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  #1  
Old 01-31-2021, 04:05 PM
bobg56 bobg56 is offline
 
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Location: Peachtree City, GA
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Default Minimum T/O RPM

I remember reading that Rotax 912 ULS engines were to have a minimum RPM of 5200 at climb out so as not to over load the engine or cause detonation. I don't see this anymore in the Operators Manuel or SL 912-016 which just mentions octane requirements and manifold pressures. My RV12 gets about 5150 rpm at VY which to me is close enough. I wonder if they got off that requirement?
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  #2  
Old 01-31-2021, 05:07 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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5150 RPM puts you right on the money...
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Jim Stricker
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PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
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  #3  
Old 01-31-2021, 06:14 PM
NinerBikes NinerBikes is offline
 
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https://vansairforce.net/community/s...d.php?t=184781
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  #4  
Old 01-31-2021, 08:11 PM
bobg56 bobg56 is offline
 
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Rotax had it in the Operating Manual about not over loading the engine below 5200 Rpm on the T/O climb but I looked for it and can no longer find that, I'm curious to know if Rotax revised this...I know a few people with Rotax engines in Zeniths and Kit Fox and they climb out 4800-4900. Although they may have in accurate tachs.
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  #5  
Old 01-31-2021, 09:31 PM
NinerBikes NinerBikes is offline
 
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Quote:
Originally Posted by bobg56 View Post
Rotax had it in the Operating Manual about not over loading the engine below 5200 Rpm on the T/O climb but I looked for it and can no longer find that, I'm curious to know if Rotax revised this...I know a few people with Rotax engines in Zeniths and Kit Fox and they climb out 4800-4900. Although they may have in accurate tachs.
I would take Rotax's advice about the 5200. My RV-12 climbs good, and cruises good, when I see 5200 rpm at Vy of 75 kts. 5200 RPM is 100 rpm over the peak torque at 5100 rpm on the motor. The motor is making good HP and good torque at that rate. You'll know it by how hard you have to step on the right rudder to center the ball on climb out. Takes a good amount of pressure.
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  #6  
Old 01-31-2021, 10:01 PM
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5200 RPM at Vy is just a smidge to fine from my experience, if someone is looking for the best all around performance.
I have found 5150 to be about the sweet spot unless flying near gross in hot conditions on a regular basis.

This value would be based on a take off in average temp at the airpot altitude commonly flown from. different altitude airports on different temp days, will result in slightly different values.
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  #7  
Old 02-01-2021, 08:38 AM
bobg56 bobg56 is offline
 
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I agree, 5200 would be a bit too much, probably even exceed 5800 in level WOT, I can get about 5650 and I'm happy with my pitch setting. R.O.A.N. has the 5200 RPM as the minimum target, even suggesting 5500-5800 for climb out, they have this info in their Video section regarding causes of Detenation, although it's dated 2010...I'm just wondering if ROTAX is backing off from their stance on this...RPM like this would be good if you wanted climb performance and nothing else.
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  #8  
Old 02-01-2021, 11:32 AM
NinerBikes NinerBikes is offline
 
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Quote:
Originally Posted by bobg56 View Post
I agree, 5200 would be a bit too much, probably even exceed 5800 in level WOT, I can get about 5650 and I'm happy with my pitch setting. R.O.A.N. has the 5200 RPM as the minimum target, even suggesting 5500-5800 for climb out, they have this info in their Video section regarding causes of Detenation, although it's dated 2010...I'm just wondering if ROTAX is backing off from their stance on this...RPM like this would be good if you wanted climb performance and nothing else.

I see about 5650- 5700 at WOT, level flight at 4500 ft ASL, depends on the day. Cold mornings, around 45 to 50F here in So CA, with altitude pressure of 30.20 are on the high end. August summer mornings with temps near 80 to 85 F are the lower end. Motor seems to run much richer in the summer time, a little bit leaner in the winter time, looking at the color of the spark plugs.

My interest is in cruise performance, around 6000 to 9000 ft at 5200 to 5350 rpm. I like seeing my EGT's no higher than 1400, 1300's, even 1200s is better. If your EGT's are up there, you're lugging the motor and working it too hard.

The Rotax is a short stroke, overbore built motor. Designed for rpm, less for torque and lugging the motor. Spinning fast and lightly loaded over more power strokes per minute is what it does well, less work performed, per powerstroke. It allows you to pull the throttle back about 1 1/4" from the firewall at around 5200 rpm cruise, and keep the needle in the main jet region of the Carb, instead of running full rich, at full throttle, at least that's what I am seeing, around 4500 ft.

Keep in mind, Bombardier / Rotax's engineering experience is in building snowmobile and Personal Watercraft powerplants. They all wind out, pretty high.
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Last edited by NinerBikes : 02-01-2021 at 11:42 AM.
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  #9  
Old 02-01-2021, 01:51 PM
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Quote:
Originally Posted by NinerBikes View Post
I like seeing my EGT's no higher than 1400, 1300's, even 1200s is better. If your EGT's are up there, you're lugging the motor and working it too hard.
Can you provide a reference to info that substantiates this?
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Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #10  
Old 02-01-2021, 02:14 PM
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Piper J3 Piper J3 is offline
 
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This is typical. EGT's closely matched near 1300F while making published cruise speed at just under 5500 RPM.

"How sweet it is" - Jackie Gleason
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__________________
-
Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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