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Thread: Takeoff power fuel flow

  1. #11
    Senior Member Andy's Avatar
    Join Date
    Dec 2019
    Glendale, AZ

    Default Re: Takeoff power fuel flow

    Well, the voyage of discovery continues. I found out that the fuel servo on my Lycoming built engine is not made by Precision Airmotive. According to Precision my servo is made by Avstar. The Lycoming provided data seems to indicate a Lycoming part number for the servo but it seems likely it's the AVX360-1. (edited URL to point to experimental kits 10/13/20)

    Lycoming test data for my engine was provided with my FX-3. I plotted the Lycoming airflow and fuel flow test data and the upper and lower fuel flow limits for each test point. Fuel flow for the rated power test is not included so I extrapolated (best guess of curve shape) to the rated power fuel flow.

    Lycoming fuel flow plot.pdf

    It appears that my engine is set up to run a bit on the rich side but passed all applicable Lycoming tests. I'm left wondering if Lycoming built engines are set up to run richer at rated power than engines sourced from other manufacturers.
    Last edited by Andy; 10-14-2020 at 07:56 AM.

  2. #12
    Senior Member
    Join Date
    Mar 2016

    Default Re: Takeoff power fuel flow

    Might also be interesting to extrapolate the upper and lower test limits.

    Your extrapolated data point looks to be on the upper test limit, but this is a guess, cures do not look linear.

    Can't help with your particular concern as I fly one of those old fashion carbureted engines.
    Dan Arnold

  3. #13
    Junior Member
    Join Date
    Dec 2019
    Pagosa Springs, CO

    Default Re: Takeoff power fuel flow

    I built an RV-8 with IO-360 in the early 2000s. The engine was built by LyCon in Visalia, and dyno'd at 205HP. It also had lightspeed ignition. I spent a lot of time testing this engine in my zeal to win air races.

    First, you are quoting "best power" fuel flows, but actually, at take off and climb airspeeds, the engine is set up to use more than that. That is because the lower airspeeds do not cool the engine as well, or as evenly across the cylinder, and the extra fuel helps with cooling, and especially detonation margin. It is detonation margin that is the mysterious bug a boo, but detonation surely does destroy engines, and a little extra fuel is cheap.

    If you were straight and level at full power, you would lean the engine to a point 125 to 150 ROP, and then you would see the 15 gph the manual is specifying.

    John Huft

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