ORIGINAL: GREG DOE

G.S.G. Most of my SR MkII end up with a little right thrust, but not everyone. I use right thrust to reduce, or eliminate a ''hook'' in a left pylon (usually full up elevator) turn. The condition I'm describing can also be caused by a heavy left wing, or excessive aileron hinge gap. There are some other causes, such as missaligned tail surfaces, but we won't go into those right now. On your first test flights try full up elevator turns to both the right and to the left. All things being equal, the most common reaction is for your airplane to ''hook'' or ''tuck'' to the left, because as it decelerates in the turn, torque will make it roll left, but not all airplanes react the same. If you are really lucky your airplane will pull true in both directions. Usually if they ''tuck'' in a left turn, they will climb in a right turn. Sometimes, for no explainable reason, you will get an airplane that ''hooks'' to the right, and climbs to the left. If my airplane responds this way, I don't shim in right thrust. For thrust shims I laminate multiple layers of fiberglass cloth between two pieces of plate glass. I use approximately 4 oz. per sq. yd. cloth. The first two layers are slightely larger than the back of my motor mount, about 1/2 in on each side. Then the next 6 or 7 layers of cloth each get smaller by a 1/4 in. and are arranged so one edge of the sandwich is only 2 layers thick, and the other edge is 8 or 9 layers thick. The whole sandwich is clamped between the two pieces of plate glass, so you end up with a ''wedge''. I use PVA (poly vinyl alcohol) as a release agent. After the wedge cures I cut out a circle the size of my motor mount. My thrust shims are probably over kill! Another test to perform, before putting in any rudder trim, is to fly your airplane directly over your head. When it is going away from you observe if the nose is hanging to the right or the left. If you are lucky it will be tracking straight, but frequently the nose will be ''hanging'' to the left. Try shimming in right thrust to get it to fly straight, instead of using right rudder. I probably ''over trim'' my airplanes, but I like to have them flying at their best when I crash them. Now everyone knows my trim secrets. Greg