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Propeller / Engine RPM restrictions
- Thread starter emsvitil
- Start date
BillL
Well Known Member
If it is done, the prop manufacturer installs a few dozen (a lot) strain gages along the blade, attaches to an engine an runs it in a test cell. They see what modes of vibration are induced in the blade and determine if it is within limits. I am sure they also have a calibrated model too, but this is done for a wide range of combinations.
No, prop balance is a completely different thing. The blades act like tuning forks and vibrate in many different modes. This is excited in several different ways by the engine.
Go the the Kitplanes magazine website (you have a subscription, right?) and download "Good Vibrations Bad Vibrations", by Marc Cook, from the November 2006 issue. It's a ride-along as Hartzell does the vibration study for certification of the IO-390/Hartzell BA prop combination.
i came across the same problem as Ed. I do have to determine the RPM restrictions for my setup (IO-375/Hartzell CS 72") for the POH.
Is there any way to "feel" the RPM ranges during flight? Or are that vibrations something only the propeller notices? so that only the prop manufacturer is able to figure that out in a test cell with some fancy equipment?
Is there any way to "feel" the RPM ranges during flight? Or are that vibrations something only the propeller notices? so that only the prop manufacturer is able to figure that out in a test cell with some fancy equipment?
For certiied aircraft the manufacturer have checked that the engine/ prop
combination is safe, restricted rpm may show in the POH.
If you have a certified prop, the manufacturer have most certainly tested
it with certified engines. A standard experimental clone like the IO-360
can be treated like a certified engine.
When you have a stroked experimental like the IO-375 it might not have
been tested vibration vise and then you are on your own. Experimental.
A metal prop is more sensitive for vibration and sometimes require a
crankshaft with dampers like the IO-360-A1B6.
A wood or composite prop dos not have the metal fatigue problems on the blades. It is my own opinion that a composite prop has low risk to
impose dangerous vibrations to a crankhaft.
combination is safe, restricted rpm may show in the POH.
If you have a certified prop, the manufacturer have most certainly tested
it with certified engines. A standard experimental clone like the IO-360
can be treated like a certified engine.
When you have a stroked experimental like the IO-375 it might not have
been tested vibration vise and then you are on your own. Experimental.
A metal prop is more sensitive for vibration and sometimes require a
crankshaft with dampers like the IO-360-A1B6.
A wood or composite prop dos not have the metal fatigue problems on the blades. It is my own opinion that a composite prop has low risk to
impose dangerous vibrations to a crankhaft.
BillL
Well Known Member
No, unlikely to feel it.
Mostly only the prop and engine crank "feels" it.
Go read the article DanH just posted. A little flowery, but it is excellent and shows what engineers do to validate the application of a propellor. (or anything else that is important) This kind of engineering is what sold me on the Hartzell composite.
