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Bungee tube failure

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rob1fras(at)bigpond.com
Guest

Posted: Thu Feb 03, 2011 1:53 am Post subject: Bungee tube failure

Hello Kitfox pilots ,

 I had a suprise recently, the morning after an  interesting flight looking at local floodwater [and a good 3point landing]  .

  I pulled kitfox 2 from hanger over a very  slight lip in door way of hanger and noticed a strange noise .I found a broken  tube on the undercarriage .

 The tube takes the strain of the 6 bungee wraps and  had failed completely under the 2nd wrap and had thus been concealed from   normal inspection . I am going to sleeve the tube to prevent another  failure.

 Needless to say the consequences could have been  disastrous had the failure occurred during landing or takeoff.

 The aircraft has  had its share of rough  landings during training and has done over 700 hours not sure of number of  landings as I am not the original owner /builder.

 I suggest everyone with a few hours on bungee gear  attempt to check for cracking by moving bungeewraps sideways a little ,one at a  time to carefully check for hairline cracking .

 regards to all.

 Robert Fraser

   [quote][b]

WurlyBird

Joined: 16 May 2008
Posts: 207
Location: North Pole, Alaska

Posted: Thu Feb 03, 2011 2:10 am Post subject: Re: Bungee tube failure

That is pretty good advice, particularly since I average about 3-4 landings per hour logged on my plane and the average of those is certainly not a "greaser".  I definitely plan on checking that out when I get home.  Of course I am also going to replace the bungees so that will aide in a good visual of the area.



Thanks for sharing your experience.

_________________
James
Kitfox 3 / 582 / 70" IVO 2 blade GA
50 hrs on the 582 swapping for HKS 700E and Avid Cowl.

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Thu Feb 03, 2011 2:24 am Post subject: Re: Bungee tube failure

Good work and luck.



I think the earlier model has a 035 wall tube and later .049



big tensile difference.



Check my latest Kitfox Stall video............



how bout a video on the busted landing gear?  



Would be great for all Kitfoxers.

_________________
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PMorel

Joined: 09 Jul 2007
Posts: 62
Location: Locust Grove, GA USA

Posted: Thu Feb 03, 2011 7:42 am Post subject: Re: Bungee tube failure

I too had experienced gear failure due to use of a thin walled replacement gear.  Luckily, this happened during a slow taxi after landing.  If this happened upon landing, it could have been catistrophic.  It appears the thin wall tube was weakening after each landing and shows a flat area on top of the tube at the break.  There's a lot to be said for a Grove Gear.

gear failure.jpg

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carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Thu Feb 03, 2011 11:55 am Post subject: Re: Bungee tube failure

PMorel...On your pic, it looks like the weld on the underside was a little cold and let go, allowing the remaining circumference of the tube to oil can and finally fracture. I agree however that the thick-walled tubing is a good idea, especially at this highly stressed point.



Curious though.  As I recall, most of the stress failures in Model 1's and 2's were up in the carry through webbing over which the bungees wrap in the cockpit.  In fact, the factory told me when I got mine back in 1991 (ser# 707) that it was actually a kind of Model 2.5 since they included extra diagonally welded tubing in this area that would eventually be included in Model 3's and up.



Chris Carlisle

Model 2 (.5), 582, C box

Sioux Falls, SD

nichzimmerman

Joined: 04 Feb 2011
Posts: 2
Location: Warner Robins, GA

Posted: Sat Feb 05, 2011 9:08 am Post subject: Re: Bungee tube failure

Anyone know when the factory switched from the thin wall to the thicker wall?  I have a Model 2 (389) and wonder which type of gear I have.

_________________
Flyin' a Kitfox 2
Rotax 532

brubakermal(at)yahoo.com
Guest

Posted: Sat Feb 05, 2011 7:10 pm Post subject: Bungee tube failure

my ser # is 347 and i am wondering the same thing .  would all mod 3 have the thicker tubes , JOHN ?

 

Malcolm Brubaker 

Michigan Sport

Pilot Repair 

LSRM-A, PPC, WS

(989)513-3022  



 

   From: nichzimmerman <nichzimmerman(at)yahoo.com>

To: kitfox-list(at)matronics.com

Sent: Sat, February 5, 2011 12:08:18 PM

Subject: Kitfox-List: Re: Bungee tube failure



--> Kitfox-List message posted by: "nichzimmerman" <nichzimmerman(at)yahoo.com (nichzimmerman(at)yahoo.com)>



Anyone know when the factory switched from the thin wall to the thicker wall?  I have a Model 2 (389) and wonder which type of gear I have.



--------

Flyin' a Kitfox 2

Rotax 532





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=                         -Matt Dralle, List ==========



         [quote][b]

akflyer

Joined: 07 May 2007
Posts: 574
Location: Soldotna AK

Posted: Thu Mar 03, 2011 9:16 pm Post subject: Re: Bungee tube failure

I posted on this same issue a couple years ago.  When I bought my Avid it was because it had been on its back TWICE due to the exact same failure.  I was in the process of rebuilding mine when I was out flying with my brother in his Mod II KF and we ended up looking at dirt through the windshield due to the left gear leg folding up.



Hmm, that was kind of another one of my funny stories.  My brother shows up from OK after being gone from alaska for 10 or 12 yrs.  A few days after he shows up he got arrested on an outstanding traffic warrant from years ago haha.. he spends 6 days in jail and I go pick him up from the jail house and we head straight to the airport cause he needs to fly to clear his head of all his bad luck.  His first off airport landing at a buddies dirt strip results in us hanging in our seat belts kinda laughing (when the gear folded).  Welcome home bro!!



OK so at any rate, I learned a few valuable things about the gear leg design.  There have been lots of failures of this nature and all start at the toe of the weld with the crack propagating around the tube.  When you have your safety cable wrapped around that part of the tube it does absolutely ZILCH for you when the tube breaks.  I made my cables just a tad longer and I run it inside the triangle where the angled down tube comes in so you still have the safety cable in place when the tube breaks.



I went with the Avid wide / heavy gear (we used this gear on a couple of local kit foxes including my brothers).  I chose to cut the tab off the end of mine and slid a tube INSIDE the gear leg so I had a good tube without any welds to start the fracture on.  Welded the tab that holds the bungees from slipping off back on and now have a double tough tube for the bungee to wrap around.

_________________
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Leonard Perry aka SNAKE
Soldotna AK
Avid "C" / Mk IV
582 (147 hrs and counting on the rebuild)
IVO IFA
Full Lotus 1450
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I would rather die trying to live, than to live trying not to die....

carlisle

Joined: 20 Jun 2009
Posts: 72
Location: Sioux Falls, SD

Posted: Fri Mar 04, 2011 8:32 pm Post subject: Re: Bungee tube failure

I'm still wondering, does anyone know when they changed over to the thicker (.049?) tubing?



Chris

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Sun Mar 06, 2011 4:14 pm Post subject: Re: Bungee tube failure

Here's a PDF of an old "Kitfox Times" news letter.  It does not say when the thicker walled tubing was used in the landing gear.  It does give some specifics on wing spar and and lift strut carry through tube size and thickness and lift strut diameter and thickness.  The second and third pages are reversed in the PDF.

kitfox_diffs.pdf

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_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

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