912S Should not run under 5000 rpm

[John Waterson]

A customer of mine mentioned that when speaking to a chap who claims to be an authority on Rotax engines, he was told that running a 912S under 5000 RPM continuously is bad for the engine. That low rpm for protracted periods of time puts undue strain on certain engine components. Has anyone heard this from a different source? I personally prefer to run the 912S at around 4800, it seems to sound good and gives a good fuel efficiency to airspeed. Or km per litre is you like.

[Mogas]

From what I remember when we did the Rotax course and also ref recent Rotax SB, there has been a lot said about loading the engine at low RPM and how this can lead to damage.
I also see no reason not to run the engine at about 4800 provided it is not working too hard. If I overload mine by going too course on the VP a definite unhappy buzz sets in and I guess that is what they are talking about.
Mogas

[janvdm]

The Rotax manual quotes various manifold pressures at different power settings, ie 55% @ 4300 rpm @ 24 inch Hg : 75% @ 5000rpm @ 26 inch Hg : take off power at 5800rpm @ 27.5 inch Hg, so I take it that you can fly at those rpm's if your prop is set to maintain specified Manifold pressures, is this correct ?? tell me.....

I fly a Sting RG VP prop and my favourit propsetting is at 4400 rpm at 25 inch Hg which gives an indicated airspeed of avarage + -215 kph if I remember correctly, in which case my engine temps are much lower than cruising at 5000rpm, remember that I fly in +40 dig C ambiant some times, there is plenty power availlable at that setting to increase speed an course out prop further to go up to 240kph round 5000 rpm within specified manifold preasure. I have a manual trim on the prop

Mike and James flew between 4800 and 5200 rpm

What does the experts say?

Hearing from you

Regards

Jan

[Rudix]

There is no reason you cannot/should not run the 912S below 5000 rpm PROVIDED we are not talking about an engine that will only run below 5000 rpm at WOT, in other words it is not good to load the engine down so much that it would not rev above 5000 rpm.

If you do load the engine down that much you will increase wear, you have higher pressures (inside the cylinder and on the bearings) and a lower volume of oil, a recipe for early failure.

If the engine is propped to rev at lets say 5500 rpm and you throttle back to below 5000 rpm it will be fine, if you run a VP prop you can increase pitch to drop the revs, but you should nor run the engine at WOT and then increase pitch to drop revs to lets say 4400 rpm, that engine will not see TBO....

Fly safe,
Rudi

[kill_devil]

see Rotax Service Letter SL-912-016 & SL-914-014
Essential Information Regarding Engine Behaviour, Performance and Manifold Pressure Data

1. Engine speed over 5500 RPM is restricted to 5 minutes maximum
2. Take off RPM at WOT (wide open throttle) should not be below 5200 RPM to avoid overloading the engine
3. Continuous use of engine speed below 5200 RPM at WOT should be avoided.

[Massimo]

Rudix and KD said it best. Its the WOT setting thats important. see here

http://www.rotax-owner.com/SI_TB_Info/S ... 12-016.pdf

[thermalator]

This super conservative aviation industry never ceases to amaze me.

The Automotive industry faces precisely the same issues, & they quietly got their engineers to fix it (decades ago), by measuring & controlling the MOST important parameter in any engine - ie. knock sensors

All we get from 200k rattex's is vague SL's

titles containing "Manifold pressure" that then tell you a MP guage is essential, then fail to mention any specific manifold pressure

Fail to mention that the 912S is more susceptible than 912 80hp

Strange thing is BRP's Water/Snow/Land products have the very best in fadec's and you won't find such crap in their operating instructions.

[Boet]

Fly it at 5000rpm. If you "baby" a piston engine, you do more bad than good. New engine? Fly it at a HIGH power setting for the first 10 hrs or so, and you will have a well run-in trouble free engine.IE: DO NOT BABY THE ENGINE WHILE RUNNING IT IN. It will only glaze the cyl walls and suip olie. My firsthand experience.

[vernon11]

Thanks Boet.
I am about to start running my new 912s. Will take your advise.
Vernon.

[Low Level]

Fly it at 5000rpm. If you "baby" a piston engine, you do more bad than good. New engine? Fly it at a HIGH power setting for the first 10 hrs or so, and you will have a well run-in trouble free engine.IE: DO NOT BABY THE ENGINE WHILE RUNNING IT IN. It will only glaze the cyl walls and suip olie. My firsthand experience.

Been there, seen that on superbike engines. Worst thing you can do is running it at constant revs for long periods. Work that throttle, and vary the revs often.

.......and don't let the engine labour - EVER.


Labour - work hard at low revs.

[Boet]

low lever, we are not do`in da moutorbaaik thing here. We talkin` bout da errouplyns. Ve flaai HI -level?? Yes. you are of course right. BUT for motorbikes.