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lgold(at)quantum-associat
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 Posted: Wed Mar 05, 2008 9:18 am Post subject: 912 with low RPM |
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I need to know whether the settings on my new aircraft will adversely impact my 912ULS.
I like the way my plane flies with a high prop pitch. Because of this, the 912ULS never gets near its rated maximum RPM. On full-throttle takeoff the engine only goes up to 5100-RPM; in level flight, the maximum RPM is 5370 near sea level on a 50-degree day.
Also, I like flying with my UL flying club, which often requires that I cruise very slowly, at 3900-RPM rather than going at my normal cruise of 4800-4900-RPM.
Specifically, will the fact that I cannot reach rated maximums and I often run at 3900-RPM have a negative impact on the 912ULS engine?? Also, if cruising at 5100-RPM for long periods (near full throttle) will this adversely affect the engine?
Any advice here is welcome.
Les
Zenith CH701 N67MG
[quote][b]
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fredmessinger(at)gmail.co
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| Posted: Wed Mar 05, 2008 9:41 am Post subject: 912 with low RPM |
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From http://www.rotax-owner.com/support/FAQs.pdf
Avoid low idle speeds; at idle the piston pulses are more pronounced and the gearbox has to deal with a lot of pulsing. This is worse when compounded with a heavy prop. (Rotax has a limit for the propeller "moment of inertia")
On 3/5/08, Les Goldner <lgold(at)quantum-associates.com (lgold(at)quantum-associates.com)> wrote: [quote]
I need to know whether the settings on my new aircraft will adversely impact my 912ULS.
I like the way my plane flies with a high prop pitch. Because of this, the 912ULS never gets near its rated maximum RPM. On full-throttle takeoff the engine only goes up to 5100-RPM; in level flight, the maximum RPM is 5370 near sea level on a 50-degree day.
Also, I like flying with my UL flying club, which often requires that I cruise very slowly, at 3900-RPM rather than going at my normal cruise of 4800-4900-RPM.
Specifically, will the fact that I cannot reach rated maximums and I often run at 3900-RPM have a negative impact on the 912ULS engine?? Also, if cruising at 5100-RPM for long periods (near full throttle) will this adversely affect the engine?
Any advice here is welcome.
Les
Zenith CH701 N67MG
[b]
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fredmessinger(at)gmail.co
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| Posted: Wed Mar 05, 2008 9:42 am Post subject: 912 with low RPM |
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Woops....sorry - brain fart. That was for idle speeds...
On 3/5/08, Les Goldner <lgold(at)quantum-associates.com (lgold(at)quantum-associates.com)> wrote: [quote]
I need to know whether the settings on my new aircraft will adversely impact my 912ULS.
I like the way my plane flies with a high prop pitch. Because of this, the 912ULS never gets near its rated maximum RPM. On full-throttle takeoff the engine only goes up to 5100-RPM; in level flight, the maximum RPM is 5370 near sea level on a 50-degree day.
Also, I like flying with my UL flying club, which often requires that I cruise very slowly, at 3900-RPM rather than going at my normal cruise of 4800-4900-RPM.
Specifically, will the fact that I cannot reach rated maximums and I often run at 3900-RPM have a negative impact on the 912ULS engine?? Also, if cruising at 5100-RPM for long periods (near full throttle) will this adversely affect the engine?
Any advice here is welcome.
Les
Zenith CH701 N67MG
[b]
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fredmessinger(at)gmail.co
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| Posted: Wed Mar 05, 2008 9:43 am Post subject: 912 with low RPM |
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This is the applicable snippet....anyway check out the whole FAQ. Very interesting.
Do not take off or cruise at low engine speeds. The engine was designed to take off at 5800rpm and run its whole life at 5500 rpm; the ignition, carburetion and valve timing are all designed to be at their best at this rpm.
o Low piston speeds actually contribute to piston wear as the "rocking motion" duration is increased.
o High prop loading at low rpm increases stress throughout the drivetrain.
o More combustion byproducts (carbon and lead) build up in the cylinder head with low engine speeds.
On 3/5/08, Les Goldner <lgold(at)quantum-associates.com (lgold(at)quantum-associates.com)> wrote: [quote]
I need to know whether the settings on my new aircraft will adversely impact my 912ULS.
I like the way my plane flies with a high prop pitch. Because of this, the 912ULS never gets near its rated maximum RPM. On full-throttle takeoff the engine only goes up to 5100-RPM; in level flight, the maximum RPM is 5370 near sea level on a 50-degree day.
Also, I like flying with my UL flying club, which often requires that I cruise very slowly, at 3900-RPM rather than going at my normal cruise of 4800-4900-RPM.
Specifically, will the fact that I cannot reach rated maximums and I often run at 3900-RPM have a negative impact on the 912ULS engine?? Also, if cruising at 5100-RPM for long periods (near full throttle) will this adversely affect the engine?
Any advice here is welcome.
Les
Zenith CH701 N67MG
[b]
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jack.kuehn(at)gmail.com
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| Posted: Wed Mar 05, 2008 11:31 am Post subject: 912 with low RPM |
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I had my prop set like your at first, and the engine burned a slight
bit of oil. The Rotax technician at Lockwood said it would not hurt
the engine, but it was like lugging it a bit. This engine really
likes to spin up! When you flatten the prop, you get the full
horsepower you paid for! That extra few percent of power makes a big
difference, and you do not have to use it if you do not want to. You
might just need it in a bad wind situation or downdraft.
