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Thread: A much faster Kitfox?

  1. #11
    Senior Member av8rps's Avatar
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    Default Re: A much faster Kitfox?

    Skot,

    I'm curious, have you ever tested your Vixen to see just how fast it will go wide open? So many times when we are talking about speeds one guy means at x rpm, while another is using y rpm. So I've learned to ask people "What will it indicate as well as show for true air speed when wide open throttle, straight and level, at a reasonable altitude of say 7,500 ft? And what is the engines rpm at your max speed".

    Doing it this way is a really good way for us to compare our fleet so we can figure out what mods really makes them go faster.

    Now I don't want anyone tearing the wings off their airplanes in an effort to find out that number, but it would be interesting to know if most of our fleet could even come close to their VNE.

  2. #12
    Administrator DesertFox4's Avatar
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    Default Re: A much faster Kitfox?

    Skot- I couldn't remember if your Vixen's gear had that fairing mod or not but sure sounds like it has.


    Paul- I've had my model 4 with a 912uls to 132 mph wide open throttle many times. Usually at 3,500 feet or so altitude with the Ivo Lite prop. with rpms
    in the 5,600 to 5,700 range for just a minute, two at the most. I have no wheel pants, spinner, jury strut fairings or horizontal stabilizer fairings. I do have gas cap fairings and strut fairings and the wide body modification along with the razorback mod. Empty weight 659 lbs.
    My airspeed indicator and gps are within 1 mph on a zero wind day. We actually have quite a few zero wind days here in Phoenix.

    Some years back Michael Gibbs had the exact same model 4 Kitfox with the same engine but with wheel pants, large spinner and streamlined jury struts and an Ivo Medium prop and he could hit VNE (140 mph) in level flight under the same conditions. I can't recall what his empty weight was but I think slightly heavier than mine. He also climbed that Kitfox up to 17,999 feet in altitude and still had a little more ceiling left.


    DesertFox4
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  3. #13
    Senior Member Esser's Avatar
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    Default Re: A much faster Kitfox?

    I don't think anyone will rip their wings off if it's within reason. A really good advantage to the Kitfox is that is has push rods which helps with flutter. The bad thing is it has a flexible wing which is not good. Also, I don't know how well the flapperons are balanced as I havent got that far yet. On that note, the flapperons don;t seem that stiff. You could inject a dense foam in them but you will certainly get corrosion issues if you do that.

    All that being said, I do think the Kitfox has some efficiencies to be gained. If you want to go faster, that is a different story.

  4. #14
    desertfox1's Avatar
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    Default Re: A much faster Kitfox?

    Murle and I built our planes side by side in his shop(94-96), good times!
    We enclosed the landing gears and did a bunch of other mods. I'm in the
    plastic business so was able to form the parts as we came up with ideas.
    I have done the gear enclosure mod on several planes since then, including yours Skot. I think the exposed gear is the biggest source of drag after the
    round tube struts.

    I'll try to post a pic of the latest fairing Bill and I are working on. Just what
    you were talking about Paul, 4.5 inches and under a pound per strut.

    Phil
    Attached Images Attached Images

  5. #15
    SWeidemann's Avatar
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    Default Re: A much faster Kitfox?

    Phil,

    Do you, or will you make these parts for other Kitfox fans?

    Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  6. #16
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    Default Re: A much faster Kitfox?

    I can easily exceed VNE in level flight with N85AE if I firewall the throttle
    with my IO-240B, I have a 74" Sensenich prop on it. The engine is very
    smooth thanks to recent dynamic balance of the prop, but ...

    It feels like a runaway train at 140, and it's NOT a comfortable speed at
    all. The plane is all wrong for going fast ...

    My Dad (the one with the PhD in Aero Engineering) told me once - Don't
    waste your time trying to make it go fast the shape of the plane is all
    wrong. If you want to go fast build a different plane.

    Jeff



    Quote Originally Posted by av8rps View Post

    Now I don't want anyone tearing the wings off their airplanes in an effort to find out that number, but it would be interesting to know if most of our fleet could even come close to their VNE.

  7. #17
    Senior Member av8rps's Avatar
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    Default Re: A much faster Kitfox?

