912 ULS no more than ~4800 RPM

We are a bit off topic, but in this RARE instance, I think Bill might have an oversight in his power/rpm equation.  I believe he is referring to the affinity laws as they apply to a fan or propeller.  It is true that as you increase the speed of a propeller the power required to spin it increases as a cube function. However, this assumes the propeller maintains the same diameter, pitch and form.  In this case the pitch is being reduced in order to achieve a higher RPM, so the equation is void because you are unloading the engine in order to enable it to spin faster.  You will make more HP at a higher RPM, but this will be as per the engines power profile, not a cube function of propeller speed. As Nicola states, it is more linear.  When the propeller is left in a fixed position, and can be turned faster by the available power of the engine, then Bill would be correct, power increases by the cube of RPM.    

"You will make more HP at a higher RPM"

True, but the prop becomes less efficient for cruise and better suited for climb. It's a balancing act. This is what you're leaving out of the equation. 

Ground adjustable will never be better than an in flight adjustable prop. So we have to choose a pitch that compliments the aspects of our needs and creates a balance between them unless you have a need for the flatter pitch climb setting.

Jeff, Roger, Nicola,
You are correct and I stand corrected, 

But, as stated, the principle is still valid.
As you unload the prop to increase the RPM the engine will move more air and fuel and therefore produce more Power.
I agree It will not be a cube function, but it will be a significant increase.
Even if linear; 5100 to 5600rpm is 10% in the right direction.
And an additional ~10hp will be noticeable.

Thanks, for calling me out.
Bill.

Hi Bill,

Sorry.

I wasn't calling you out just stating that you are correct that the 5800 pitch setting does give more torque and HP and if someone did have a prop pitch set way too course to only get 4800 rpm it definitely needs adjustment. Not only do you get poor performance, but the stress on the engine goes way up.

I was just saying that since we only get to use ground adjustable props in the US for Light Sport it's usually better to find a good balance between climb rpm and cruise. Nothing wrong with getting 5800 rpm at WOT in level flight so long as someone understands that's aimed at better climb and cruise rpm and fuel use will suffer some. There are certainly times when you need a pitch like that, but for the average pilot out there a WELL BALANCED pitch for different flight characteristics is usually better. We're only talking 150 - 200 rpm difference, but it does make a difference during flight. Yes it would be nice if all of us could use in flight variable pitch props to maximize both climb and cruise. Either way we'll make it work.

Have a good day and thanks for all your insight, help and knowledge on the forum. I know everyone appreciates it. Me too. ?

Shame we don't live closer or I'd buy you lunch. ?

I've had several aircraft MFG's set a prop pitch to only get 5200 WOT in level flight. I've changed them all to get 5600-5650 rpm WOT in level flight at their average altitude and they all thought they had a turbo then because of the difference the 400+ rpm gave them. Plus their fuel use dropped and the engine temps dropped. The difference between the 5200 WOT and the 5600 WOT gave them all better climb, faster cruise at lower throttle settings, lower fuel usage and lower engine temp on climb and less stress on the engine. The owners that have a pre mid 2006 engine has a different crank case (1500 hr. case vs the 2K hr. engine case) and over pitching too far could cause a crack in the crankcase. I bet I've set a couple hundred prop pitches over the many years.