Prop pitch

[jrthomas]

I am trying to optimize my prop pitch in search of the perfect setting for cruise and climb. I was making about 5400 rpm on climb out, which gave a good climb rate but I could pass redline at full throttle in level flight. 5000 rpm gave about 95mph and 5500 close to 110. By the way, I have a Model 4/912ul with 22" Dessers. I added 1 degree of pitch. It gave a big boost in cruise but now only making about 5000 rpm on climb out. It still climbs good but my concern is am I lugging the engine. I know Rotax says not to overprop. What's the opinion? Should I remove 1/2 degree? James Thomas

[Av8r3400]

What kind of prop?

[jrthomas]

Prop is a Kiev. I flew it yesterday, solo with 1/2 fuel. As best as I can tell, I picked up about 7 mph cruise. I like the improved cruise but I'm concerned about over stressing the engine with too much pitch. With the old pitch setting I've seen as much as 1500 feet per minute climb solo. I didn't have much time yesterday to check the rate of climb. I ran into rain so I cut my flight short. It was pretty hot and humid too.

[kmach]

At wide open throttle, level, at your normal cruise altitude, Aim for 5500 to 5600 rpm.

Climb rpm should be 5300 rpm or above to not lug engine.

[jiott]

I agree with Kevin, although I might go just a little more at WOT level normal cruise-say about 5650 rpm to give just a little better climb, but not overspeed at WOT level cruise.

By the way, there is lots of good discussion on this topic on the Rotax Owner forum website.

[jrthomas]

Thanks to all for your advice. Yesterday I was showing a solid 5600 rpm (maybe a little more) at full throttle in level flight and indicating about 117 mph. The Kiev pulls good, maybe too good only making 5000 rpm on climb out. That was my main concern, that over propping might be unnecessarily stressing my 912. I made a call this morning to the best Rotax man I know.(He's well trained and experienced with the 912's.) His opinion is that it would be a good idea to back off the pitch a little, maybe split the difference and back off the pitch about 1/2 degree. He was concerned as I was that too much pitch is not a good thing. My cruise at 5000 rpm went from about 95 mph at the old pitch (5150 rpm static) to about 102. I like the added speed but not sure 7 mph is worth sacrificing climb out performance. So my plan now is to remove 1/2 degree and see how it does. Thanks again, James Thomas