Originally Posted by robsrich
Remember when the RRPM gets to a low setting in an R22 or R44 or a similar piston, you have actually wound down the engine.
I would say that in any piston helicopter where the pilot is in direct control of the engine RPM (which on paper excludes the Robinson), there is no hazard in running the RPM at just above middle green. For example, the 300CBi's green range is (rotor/engine) 442/2530 to 471/2700. As long as you are running comfortably below maximum power, there's plenty to be gained by dropping the RPM down to something in the range of 460/2640 - reducing pilot workload and fuel burn. I advocate keeping the RPM at the top of the green whenever MP is within 1" of maximum, or altitude is less than 450', and anytime you need performance from the rotor system (climb, OGE hover, speeds below 40kt). Remember that the
300C's redline is 3200/471, but Huges/Schweizer lists 3100/456 as recommended operating RPM.
All that being said, I would not operate a very low inertia system like the R22 (which at redline is operating the engine at 2652 RPM - already on the back of the torque curve for the O-360) at anything less than the top of the green - the margins on that ship are already too close.