Very interesting!
I guess this tread is more or less completed, but anyway....

I have seen some of you have been mentioning sweept flying wings, witch use wing-twist (washout) rear of NP, or airfoils with positive Cm to get a positive pitching moment around NP. CG is then located in front of NP to counteract and make stable flight.
If the twisted wing tips (lets say -2°) create downforce or upforce is not really relevant, this will vary upon angle of attack and the importent thing is that they provide a positive pitching moment around NP.

As I see it, this is not different from conventional planes, witch use the tail to get a positive pitching moment around the NP.
As mentioned before in this tread even a fully symetric acro model need a few clics of uptrim to fly stable. When inverted the same plane need a little down elevator to "turn" the pitching moment the other way around.

Isn't it then correct to say that the tail on that same plane totaly creates a lift when AOA is positive (level flight), but it also creates a downforce relative to the main wing due to the up-trim?

Of course if the mainwing airfoil has a negative moment the stab must have more negative AOA relevant to the mainwing to counteract so that the total pitching moment around NP is still positive.

In other words, whether the tail is creating lift or not change and isn't really relevant to stability, but the pitching moment it creates around NP is.

or ....?

Olav, Norway