 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
JetPilot
Joined: 10 Jan 2006
Posts: 1246
|
 Posted: Tue Oct 26, 2010 12:04 pm Post subject: Rotax 912 Series Engine Cruise RPM's |
 |
|
| lcfitt(at)sbcglobal.net wrote: | Regarding the cruise RPM, the max cruise is 5500 and most of the guys I flew
with ran that or close to that as we allways flew at the speed of the
slowest airplane. I also know folks that use that as a max RPM - Just flew
in a SeaRay that the guy maxes at 5300. I have heard Eric Tucker say 5500
is fine for contiuous cruise. I also understand that the biggest factor
with RPM and the 912, is running it too slow in cruise as torsional
vibration at the lower RPMs are not good for the gearbox. Keep it over 5000
to 5100 minimum in cruise.
Lowell Fitt
Cameron Park, CA
Model IV-1200 R-912 UL
Currently focusing on the Left Wing Rudder Gapseal Cuffs and Landing Gear
Fairing
--- |
The above information is simply wrong. There is NO information by Rotax that says you can not cruise your 912 series engine at less than 5000 RPM. Think about it, an engine you were required to run at 5000 RPM or more ( about 75 % power or more ) all the time would be pretty useless in many sport airplanes. Since this issue has come up a lot, and since Lowell has been posting bad advice on this, I felt it necessary to take the time to look this up in the Rotax manual and service bulletins. What Rotax says is to avoid high RPM settings with high throttle settings which would lug the engine.. ( This is good advice with any aviation engine. ) So you can take Lowell's third hand ( here-say ) advice or you can operte your engine according to what Rotax publishes. Below is what Rotax says:
After a pretty good search, I found ZERO publications limiting cruise of 912 engines below 5000 RPM. Second, there are many mentions operating RPM's, INCLUDING crusing below 5000 RPM. Here it is straight from the Rotax operators manual:
http://www.rotax-aircraft-engines.co...kus/d04670.pdf
Page 5-3 Revision April 01 2010
" RUN THE ENGINE ACCORDANCE WITH THE FOLLOWING TABLE "
They list RPM's of
5800 RPM
5500 RPM
5000 RPM
4800 RPM
4300 RPM
The graphs on the previous pages cover the full RPM range from 2500 to 5800 RPM.
There is a service letter Rotax SL-912-016 that warns against " HIGH ENGINE LOAD WITH LOW RPM " and a couple other things.
http://www.rotax-aircraft-engines.co...kus/d04670.pdf
http://www.rotax-aircraft-engines.co...kus/d04645.pdf
Given the huge number of us flying with Rotax 912 series engines, this is an important subject that will have a direct impact on the way many of us fly.
Mike
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
|
| Back to top |
|
 |
Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
|
| Posted: Tue Oct 26, 2010 12:57 pm Post subject: Re: Rotax 912 Series Engine Cruise RPM's |
|
|
Hi Mike,
Your right that it is not written in the manual. The only place to get this info is to look at the published engine torque curve (5000 rpm max torque), take Eric's class where he will tell you or talk to one of the people from the factory where they will tell you that the engine was engineered to run between 4800-5200 rpm for cruise. Yes it will run lower, but it isn't good for it. Eric will tell you 5000-5300 is a really good place to be.
Your 912 (UL or ULS) can do a lot of things and will run there, but what is healthy for the continued longevity of the engine is a different story.
Just like cholesterol and smoking. Won't kill you today, but the accumulative affects over time are destructive.
We work on "Best Practices" from accumulated history since 1989 for the 912. Keep the best and toss out what causes premature rebuild or extra maint.
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
|
| Back to top |
|
|
JetPilot
Joined: 10 Jan 2006
Posts: 1246
|
| Posted: Tue Oct 26, 2010 4:12 pm Post subject: Re: Rotax 912 Series Engine Cruise RPM's |
|
|
Hi Roger,
You are one of the most knowledgeable people on the Rotax 912 that I have ever seen post on any forum. You are the first guy I would go to if I ever had a 912 question ! ( I am still using the oil filters based on your research. )
Many planes, such as mine, and the twin engine AirCam are happy with cruise RPM's in the mid 4,000 RPM range. My plane feels best at 4200 RPM and that is where I have always cruised at. Since Rotax publishes power curves and specs for low RPM's, why is this bad ? My theory is that somewhere along the line some Rotax guy wanted to prevent people from propping their Rotax 912' in the 4,000's and running a very high throttle setting therefore " Lugging the engine " The Rotax service bulletin even talks about this.
Rotx has given us a huge amount of information from on RPM's in their manuals and service bullitens, Maximum RPM limitations, Minimum idle RPM, Power VS RPM in cuise, etc. Things like minimum idle will not destroy the engine fast, it happens over time, but Rotax still takes the trouble to tell us. I think that if cruising below 5000 RPM's was in any way bad, Rotax would have told us. I believe that someone close to Rotax early on misunderstood the over propped condition with high power and the " Cruise Above 5000 RPM " myth started.
I was hoping you would comment on this, so if I a missing something, by all means let me know !
Mike
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
|
| Back to top |
|
|
Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
|
| Posted: Tue Oct 26, 2010 7:13 pm Post subject: Re: Rotax 912 Series Engine Cruise RPM's |
|
|
Howdy Mike,
It is two things and there are of course a few variables that we could talk ourselves to death over. The main two issues without throwing in all the variables is vibration and metal stress or lugging if you like that term. Now of course prop pitch plays a part here. Low 4000's aren't good to stay at for long periods. We all operate in high and low rpms we just usually never stay there. The engine torque is set up to come on strong at 4800, 5000 max torque and at 5200 the torque is where it was at 4800. This 400 rpm range is it's sweet spot so to speak. As the rpm climbs past 5000 the engine torque starts to drop off and continues to drop, but as the rpm climbs the HP goes up until it hits it's theoretical design peak at 5800 rpm.
The publishing of the data you speak of is just part of the technical data that was tested and produced by Rotax. Some times I think we all are subject to too much info and we don't always know what to do with it, me included because I'm the analytical type anyway. I have been to a number of Rotax classes over the years and in all of them this question comes up. In every class the answer over the years has been the same. Cruise somewhere between 4800-5300 rpm. This rpm will depend of course on how you have your prop set and to some degree on your plane.
You should run the higher rpms if using Avgas to help keep the lead blown out.
Our little engines will fly what ever rpm we choose and even if you do other not so good things to them, but what I think many of us want is a reliable engine, one that we don't have to maint. often, shell out any more money than we have to and keep it in good health so it will be that way to TBO. Doing non recommended things to it like eating high cholesterol foods or smoking will only cause its earlier than normal demise, which means a bunch of money out of your pocket. Doing the right thing by our Rotax engine is like keeping it on a healthy diet and exercise routine for life. I'm not doing such a good job on that part with my body, but my Rotax will out live me. 
I'm never here to dictate how someone should run their engine because it is their engine, but only offer suggestions to keep it the way I know people want it, in good solid shape for many years.
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