    Jeff,

    I'm not surprised that a IO-240 powered Kitfox will easily exceed VNE. The non rotax aircraft engines still seem to be all around the best for flat out speed. Granted, I do remember an article years ago where they did a fly off between a Kitfox 5 IO-240 vs a Kitfox (4?) with a Rotax 914, and they were both really fast airplanes, with the 914 being just a bit faster (150+ mph as I recall), but it was using higher altitudes to get it.

    My model IV seems to not hit the "wall" that previous models I've flown do. I attribute that 90% plus to the Riblett airfoil. One day I put my Kitfox amphib in a long shallow dive while trying to catch up with some buddies that were flying about 500 ft below me, and because I was a bit fixated on where they were, I wasn't paying attention to my airspeed indicator. When I finally leveled out and passed them like they were standing still I looked down at my ASI to see I was going 155 mph! A really DUMB mistake on my part (and I won't ever do that again), but I have to say I never noticed that the airplane was struggling to go that fast. In fact, I'm pretty confident it would have gone faster had I not leveled off.

    One of my favorite antique planes is a Monocoupe. The Kitfox so much reminds me of a Monocoupe. And when you study them, they went like hell on not a lot of power. Yet, they didn't use any kind of a special airfoil, and the general concept of the airplane was pretty much like our modern day Kitfoxes. So I really do believe our Kitfoxes have much more potential for speed.

    Again, I'm not saying we need a 200 mph Kitfox, but it sure would be nice if we could cruise closer to VNE without having to run wide open. Your Kitfox is what I believe to be the exception to the fleet, and probably a good example of what we can accomplish if we clean it up more, put more power on it, or both.

  8. #18
    Senior Member av8rps's Avatar
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    Default Re: A much faster Kitfox?

    Those look awesome Phil! Yup, just like I was talking about.

    Quote Originally Posted by desertfox1 View Post
    Murle and I built our planes side by side in his shop(94-96), good times!
    We enclosed the landing gears and did a bunch of other mods.....

    Phil

  9. #19
    Senior Member av8rps's Avatar
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    Default Re: A much faster Kitfox?

    Steve,

    Well, you and Michaels Model 4's are just more proof of the potential our planes have for higher speeds. So just imagine if we could do more clean up on them and go even faster...

    I think there is something special that happened when the Murle Williams wide cabin mod was done on some of those Model 4's. I'm thinking it must give the short fuselage better aerodynamics / taper, much like the new Kitfox has being wider, and not requiring doors that are bubbled out.

    So how about short or long wings? I'm pretty convinced the 4's with the Speedster (short) wing are faster than the long wing. But with the newer and heavier Kitfoxes, the short wing wouldn't work as well as the long wing for speed as it has to fly at too high of an angle of attack even when at cruise. Anybody have any thoughts about that?




    Quote Originally Posted by DesertFox4 View Post
    Skot- I couldn't remember if your Vixen's gear had that fairing mod or not but sure sounds like it has.


    Paul- I've had my model 4 with a 912uls to 132 mph wide open throttle many times. Usually at 3,500 feet or so altitude with the Ivo Lite prop. with rpms
    in the 5,600 to 5,700 range for just a minute, two at the most. I have no wheel pants, spinner, jury strut fairings or horizontal stabilizer fairings. I do have gas cap fairings and strut fairings and the wide body modification along with the razorback mod. Empty weight 659 lbs.
    My airspeed indicator and gps are within 1 mph on a zero wind day. We actually have quite a few zero wind days here in Phoenix.

    Some years back Michael Gibbs had the exact same model 4 Kitfox with the same engine but with wheel pants, large spinner and streamlined jury struts and an Ivo Medium prop and he could hit VNE (140 mph) in level flight under the same conditions. I can't recall what his empty weight was but I think slightly heavier than mine. He also climbed that Kitfox up to 17,999 feet in altitude and still had a little more ceiling left.

  10. #20
    rocketman2tm's Avatar
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    Default Re: A much faster Kitfox?

    Seeing as a 200 mph Kitfox was mentioned, I feel that I should share an article about a turboprop Kitfox I found.

    http://www.aero-news.net/index.cfm?d...1-902f64bdadf0

    This was from the Skystar days. I doubt that they ever sold any. Did anyone ever see this beast or see it fly?
    John Grueter
    N188LR
    Kenosha, WI
    Series 7 Super Sport - flying!

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