ivor.phillips wrote:I would never run my rotax 912/4 below 4800rpm because you will get a reduced fuel consumption but to the decrement of the reduction gearbox , so what you save fuel wise you will put back in gearbox overhaul,
I have not heard this before, is there any Rotax reference for it, or recommendations on permitted/advised operating range?
I find that at about 4600 the noise level starts to increase a lot (despite ANR headset) which is a nuisance, so when bimbling rather than journeying I tend to go slow. This is a 912 in a Kitfox 4 Speedster.
Having done two Rotax factory visits and asking many questions regarding cruise RPM nobody suggested a RPM below 4800 was good,
The main reason given was increased wear on the slipper clutch and gearbox components,
This is from the Rotax owners website,
Re: Rotax 912ULS Cruising RPM !!!!
by Roger Lee » 3 years ago
Your engine is rated to run continuously at 5500 rpm all day long. The majority run usually between 5100-5300 from what I have seen over the years and what is talked about on the forums. I've seen some that run the engine from 5400-5500 all the time. It was never designed to run down in the 4K's all the time. Those people cruising at 4200-4800 are wrong. The 4200-4800 cruise all day people should attend a Service level Rotax class and get some education. This should pull people up out of the 4k's. Many that I talk to on forums use 5100-5300 all the time. The engine runs leaner down in the mid 4k's too.
Where did the 4k rpm people get that type of info because it isn't in print anywhere and it's talked about on all the forums not to cruise in the 4k's, but in the 5k's.
Let the other guys do their thing and you can run somewhere around 5100-5300 and know you're doing better.
Many pick these rpms to cruise at because there is a speed vs fuel crossover point where more rpm doesn't help speed that much, but just uses more fuel.
Having the prop pitched to help your cause is a must too.
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