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Thread: Fuel Consumption Calibration

  1. #1
    Senior Member jiott's Avatar
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    Default Fuel Consumption Calibration

    I have a Dynon (EIS) fuel flow sensor in my SS7 with 912uls and needed to calibrate it. So I made a 2 hour flight at a constant 5000 rpm cruise speed, starting with completely full tanks and then filling up to full again with an accurate reading of gallons actually used at the end of 2.0 hours. By comparing this actual amount with the amount the fuel computer said I used I could come up with a correction factor to modify the "K" factor used by the sensor/computer. Now I should have a very accurate reading for at least this one condition of moderate 5000 rpm cruise. The part that pleased me the most was the gallons/hour burn rate at these conditions of just a hair over 4.0 gph. Now that's economical flying in my book! TAS was real close to 100 mph. Love this Kitfox and its Rotax engine.

    It is very comfortable flying also. The other day I had a buddy of mine, who flys a Super Cub, along as a passenger in my Kitfox and he was amazed at how quiet and vibration free it was. We could actually have very comfortable conversation with each other (over the intercom of course) during the flight. Of course all you long-time Kitfox/Rotax owners already know all of this; but for me I am continually discovering all the many good things about our birds the more hours I put on it.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  2. #2
    Administrator DesertFox4's Avatar
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    Default Re: Fuel Consumption Calibration

    The Super Sport and the Rotax 100 hp. is a very competent combination.
    Happy you are getting along with your 912ULS. It should treat you well for years to come. Love that fuel burn.


    DesertFox4
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  3. #3

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    Default Re: Fuel Consumption Calibration

    Hi Jim
    Thanks for the info at 5000 RPM.
    Since I recently started flying a model 4 912S, I was curious what the fuel burn was at various RPM's.
    I am sure that fuel burn varies with many variables such as prop pitch, aircraft weight and density altitude.
    Have you noticed what your fuel computer says for fuel burn at full throttle climb out and 5200 and 5400 RPM cruise?
    What RPM is considered a cruise RPM for the 912S?
    The fuel flow on my model 2 with a 582 would show 6.8 gph on climb out at sea level, so I am curious what the 912S does.
    Herman

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    Administrator DesertFox4's Avatar
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    Default Re: Fuel Consumption Calibration

    Herman, my model 4 with the 912ULS, Ivo in-flight adjustable Patriot prop:

    Wide open throttle on take off will show approx. 7.2g.p.h.
    Right now my prop is "fixed" for cruise so take off rpm's are in the 5200 range but 5800 rpm's on take off yielded the same approx. fuel burn.

    Cruise rpm's will range from 5200 to 5600 depending on need for speed.
    Fuel burn will range from 5.5 gph to 6.1 gph at these rpm's.


    DesertFox4
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    Default Re: Fuel Consumption Calibration

    Hi Desert Fox
    Thanks for the fuel burn info.
    Since you mentioned that you have the Patriot Ivo IFA prop, do you have any idea how it would perform in comparison to the 72" Warp drive taper tip that came on the model 4- 912S I recently acquired.
    Is the Patriot the medium 3 blade?
    I am considering this prop but like to know what to expect before I let go of $2700.
    I have an Ivo IFA prop on my model 2 -582 and found that it allows me to have full RPM's for take off and then add more pitch to reduce fuel burn but it did not increase the cruise speed over the fixed pitch Ivo.
    Herman

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    Administrator DesertFox4's Avatar
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    Default Re: Fuel Consumption Calibration

    The Patriot would be considered one of the "lite" 3- blade props from Ivo. The Medium is a heavier prop and much more money. I've never flown a Warp prop so can't compare for you. On my 912ULS the inflight increased cruise about 15 mph. over fixed.


    DesertFox4
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  7. #7
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    Default Re: Fuel Consumption Calibration

    My IVO ultralight IFA prop also increased cruise by about 15 mph over the GSC. I have a 912UL on a Vixen.
    The big advantage though is being able to get full RPM on take off!
    I have found that the very small planetary pinion on the Ultralight model has a limited lifetime though. Keep a spare.
    Cheers
    Don

  8. #8
    Senior Member HighWing's Avatar
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    Default Re: Fuel Consumption Calibration

    One more thought on fuel burn. The prop discussion is very informative, but there is one more factor to consider.

    When we were doing our annual flight of six to the Idaho back country we always flew at the speed of the slowest airplane. On our first trip, we stopped at Winnemucca, Nevada after the first three hour leg for fuel. Everyone stood around each fueling airplane watching the pump tick away. I don't recall all of the numbers, but the largest fuel burn was 12.6 gallons. The lowest load was 7.2 gallons a Model IV with every fairing option who had actually flown an additional 30 minutes to hook up with the flight. The burn rates were at almost exactly the same airspeeds.

    Granted, the fuel burn as it relates to RPM should be pretty much the same . In our flight, the least aerodynamically clean airplane was at maximum cruise throttle to maximize speed, whereas the cleanest airplane (7.2 gallons per three hours) averaged about 4700 RPM in cruise.
    Lowell Fitt
    Goodyear, AZ


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