Customised Propeller 39×12 For UMS 7/360cc Engine

A customised propeller of 39×12 for the UMS 7-360cc engine. That is 39 inches in diameter with a 12-inch pitch, which is a large, coarse blade matched to a 360cc seven-cylinder radial.

Propeller size is chosen with the engine, not separately. On a radial of this displacement the engine produces its torque at low rpm, so it needs a large diameter to move the volume of air the airframe needs. The 12-inch pitch sets the speed the blade is designed to fly at; a coarse pitch on a large diameter suits an engine that makes its power slowly and pulls rather than revs.

The listing identifies this as a customised propeller for the UMS 7/360cc specifically, which means the diameter, pitch and mounting are sized for that engine rather than adapted from a general-purpose blade.