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Thread: Classic Model 4 1200 vs Model 5

  1. #21
    Super Moderator Av8r3400's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    Not yet...
    Av8r3400
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  2. #22

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    Default Re: Classic Model 4 1200 vs Model 5

    $.02
    I have a Model 4 1050, 80hp 912 with 13 gallons onboard. I am sized at 5'11" 235lbs, the fit is fine, fine enough to fly from near KMSP to KWVI in 2 days of flying about 19hrs and 59 gallons of avgas. I flew The Rockies, Wasatch and The Sierras in one day and Came over Yosemite at 16500msl and decided to quit climbing because it was so cold. My climb at 16500msl was 500fpm, on a 80HP 912.
    The limiting time for me is a sore butt, after 3 hours in any plane I am ready for a leg stretch. The real question is, what is YOUR mission profile? For me an airplane that will go 3 hours before needing fuel is plenty, 95% of my use is 3 laps around the patch. Figure out your mission, and buy the appropriate plane, wanna travel fast and high, Questair Venture.

  3. #23
    Hockeystud87's Avatar
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    Red face Re: Classic Model 4 1200 vs Model 5

    Hey my grandpa kept his model 4 at Wattsonville as well! Did all his test flying out there.

    Quote Originally Posted by av8rps View Post
    I remember years ago asking a Rotax rep about the results they obtained after flying their testbed Model IV Kitfox Speedster that they had put a 914 on. He said the Speedster with the new engine would hit 140 in a mild climb. Unfortunately they felt the Speedster was so overpowered that they weren't going to promote that engine in that airframe. Funny, I didn't know you could overpower a plane until talking with him...
    Alright I'm gonna bite. So I was under the impression the 4 wasn't able to fit the larger motors on them. I assume this would require a custom firewall/mount and aft balance adjustments?

    Also if you're pulling 140 in a climb that would make me think you'd have to lug it just to stay under VNE in cruise. IDK how good of a setup that would be. Maybe if you had a adjustable prop you could play with pitch to not have to lug the motor in cruise. The pitch it more for fast climb?! IDK how that would work. I had a RC plane that I did a similar thing like this to. So big a motor up front I literally put lead in the back for balance. I could hover it at about 1/2 throttle and climb away fast at full throttle. I only cruised around 1/4 throttle. I think at some point your engine is so much power you're just not able to run it appropriately or how it was designed.

    Just spit-balling cause you peaked my interest. Now someone needs to try it! Little off topic.
    Last edited by Hockeystud87; 01-15-2019 at 02:03 PM.

  4. #24
    Senior Member av8rps's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    A 914 on a Model IV is probably a bit tight to fit under the cowl, but the weight is a minimal increase compared to the regular 912. So weight and balance would be no issue at all.

    Lugging the engine to keep it from over speeding is also not an issue. I have flown 912 engines for hours at lower rpms, 1/3 to 1/2 throttle with no issues at all. A 914 would be no different. You can always throttle back if you are concerned about over speeding the airframe or you just want to fly slower and enjoy the scenery.

    A 914 in a Model 4 on paper will have some astonishing numbers, and the performance might even be intimidating to some. But for many of us, that will just make it more fun! I still don't know if there ever has been an overpowered airplane (smile)

    I grew up flying model airplanes, including RC. The scaling factor of model verses a real airplane simply doesn't compare. If one could build a real airplane like a model, assuming a 1/4 scale model Kitfox would weigh 15 pounds, then a full scale Kitfox would only weigh 60 pounds, which we know isn't possible. That is scale factor. So models end up with impossibly good power to weight ratios. Probably not telling you anything you didn't already know, but I explained all that for others that didn't.

    Hmm? I wonder what would it take to get my Model 4 to hover???
    Last edited by av8rps; 01-16-2019 at 07:14 PM.

