Kitfox III, bent tube

[JorgeEC-YUQ]

Hi everybody,

I would like to know your opinion, please see the pictures of my last found...

I discovered a slightly bent tube and a crack when replacing the bungee chords on my kitfox.

Seems like the bungee chord was longer than it's suppose to be and the safety cable made contact with the gear leg thus bending the structure.

Cheers,
Jorge

[Av8r3400]

That is a very common problem with these planes.

Here is a thread when I did nearly the same exact repair.

[JorgeEC-YUQ]

Thanks for the link Larry,

It seems quiet common indeed. What welding method did you used? What is the material of the tubing?

Thanks!

[avidflyer]

This is also a weak link on Avid Flyers, I would suggest filling in as much of the seat truss as you can with some .040" steel sheet. Jim Chuk

[Av8r3400]

Jorge-- the tubing is 4140 steel, I believe I used .049" wall for the repair. The tube gets sleeved on the inside and rosette welded to hold the sleeves in place.
If you choose to stay with the bungee gear, I would recommend doing as avidflyer suggested and put some webbing in that truss to keep this from happening again.

I put webbing in my side trusses to reinforce for the grove gear on my Mangy Fox project. Something like that would help the bungee truss.

[JorgeEC-YUQ]

Thanks for your replies,

I was going trough the FAR instructions for the repair ... Seems like I need a good welder.

Is it meant to be TIG welded only or what kind of welding machine did you guys used?

Thanks again,
Jorge

[JorgeEC-YUQ]

Hi,

Thanks to a friend of mine who is aeronautical engineer we have finally located a shop in my area wich can provide with the steel required for the repair. I can tell you is not easy in Spain ...

Now reviewing this thread I got confused ... Larry you mentioned the steel in the frame is 4140 and not 4130? I guess the procedure of welding would remain the same with both grades?

Also my friend asked me for the "heat treatment" (normalize?) of the original tube since the strength of the new material has to be the same ...

Any ideas?

Cheers,
Jorge

Jorge-- the tubing is 4140 steel, I believe I used .049" wall for the repair. The tube gets sleeved on the inside and rosette welded to hold the sleeves in place.
If you choose to stay with the bungee gear, I would recommend doing as avidflyer suggested and put some webbing in that truss to keep this from happening again.

I put webbing in my side trusses to reinforce for the grove gear on my Mangy Fox project. Something like that would help the bungee truss.