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Need advice - in flight adjustable prop

in 912 / 914 Technical Questions 6 years ago

  • Re: Need advice - in flight adjustable prop

    by » 6 years ago

    Not a bad idea Bill.
    Wouldn't it be a good idea though for him to get the prop ground adjusted and set up properly though?
    Then he should be able to set full fine and blast away! :)


    That would get it close and if Close Enough is Good Enough for you, then you'll be golden.
    Full FINE will be good for the Density Altitude on the day that you set it up.
    On the next Hot day with a Low-Pressure Front passing, you may need to COARSE it up a little.
    If you fly in the Winter, you may want a little more FINE than might be available.

    I have seen density altitude at the local field vary from Plus to Minus 3000 ft from Summer to Winter.
    It sounds funny when the AWOS reports a Density Altitude of Minus 2700 ft!

    If you are going to be reluctant about adjusting your Adjustable Prop, it defeats the purpose of why you spent the extra money on being able to get the max power out of the engine.

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

      
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  • Re: Need advice - in flight adjustable prop

    by » 6 years ago

    Hmm... Very good thought. I am constantly keeping an eye on my RPM Gauge - in fact I have had a new gauge fitted right in front of the pilot to enable this.
      
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  • Re: Need advice - in flight adjustable prop

    by » 6 years ago

    I have a 912ULS with a constant-speed propeller and I too was wondering what RPM to use when cruising at maximum speed (full throttle). I'd already read the service bulletin. So if I understand what was said in this thread so far, it is much better to cruise WOT at or near 5500 rpm, instead of closer to 5200 rpm, correct?

    But what about when I decide to throttle back a bit, such as to try to be more efficient. When cruising (not climbing/descending) is it basically best to be at 5500 rpm all the time? Would you ever need to go lower? Remember this is a CS prop so I can be wide-open at 5500 or at 5200, and I can be at 75% power at 5500 or at 5200, because I set the RPM target to whatever I want.
      
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  • Re: Need advice - in flight adjustable prop

    by » 6 years ago

    Ed,

    Earlier in the thread Roger advised around the 5200 for cruise. That's where I have always set mine.
      
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  • Re: Need advice - in flight adjustable prop

    by » 6 years ago

    The blanket recommendation of 5200-5300 rpm is fine if you have a fixed pitch prop like 90% of the owners have.
    If you are in the minority of the folks with adjustable props, if you were to set 5200 rpm at WOT by COARSING the prop, you would be lugging the engine.
    5500 rpm at WOT is OK. 5200 rpm at WOT is definitely NOT!
    You can cruise at 5200 rpm, just make sure your Manifold Pressure (MAP) is below 27 inches.
    75% cruise power can be had at 5000rpm at 26 inches. or 5500rpm at 22 inches.

    To set a 5500 cruise, reduce the throttle to lower the MAP and FINE the Prop to increase the RPMs.
    This is the equivalent of downshifting in a car. Lots of RPM, and not much torque. Same Power.
    Cylinder pressures will be low, the engine will run cooler, and last longer.

    An In-Flight Adjustable Prop is a Poor-Man's Constant-Speed Prop.
    The only real difference is that the constant-speed prop has a governor,
    and the In-flight Adjustable prop's governor is You!

    Set the MAP with the Throttle and set RPM with Prop Pitch.

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

    Thank you said by: Jason Knight
      
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