RE: DLE222 Starter System - The Project
Propeller Inertia Forces
For initial starting rotation, the rpm involved is small compared to running rpm. Even though there are other forces acting like the aerodynamic drag on the blade surfaces but it will not be considered due to too small when compared to the INERTIA forces to turn the prop itself.
The common propeller size for 222cc engine is 32 x 12. The mass of this propeller is 350gram or 0.35kg. For ease of calculation, we consider each blade leaf is 0.175kg and act at the central point between the engine shafts to blade tip i.e. at 8 inches away from engine center.
Per propeller leaf,
F = ma, 0.175kg x 9.81m/s^2 = 1.72N
Negative inertia torque = 1.72N x 0.2032m (8 inches) = 0.35Nm
Therefore for the whole propeller, 0.35Nm x 2 (2 leaf prop) = 0.7Nm