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Thread: Takeoff power fuel flow

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    Senior Member Andy's Avatar
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    Default Takeoff power fuel flow

    I've been crunching some takeoff performance data and am surprised by the fuel flow of my FX-3. Most takeoffs, including the first factory test flight at Yakima, show peak fuel flow greater that 17 gallons/hour. All the takeoffs have been at higher density altitude than sea level and maximum power, as computed by G3X, is typically 90% or less.

    Lycoming IO-360 data show a fuel flow of 89.3 pound/hours (14.9 gallons/hour) at maximum power mixture and 180 hp. At 90% power and max power mixture the fuel flow is 82 pound/hour (13.7 gallons/hour).

    I have data for another FX-3 and its fuel flow at takeoff power is about 13 gallons/hour which seems to match the Lycoming fuel flow data.

    Why would my almost new FX-3 have such high fuel flow at takeoff power? Is it normal to have to adjust the fuel injection after taking delivery of an FX-3?
    Last edited by Andy; 10-11-2020 at 07:53 AM.

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    Member hawgdrvr's Avatar
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    Default Re: Takeoff power fuel flow

    Are you taking off full rich or would you find a mixture setting at some future date for takeoff other than full rich? In the sport cub I did training in I think the mixture was at a set point other than full rich. I'm curious if the same would hold true after break-in to find a mixture "set" vs. full rich for takeoff?
    Neal
    FX3 On Order (May 2021)
    Richmond, VA

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    Senior Member Andy's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by hawgdrvr View Post
    Are you taking off full rich or would you find a mixture setting at some future date for takeoff other than full rich? In the sport cub I did training in I think the mixture was at a set point other than full rich. I'm curious if the same would hold true after break-in to find a mixture "set" vs. full rich for takeoff?

    Isn't the Sport Cub carbureted rather than injected?

    All my takeoffs have been full rich except when operating with density altitude over 5,000 ft. Obviously the fuel flow can be reduced at lower density altitudes but I would have expected the full rich position to give a fuel flow not greater that Lycoming specified flow for sea level maximum power mixture.

    The SILVER HAWK EX® EX-5VA1® SERVO KIT documentation includes this -

    "Precision Airmotive’s LLC Web Site has information and various links for assisting the aircraft operator in the determining if the engine is too rich or lean with the mixture lever in the full rich position."

    I have not been able to find those references yet.

  4. #4
    Member hawgdrvr's Avatar
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    Default Re: Takeoff power fuel flow

    Yes, it's carb. I am speaking from no experience, just thinking out loud. Also, does takeoff fuel flow really matter? It's like afterburner on F-16's. Cruise is what matters. Or on the A-10 we called it "afterfan"
    Neal
    FX3 On Order (May 2021)
    Richmond, VA

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    Senior Member turbopilot's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by Andy View Post
    I've been crunching some takeoff performance data and am surprised by the fuel flow of my FX-3. Most takeoffs, including the first factory test flight at Yakima, show peak fuel flow greater that 17 gallons/hour. All the takeoffs have been at higher density altitude than sea level and maximum power, as computed by G3X, is typically 90% or less.

    Lycoming IO-360 data show a fuel flow of 89.3 pound/hours (14.9 gallons/hour) at maximum power mixture and 180 hp. At 90% power and max power mixture the fuel flow is 82 pound/hour (13.7 gallons/hour).

    I have data for another FX-3 and its fuel flow at takeoff power is about 13 gallons/hour which seems to match the Lycoming fuel flow data.

    Why would my almost new FX-3 have such high fuel flow at takeoff power? Is it normal to have to adjust the fuel injector after taking delivery of an FX-3?


    One of my frustrations considering the FX-3 was the lack of documentation. Did they give you an engine manual for the CC363i? I don't see one online.

    Based on CubCrafter's press release the CC363i uses the Precision Airmotive’s Silver Hawk EX fuel injection system. Given the horsepower rating it would appear this engine most likely uses the Silver Hawk EX-5VA1 Servo Kit but there is no cross reference for engine type. While there is a setup procedure for idle mixture. There appears to be no setup for max fuel flow, instead suggesting a clogged injector or faulty gauge for high fuel flow readings.
    Last edited by turbopilot; 10-10-2020 at 09:07 PM.
    Bob Anderson, CC11-00316, N382RA (soon CC11-00435, N94RA)

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    Senior Member Andy's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by turbopilot View Post


    There appears to be no setup for max fuel flow, instead suggesting a clogged injector or faulty gauge for high fuel flow readings.
    Since my initial post I have read the Silver Hawk EX documentation and the RSA-5 documentation including some sections of the training manual. The reference to a clogged injector giving a high fuel flow indication was puzzling - until I read the section that described how fuel low metering could be implemented with a fuel pressure gage upstream up the servo output.

