ORIGINAL: MTK
David, one of the main reasons a model pushes to the undercarriage in knife edge flight is the relatively low location of the center of pressure (CP), on the vertical stabilizer. The vertical downward force (moment) generated in such an arrangement is too small to counter enough of the natuiral down pitch moment any wing generates. The simple change of lowering the stab has a marginal affect on the knife edge, if that is all that is done.
...
You lost me here... what "natural down pitch moment" any wing generates? We talk about symmetrical airfoils here... no moment at all, as far as I know....