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Thread: whats the heaviest motor ever put on a Kitfox

  1. #1

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    Default whats the heaviest motor ever put on a Kitfox

    I was watching a couple videos from Oshkosh this year about the different motor that were on display and came across the delta Hawk seems like a cool motor I am just in the beginning stages of research on a kitfox plane and if I am going to build one or not. I live in Hawaii and trying to get one shipped is going to be crazy expensive so I am trying to save $$$$where I can the deltahawk is really heavy though not sure it would make a good candidate or not since dry it weighs like 340lbs.
    been looking at all the auto motors but cant wrap my head around them being a good long term solution with the High RPM they run. Might be wrong but a automobile engine usually run at 2000-2500 or lower when cruising but in cruise mode I am seeing them on youtube run in the high 4000's.

  2. #2

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    Default Re: whats the heaviest motor ever put on a Kitfox

    Guess i should have listened more carefully to the video they want $$$$$$$ for that motor i think ii could buy 2 kitfoxes for what they want for the motor

  3. #3

    Default Re: whats the heaviest motor ever put on a Kitfox

    Car engines and Airplane engines have pistons and are internal combustion engines.
    That's about where the similarity's end.

    A car engine is designed to operate in the low rpm range coupled to a transmission with periodic high rpm pulls to make maximum power for brief moments of acceleration.
    A car engine when cruising down the road is not making much more then 20 to 25hp at any given time just maintaining 65mph.

    An aircraft on the other hand has to not only propel a plane forward with thrust, it must also do so with enough force to generate wind that allows for the creation of lift. Enough so to at least over come gravity's pull and over come the drag made from the plane going through the air. This requires more hp then merely rolling a car along a road where only wind drag is being dealt with on a car. As simple as I can put it anyways. Higher HP is needed at any given time thus the higher rpm being required. They are two different things requiring two different applications of engine use.

    An airplane engine is designed to run at nearly maximum rpm all day long with out issue.
    A car engine is not.

    Now, yes, some people have used car engines on airplanes and had good results but car engines are typically heavier as you've seen. So why take the weight penalty for an engine that was not designed or intended for constant high rpm use as needed in an airplane?

    It hard to beat a Rotax, 100hp at 140ish lbs dry weight.
    You might want to look into the Yamaha RX1/Apex motor. 150hp at not much more then the rotax in weight. They are abundantly available in Yamaha Snow mobiles and it seems to be becoming a more frequent choice for engine in airplanes. And they can be picked up for far cheaper then a Rotax 912 will cost you new. Of course you'll have to fab and make parts to fit it so it will still cost you some. I know one guy on youtube is building a Kitfox with this engine, he's having to fabricate motor mounts as Kitfox Aircraft does not have a FWF package for this engine. But Just Aircraft has put them on a few of their planes and I believe their is a FWF package for their aircraft now. So maybe in time we might get one for the Kitfox. In a few years time I may consider going this route if I end up building a kitfox myself.

    Best luck in your planning and search.

  4. #4
    Senior Member efwd's Avatar
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    Default Re: whats the heaviest motor ever put on a Kitfox

    I'm not sure of the weight but John McBean told me that the heaviest engine they have installed on the Series 7 was the Rotec 7 cylinder radial. That was three or four years ago. Since then they have installed the 915 as well as another larger engine on the STI plane. I don't recall what engine it was. I was at the factory at the time that engine was in a crate. 180hp if Im not mistaken. A guy had his KFS7 at Oshkosh last week that had a 9 cylinder Rotec.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  5. #5

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    Default Re: whats the heaviest motor ever put on a Kitfox

    I chatted with the guys at Rotec (maker of the 7 and 9 cyl radials). They said the 9 cylinder engine basically made it a single seat airplane since with 2 real size humans, they only had capacity for about 45 minutes of fuel. That ended the conversation for me... Even the 7 cylinder weighs about 80 pounds more than the 912. As much as I love the look, pretty much squished that dream from a realistic use-case perspective.
    Steve
    SS7 in work

  6. #6
    Senior Member efwd's Avatar
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    Default Re: whats the heaviest motor ever put on a Kitfox

    Precisely the realization I experienced as well. I can probably state that the Rotec engine install that the factory had on their plane, sold me on the KF. Then reality struck. That is how I came to the 912iS. Not regretting it though. The operation of the 912iS is simple and all the data right on the screen.
    Eddie Forward
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    Senior Member Slyfox's Avatar
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    Default Re: whats the heaviest motor ever put on a Kitfox

    Quote Originally Posted by efwd View Post
    I'm not sure of the weight but John McBean told me that the heaviest engine they have installed on the Series 7 was the Rotec 7 cylinder radial. That was three or four years ago. Since then they have installed the 915 as well as another larger engine on the STI plane. I don't recall what engine it was. I was at the factory at the time that engine was in a crate. 180hp if Im not mistaken. A guy had his KFS7 at Oshkosh last week that had a 9 cylinder Rotec.
    absolutely my thought and there are people putting it in the 4. how do you spell heavy... HEAVY. so heavy you have to put the battery way in the back and I'm sure some more weight back there. yes they will fly, but how they handle next to my 4 is a serious question.
    steve
    slyfox
    model IV 1200-flying
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  8. #8
    Senior Member jmodguy's Avatar
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    Default Re: whats the heaviest motor ever put on a Kitfox

    Quote Originally Posted by efwd View Post
    I'm not sure of the weight but John McBean told me that the heaviest engine they have installed on the Series 7 was the Rotec 7 cylinder radial. That was three or four years ago. Since then they have installed the 915 as well as another larger engine on the STI plane. I don't recall what engine it was. I was at the factory at the time that engine was in a crate. 180hp if Im not mistaken. A guy had his KFS7 at Oshkosh last week that had a 9 cylinder Rotec.
    I believe you were thinking of the O-340... The videos of John flying it looked pretty good 👍🏻
    Jeff
    KF 5
    340KF

  9. #9
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    Default Re: whats the heaviest motor ever put on a Kitfox

    Not sure if it’s the heaviest but I’m putting in a Lyc 0-233 which weighs 210lb dry together with a Airmaster CSP which weighs 24lb. I can still take 2 people and full fuel but have to reduce baggage which is no big deal.
    David
    SS7 Builder

  10. #10
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    Default Re: whats the heaviest motor ever put on a Kitfox

    While I would hate to be the winner in this fat engine contest, my Continental IO-240(125HP) weighs in at a portly 250ish lbs with accessories. At least this is what I thought when I installed it years ago. At OSH this year while wandering around I saw specs for the IO-240 that had it weighing 277 lbs, yikes!. Having said that , I have to say my Series 5 performs great and here in the east haven't found any airstrips I can't get in and out of. Prop is a 11 lb wood sensenich. We cruise at 120 mph true , takeoff dist -350' solo, and land 350' if i try hard. Bruce N199CL

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