  5. #25
    Senior Member Esser's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    I am at the forward limit of my C of G when solo on my Model 7 with a 914 and a constant speed prop. I also have an intercooler which the 914 pretty much NEEDS I don't think on a model IV there is much room to have a straight forward intercooler install.
    ------------------
    Josh Esser
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  6. #26
    Super Moderator Av8r3400's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    Josh - I'll show you the weight and balance on the Mangy some time...
    Av8r3400
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  7. #27
    Senior Member av8rps's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    The Model 4 is easier to balance with extra forward engine weight because the nose is so much shorter than later models that have the longer nose. In fact, a little more weight forward on a typical Model 4 would be a good thing.

  8. #28
    Senior Member HighWing's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    When building my second Model IV, I moved the 912 a bit forward with a new engine mount to help recover some of the baggage sack capacity I lost in the first one when I put all the fairings and gap seals in the empennage. When weighing for CG, I discovered I was very close to the forward limit. Thinking about it, I remembered when I was working at United Airlines on the ramp. This was shortly after the Arab Oil Embargo. It was determined then that Max fuel efficiency was flying with CG at close to the aft limit. Very often all luggage was loaded in the aft pit. And if not full, passengers were spaced to achieve an aft CG. I decided to put 5 lbs of lead in the tail pending a tailwheel upgrade. CG still a bit forward, but hopefully a flatter elevator and a bit more speed and efficiency - assuming a Kitfox is at least a tiny bit similar to a 747.
    Lowell Fitt
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  9. #29
    Senior Member PapuaPilot's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    Quote Originally Posted by av8rps View Post

    I grew up flying model airplanes, including RC. The scaling factor of model verses a real airplane simply doesn't compare. If one could build a real airplane like a model, assuming a 1/4 scale model Kitfox would weigh 15 pounds, then a full scale Kitfox would only weigh 60 pounds, which we know isn't possible. That is scale factor. So models end up with impossibly good power to weight ratios. Probably not telling you anything you didn't already know, but I explained all that for others that didn't.

    Hmm? I wonder what would it take to get my Model 4 to hover???
    Sorry, but the numbers you used for scale factor are incorrect. If you scaled up a 15 lb. 1/4 scale plane to full size it would weigh 3375 lb. You have to cube the numbers to scale the weight factor.

    If we scale down a 1550 lb. Kitfox to 1/4 scale you would do the cube root of 1550, which equals 11.6 lb. A 1200 lb. KF4 would be 10.6 lb.

    The same thing is true with power. If you want to power a 1/4 scale version of a 100 HP engine you would need a 4.6 HP engine (that weighs 5-6 lb. too).

    Lastly, if you want to hover your KF4 you will need about 1200 lbs. of static thrust. That might take a slightly bigger engine up front. The engine on Draco might be enough. We are all waiting for your video.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  10. #30
    Senior Member av8rps's Avatar
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    Default Re: Classic Model 4 1200 vs Model 5

    Phil that was my point... scale factor is not so simple as just increasing the weight by 4.

    As an aside, my 680 lb 912uls Highlander when flown light and in cool temps will "Hover. Seriously. I was practicing full power departure stalls one no wind fall evening when I discovered that with full elevator and the nose essentially straight up it just hung there and as long as I kept the power on full it would just hang there with no forward speed, and never did stall. I asked other Highlander owners if their planes would do the same and learned that some other lightweight and 912 powered Highlanders did the same thing.

    But we don't really believe we are hovering. While it feels like you are straight up you aren't quite, so the undercambered wing is still producing lift, and that lift is just enough combined with the thrust the prop is making to make the plane feel like it is hovering. One day I'm gonna get a drone to film that as I'm guessing it will look pretty weird. Even my early super lightweight Avid Flyers wouldn't do that. I'm guessing only because they had much smaller elevators. All I know is that it sure feels strange...

    Quote Originally Posted by PapuaPilot View Post
    Sorry, but the numbers you used for scale factor are incorrect...

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