>I'm flying a 2 channel poly and when I'm thermalling >it does not want to hold it's bank angle. I end up >feeding constant rudder input
This is the nature of most polyhedral models. If you want to reduce or eliminate this, make the vertical stabilizer a bit larger (or reduce the overall dihedral of the main wing). You can just tape some cardboard onto the vertical stabilizer to experiment to try out the effect. Most 2 channel polyheral models are designed to have a lot of built-in stability along all 3 axis, roll pitch and yaw. Within reason, most polyhedrals can be turned just using rudder, without using elevator, relying on pitch stability to stabilize the turn. How much rudder input is required to maintain a turn depends on the models setup. Pitch stability is the result of having center of gravity in front of the center of lift (ignoring the lift/sink component from tail), and having some down force at the tail to compensate. If the nose drops, model picks up speed, increasing down force on the tail, rasing the nose and slowing the model down (and vice versa). Elevator can be trimmed to cause a model to glide at a specific speed. Roll and yaw stability in a polyhedral compete with each other. If a model drops a wing, it goes into a slip. Because of the dihedral, the cross wind component across the main wing flows under the lower wing and over the upper wing, creating a roll correction torque to level the wings. At the same time, that same cross wind component pushes against the fuselage and tail, creating a yaw correction torque, causing the model to yaw into the direction of the slipping flight path (which is slightly downwards), this is termed weathervane effect. You can decrease roll stability by increasing yaw stability, which can be done by increasing the size of the vertical stabilizer. Try securely taping or othersize attaching some balsa to the vertical stabilzer or the rudder to increase it's size, and add a bit of nose weight to compensate for the weight at the tail. This works because the model will respond to a slip with corrective yaw before there's enough time for roll correction to level out the wings. The result is intially a downward spiral, but pitch stability will stop the descent and the final result will be a nearly coordinated turn. You could also decrease roll stability by reducing the overall dihedral, but this takes more work than making vertical stabilizer bigger. I have one polyhedral model that is almost neutral in roll stability because of the size of the vertical stabilizer (and possibly because of some double centering of the rudder). Note, if the vertical stabilizer were too small, then a model constantly overcorrects, resulting in a cycling rolling/yawing motion, termed dutch roll. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
