Louis9624,

If the down thrust angle is like specified by the designer, it is possible that your middle wing model has a different problem than what you suppose.

If the CG is located too forward, you may be trimming the elevator up to compensate.

This may introduce a decalage for which your neutral model has not been designed.

That incidence difference between wing and tail may make it sensible to speed changes.

Just try a shallow dive with no engine and see if it noses up when it picks speed.

Check this link out:

http://www.charlesriverrc.org/articl...GMarkDrela.htm

Regards!