Rotax 912 Idle RPM

by Drew Archer in 912 / 914 Technical Questions 13 years ago

Hello all I am a low time student. I am wondering what the PROPER RPM setting should be for a 2007, Rotax 912. When I started training, the idle was around 900RPM (noted because my CFI would always remind me not to let it stay there for any peroid). Plane goes in for service requiring and engine removal and came back with a 1800rpm idle. The plane goes in for it's latest 100hr and comes back and now it's at 2500rpm which the school finally questioned. The mechanic who doesnt like being questioned about his work says the manual says it should be at 2500RPM/Idle.

Which is correct?

Thanks for your time!

Re: Rotax 912 Idle RPM

by Roger Lee » 13 years ago

Roger Lee

129 5.31k 5.12k

Hi Drew,

Tell him you don't question his judgement at all, just ask him to attend a Rotax school and make up his own mind. :silly: (Just kidding of course)
If a mechanic doesn't like to be questioned maybe it's the perfect time to question him. If no one ever wants to answer questions that's one red flag for me.

You didn't say which 912. The 912ULS 100 HP or the 912UL 80 HP. The ULS 100 HP should be around 1800 at idle and when you are just sitting on the ground after the engine is warmed up and waiting then 2000+ is better. The first warm up of the day should be around 2200 - 2400 rpm.
If you have the UL 80 HP then you can be a little lower like around 1700-1800 because this engine has a lower compression. The 10.5:1 on the ULS needs the higher rpm at idle to run smooth and not beat the gearbox up with unwanted vibration. 2500 for just idle is a little excessive. It won't hurt any thing, but you may be riding your brakes during taxi or floating longer on landings when you may want a short landing. No 912 series engine should ever be set too low as it just causes vibration which will cause early and unnecessary maint.
There is no place in the Line Maint. manual that says to set the idle at 2500 rpm. If the mechanic had attended Rotax school he would already know this. The only place 2500 rpm is mentioned is in Line Maint. manual Section 8 under test run where it says to use 2500 rpm to warm up to an operating temp of 122F.

Tell the mechanic you are trying to be a good student and learn more about your engine and to show you in the manual where it says 2500 for idle since there seems to be conflicting views.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Rotax 912 Idle RPM

by bill martin » 13 years ago

bill martin

10 757 0

Drew,

My 912S idles best slightly over 1800. Your 912 may idle a little slower but probably not much. If I idle much lower, the idle begins to get rough and that can be hard on the gearbox over time. Only time I use 2500 is during warmup and on descent and final approach (sometimes).

Bill.

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Re: Rotax 912 Idle RPM

by milo avram » 13 years ago

milo avram

2 20 0

please remember there are 2 different "idle r/min.'s",

1st. engine idle, good for security and handling, (airplane), (1 400 - 2 000 r/min.),

2nd. operation idle, good for engine and thus security, (2 000 - 3 000 r/min., depending on 20 different factors, rotax mentions 2 500 - 2 750 r/min.),

Â¡ whenever SAFE and sensible !,

cheers,

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