the aircraft performs the same going downwind as it does into wind...
I understand the theory you are talking about RDA, the whole "flying in a moving mass of air" theory. However this theory is slightly flawed when applied to heavily loaded aircraft. Say for instance you are taking off with a 10kt x-wind from the right with an obstacle straight ahead (say trees) but clear ground left and right, which way do you turn immediately after takeoff??? I will go into wind everytime, in this case right, especially with a full can. The moving mass of air theory doesn't take into account inertia. I am not very good at explaining this but here goes..
You are flying across the wind and turn downwind, the aircraft does not immediately accelerate with the wind due to the inertia. There will be an initial reduction in performance until the aircrafts inertia is overcome and then the aircrafts performance will return to the previous level. The performance reduction is only momentary, however flying a fully loaded ag plane, it can be that moment where you get that sinking feeling.
When the aircraft is light, the performance drop is so minimal it doesn't register, however when it is fully loaded the problem is exacerbated.
Like I said, I am not very good at explaining it I'm just an ag pilot,someone else might be able to do a better job than me. I am sure some people may disagree or like to shoot holes in my theory, but i'd love to hear some discussion on it.
3 way valve
PS Sorry LLD this is way off the thread you started!