30 deg off, i.e more or less all of the wind. So use 90-30, i.e. 60 Kts as your estimated groundspeed.
(Dalton values would be a hdg of 350.4 deg and a GS of 64 kts, so it's close enough for visual navigation backed up by pre-planned visual fixes - and anyway, who said the weather-guesser was 100% right in the first place!)
PS - Sorry, newguy, guess we both replied at the same time!!
[ 06 October 2001: Message edited by: BEagle ]
Similarly, your groundspeed is affected by a wind at 90-30 deg off, i.e more or less all of the wind. So use 90-30, i.e. 60 Kts as your estimated groundspeed.
(Dalton values would be a hdg of 350.4 deg and a GS of 64 kts, so it's close enough for visual navigation backed up by pre-planned visual fixes - and anyway, who said the weather-guesser was 100% right in the first place!)
PS - Sorry, newguy, guess we both replied at the same time!!
[ 06 October 2001: Message edited by: BEagle ]
