When we originally read this, it matched up perfectly with our experience, and we had no trouble with our planes flying well, in a circle of approximately constant radius. But during this morning's flying session we had an experience that has us scratching our heads.jander14indoor wrote: . . .Now the rest of the trim is just to keep the turn a constant size over the full speed range these planes fly at.
The prop is actually set with its access down and left to offset the excess lift at high torque (max winds) and off set the excess left wing lift (which increases left turn radius, sometimes to point of right turn) at higher speeds with left thrust.
The tilt of the stab to the right causes a left turn because of force vectors. To all intents and purposes the lift from a flat wing or stab is perpendicular to the surface left to right. If the surface is tilted right that force vector points up AND right. That right component pushes the rear of the plane right, pivoting the nose to the left. Another left turn. This force becomes dominant at slower speeds.
The vertical stab is typically set for a left turn too. But set properly it doesn't so much control turn, but just minimize drag in a plane that's turning anyway.
. . .Hope that makes sense, if not, feel free to keep asking questions.
The plane in question has twin stabilizer end plates at an angle of about 15 degrees from vertical. The stab is angled and the tailboom is set at an angle consistent with a left turn. The thrust line is angled to the left. Originally, we had the tailboom angled too much, and the plane flew in a circle with a diameter of only about 15 feet. Too tight, but it flew well enough to do 2:45 in a venue with about 25 feet of flyable height. This plane was also flying the bonus wing with a 7 cm chord. Not too bad, but we wanted to enlarge the circle, so we decreased the tailboom angle.
The first few flights were made with a prop pitched to P/D = 1.5. This went pretty well, with a nice circle of about 30-35 feet, though we did notice that it took a little while for the plane to start circling properly. This was easy to compensate for by shifting the launch position to a different part of the gym.
Next, we wanted to try a prop with a higher pitch - P/D = 1.7. Now the plane really didn't want to turn; it headed for the side wall, not quite a straight line, but pretty close. We retrieved it from its landing spot and relaunched, and then it circled to the left, , about diameter about 30-35 feet.
So it appears that the plane doesn't want to turn when the torque is at its greatest, and the plane is flying fastest. Do I remember hearing that the rudder is more effective at higher speeds? If so, do the above observations suggest that we increase the tailboom angle a bit? We are planning to try this, of course, but we have the usual problem that gym access is severely limited, as we are not basketball players, or the like:( So if we can get an idea of what else to try, it might help us to save some time.