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3 blade versus 2 blades....

in General Tech Discussion 9 years ago
I have a 912 80 hp engine in my Merlin EZ. I've been running a 2 blade 72" IVO and it has always been vibrations. Carbs are balanced, prop is good etc. Anyone have any thoughts on me running a 3 blade with the same diameter. Will it be smoother and will it lower the speed of the plane. I'm doing 85-90 mph now at 5300 rpm. I would of course have to lean out the blades some. (ground adjust prop).

Andy C-IKEA
MerlinC-IKEA.jpg (You do not have access to download this file.)

  • Re: 3 blade versus 2 blades....

    by » 9 years ago

    Hi Andy,

    If you can only get 5300 rpm at WOT in level flight you are way over pitched. Shoot for something around 5600-5650 rpm.
    Your two blade prop may only need a dynamic balance.
    That said a three blade is usually smoother and I would personally drop in size down to a 68". There are several decent props out there, but I have gravitated towards Sensenich over the last few years.

    Bottom line it will boil down to a personal choice.

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

      
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  • Re: 3 blade versus 2 blades....

    by » 9 years ago

    Remos Aircraft went to a 3 blade prop cut down on noise and vibration, I have flown the plane with both and there is a difference. Even the US Military is adding blades to reduce vibration related maintenance cost on various aircraft.
    Thank you said by: Andy Gustafsson
      
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  • Re: 3 blade versus 2 blades....

    by » 9 years ago

    I was somewhat unclear in my question. 5300 is my cruise rpm. I can get it up to 5500 rpm no problem. If I put a third blade on my IVO (same diameter) I understand that I get rid of lots of vibrations but is the speed suffering from an added blade? (I have checked the balance and it is 1 gram difference between the blades.) I was thinking to keep the diameter of the prop. I don't know if me cutting the blades down to 68 in. will be advisable? Is the 80 hp 912 enough to spin a 72 in?

    Andy.
      
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  • Re: 3 blade versus 2 blades....

    by » 9 years ago

    I think Sensenich or a company like them would be the one's to ask for those kind of details.
    Thank you said by: Andy Gustafsson
      
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  • Re: 3 blade versus 2 blades....

    by » 9 years ago

    A 3 blade is much smoother.
    The IVO is a very heavy prop and if it is not dynamically balanced it can have a lot of vibration.
    The pilot will be amazed at the vibration/noise difference after a dynamic balance.
      
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