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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. #1

    Join Date
    Nov 2009
    Location
    Oregon
    Posts
    154

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

    So here's the scenario, looking for feedback on what
    I experienced:

    Model 3, 90hours total time, I have 50 of those since I purchased it.
    9am in Oregon
    winds @ 800ft AGL: 10-15mph from the north.
    Direction flying: South
    Airspeed Indicated: 75mph
    Thermals: Moderate to Heavy, it's a 100degree day now.
    Engine: 582
    RPM: 5000ish
    Load: 950lbs gross

    While minding my own business the wings suddenly
    began oscillating up and down, both sides it appeared. Lasted
    3-4 seconds. I was about a mile south of some rolling hills.

    I pulled the power to 4000, pulled the nose back a touch to drop
    it below 70mph... and waited. It stopped. Full inpsection shows
    NOTHING loose etc... remainder of flight was normal (but quite
    gusty, bumpy, and not much fun due to weather).

    So please avoid wild speculations (I can do that on my own haha!)
    if you've had this happen or KNOW what this was from experience
    preferably in a model3 please let me know... just wanting to double
    check this isn't a known issue of any kind and was truely just the
    airflow/thermals that prevailed.

    Thanks in advance!
    ~Wild

  2. #2
    Senior Member cap01's Avatar
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    Apr 2009
    Location
    yelm, wa
    Posts
    694

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

    i have the long wings on my model IV and they will move up and down at the tips when i get into choppy air . it is a little unnerving at first , but you get used to it . ive been in some pretty rough air and they have really been flapping but nothing has happened .
    chuck
    kitfox IV 1050
    912ul warpdrive
    flying B , yelm, wa

  3. #3
    Senior Member
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    Oct 2008
    Location
    Milton,Fl
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    217

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

    Chuck,
    I venture to say this is normal movement in the wing. My model 4 wings do that also. I was a little supprised in the beginning when I saw that much movement but it dosn't bother me at all now. Your eyes are almost level with the bottom of the wing and any flex in the wing you will see right away. The wings are just a couple of aluminum pipes with non rigid covering (unlike a metal aircraft) so really they should be expected to flex. Bottom line is there have been no inflight structural breakups of the Kitfox (see new Kitplanes mag) so I think you have nothing to worry about.
    Flutter,on the other hand,is much more violent and a whole different ball game but that's not what it sounds like from your discription.
    Talk about wing flex the B-737 I used to fly would flap its wings all over the place in rough air !
    Dick

  4. #4
    Senior Member Mnflyer's Avatar
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    Jun 2008
    Location
    West Central MN
    Posts
    213

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

    HI dido on the previous posts, as Dick posted the main spars a alum tubes very strong and flexible, I've seen the flex on my plane also does get your attention the first few times.
    GB
    Flying a HKS Kitfox III and a Champ

  5. #5

    Join Date
    Nov 2009
    Location
    Oregon
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    154

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

    Well I'm not sure where "flex" ends and "flutter" begins. I've seen the wings flex a little, and that's ok.... but it was vibrating my control stick in my hand pretty hard - had to hold on pretty tight - It was the wings, not the flaperons.

    It was harsh enough I thought I had a prop blade change pitch.... does that still match with 'flex' or would someone call that 'flutter'? and if it's flutter, was that still acceptible behavior for the model 3?

  6. #6
    Senior Member cap01's Avatar
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    Apr 2009
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    yelm, wa
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    Default Re: My wings began flapping - scary - what was it?

    i have never felt anything in the stick that felt like a flutter so im just seeing flexing . they can be a wild ride in rough air .
    chuck
    kitfox IV 1050
    912ul warpdrive
    flying B , yelm, wa

  7. #7
    Senior Member Dorsal's Avatar
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    Sep 2008
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    Central, MA
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    Default Re: My wings began flapping - scary - what was it?

    An engineering response (not based on my limited experience as a KF pilot)
    IF the motion was up and down as though someone had grabbed the plane by the wingtips and shook it (vs porpoising) and IF it was symmetric (not much roll involved) then I expect the following.
    All mechanical systems where flex is involved have a natural response such that if you could grab the plane by the tips there would be some frequency that you could shake it at to excite that response. IF the thermals you where experiencing where the sharp staccato type then it is possible that you hit a set at just the right speed to excite this behavior. If this was the case then slowing down, speeding up or just getting out of that set of bumps would cause it to stop.
    There is allot of hand waving and assumptions in this theory and I may be way off the mark so take it for what its worth.
    Thoughts from others who may know better?
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  8. #8
    Senior Member
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    Milton,Fl
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    Default Re: My wings began flapping - scary - what was it?

    WildIrish,
    You "might" have something else other than "flapping". Is there anyone in your area that has a Kitfox you could check with ? How about giving John McBean a call to see if anyone has had that problem before. He might have some ideas of locations to check on the wing for loosness.
    IF it is flutter, I would expect the wing to be moving much like a "venetian blind "in the wind rather then just up and down . In any case the normal flapping is not a violent action and I don't think you would feel it too much in the stick.
    Flutter is normally caused by a control surface that is loose (such as a trim tab,aileron,etc) causing the main surface to move.
    If it was my plane I would check every nut and bolt at the wing attachment,strut,flaperon,etc.
    It is tough to analyze tihs without being in the aircraft. In any case,have it checked out. I still think it is "flapping" but better safe than sorry.
    Just my opinion.
    Dick

  9. #9

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

    As a potential Kitfox owner... I'd like to know how the plane handles in rough air? On windy days, one gets bounced around pretty well in a 152 (my trainer)... but the 152 has 200-300 lbs on the later model Kitfoxes.

    I don't mean to hijack the thread, but perhaps it's all related.

    Thank you in advance.

    Andrew
    NOKITFOXYET

  10. #10
    Senior Member
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    Milton,Fl
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    Default Re: My wings began flapping - scary - what was it?

    Andrew,
    Does the term "cork" for the Kitfox strike a note?
    Dick

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