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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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 Posted: Thu Aug 01, 2013 5:35 pm Post subject: Rotax 912ULS Stumble below 4000 RPM on final ONLY** |
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Hello all. I've got a Zodiac 601 XL-B with a Rotax 912ULS and a warp drive three blade.
It's set at 15 degrees pitch, giving me 5500 RPM CLIMB OUT, 5200-5300 static. This engine runs flawlessly on the ground. It has only 175 hours on the engine. New plugs, carbs synced, oil changed. Fresh fuel lines. All parameters are well within margins. Climbs and runs like a top, and is happy at 5500 cruise. The airplane does 100-110kts straight and level at 5500 rpm. Fuel burn is approximate at 3.5-4.1 gal/hr.
I fly my pattern at 90kts, with 70-80 on final.
When I pull the power back gradually to slow it for flaps and turning base, anything under 4k and it shakes and thuds. Maybe that speed unloads the prop? I don't know. Like I said, runs like a top on the ground. It's only running like a bag of hammers in the circuit pulling back under 4k. It is a slipper clutched plane.
Any help is appreciated!
Thanks in advance!
Chad
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C-GYXQ. 912ULS. 601XL-B |
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Fri Aug 02, 2013 5:58 am Post subject: Rotax 912ULS Stumble below 4000 RPM on final ONLY** |
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Chad,
Sounds to me like you have one of your throttle cables hanging up. By that I mean the internal cable on the outer shroud. I had this happen on my Kitfox during approach throttle reduction. Lubing the cables helped for awhile but then I finally replaced them and that solved my problem.
Dick Maddux
912UL
[quote][b]
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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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| Posted: Fri Aug 02, 2013 6:27 am Post subject: Re: Rotax 912ULS Stumble below 4000 RPM on final ONLY** |
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Dick,
Thanks for the reply. Makes sense but at the same time doesn't ? It doesn't do it on the ground. Maybe because I'm not going from very high throttle down to 4000 on the ground? Good point though, I'll have to check.
Chad
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C-GYXQ. 912ULS. 601XL-B |
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BARRY CHECK 6
Joined: 15 Mar 2011
Posts: 738
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| Posted: Sat Aug 03, 2013 2:20 am Post subject: Rotax 912ULS Stumble below 4000 RPM on final ONLY** |
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Chad:
Three things come to mind:
1 - You have a prop/engine balance issue and it shows up at a a particular RPM range.
2 - You have a gear train issue - Someone else can comment on this.
3 - You have a control surface rigging/flutter issue. <-- This is low on my guess factor list.
Barry
On Thu, Aug 1, 2013 at 9:35 PM, SIDESLIP <Chad2007(at)rogers.com (Chad2007(at)rogers.com)> wrote:
[quote] --> RotaxEngines-List message posted by: "SIDESLIP" <Chad2007(at)rogers.com (Chad2007(at)rogers.com)>
Hello all. I've got a Zodiac 601 XL-B with a Rotax 912ULS and a warp drive three blade.
It's set at 15 degrees pitch, giving me 5500 RPM CLIMB OUT, 5200-5300 static. This engine runs flawlessly on the ground. It has only 175 hours on the engine. New plugs, carbs synced, oil changed. Fresh fuel lines. All parameters are well within margins. Climbs and runs like a top, and is happy at 5500 cruise. The airplane does 100-110kts straight and level at 5500 rpm. Fuel burn is approximate at 3.5-4.1 gal/hr.
I fly my pattern at 90kts, with 70-80 on final.
When I pull the power back gradually to slow it for flaps and turning base, anything under 4k and it shakes and thuds. Maybe that speed unloads the prop? I don't know. Like I said, runs like a top on the ground. It's only running like a bag of hammers in the circuit pulling back under 4k. It is a slipper clutched plane.
Any help is appreciated!
Thanks in advance!
Chad
--------
C-GYXQ. 912ULS. 601XL-B
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SIDESLIP
Joined: 14 Oct 2012
Posts: 78
Location: CYOO
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| Posted: Sat Aug 03, 2013 2:48 am Post subject: Re: Rotax 912ULS Stumble below 4000 RPM on final ONLY** |
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Brand new prop. Brand new hub. Brand new extension. Smooth as silk at full throttle. When I mean runs rough below 4000, I mean its only firing on half the cylinders. It's THAT sputtery. Although yesterday I flew it and brought the power back REALLY slowly, and it didn't seem to do it hardly all the way to idle. I let it idle, as I lost altitude, then smoothly smashed it to the firewall. ZERO hesitation and took me from 50kts DIRECTLY to 100kts! Stuffed me in the seat. I was pleasantly shocked. The slipper was checked by a Rotax tech only 20 hours ago. It was good.
The throttle cable thing sounds legit to me....
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