Cruise rpm 912 above 5k?

Hello Steven

This topic has been discussed MANY times before! See below links to read what has been already discussed as I am sure you will find the answer you seek!

https://www.rotax-owner.com/en/912-914-technical-questions/5405-cruise-rpm-in-912-motor

https://www.rotax-owner.com/en/general-tech-discussion/5812-rotax-912uls-cruising-rpm

https://www.rotax-owner.com/en/general-tech-discussion/7493-cuise-rpm-and-prop-pitch

https://www.rotax-owner.com/en/912-914-technical-questions/580-912-uls-engine-wear-at-take-off-wot-rpm

Much appreciated!

You shouldn't cruise all the time in the 4k's. It was designed for that.

Your prop is over pitched. Anything under 5500 is over pitched for a fixed pitch prop. If all you get is 5200 rpm at WOT in level flight then reduce the prop pitch by about 2 degrees to get somewhere right around 5600-5650 for your best all around balanced performance. (cruise speed, climb, fuel economy and engine temp and less stress on the engine) Leaving this engine at 5200 WOT causes way too much stress on the engine and in earlier years i.e. before the crankcase change in 2006 it would sometimes crack the case on top.  A 5100-5300 rpm cruise seems pretty normal for fixed pitch folks.

If you had a variable pitched prop then we could make better adjustments for climb and cruise during flight.

Hi Steven. If you installed a fixed pitch prop that is within the recommended Rotax mass moment inertia, set the prop static rpm within the range recommended by the prop manufacturer at WOT for the Rotax 912 UL (you state 5,200 rpm, which is a bit too slow for my prop, but it’s acceptable according to Rotax).  So what prop are you using and what data did you use to set that 5,200 rpm?  If you dynamically balanced the prop as recommended by Rotax, synchronized the carbs, and operate the engine in accordance with the limitations in Ch 2.1 of the operators manual, cruise at whatever rpm you wish. There is nothing in the current Rotax 912UL Operators Manual, Installation Manual, Line Maintenance Manual, or Heavy Maintenance Manual regarding a minimum cruise power setting to avoid stress on the engine. Unless you are cruising at WOT.  That can cause troubles.  See para 3.1.2 here https://www.rotax-owner.com/pdf/SL-912-016.pdf. 

Hi Steven,

"but it’s acceptable according to Rotax"

5200 WOT rpm in level flight isn't okay with Rotax. Rotax talks about 5200 rpm for take off rpm not WOT in level flight