Common logic fails here, because the the commonsense explanation that the
upwind and downwind differences ought to cancel out only works if the
relationship is linear. If you do the math, the relationship between the
round trip time, round trip distance, TAS and wind speed is nonlinear:

time = distance/speed

round trip time = time out(upwind) + time back(downwind),

= D/(T - W) + D/(T + W), where D = leg distance, T = TAS, W = windspeed

= [D(T + W) + D(T - W)] / [(T - W)(T + W)], using x/y + z/w = (xw + yz)/yw

= (DT + DW + DT - DW) / (T^2 - TW + TW - W^2)

= 2DT / (T^2 - W^2)

2D is the round trip distance, so in words: round trip time = (round trip
distance x TAS) / (TAS^2 - windspeed^2)

[As a check, this reduces to: round trip time = round trip distance / TAS,
when windspeed = 0]

Hence the relationship is nonlinear with respect to wind speed. That isn't
normally so obvious because usually TAS wind speed. It's more obvious in
the original post because the poster chose a wind speed much closer to TAS.
[Work it out for windspeed = 10 kt and the other data in the original post,
and the upwind and downwind differences do almost cancel out. Then work it
out for windspeed = 199 kt!]

nuke

"arcwi" wrote in message
...
Yes, but the common logic suggest that you also spend less time in
tailwind
that in head wind - and if there is no wind the two should cancell each
other... Or should they...

"Stefan" wrote in message
...
arcwi wrote:

Can someone explain the difference?

You spend more time in headwind than in tailwind.

Stefan