    The FX-3 fuel flow indication is derived from a turbine style flow sensor, not from a pressure sensor. FX-3 high fuel flow indication cannot be caused by a blocked injector.

    I hoping some FX-3 or EX-3 owners will contribute takeoff fuel flow information and comment on whether they use full rich setting below 5,000 ft density altitude.

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    Member kiwibob's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by turbopilot View Post


    One of my frustrations considering the FX-3 was the lack of documentation. Did they give you an engine manual for the CC363i? I don't see one online.

    Based on CubCrafter's press release the CC363i uses the Precision Airmotive’s Silver Hawk EX fuel injection system. .
    Hi Andy

    It was a bit of a song and dance to find out but Darren Jones at Aero Sport Power confirmed to me that the engine is based on the Superior XP360 and give me a manual (XPOM360) which says in part "IO-360 series engines are equipped with a direct cylinder injected RSA-5- AD1 fuel injection system."IO-360 series engines are equipped with a direct- port injected RSA-5A (FAA-certified) or EX360-1 (experimental) Precision Airmotive fuel injection system, or Airflow Performance FM-200 fuel injection system"

    PM me if you'd like a copy.
    Bob Gray, FX-3 #38, ZK-FXC

  8. #8
    Member kiwibob's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by Andy View Post
    I hoping some FX-3 or EX-3 owners will contribute takeoff fuel flow information and comment on whether they use full rich setting below 5,000 ft density altitude.
    Andy,

    The manual I referred to earlier recommends start, run up and t/o on full rich except at altitude. The two graphs show 17+gph on t/o in my aircraft. One was my first flight (full rich though out) and the second after about 110 hours and shows it's not changed.
    Screenshot 2020-10-12 at 14.48.49.jpgScreenshot 2020-10-12 at 14.49.56.jpg

    The manual also shows Take-Off Power Fuel Mixture Curves and says t/o 29" x 2700 rpm should be in the range 87-95lbs/hr (14.1-15.4 gph) if I read it correctly. I have no idea if this means I should adjust the full rich setting.

    I lean to LoP based on the fuel flow shown in the graphs which are also in the manual.

    Cheers
    Bob Gray, FX-3 #38, ZK-FXC

  9. #9
    Senior Member Andy's Avatar
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    Default Re: Takeoff power fuel flow

    Bob,

    I have the Lycoming built engine and the CCX-2000 maintenance manual refers to LYCOMING OPERATOR’S MANUAL #60297-12 & LYCOMING OVERHAUL MANUAL #60294-7. These manuals cover multiple variants of the engine and each has different fuel flow specifications. If CubCrafters specifies which engine in these manuals is most similar to the CC363i I have not found that reference yet.

    I only became interested in this because I compared takeoff performance data for my FX-3 with another FX-3 and the difference in fuel flow was quite obvious.

    It may well be that 17-18 gph is the correct flow for my CC363i but, if it is, maybe those with 13 gph flow should be concerned. It would be surprising to me if there should be that much difference between engines.

    Andy

  10. #10
    Member kiwibob's Avatar
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    Default Re: Takeoff power fuel flow

    Quote Originally Posted by Andy View Post
    Bob,

    I have the Lycoming built engine and the CCX-2000 maintenance manual refers to LYCOMING OPERATOR’S MANUAL #60297-12 & LYCOMING OVERHAUL MANUAL #60294-7. These manuals cover multiple variants of the engine and each has different fuel flow specifications. If CubCrafters specifies which engine in these manuals is most similar to the CC363i I have not found that reference yet.
    Andy
    Thanks Andy,

    I only got the CCX-2000 maintenance manual late in the piece, after I got the Power Sports info. I'd not noticed that Lycoming reference so I'll take a closer look.

    Certainly it's confusing
    Bob Gray, FX-3 #38, ZK-FXC

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