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Prop diameter

in General Tech Discussion 7 years ago
Will changing my 3 bladed Warp Drive prop on a pusher from 66" to 68" improve my cruise speed.

  • Re: Prop diameter

    by » 7 years ago

    What Engine? What Plane? What is your WOT Engine Speed? What is your cruise Speed?

    Your Speed at cruise is all about Power.
    If your current WOT at Cruise is anything other than 5500rpm, you need to adjust the prop that you already have First.

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

      
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  • Re: Prop diameter

    by » 7 years ago

    Hi William,
    2" isn't going to make much of a noticeable difference and I wouldn't go to a 70".
    I did find that a sweet spot for a balanced all around prop rpm was 5600-5650 for the ground adjustable guys.. This gave a good balance between climb, cruise, fuel economy and engine temps. More rpm gave you a better climb prop, but it then suffered a tad in cruise and fuel. Anything under 5500 max rpm WOT in level flight is a waste of climb, cruise, fuel and increased engine temps.

    I did a big prop research project about 7 years ago. I tested 14 different props of different diameters, flex (stiffer vs more flex) and different shapes.
    My research was different from any prop Mfg in the US and maybe the world. I had 4 aircraft of all the same make and model and were even Mfg within a couple months of each other. Actually I had 8 of the same, but only used the 4. We take off side by side in pairs and I was the only one setting them up for control of the max rpm. Setting up testing and doing all flight maneuvers side by side shows much more than just guess work if you only flew one at a time and under different conditions for each. It compares each prop to the exact same flight conditions at the same time that I set up for take off, cruise and time of day conditions.
    Bottom line is most prop Mfg's will tell you they have the best thing since sliced bread, but they all really perform close to the same. Will a 68" do better than a 64", for the most part yes.

    I will say this about the Warp. In cruise it flew the same speed as others at the same rpm, but suffered a lot in climb compared to others. This is due to the flat straight blade design I'm sure. I experienced this big time on my own CTSW once compared to others. Warp is a good dirt field type prop and holds up well to nicks, but isn't so great if you hit something really solid and transmit that shock to the engine. A light composite might not hold up as well to rocks, but is a lot nicer to the engine if you strike something solid.

    I used to be a Warp fan, but after all the testing I've moved on.

    p.s.
    I sent my results of this research to the prop companies. Funny no one wanted to publish the results. I guess they just didn't want to look like all the other prop Mfg's. :)

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

    Thank you said by: William Holloway
      
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  • Re: Prop diameter

    by » 7 years ago

    Hi Roger

    It seems that the results of your survey are very interesting. You should show to us here.

    Let me ask you another question regarding the number of the propeller blades.

    What are the pros and cons of a 2 or 3 blades propeller both equaly configured to max. eficiency?

    Regards
      
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  • Re: Prop diameter

    by » 7 years ago

    2 vs 3 blade didn't make any difference flying, but the static rpm on the ground during setup was quite different. The 2 blades have a wider more pronounced frequency through the aircraft hull where the 3 blade had a narrower frequency and felt smoother. Props I tested were 64" to 70" 2 and 3 blade.

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

      
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  • Re: Prop diameter

    by » 7 years ago

    Question: When you are talking 5500 WOT speed are you talking engine 912, 914 or 582. I fly a 582 and have it set WOT of 6500. Would my take off and cruise benefit from a reset to 5500. Thanks
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