Thinking over Peter´s result:
Basically, there are five rolling moments during horizontal flight:
1. Motor torque
2. Aerodynamic moment, depending on angle of attack, wing warp, flap position, (Rabe-) rudder, trim tabs etc.
3. Centrifugal force times the vertical distance between the CG and the leadouts
4. Weight (including lines) times the distance to the lift vector
5.The spiralflow torque, determined by Peter for the first time IMHO.
Flying overhead, only moment "4" becomes zero, because there is no lift.
Motor torque can be measured by its current, but all other moments are difficult to measure during flight....
Regards,
Wolfgang