In reply to darock, I have moved the engine vertically +/- 1/4" from some nominal location and the stab +/- 3/4" vertically, and neither of those moves changed the knife edge trim much.

When moving the engine a larger distance than 1/4", the move was confounded by inadequate/incorrect dihedral which then produced additional unwanted effects in roll and pitch upon rudder application. It didn't matter whether the model was in S&L of knife flight. As far as the stab is concerned, 3/4" isn't enough vertical movement. However, any more movement than that causes other undesired effects in overall flying quality of the model, and wasn't pursued (tail wobble in roll for example)

After getting the engine at the correct location such that no roll couple was effected, 2 things helped the pitch to landing gear problem for a given fuse design (a bulbous top fuse with essentially a flat bottom): 1) adding a dorsal fin about 12"Lx1 1/2"Deep in front of the fin at its base. 2) an increase in rudder span above the stab (added an aerodynamic balance). Both of these moves essentially raise the CP of the vertical tail, such that the vertical down moment when rudder is applied is greater than before the changes.

To boot, the balance on top of the rudder increased rudder effectiveness such that snapping maneuvers improved (promoted quicker inboard wing panel stall and recovery).


MattK