climb rpm
in 912 / 914 Technical Questions
7 years ago
What are typical take off and climb rpm for the 912 series?
Looking at a recent Service Letter, Rotax says not to run WOT below 5200 rpm, including take off, yet most users here find best overall operation with a fixed prop set to give around 5600 rpm at WOT cruise. These two operating points don't appear consistent. Is this precaution from Rotax something new, and if so, what prompted it?
Looking at the power curves in the Operators Manual, the 5600 rpm WOT recommendation derates the engine to 95 hp. I imagine such a prop setting is optimized for economical cruise--which is just where I'd want to optimize the engine.
Derating the 912S is very reasonable. The "100 hp" claim by Rotax is rather a stretch. If you take the continuous rating (which is how most of the traditional 4 cylinder engines are rated) and convert from metric hp to imperial hp, and you make an adjustment for crankshaft hp to prop shaft hp, you get about 91 hp, which is closer to that 5600 rpm WOT cruise rating. (No complaints about the 91 hp, though; it flew very nicely in an LSA I recently tried, and that plane was near the LSA maximum weight.)
Looking at all the notes associated with this section of the S.L., I suspect their concerns with WOT were first raised from use with constant speed props, but the caution is more broadly worded to include fixed props.
Looking at a recent Service Letter, Rotax says not to run WOT below 5200 rpm, including take off, yet most users here find best overall operation with a fixed prop set to give around 5600 rpm at WOT cruise. These two operating points don't appear consistent. Is this precaution from Rotax something new, and if so, what prompted it?
Looking at the power curves in the Operators Manual, the 5600 rpm WOT recommendation derates the engine to 95 hp. I imagine such a prop setting is optimized for economical cruise--which is just where I'd want to optimize the engine.
Derating the 912S is very reasonable. The "100 hp" claim by Rotax is rather a stretch. If you take the continuous rating (which is how most of the traditional 4 cylinder engines are rated) and convert from metric hp to imperial hp, and you make an adjustment for crankshaft hp to prop shaft hp, you get about 91 hp, which is closer to that 5600 rpm WOT cruise rating. (No complaints about the 91 hp, though; it flew very nicely in an LSA I recently tried, and that plane was near the LSA maximum weight.)
Looking at all the notes associated with this section of the S.L., I suspect their concerns with WOT were first raised from use with constant speed props, but the caution is more broadly worded to include fixed props.
