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Thread: KF IV Support Tube Break

  1. #11
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    Default Re: KF IV Support Tube Break

    Quote Originally Posted by P Morel View Post
    Had a great day flying on Saturday. Made it to a couple lunch fly-ins and then back home. Taxi back to my hanger on turf and just before pulling in, I heard a loud "POP". I stopped but didn't see or feel anything unusual. I taxied another 30' and parked on my pad in front of my hanger. As I opened the door, it seemed to scrape on the bottom like it was mis-aligned. I looked at the opening and found my fabric on the frame under the door wrinkled. I removed my seat and found the angle support tube broken. This was a clean break and not on the weld.

    My Kitfox IV Speedster is a taildragger with just over 700 hours. Metal fatigue? Has anyone with a IV had any type of tube failure? Especially in this area?

    The repair will begin this week but the big question is what caused this failure and what kind of stress is placed on this area that would cause separation, especially in this area of the fuselage? If taxi on turf might add to the stress of an airframe, I would think any type of structural failure would be somewhere else on the airframe.

    Another question, are the angle support tubes the same gauge metal as the rest of the airframe?

    Any suggestions?
    Better after landing than while landing. That is a oh **** if I have ever seen one. I'm flag you arrived home safely. A good welder, some fabric work anf a little paint good as new. Too bad the repair will take about a month. A little nerve racking to have something like that happens.
    Paul Zimmermann
    LSRM-A
    Garland, Texas

  2. #12
    SWeidemann's Avatar
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    Default Re: KF IV Support Tube Break

    I will be following your findings on the rest of the airframe with interest. I assume all Kitfox airframes are similar in the way the fuselage tubing is constructed. Also would like to know too if others have had similar failures.

    Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  3. #13

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    Default Re: KF IV Support Tube Break

    Quote Originally Posted by P Morel View Post
    Had a great day flying on Saturday. Made it to a couple lunch fly-ins and then back home. Taxi back to my hanger on turf and just before pulling in, I heard a loud "POP". I stopped but didn't see or feel anything unusual. I taxied another 30' and parked on my pad in front of my hanger. As I opened the door, it seemed to scrape on the bottom like it was mis-aligned. I looked at the opening and found my fabric on the frame under the door wrinkled. I removed my seat and found the angle support tube broken. This was a clean break and not on the weld.

    My Kitfox IV Speedster is a taildragger with just over 700 hours. Metal fatigue? Has anyone with a IV had any type of tube failure? Especially in this area?

    The repair will begin this week but the big question is what caused this failure and what kind of stress is placed on this area that would cause separation, especially in this area of the fuselage? If taxi on turf might add to the stress of an airframe, I would think any type of structural failure would be somewhere else on the airframe.

    Another question, are the angle support tubes the same gauge metal as the rest of the airframe?

    Any suggestions?
    Paul sorry to hear about the break. It is hard to see in the 2 nd picture but there appears to be a small vertical crack going into the weld directly above the break. A close up of the break and the mentioned weld would help. What I am looking at disappears into the shadow. I am thinking the crack developed from the weld and propagated around the tube. Unusual break that's for sure.
    Kurt A

    Kitfox II,
    Rotax 912,
    1100 gross
    Fixer Upper Project

  4. #14
    Senior Member t j's Avatar
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    Default Re: KF IV Support Tube Break

    With the way this area is constructed, I can't picture in my mind how that tube could fracture and separate a half inch without compromising one of the adjacent welds.

    The fabric repair you see was not the same damage as yours. It was to replace the bungee truss.
    Attached Images Attached Images
    Tom Jones
    Classic 4 builder

  5. #15
    Senior Member Geowitz's Avatar
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    Default Re: KF IV Support Tube Break

    Obviously just a guess by looking at the pics, but my first thought as described by Lowell is a heat affected zone crack from the welding process... perhaps put into more and more tension throughout your 700 hours of flying, taxiing, and maybe an occasional less than stellar landing? Also, you do kind of have a long and potentially bumpy taxi to your runway.

  6. #16
    SWeidemann's Avatar
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    Default Re: KF IV Support Tube Break

    Regarding broken tube at 700 hours on a Kitfox IV:

    One thing I have noticed about the Experimental aircraft fleet is that most (Experimental) airplanes out there are relatively low time as compared to the General Aviation fleet of certified aircraft. In this case, compared to Certified aircraft, 700 hours is not much time on an airframe, although in looking at Barnstormers I seldom see homebuilts with more than a thousand hours on them. For instance, I would say most older Cessnas have thousands of hours on them and just keep going, with maintenance done as needed and according to the long list of AD's that is generated. Since a Kitfox fuselage is tube and fabric, it would be similar to something like the Taylorcraft, Aeronca & Champion, Piper Cub, Carbon Cub and collection of others that are durable and have been flying safely for years. Without checking, I would assume there are similar failures in other tube & fabric aircraft. For our aircraft, they are Experimental and we need to stick together and share information about what has happened to our planes to prevent further problems.

    I am hoping and expecting that IF there are other Kitfox owners/builders out there that have a similar problem that they please speak up. If this tube break is happening to more than one of us, shouldn't there be a Service Letter or some other documentation for inspections and an airworthy fix? I for one, want to know about it.

    My 2 cents, Skot
    Kitfox Vixen 912 ULS
    N24V at C29

  7. #17
    Senior Member jiott's Avatar
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    Default Re: KF IV Support Tube Break

    The x-brace tube that broke is definitely put in tension during a hard landing on the main gear, or a hard bump during taxi. The fact that there is a gap at the break with no load on the gear indicates there is permanent deformation in the structure. I would bet that if you put a straight edge along the bottom longeron under the seat area you will see that it is bowed and not straight.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #18

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    Default Re: KF IV Support Tube Break

    I have heard of what sounds like an identical occurrence here in Austria. I will alert the owner and he will probably jump on this thread to explain what happened and how he repaired it. Same Kitfox I.e. Mk 4 speedster but I think with well over 2,000 hours. The owner described what happened while we were standing next to the plane and everything he told me matches with what Paul has described. I only saw it after the repair. I did my kitfox endorsement in that Mk 4 and it has been in one ownership since the build and well flown and cared for.

    Paul I hope it's some comfort knowing you aren't the first.

    Kerry
    S5 Outback
    OE-AMJ

  9. #19
    P Morel's Avatar
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    Default Re: KF IV Support Tube Break

    Quote Originally Posted by Auster View Post

    Paul I hope it's some comfort knowing you aren't the first.

    Kerry
    S5 Outback
    OE-AMJ
    Thank you Kerry, that's what I was wondering. Am I the only KF4 owner that experienced this problem? I did an inspection on all the welds that I could see and found no indication of weak welds or cracks. Kitfox makes a great plane and safe plane. The factory workmanship is superb.

    I'm posting a few preliminary pictures on the beginning of my repair. I'm only in the fitting stage and know that I need to remove more powder coat and fabric.

    BTW, I'm also planning to change to the Grove gear that I think might give me that warm and fuzzy feeling ...
    Attached Images Attached Images
    Paul Morel
    912 Speedster

  10. #20
    Senior Member cap01's Avatar
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    Default Re: KF IV Support Tube Break

    don't you just hate cleaning the powder coat off the tubes . the high speed with a scotchbrite wheel seemed to work the best . also have used the propane torch method and melted the powder coat off .
    looks like that splice will make a nice repair
    chuck
    kitfox IV 1050
    912ul warpdrive
    flying B , yelm, wa

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