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Thread: Cruise rpm

  1. #11
    Super Moderator Av8r3400's Avatar
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    Default Re: Cruise rpm

    I removed the carb heat setup in favor of the dual filters. My filters (K&N) are about 6" in diameter by 2" thick.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  2. #12

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    Default Re: Cruise rpm

    I'm close to Ava8tor3400.

    5200 = 105 MPH (ias) 3.5 GPH @1500ft
    5000 = 102 MPH (ias) 3.2 GPH @1500ft

    I generally cruise around 5000 rpm. I have a Warp standard three blade and 80HP 912ul.


    Scott

  3. #13
    Newkid's Avatar
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    Default Re: Cruise rpm

    I think you can cruise at whatever RPM your heart desires just so long as it's above 5000 RPM. We used to have a little IV Speedster with a 912 UL and a Powerfin 3 blade, and we used to cruise at 5700 to 5800 RPM all day long. Full bore strait and level was about 6100 RPM. We have a friend that did the same thing in his Rans S-7 except he had a UL with high compression pistons. His motor now has 1600 hrs. on it and is still running strong. Both planes burned right around 4 gph.
    Ty
    Kitfox IV-1200
    912

  4. #14
    RIVERFOX's Avatar
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    Default Re: Cruise rpm

    Hey guys thanks for all the input. This time of year I do a lot of air to air photography of "birds of prey" along the St. Croix River and I spend much time at 4000 rpm and 40 IAS. One service center said stay above 4900 rpm and the other said 4000-4200 rpm was fine and no problem at all. Don't know who to believe. All my temps for coolant, EGT and oil are fine. I see no reason why those rpm's would be harmful. Can anyone give me a good reason why those slower rpm's would be detrimental?
    Kurt
    4-1050
    80hp
    Warpdrive
    Osceola, Wi.

  5. #15
    Administrator DesertFox4's Avatar
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    Default Re: Cruise rpm

    riverfox, years ago I was told to stay out of the 4300 to 4800 rpm range for continuous operation in the 912 series engines. You are below that rpm so from what I've understood you should be ok. You should be getting some incredibly low gals. per hour readings at 4000 rpms.


    DesertFox4
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    7 Super Sport
    912 ULS Tri-gear


  6. #16
    Senior Member HighWing's Avatar
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    Default Re: Cruise rpm

    My take on the low RPMs has very little to do with the engine and all to do with the torsional vibration strain on the gear box. But who knows?

  7. #17
    Administrator DesertFox4's Avatar
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    Default Re: Cruise rpm

    Lowell, that's my understanding too that the restrictions are for the gearbox at those rpms.


    DesertFox4
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  8. #18
    RIVERFOX's Avatar
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    Wink Re: Cruise rpm

    4200 rpm got me 1.87gph on my last check.
    4600 rpm got me 2.31gph. In fact I used that power setting for take off and did one hour, landed and checked as soon as I landed. Sure beat my Citabra fuel consumption.
    Kurt
    4-1050
    80hp
    Warpdrive
    Osceola, Wi.

  9. #19
    Super Moderator Av8r3400's Avatar
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    Default Re: Cruise rpm

    Per the seminars by both LEAF and Lockwood:

    5200 rpm minimum at full throttle for take off. Less than that leads to excessive manifold pressure. Caused by too course pitch in the prop.

    Engine redline is 5800 rpm for 5 minutes maximum.

    Maximum continuous RPM is 5500 rpm.

    I've never heard of problems with low RPM settings.



    This is how I operate my engine. If you want to do otherwise, that's up to you.
    Last edited by Av8r3400; 10-12-2010 at 07:15 PM.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  10. #20

    Default Re: Cruise rpm

    The Rotax Operator's Manual for 912 series engines (Page 10.8, section 10.1.2.1) recommends running the engines at the following cruise power settings:
    max cruise of 5500, 75% at 5000, 65% at 4800 and 55% at 4300. I'm not saying it's the bible but it's the only source I've got.

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