Seanychen,

You have obviously put much thought into this issue of wing rock, but I believe you don't really understand the yaw thing yet. It's not yaw stability we are concerned with in an upright harrier. It's the lack of smooth air flow over the aft fuselage and the vertical. In high alpha flight, the ailerons are only working at all due to the prop blast over them , but they really aren't efficient as roll control surfaces anymore. To deflect the ailerons in a harrier, the result you get is due to the lack of symmetry from left to right, not necessarily the fact that one wing is creating more lift than the other. In other words, they become drag controls on the wings, and they respond accordingly. The rudder and vertical, on the other hand are the only surfaces on the plane that are not at a critical angle of attack, thus remaining effective. Since they are blocked by the lower fuse and the horiz tail when upright, even though they are not stalled, they have no clean air to work in, which makes them feel inadequate. Size, therefore, in this case at least, doesn't matter. My next mod will be to add a turtle deck to the lower fuse on the f90,which resembles the upper surface. Hell, it may even have an effect on the tucking during knife edge.