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Bing 64 carb slide dampening

in General Tech Discussion 8 years ago
Hi folks,

Out of interest has anyone looked into the impact of turbulence or g on the CV carbs. I am wondering if we might see mixture fluctuations if the dampening is insufficient slides are sticky and or g transitions are rapid. Also wondering how much the slides might move at say 1-0g and 2g 4g etc. Do we think mixture would be impacted with slide depressions/uplifts? Theoretically not as the airflow is also reduced along with the jet size, but what about abrupt transitions? Curious.

  • Re: Bing 64 carb slide dampening

    by » 8 years ago

    Hi Jason,

    Could there be a momentary change, possibly. people have been flying in rough flight conditions since the begining with the Rotax. I haven't heard of anyone with any issues. The air pressure should be fairly steady and any G force would be so momentary I don't see it making any real impact.

    Maybe someone else here has another outlook?

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

      
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  • Re: Bing 64 carb slide dampening

    by » 8 years ago

    I am going to go out on a limb and posit a theory...

    Under normal operation, as the throttle is opened, more air flows through the carb.
    The slide opens to maintain a constant velocity (CV) and constant pressure in the venturi.
    The rising slide opens the needle valve slightly, admitting more fuel.
    More air plus more fuel equal no change in the fuel to air ratio.

    Now along comes a turbulence bump that raises the slide slightly.
    The Throttle remains stationary so the air flow quantity remains constant.
    The air velocity decreases due to the increased venturi cross section.
    The venture pressure increases. (Vacuum/Suction Decreases.)
    The needle valve opens slightly producing less restriction on the fuel flow.
    The reduced venturi suction cancels the reduced fuel restriction, resulting in the fuel flow remaining mostly constant.
    Constant air flow plus constant fuel flow equals no change in the fuel to air ratio.

    As long as the turbulent event is short lived and withing reasonable limits, the Fuel/Air ratio remains mostly stable through the event.
    This may be a reasonable explanation as to why the engine is not reported to misbehave during turbulent events.

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

      
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  • Re: Bing 64 carb slide dampening

    by » 8 years ago

    Thanks for the views there.

    The theory looks sound on a steady state analysis. I am a little curious about the transitions. Usually a flow needs to travel around 7 times the length of the disturbance before the pressure gradient is fully propagated hence most CV carbs have dampening mechanisms? I am not quite sure from the diagrams how the Bing 64's manage dampening. Thinking of slide valve carbs without butterfly valves where the slides are affected mechanically (by the operator) and the way they manage transitions... What happens with rapid transitions if the Bing slides are sticky. Interesting that in a max rate turn you will get a partial throttle close which may well protect the engine from the overload limitations from SL-912-016 if the RPM falls below the 5200. Nice how other considerations seem to work out when the theory is tested. Still wondering what might happen say with a undampened slide or one that say suck partially down at WOT and or stuck up at cruise power after throttling back after take off. I wonder if this last condition could create a lean condition if there is a constant we are missing in the various pressure heads or are we just looking at larger fuel droplets and less atomization. And then how this all changes at different density altitudes, has me a little confused I must say.
      
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  • Re: Bing 64 carb slide dampening

    by » 8 years ago

    I think the quick change that is only momentary happens too fast for anything to really effect anything. If it did constantly change things your rpm would be all over the place.

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

      
    Report
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