1. Set up your test differential.
2. Disable any aileron-rudder coupling
3. Launch and fly the plane overhead at your normal thermal circling speed. Rock the wings back and forth with an application of aileron, and observe the fuselage for yaw. At the perfect differential setting, there will be no yaw with application of aileron.
- If the plane yaws into the turn (toward the low wing), decrease differential.
- If the plane yaws out of the turn (toward the high wing), increase differential
4. Make adjustments and repeat.
This is a satisficing procedure -- the ideal differential will be different at different airspeeds, so about the best you can do is get it approximately right and compensate with rudder.
