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I was looking at the lower carry thru on a kitfox 4 1050 to see what I should do to my model 1 to beef it up, honestly I cannot see much difference, the only thing I could visually see is there is a triangle gusset on the bottom, which runs back on to the round tubing about 2 inches further than mine does, is that it or did they use heaver tubing anybody know.
the original owner of my kit had the carry thru mod accomplished . he was good to well document it in the builders log and also pictures . from what I understand about the mod is that it was to increase the gross weight of the plane to be used on floats . pretty sure that he had intended use the plane on floats as i have the skag thing that goes on the lower fuselage when floats are installed .
is is a pic of mine is this what they looked like in 1985 or has it been updated.
found the picture of the mod that was accomplished to my model IV 1050 . in the builder log he describes it a being a retrofit kit that increases the gross weight of the 150 to 1250 lbs . he drilled the fitting and installed a 4130 steel rod and welded it in place . i assume both sides although he doesn't specifically say both sides .
wonder it that goes all the way thru, hey thanks for the pic. that looks exactly like what im doing with my upper front carry thru light weight but strong
he doesn't mention drilling and welding on the other side . seems to make sense that the other side needs to be welded also . he did include a sketch in the log that shows the rod going all the way across .
another weak point , at least on the model IVs , is the cross fuselage bulkhead where the bungees attach . seems that the grove gear eliminates that problem .
This was a modification that was a word of mouth from the factory. Never a printed word but several friends (trusted) mentioned it to me as a 1050 to 1200 upgrade. I recall it as a rod threaded at both ends and fastened through drilled holes with nuts on both ends. I don't recall the rod diameter recommended. Welding seems to be an upgrade. What I see in the picture suggests a tube welded in drilled holes. It would be welded on both ends as the intent was to increase strength in tension across the carry through.
A simple mod to improve the strength of the lower strut attachment area is to make a flat 4130 strap that attaches at each strut attach bracket, running between the bottom of the fuselage (even if covered already). Ideally would be to do it before covered so you could tack it onto the cross tubes and longerons prior to covering, further strengthening it all. But it can also be done over the top of covering.
Another good mod is to add some gussets where the wingspar carrythrough spar tubes attach to the fuselage tubes. That ties the carrythrough tubes (spars) into the fuselage tubes, providing even more strength. And if you can, add some more 4130 to the spar carrythrough tubes for even more strength.
When one looks at how the lower longeron wingstrut attach brackets are attached on the early Kitfoxes, anything you can do to insure or improve the strength of those brackets is a good thing to do in my opinion.