stab placement

[Michael]

Given your initial geometry, lowering the horizontal tailplane puts it in lower in the downwash flow from the wing, where the downwash is more severe. This effectively makes the h. tailplane AOA a little more negative,resulting in a need for down elevator trim change to restore hands-off straight and level flight (assuming the c.g. is aft of the wing aerodynamic center). This down elevator trim in knife edge will push the nose toward the belly, i.e., reduce the up elevator mixing you now have.

Roll coupling in knife edge (assuming a straight model) is a function of dihedral angle.

Mike Nauman
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