RPM restriction for 3 bladed prop question

[Jettech]

Is there still a RPM restriction for 3 bladed prop, The POH for a M20C Rangers limits RPM from 2000 to 2300, Does that apply to a 3 blade prop?  

[Hank]

It should be in the prop documentation. My C had a 3-blade Hartzell installed a couple of years before I bought it, I live with the markings on the tach. Seems the top of my "avoid constant running" zone is 2250, and I cruise at 23"/2300 when low (less than 4000 msl). She runs good there.

[A64Pilot]

It will of course vary with which prop on which airplane.

It should be in the STC documentation, and the Tach should reflect the STC if instructions were followed, sometimes they aren’t.

[Jettech]

Thanks I'll do some digging

[tony]

The restriction in your POH is do to the interaction between the blade passage frequency and a harmonic interaction with the crank.  With a two bladed prop the blade passage frequency is twice the rpm of the engine.  With a three bladed prop 3 times.  Just do the math and adjust the restrictions down.  

[Matthew P]

If it isn't the original (make, model, part number) prop then the restriction in the POH is worthless, you need to look through the historicals and look for the installation and STC for that prop, it should state the avoid range for that prop/engine configuration.

 

[cliffy]

The restrictions are prop specific  You have to find the STC and read its restrictions for YOUR airplane and have the correct markings and placards installed. 

You should have a panel placard with the restrictions on it.  The original handbook numbers are wrong for your 3 blade.

[christaylor302]

N


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