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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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 Posted: Fri Dec 29, 2006 8:40 pm Post subject: Rotax 912-S Users, What RPM do you look for on takeoff ? |
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I have been reading the Rotax manual and it says the RPM limit is 5500 - 5800 for only one minute, with no limitation below 5500 RPM. Are you guys proping your planes to takeoff and climb out below 5500 RPM at full throttle ? Or are you seeing higher RPM's than that in the climb and pulling the power back before you exceed one minute ? Will the engine last longer if it is setup to run under 5500 RPM no matter what the throttle setting ?
Thanks,
Micheal A. Bigelow
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"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Sat Dec 30, 2006 5:35 am Post subject: Rotax 912-S Users, What RPM do you look for on takeoff ? |
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Jet Pilot,
I have my 912UL prop pitched so that I get 5,500 RPM at full throttle
in straight and level cruise configuration. With this prop and engine
combination I get only about 4950 rpm static on the ground and about
4800-4850 at full throttle at Vy climb speed. This is the best pitch
setting for maximum cruise performance. If you want better climb,
decrease the pitch a bit (get higher rpm static and climb). This will
of course put your full throttle in straight and level rpm up higher. I
would never pitch it such that you get more than 5800 rpm in full
throttle straight and level flight, but you can if you want to.
As was stated in some recent posts, stresses on reciprocating engine
parts go up dramatically with increase in engine rpm, so life of an
engine at a constantly higher rpm will probably be affected.
Thom in Buffalo
do not archive
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sat Dec 30, 2006 6:28 am Post subject: Re: Rotax 912-S Users, What RPM do you look for on takeoff ? |
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Good Morning:
I don't think Thom is flying a MKIII, so his take off rpm is not going to be the same as what I see.
I prop my MKIII same same Thom, 5500 rpm straight and level. Gives me best take off, climb, and cruise.
Prop it 5400 static.
Will see 5200 to 5300 rpm on climb, depending on air temp.
A few feet after the MKIII begins its takeoff roll, like 10 to 20 feet, rpm will be pulled from 5400 down to 5300.
Flying a 912ULS slowly will not increase service life. If anything, it will shorten it. This engine is designed to cruise at 5500 rpm max continuous. The manufacturer would not publish these numbers if they thought it would shorten the 912ULS's life. I normally cruise 5000 to 5200 rpm. Many flights over the Rockies have seen wide open throttle for several hours as we climb to 15,000 feet to get across the mountains.
If you fly with an inflight adjustable prop you can takeoff at 5800 rpm, climb for 5 minutes at 5800 rpm, then pull it back to 5500 rpm for cruise. However, it is noisier and the MKIII rougher riding at those speeds. 5000 is much quieter.
Take care,
jhauck
mkIII
PS: Another very important point is, the 912 series engines need at least 190F oil temp to burn off moisture and contaminants in the oil. You will not see this by flying less than 5,000 rpm. Also, slow flight will not keep the engine clean. When I fly local area for a while, the engine is starting to get carboned up and dirty. Usually, after the first day or two of a long cross country flight I can tell she is getting cleaned up by the sound, feel, and performance of the little 912ULS. I like to keep her happy.
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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rlaird
Joined: 10 Jan 2006
Posts: 373
Location: Houston
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| Posted: Sat Dec 30, 2006 9:03 am Post subject: Rotax 912-S Users, What RPM do you look for on takeoff ? |
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I'll second what John is saying -- no surprise there since he's my 912S mentor!
On take off, I get to about 5350 rpm... with 1-up, I cruise between 4950 and 5200 rpm, all day long, depending on how fast I want to go.
-- Robert
MkIIIc w/912S
On 12/30/06, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:[quote] --> Kolb-List message posted by: "John Hauck" <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)>
Good Morning:
I don't think Thom is flying a MKIII, so his take off rpm is not going to be the same as what I see.
I prop my MKIII same same Thom, 5500 rpm straight and level. Gives me best take off, climb, and cruise.
Prop it 5400 static.
Will see 5200 to 5300 rpm on climb, depending on air temp.
A few feet after the MKIII begins its takeoff roll, like 10 to 20 feet, rpm will be pulled from 5400 down to 5300.
Flying a 912ULS slowly will not increase service life. If anything, it will shorten it. This engine is designed to cruise at 5500 rpm max continuous. The manufacturer would not publish these numbers if they thought it would shorten the 912ULS's life. I normally cruise 5000 to 5200 rpm. Many flights over the Rockies have seen wide open throttle for several hours as we climb to 15,000 feet to get across the mountains.
If you fly with an inflight adjustable prop you can takeoff at 5800 rpm, climb for 5 minutes at 5800 rpm, then pull it back to 5500 rpm for cruise. However, it is noisier and the MKIII rougher riding at those speeds. 5000 is much quieter.
Take care,
jhauck
mkIII
PS: Another very important point is, the 912 series engines need at least 190F oil temp to burn off moisture and contaminants in the oil. You will not see this by flying less than 5,000 rpm. Also, slow flight will not keep the engine clean. When I fly local area for a while, the engine is starting to get carboned up and dirty. Usually, after the first day or two of a long cross country flight I can tell she is getting cleaned up by the sound, feel, and performance of the little 912ULS. I like to keep her happy.
--------
John Hauck
MKIII/912ULS
hauck's holler, alabama
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=84455#84455 [quote][b]
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_________________
~~~~~~~~~~~~~~~~~~~
Robert Laird
formerly: MkIIIc w/ 912ULS & Gyrobee
current: Autogyro Cavalon w/ 914ULS
Houston, TX area
http://www.Texas-Flyer.com |
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Sat Dec 30, 2006 9:11 am Post subject: Re: Rotax 912-S Users, What RPM do you look for on takeoff ? |
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John Hauck,
You are correct that I'm not flying a MkIII. You are also correct in stating RPM that results from a 5,500 rpm full throttle s&l cruise pitch will differ between airplanes. It will aslo differ between the same airplane with different props. The Warp Drive with tapered tips (as I think you have on yours) has a reportedly higher static and climb (Vy) rpm than other props when pitched for 5,500 rpm full throttle S&L flight.
As you know it is a try and test and try again until you get what is right for your particular airplane/engine/prop combination. I would guess that your starting point rpm recommendation of 5400 static is probably much closer to what he needs than what my airplane requires for the same max cruise rpm. My point was that ultimately the 5,500 rpm full throttle in cruise is a good target rpm (not the only one of course) that will most likely take a few tries before getting it right.
do not archive
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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