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Pitch for Gyrocopter with 914

in 912 / 914 Technical Questions 7 years ago
Hi
I have a 914 on my 2-seater gyrocopter and I am unsure of the optimum pitch setting for this type of aircraft. Having read the wonderful blogs by Roger it seems clearly articulated that my pitch for a 914 be adjusted to reach 5600-5650 rpm @ WOT in level flight @ an average altitude.

Most of these forums discuss cruise rpms much higher than I typically use on this gyro.
To be clear my gyrocopter meets it's usual cruise speed of 75 knots while at 4500-4600 rpm (one person up, or 4800-4900 when two persons up). When I use an engine rpm around 5200 I am getting up close to the VNE of 100 knots.

As I fly typically with a lower cruise rpm compared with the aircraft mostly discussed on these blogs, is this guide of 5600-5650 still the correct rpm for setting propeller pitch ?

One observation is that the 5600-5650 setting is good for takeoff and climb when two persons up.

One final question, when we mention WOT on a 914 ... I assume this is with the turbo fully engaged, ie 115 HP ?

Thanks for the consideration of this question.

  • Re: Pitch for Gyrocopter with 914

    by » 7 years ago

    Yes, WOT means giving it every last bit that is available.

    Whatever speed and rpm you use cruising at partial throttle has little to do with setting pitch.
    The engine produced Maximum Continuous Power at 5500rpm at WOT.
    Anything else is reducing the power available.

    Setting ~5600 at WOT in level flight (Cruise) is a reference point.
    It controls the risk of overspeeding the prop inadvertently.
    It is not assumed that you will routinely be flying at this setting.
    5500-5800rpm is limited to 5 minutes.

    You will naturally be reducing the throttle to suit your needs.
    The implication is that a 5600 cruise will also produce maximum continuous climb performance at ~5500rpm at WOTat a reduced airspeed.
    When you need to climb in a hurry you need all you can get. WOT!

    Over pitching the prop to lower the rpm's does neither the engine's life nor the aircraft's performance any good.
    There is no valid reason to set it for any thing other than Max performance.

    You are obviously over powered. Not a bad thing!
    It will climb like a rocket but will need to be held back in the cruise.

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

      
    Report

  • Re: Pitch for Gyrocopter with 914

    by » 7 years ago

    Hi Bill

    Thank you for the efforts in response. Yes I am overpowered most of the time and it does climb like a wee rocket with only me !!
    With a big friend in the back and full fuel loading it is good to have the extra, especially on a higher altitude field takeoff.

    I will try the new pitch settings as I suspect the machine is 5400 WOT, at least on climb.
      
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  • Re: Pitch for Gyrocopter with 914

    by » 7 years ago

    Hi Tony,

    One of the big considerations here is not to overstress the engine parts with a prop set too coarse. A 914 with a ground adjustable prop does leave some performance on the table. So now you need to pick a BEST ALL AROUND BALANCED prop pitch for all occasions with climb, cruise, engine temps, fuel economy and engine stress factors considered. Try the 5600-5650 WOT setting and see if you like it. If you don't the nice thing about a prop is it can be changed, but I don't know of anyone I have ever dealt with want to change it back.

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

      
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  • Re: Pitch for Gyrocopter with 914

    by » 7 years ago

    Hi Roger

    I will make this adjustment now. I collected some data in the air yesterday which I didn't have. Frankly I didn't expect the wonderful response from you experienced guys.

    Data was collected at an altitude of 1200-1500 feet ASL, which I understand seems low but that's where we are most often in the gyro.

    Take off WOT
    rpm Manifold Pressure
    5350 40 (approx.)

    At altitude
    rpm Manifold Pressure
    4600 27.5 Cruise RPM
    4700 28
    4800 29
    5000 30.5
    5200 32-32.5
    5550 40
      
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  • Re: Pitch for Gyrocopter with 914

    by » 7 years ago

    You can afford to flatten the pitch a little.
    5350 in the climb is a little low.

    My personal choice would be to get above 5500 in the climb, and when it speeds up when leveling off for the cruise, just back off the throttle as needed.
    You will never be cruising at anything near WOT anyway.
    You will be surprised at how much another 200rpm will make in the climb performance.
    Do you recall your current rate of climb?

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

      
    Report
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