Jack
On Wed, Mar 5, 2008 at 10:15 AM, Les Goldner
<lgold(at)quantum-associates.com> wrote:
| Quote: |
I need to know whether the settings on my new aircraft will adversely impact
my 912ULS.
I like the way my plane flies with a high prop pitch. Because of this, the
912ULS never gets near its rated maximum RPM. On full-throttle takeoff the
engine only goes up to 5100-RPM; in level flight, the maximum RPM is 5370
near sea level on a 50-degree day.
Also, I like flying with my UL flying club, which often requires that I
cruise very slowly, at 3900-RPM rather than going at my normal cruise of
4800-4900-RPM.
Specifically, will the fact that I cannot reach rated maximums and I often
run at 3900-RPM have a negative impact on the 912ULS engine?? Also, if
cruising at 5100-RPM for long periods (near full throttle) will this
adversely affect the engine?
Any advice here is welcome.
Les
Zenith CH701 N67MG
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Wed Mar 05, 2008 2:02 pm Post subject: Re: 912 with low RPM |
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Hi Les,
Let's take a look at the reasons for the correct rpm at different speeds.
First the 912 80hp only has 9:1 compression where as the 912 100hp has 10.5:1 compression. The low idle rpm will cause the 912uls (100hp) to lug or a better term is to chug because it is fighting against the high compression. The 80 hp doesn't have that problem because of the lower compression. Rotax wants the idle on the 100 hp set to at least the 1800 mark give or take a few rpm. 1400-1600 is too low and just beats on the gearbox and components. Warm up in the morning should be done at 2000-2400 rpm because it is easier on the engine and it will not hurt it because the engine is not under an in flight load. Sitting there warming up at 2400 rpm has a lot less load on the engine than in flight rpm of 5000. This came right from Rotax. I just finished their new version of their service center school.
This engine was designed to run cooler and smoother at higher rpms. Mid range rpms of 4400-4800 run hotter egt than running it at 5000-5200rpm and cause more vibration. It can have a continuous running at 5500, but it will be easier on the engine's wear over the 1500hr TBO time to run it down around the 4900-5200 mark. Anything that runs higher and higher rpms have to burn more fuel, cause more over all stress, friction and wearing of parts. That's just the way it is when metal parts run together. There are at some point issues with engines running to low and rpm and of course too high. Rotax designed this engine to be run for the everyday normal use from 4900-5200. Yes you can run it all the time at 5500 without any real issues, but you will encounter more wear and tear on parts over the life of the engine. As far as running it above 5500 rpm you can, but for 5 minutes or less. If you do not have a need for the extra climb performance or you do not fly at high altitude (7k feet or more) then setting the prop to turn 5500 rpm WOT is a good place to be. If you fly your plane and you are heavily loaded a good part of the time, fly out of a high density altitude most of the time or fly high then you may want to set up the prop to turn 5600-5750rpm WOT. At the higher rpms you can only fly there a short time anyway like takeoffs, but if you fly at 8k-10k feet you will be able to turn the prop faster, make a little more HP at those altitudes and go a little faster at those high altitudes. This is not guess work, but I have proved this to many. Having the prop set to achieve 5500 or a tad more can benefit you on a bad landing too. If you bounce or flare back into the air and need power and rpm now to save your butt then a prop set to get 5500 or more will spin up faster than a prop set for 5100 WOT and will give you the little extra boost to save your plane when you are hanging on the edge of a stall.
The everyday torque curve for for the 912uls states close to this. As the engine rpm climbs so does the HP. The torque will climb a little faster than the HP. The torque's best rpm setting is between 4800-5200 rpm then torque starts to drop off, but HP still climbs as the rpm climbs. No one gets a true 100 hp out of their engine for several reasons, but having an engine that only gets 5100-5200 WOT is really doing the flight performance and the engine a disservice. Having it set up to run 5500 WOT straight and level is good and if need be, only for specific reasons, more rpm and a little more hp can be achieved. This engine was set up to be more flight specific than most know.
You will get better fuel economy if your prop is set to 5500 WOT verse 5100 WOT. You have to give it more fuel to try and achieve the 5100 WOT, but less fuel/throttle to get 5000-5100 when the prop is set for 5500 rpm because you will be able to throttle back more to get the speed you want.
But it is a great engine and almost bullet proof. Treat it right and it will last for ever. I have some friends that have 2800-3200 hrs on their 912uls engines and have never had an issue or rebuild. I have been flying and working on 912's for 7 years.
| | - The Matronics RotaxEngines-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:
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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Rich L
Joined: 23 Feb 2008
Posts: 63
Location: North Idaho
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| Posted: Thu Mar 06, 2008 3:43 am Post subject: Re: 912 with low RPM |
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I want to thank Roger for the informative note on the 912ULS RPM. It is framed and hanging on my hanger wall for all the visiting "experts".
Rich L
North Idaho
Back-Country Kitfox 7
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Fri Mar 07, 2008 1:53 pm Post subject: Re: 912 with low RPM |
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Be kind to your engine or else.
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| Magnetic oil plug from a 912ULS. |
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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