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Shaft RPM Targets at cruise

As a general rule owners should target shaft rpm on virtually all installations so that the engine and reduction ratio installed will  deliver ~ 1000  shaft rpm @ cruise speeds.

For example an engine rated 3000 rpm max would typically cruise at say 2300 rpm.

Divide the engine rpm by the reduction ratio in Ahead to calculate the shaft rpm speeds.

A reduction gear of 2.3 would deliver ~ 1000 shaft rpm @ cruise.  ( 2300 / 2.3 = 1000 )

Once you have an engine reduction combination that meets this rule, you can then calaculate as a starting point how this impacts on propeller diameter and  pitch within the maximum power of the engine constraint.

Shaft speeds higher than ~ 1000 at cruise tend to introduce inefficiencies due principally to the higher tip speeds involved and the fact that the corollary of higher shaft speeds will be lower propeller diameters.