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Guest Welsh Rambler

Nav log error?

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Guest Welsh Rambler

It maybe my understanding that is incorrect, but it seems the Magnetic Heading and Ground Speed given in the Nav Log are incorrect.E.g. I plan a direct route from Thule, Greenland (BGTL) to Alert, Canada (CYLT), put this into the AS2004 nav log and getMC=76 MH=84, GS=201, wind aloft is 174/30, TAS=200.Now this would be okay if the wind was issued as a mag heading, but its not (unless I'm not understanding your software correctly). So, the MH and GS seemed to be calculating against a mag course and a true wind with no allowance for variation (which averages 72 degrees West for this route.)I calculate a True Course of 004, then True Heading of 005, GS=230. Adding the variation back to get a Mag Heading of 77.This is also bourne up by a course from Thule, Greenland (BGTL) to Eureka, Canada (CYLT).AS2004.5 Nav Log: MC=307, MH=300, GS=219. Again TAS=200, wind aloft 174/30.For this route the average variation is 65W, so I make itMC=307, TC=242, TH=234, MH=299, GS=188.I'm using a CRP-5 to work out the drift/ground speed.I'm using the 2004.5 build 147 and METAR issued at 201250Z.It maybe I'm not understanding it correctly.Cheers!

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Hi,I can confirm that the code is properly converting wind direction to magnetic before it calculates MH and GS.The problem looks to be that with a direct route the average magvar is not used. Instead, in any given flightplan, each waypoint's magvar (only 1 in a direct route) is used. When your dep and dest magvar varies significantly there will be inconsistencies. This can and will be improved upon by the new route processing we are working on for the next version.You should be able to confirm this by using a flightplan with several waypoints (let FS build the plan, then import it). Each waypoint's calculations should be correct.

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Guest Welsh Rambler

Thanks for the prompt reply Damian.Trying the same exercise with a route with a few waypoints this is what I found (TAS=200)(To, MC, MH, True WIND, GS, avg variation)AS2004BGTL QQ , 54, 60, 182/30, 217, -70LT , 78, 80, 182/30, 228, -72CJQ6, 327, 325, 190/7 , 197, -81CYEU, 313, 310, 140/9 , 200, -92My calculations:BGTLQQ , 54, 52, 182/30, 228, -70LT , 78, 81, 182/30, 230, -72CJQ6, 327, 325, 190/7 , 232, -81CYEU, 313, 310, 140/9 , 199, -92As you can see the figures do marry up within reason except for the first leg. It seems like the first leg only is using a variation of zero, so like you say, the calculation is happening correctly, it seems to be fed the wrong average veriation for the start of the first leg.Sorry, I'm not trying to find bugs, I was originally just trying to 'prove' my own calculations by looking at someone elses.Hope this helps.Cheers.:-)

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