Interesting Wolfy.
Yes rpms will also govern fuel consumption as well as performance in the various phases of flight.
What I am not getting is why you would pitch to be able to over rev in level flight.
If I understand you correctly, you would of course not deliberately over rev in cruise, but simply pitch the prop that way to optimise climb performance?
So you would recommend a slightly lower pitch then, with max climb as the aim?
I guess it does fall between optimum TO and cruise, so a compromise between the two.
What did you figure was an optimum cruise rpm for the 912ULS?
But lower rpm in a petrol engine is not always the most fuel efficient, it is more to do with load on the engine.
Cruising your car in 4th as apposed to 5th (at a reasonable speed) will often use less fuel. But that is for engines with carby's not computer controlled engines.
I wanted to be able to climb out of the hole (so to speak) so optimized for max climb performance. And in an open frame machine flying at WOT straight and level was to fast to be comfortable for any length of time so the engine was not over revved often.
Yes in my opinion for your uses I would aim for 5600 static, which would probably give you about 5700 or so at WOT S and L.
Rotax considers anything under 5500 at WOT to be over loaded.
With that pitch I would think cruising continuously in an open machine would be uncomfortable at much over 5300rpm anyway.
I would think that would give you a nice cruise speed at about 5100 rpm.
I think from memory I used to cruise at about 5200 (climb prop) which was about 40-45kn more than fast enough for an open machine when you do it all day. That gave me an all day average (of every sort of flying) of 15 L per hour.
9 series rotax's become the smoothest at around 5500 that's where rotax designed them to run, I don't cruise at that rpm for the reason above plus it just sounds like it's revving if you sit there like that all day.
Naturally once you do some experimenting you will find the right compromise for your needs, but I would knock a couple of degrees off what warp has said to start at.
wolfy