Bungee Truss

[Av8r3400]

This past Airventure, I got two things: A little piece of wall candy (http://www.teamkitfox.com/Forums/showpost.php?p=17751&postcount=19) and a bent bungee truss (due to a plop landing on the UL Field).

Here's a few photos of the repair.

First, a couple of shots of the truss damage:

[Av8r3400]

Cutting out the damage:

[Av8r3400]

Welding in the new material. Angle cuts, sleeves on the inside of the replacement tubes and rosette welds to hold the sleeves per FAR requirements.

[Av8r3400]

Here's the finished repair. Thanks goes to a good friend named Dave Meyer, who is currently building an Avid/Kitfox hybrid. He is a fabricator/welder extraordinaire. Without his help, this project would still be on-going.

[Av8r3400]

The bungee gear was never my favorite. I don't care for design of the truss or the working of the gear (much less the Matco brakes on them :mad:).

So I took the Grove gear (with wheels, brakes and 600-6 tires) from my project plane and installed them on my flyer. This photo is of the plane on the scales, for a new weight and balance. For the record, net weight gain was 8 (yes, eight) pounds. Old 631, new 639 empty weight.

The second photo is for everyone who has ever wondered what a retractable Kitfox would look like....

[kitfoxnick]

Nice work I did the same thing last fall, when I hit a big hole off airport. Was the damage from the limit cable?

[Av8r3400]

I think it's a cumulative effect. One hard landing and the cable puts a dent in one of the tubes. The next one the dent grows as the tube gets weaker. Next you know the bungees are tight enough to continue the process and finally crunch, truss collapse.

The "plop" landing that bent my truss was not even very hard and it was on soft turf.

[sdemeyer]

I did the same thing last year! Then I got rid of the bungee cord gear and installed good bush gear. The safety cable is very strong :)

[HighWing]

A real nice and quite challengint repair. It looks like it was done without removing the fabric. C5's observation is pretty much mine as well regarding the limit cables. They pretty much exist to prevent a prop strike and even with the collapsed truss, I don't recall ever hearing of a prop strike on a hard landing, but lots of truss issues over the years.
Lowell

[Model 2 Madness]

Well, at least I know I am not the only one to encounter this!! :)

Here is my Model II going through repairs....

The plane was built in '92 and luckily the same Polytone paint (Intl Orange) matched perfectly!

[N276KM]

Did the limiter cables do your truss in too? I've never installed them on my Avid, and haven't (yet) regretted the decision.

I'm also really curious about your radiator placement in the 2nd to last picture. Is that temporary, or is your radiator always that low? Do you get any vibration in the airstream?

[Model 2 Madness]

Yes... the cable yanked my truss down. The radiator was just hanging in that pic temporarily. Here it is reinstalled.....

[N276KM]

Ah, makes much more sense now!

[Timberwolf]

Good on you for taking the task on by yourself. However, the circled ares worry me. The welds look well...terrible. It looks like fitup was poor so you just piled in some more metal taking the "that bead is big enough, should do the job" approach. But in taking that approach you have also introduced a tremendous amount of unnecessary heat into the joint and increased the HAZ tremendously. In the top beam it looks like you attempted to couple it together, but this would not by the proper way to do this. The whole bar needs to be replaced. It may be a different story if this was a non structural member of the airframe. However, it is one of the most important parts of the frame and sees some very high and complex loads. If you were to have a hard landing and have the area collapse, I'm not sure the insurance would be required to cover the aircraft. Though that is going in a different direction, I believe you would be wise to cut the structure out and have it professionally welded back in. I am not telling you this to try to make you feel bad, I just would hate to see something happen because this point fails.

[kitfoxnick]

Been there done that. :(

[Model 2 Madness]

Thanks for the comments Timberwolf! :) (sorry, your actual name isn't visible). I am pretty sure the welds are strong. I did not perform the welding, a friend who rebuilt a Starduster II that suffered an off airport engine out landing by a previous owner did. He did a lot of frame welding on the Starduster to get it back up to spec. Also, several guys who have built, rebuilt, and repaired steel tubed aircraft have looked over the work and told me it looks strong.

I guess the picture makes the weld not look too good.

-Steven Ragan
Ft. Hood, TX