912uls RPM setting

It always about POWER!!!

The 912ULS Makes MAX Power at 5800 RPM at WOT.

If you can not reach 5800 rpm at some point in the flight envelope, you are not using the power that is available to you.

You appear to have a lot of excess power available if you can cruise in level flight at 3900 RPM.

Setting the prop for a 4200 RPM Level cruise will generate EXACTLY the same POWER as setting it for a 3900 RPM Level Cruise. 

POWER is RPM times TORQUE.

Since you require a certain amount of POWER to fly level, 4200 RPM at a LOWER Torque is a better choice than 3900 RPM at the HIGHER Torque.

The Lower the Torque, the slower the engine wears out.

Set the prop to reach 57-5800 RPM in a WOT climb and let the Level Cruise RPM fall where it may.

Don't forget to limit the time above 5500 RPM to 5 minutes.

Thank you Bill

The age of the engine is not an issue for setting the prop to max 5700-5800 RPM? 

Even old&weak engine should be set to 5800 RPM?

I searched the forum and found, that the most set the Max rpm to 5500-5600. Do they missing power?

Does lower MAX-RPM keep the engine life?

I do not think you necessarily have a weaker engine.

You are comparing oranges to grapefruits.  There are close but not the same!

When you swapped the prop you did not address the differences in canopies or how they were rigged.

Same Weight, Fuel, Pilot???  Too many variables.

People limiting their RPMs to 5500 are limiting their power to 90%.

As stated before, it is NOT about RPM, it is always about POWER!

Running the same POWER at Higher RPMs and a lower Torque (MAP) is ALWAYS the better option.

Thank you Bill,

The Prop swap was from exact same plane (airwalf), same engine 912uls, same canopies and rigged and same pilot(me)

And as described, the same prop goes to max 5150 RPM WOT in my plane but 5550 at my friend's plane.

That made us thinking my engine is little weak...does it a correct supposition???

And if the answer is YES, is it not a problem to set max RPM to 5750 for a weak engine??? 

Another question is: higher RPM doesn't mean higher fuel consumption?  or in my case, you wrote: "4200 RPM at a LOWER Torque is a better choice than 3900 RPM at the HIGHER Torque" - is it still correct about fuel consumption?

I can't say for sure that you have a weak engine or not.

When you swapped the prop and it was the same model of airframe and canopy but not the EXACT same airframe and canopy.

The only way for certain would be to swap your engine into his airframe and have him fly with his canopy and his prop.

Enough of that.

It is ALWAYS about POWER.  Repeat that 10 times! 

Power is related to fuel consumption.

Higher RPM at a lower Torque(MAP) is the same POWER as Lower RPM at a higher torque(MAP). (Read that again!)

The same amount of POWER requires the Same amount of fuel.  Fuel = POWER.   POWER = Fuel.

Higher RPM or Lower RPM, if it is the same POWER, it will need the same amount of fuel.

Look at it another way. Your PPC flies at a fixed airspeed determined by the rigging of the canopy incidence.

In order to fly level at this airspeed, you will need a fixed and very specific amount of POWER.

If you re-pitch the prop to turn at a different RPM you will still need the identical amount of  POWER and therefore Fuel, to fly level at that same airspeed.

If you have a weaker engine, the higher RPM will produce less Torque(Strain) on the engine for any given POWER.

If you have any multispeed bicycling experience, you know that going uphill in a lower gear requires a lot more pedaling(RPM) but is also much easier on the thighs(Torque). One way or the other it is going to take a specific amount of energy to crest the hill.  No way around it!

I keep emphasizing the word POWER because it will eventually sink in that (Did I mention this before?) "It is ALWAYS about POWER!"