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Need advice - in flight adjustable prop

in 912 / 914 Technical Questions 7 years ago
Hello All,

I am new to the forums and not long ago I purchased a 2006 Sportstar that has the 100HP 912 motor. It also came factory fitted with an inflight adjustable prop, and I am looking for some advice as to how to get the best out of it. So far, those I have spoken to have given the following suggestion.

In the cruise, increase the pitch and throttle to get RPM around 5200 and MP at 27-28. Does that sound about right?

I have some questions...

1) MP - when is too much?

2) I have the SN of my engine (5647190) How do I know if it has the new crank case that was apparently changed in 2006?

Any advice you can offer is most valuable.

Cheers
John

  • Re: Need advice - in flight adjustable prop

    by » 7 years ago

    Do you have an in flight adjustable prop or ground adjustable? What is you wide open throttle (WOT) in cruise?
    A new crankcase replacement would have been very expensive and it's doubtful someone did this for just a few more hours toward TBO.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Need advice - in flight adjustable prop

    by » 7 years ago

    Hi Roger,

    Bu the crank case I mean - I have an engine number beyond that of when the crank cases needed replacing. My SN is 5647190

    My prop is In Flight Adjustable. WOT would push the RPM to 5500+ - on full fine of course.
      
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  • Re: Need advice - in flight adjustable prop

    by » 7 years ago

    When you say beyond the serial numbers I take that as newer. Your 5647190 engine is newer than the ones affected in the SB.

    Some of what I'm about to say is personal preference and others may chime in with a different opinion and all may be correct. There is a range of rpms in cruise you can fly and you'll find the best for each flight with some time in the air. (Ground adjustable props are set differently since they can't be altered in flight)
    Some may set the prop to run at 5500 rpm WOT and just fly there all the time. Some will set the prop to get 5500+ and then throttle back to between 5100-5400. You don't want it set to get less than 5500 and fly there at full throttle all the time. There are zero redeeming qualities about over pitching below 5500 rpm. You lose fuel economy, speed, higher engine temps and climb all suffer.
    i.e. Don't set it to only get 5100 at WOT and just sit there for all your cruising. Too much stress on the engine. You may find running a high rpm like 5200-5300 in cruise with the prop being able to achieve 5500 WOT gives you the best mileage vs fuel economy. I tend to like 5600-5650 WOT (I'm only ground adjustable) then cruise down around 5100-5300 depending on what my mission is for that flight. If I'm just flying around the pumpkin patch sightseeing or am I going somewhere that has some distance.

    So a lot of what you do will be just personal preference, the type of aircraft you have and the mission for that flight.
    Go out a do some flights and see what works best for you.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

    Thank you said by: John Fleming
      
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  • Re: Need advice - in flight adjustable prop

    by » 7 years ago

    Thanks Roger,

    Great info. I will do some pottering about and let you know the result.

    Question... MP - What is too high? I can't seem to find anything in the manual about max MP etc, and I don't want to over stress this engine.

    Cheers
    John
      
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  • Re: Need advice - in flight adjustable prop

    by » 7 years ago

    The 912ULS Operators Manual, Page 5-6 Shows...

    Performance Data for Variable Pitch Propeller.
    Max.Power ... 27.5
    5500 rpm ... 27"
    5000 rpm ... 26"
    4800 rpm ... 26" (25"?)
    4300 rpm ... 24"

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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