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View Poll Results: Was this weather related, or a mechanical issue?

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  • Weather/Thermals/Wind

    12 48.00%
  • Mechanical

    13 52.00%
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Thread: My wings began flapping - scary - what was it?

  1. #11
    Senior Member HighWing's Avatar
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    May 2009
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    Default Re: My wings began flapping - scary - what was it?

    My thought is that if you felt it in the stick and it took a tight grip to control it it is likely flutter. As others have suggested, check all control connections, security of the mass balance weights including the flaperon wing attachment fittings. I have flown lots of hours in some pretty rough mountain conditions, and I don't recall any wing movement that affected the stick.

    Regarding the Kitfox and stability in rough air. I think it relates to wing loading. The Kitfox can get pretty bouncy as they are light, especially the earlier models. keep in mind, though, there have been no reports of inflight structural failure. That is what keeps me going.

    Lowell

  2. #12

    Default Re: My wings began flapping - scary - what was it?

    haha... yeah re the cork, I hear you...

    The wingloading comment makes a ton of sense, bottom line, no burritos on a windy day...
    NOKITFOXYET

  3. #13
    Newkid's Avatar
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    Mar 2010
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    Default Re: My wings began flapping - scary - what was it?

    Our first Kitfox was a Model 1 with the same wing/flapeon setup you should have. The kit provided no mass balances on the flaperons and it flew fine, even at VNE. Later my dad put mass balances on it because they were supposed help prevent flutter. Well toward VNE (upper 90s) the flapperons, with the mass balances, would flutter. They were originally placed towards the outside tips of the flaperons, he moved them more towards the middle and never had flutter again. In the IVs on up the flapperons are symmetrical, and I have never heard of a flutter problem with them.
    Ty
    Kitfox IV-1200
    912

  4. #14

    Join Date
    Nov 2008
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    Fl
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    Default Re: My wings began flapping - scary - what was it?

    Check out this YouTube link. If this looks like yours you may also want to check your pants!
    http://www.youtube.com/watch?v=kQI3AWpTWhM

  5. #15

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    Sioux Falls, SD
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    Default Re: My wings began flapping - scary - what was it?

    Chuck...Sounds scary. Never experienced anything like that in my model 2. If you felt it in the stick, I wonder if the flaperons were the culprit and the wing flexing you describe wasn't a result of that rather than the primary problem. Do you have counterweights on the flaperons?

    Chris

  6. #16
    Senior Member dholly's Avatar
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    Mar 2009
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    Default Re: My wings began flapping - scary - what was it?

    As a KF-III owner I should know this, but, I believe my spar insert is a 3' or 4' extruded aluminum 'I' Beam. Compared to other twin spar tube wings --and my old Avid Mk-IV comes to mind with flat 18" long plywood inserts-- I would have thought any wing "flapping" would be minimal and visible primarily out at the tips a couple/few feet beyond the lift strut attach. For KF-III owners who have experienced 'flapping' on occasion, for reference just how much flex are we talking about here? The comment about outboard flaperon weight position did catch my attention, interesting to note that the Avid weights were toward the middle and I don't recall too many (any?) flutter posts.
    -Aeropro CZ Aerotrek A240 Tri-Gear SLSA 912uls
    -Airdale Avid+ on CZAW Amphibs 'FatAvid Floater' (building)
    -Kitfox 4-1200 TD 912ul (sold)
    -Kitfox Model III TD 582 (R.I.P.)
    -Avid Flyer Mk-IV TD (sold)

  7. #17

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    Nov 2009
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    Oregon
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    Default Re: My wings began flapping - scary - what was it?

    I did find some looseness and something that concerns me in the Aileron swivel area near the stick, I started a new post if anyone can help me by sending photos that would be great - please find the link to that new thread HERE: http://www.teamkitfox.com/Forums/showthread.php?t=1730

    Thanks to anyone who can help answer my questions on that thread!
    ~Wild

  8. #18

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    Apr 2013
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    Hillsboro, NH
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    Default Re: My wings began flapping - scary - what was it?

    Hi Folks,
    I got into some very strange flapping in my 'Fox Model 2 - but at low speed, about 50 MPH, I changed RPM, put a bit of aileron load on the stick & it quit, not sure the cause. It was only outboard of the outer wing strut attach on both sides. It has an HKS and it was passing through an RPM range where the engine's a bit rough a bit rough, but I wouldn't expect that to be anywhere near low enough frequency to cause what I saw. Thoughts?
    Larry

  9. #19
    Senior Member SkyPirate's Avatar
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    Default Re: My wings began flapping - scary - what was it?

    curious...

    was it a twisting action?

    have you towed your plane without the wing supports in place?
    Chase
    Model 5 OutBack
    912 UL

  10. #20
    Senior Member
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    Jan 2011
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    LAWRENCE, KS
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    Default Re: My wings began flapping - scary - what was it?

    I had the Zenith 601HDS, during the time the new 601XL’s were breaking the wings off in flight, so I saw the whole thing develop on the builders group. Talk about your believers and disbelievers going to war, it got real ugly. Eventually, a bunch of builders got together and had a German company analyze the design, out of their own pocket mind you, to try and find a cause.

    It took a solid year for Zenith to do anything about it, and only after the NTSB came in urged the FAA to ground all the xl’s. Zenith just stuck their head in the sand and said nothing was wrong, meanwhile wings came off. Well, to the point, for every wing that broke, 10 others fluttered, some violently, some not so much. Often times, this happened in the pattern, so it wasn’t all about speed, like you might think.

    So what caused the flutter? Zenith still says they don’t flutter, even though Zenith now sell a wing fix (a fix for a problem that does not exist?), so for the explanation, you have to go to others who were involved in the investigation. The issue is, Zenith changed from a thick bulky wing, used on my HDS to a very thin wing, used on the XL, and also changed the attachment points, which made the wing panels longer, but reduced the amount of material they attached to (so the plane would go faster). Finally, like on my HDS, the ailerons were not mass balanced, but unlike on my HDS, the XL ailerons were connected by cables, cables that could get loose. So, here is what would happen, loose aileron cables in conjunction with unbalanced ailerons would allow the ailerons to start oscillating. The thin wing allowed the oscillations to couple to the wing, and because it was thin it wouldn’t dampen out the oscillations, and under the right conditions, the wings would flutter (conditions which were never specifically determined). Zeniths “fix” add metal to the wing and attachment points, mass balanced the ailerons and added requirements to maintaining aileron cable tension. These fixes seem to have worked, as wings stopped coming off.

    So back to the Kitfox issue, I suggest rebalanceing the ailerons and removing any slop from the aileron controls, but that is just my two cents worth. and an aluminum low wing planes problems might have little to do with a tube & fabric high wing (but it couldn’t hurt).
    Roger

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