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912ULS fuel starvation in steep turns

in General Tech Discussion 9 years ago

  • Re: 912ULS fuel starvation in steep turns

    by » 9 years ago

    According to http://www.lightaircraftassociation.co.uk/engineering/Mogas/Rotax%204/Inspection%20checklist%20LAA-IC-ULM-ROTAX%204%20STROKE.pdf, I can expect about 3l/h of return fuel. If I fly farm patrol, I'm burning less than 7l/h, the error will exceed 40%. When I cruise solo I burn about 11, the error will be 25%. Since I cannot install meaningful tank level gauges, I have to rely on a fuel totalizer in conjunction with level switches and a sight glass on the last tank. So an accurate totalizer reading is important, but not more important than avoiding an engine out.

    This is what I have now. There is another option. The return line connects about 4" upstream from the mechanical pump. I can take that connection down to the boom of the aerie, where the gascolator sits. This would give me an additional 40" of vertical hose and hopefully give me some kind of pressure head that the air will find difficult to bypass.


    HawkFuel.png (You do not have access to download this file.)
      
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  • Re: 912ULS fuel starvation in steep turns

    by » 9 years ago

    I did not know that tiny hole would allow 3 l/h through it!
    Whats more amazing is you only burn 7 l/h at cruise power?
      
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  • Re: 912ULS fuel starvation in steep turns

    by » 9 years ago

    No, wish I were that lucky. 7l/h is on patrol flights, 35 knots, 3850rpm. That's where I do most of my flying.
      
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  • Re: 912ULS fuel starvation in steep turns

    by » 9 years ago

    OK, did the test flight now with the auxiliary pump switched off and the problem didn't reappear. I figure it must have been air in the fuel lines, didn't change anything else that could have made the misfire go away.. The EGTs are still not ok, but I damaged the aircraft on the ground, so will have to continue trying to find the problem when I fixed the plane.

    Thanks to everybody who helped!
      
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  • Re: 912ULS fuel starvation in steep turns

    by » 9 years ago

    Can I ask where you got the restrictor from? The only one I can find is this one

    http://www.summitracing.com/parts/atm-3277/overview/

    That I am told is 0.65mm rather than the 0.35 in the install manual. But maybe that is too insignificant to matter?

    Also, does it matter where in the chain it goes, must it go straight on the return outlet or can it go on the other end of the hose?

    Still learning about these things,

    Thanks.
      
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