NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Set and drift
From: Gary LaPook
Date: 2011 Nov 5, 23:51 0700
From: Gary LaPook
Date: 2011 Nov 5, 23:51 0700
The easiest way to do these computations is to use the law of sines which is solved on many flight computers, such as the MB4 that we have discussed before, since these are standard calculations for pilots. It is easy to solve on a calculator. WD = wind direction (or direction from which the current is coming) C = course RWA = relative wind angle (or relative current angle) WCA =wind correction angle (or current correction angle) TAS = true airspeed ( or boat speed) WS = wind speed (or current speed) GS = ground speed (or speed over the bottom) RWA = difference between course and direction that the wind (or current) is coming from sin WCA = (sin RWA/TAS ) WS if the wind is a head wind then GS = sin(WCA  WRA) /sin WCA if wind is a tail wind then GS = sin(WCA + WRA) /sin WCA Say the course is 90 and the current is coming from 130 so the RWA = 40 TAS = 120 WS = 20 (sin 40 )/120 = .005 So sin WCA = .005 store in memory. WCA = 6.1 sin (40  6.1) = .56 GS = ..56/.005 = 104 if the current was coming from 230 then the RWA would still be 40 but it would be a tailwind so you would add the WCA to the RWA and get 46.1, the sine of which is .72 divided by .005 makes the ground speed 134. Works for boats too. gl gl  On Sat, 11/5/11, P H <pmh099@yahoo.com> wrote:
