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Thread: What is the “highest” HP someone has put into a Kitfox?

  1. #1

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    Default What is the “highest” HP someone has put into a Kitfox?

    So I’m curious as to how much hp is to much, meaning the plane will hit a wall and not go any faster due to the drag, and any more hp will just get the plane up and into the air but have little effect on the top end speed.

    I know the planes not going to ever be a “fast” plane but reading most owners performance evaluation, 90 mph is to slow to get to an area to enjoy the planes other attributes.

    I have a vision, but of course I know it’s stupid but never hurts to ponder.

    TIA

  2. #2
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    I would say that generally around 120 MPH TAS is the sweet spot for my 125 HP Series 5 (Continental IO-240) . I can go a tad faster with higher power settings but everything is smoother at the 120 MPH setting which is about 65 % power. Others will chime in here ,but I suspect you will find 120 MPH to be the majic number at least on the well powered later model Kitfoxes. Bruce N199CL

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    Senior Member Dave S's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    Although I have "only" 100 hp up front, I have come to the conclusion that the current wing design works great up to about 120 MPH.


    I recall doing VNE testing to 140 and it took some coordination between power (to keep from redlining the engine) and pitching down to get to 140 - felt like the aircraft was fighting a lot of rapidly increasing drag getting to the target speed for the purpose.


    An airplane is designed around the wing and I doubt that superpowering a kitfox would result in balanced performance. It's a kitfox, not the space shuttle and I love it for what it was designed to do. I guess I never got a kitfox to find out how fast I could get out of the sky and back on the ground


    IMHO - 120 MPH is a reasonable max cruise for the design. I normally run 110-115 MPH cruise with 100 HP.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    Thanks, I’m pleased that the planes can reach 120 as nearly every review claims 90-100 max and that’s mph not knots they say.

    Hard to do any STOL when you have to spend all day getting to an area then all day getting back.

    Now with sufficient power, can an S7 be competitive at the stol drags???

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    Senior Member Slyfox's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    I am thinking at this point of a few people that have the high HP kitfox's, called I believe the Cub Killer. I think the main purpose in their mind is to get off the ground faster and climb somewhat straight up. what their top speed really doesn't matter to them.

    I personally have the 4 with the uls 100hp engine. along with the adjustable prop in flight and the fact that it is light, 650 dry. I can get some great take off's. Ya nothing like that 140+ wonder out there I'm sure, but it is fun and the aircraft handles very light with the power to weight ratio. Oh and I can fly 102kts all day long. My smooth ride is at 84kts which I do a lot for fun flying. 102kts I do to get to my play area faster. speed is important only because I have a busy schedule in my life and I only have so much time for play. can I put more horsepower on my plane, sure, but more HP cost money. sure I can do it, but I love the way it is now and I'm just going to leave it. I'm more interested in TBO at this point and I know the stock 912uls has a good one. I vote on my plane to leave it be and enjoy what I have.
    Last edited by Slyfox; 11-29-2018 at 08:41 AM.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  6. #6
    Senior Member aviator79's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    Quote Originally Posted by Rik View Post
    Now with sufficient power, can an S7 be competitive at the stol drags???
    Trent answered this definitively, didn't he? In case you didn't follow the results, he and his much upgraded KF5 placed 2nd to Draco.

    If you want to squeeze more speed out of a Kitfox so you can cover more ground more quickly, consider a turbo instead of just a bigger engine with higher nominal HP. Brandon had the STi doing 140 mph GS at 17999 on the way to OSH. Full disclosure: he had a tailwind, and did not have a readily available TAS figure. Still, being able to get into rarified air, and being able to select an altitude with favorable winds is a big plus.
    --Brian
    Flying - S7SS

  7. #7

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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    At 17,999' I'm sure he has a turbo as there's not much air up there to run an engine. 140 gs is good but as you noted tailwind. At those elevations it's not uncommon to see 50 knot tailwinds.

    It's hard to get one plane fulfill multiple missions I see.

    Just wondering if there were any S7's with the same Lycoming that the Carbon Cubs are using that are tweaked to 200 hp

  8. #8
    Senior Member jiott's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    There is an Avid Magnum in my area that has 180 hp Lyc I believe.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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    Senior Member Dorsal's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    Not sure where you are getting the 90-100 mph figure from, mine is a pretty standard 7 with 100 ponies and does 120 fairly comfortably.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  10. #10
    Administrator DesertFox4's Avatar
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    Default Re: What is the “highest” HP someone has put into a Kitfox?

    Lots of misconceptions circulating yet about cruise speeds and adverse yaw.
    I ran into those questions at the Kitfox booth at Oshkosh yet this year.

    Most attributable to the Models 1,2 & 3’s. Of course the adverse yaw issue was solved with the model 4’s and newer model’s redesigned control mixer along with larger tail control surfaces.

    The speed questions likely relate back to earlier models and some early model 4’s equipped with 2 stroke engines. If you are not cruising at 105 to 110 mph or better in a model 4 with a Rotax 80 hp and up, something is amiss.


    DesertFox4
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