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MTOW mod question

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Posted

Wasn't there a post{ I cant locate it} about a strap of molly welded to the underside of the lift strut carry through tube to help in increasing limits? Would like to see if there is info on that subject...pretty sure its here somewhere....a simple addition for me at this point for safety sake. BTW my tube is 3/4 " x .035.

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Posted

As Sed mentioned, if you are going to increase the strength of the carrythrough, you may want to consider other areas too. I plan to put KF wings (longer span than Avid) on my MKIV. I've already increased the cross section of my strut carry through. I added half of a square tube on top of the existing 3/4" .035" round tube. I also added 1/16" plates overlapping the ends of this tube going all the way to the bolt holes for the struts.

 

My thinking is that because this is mainly a tension member, the shape of the additional cross section isn't that important (It's also very well braced laterally for compression anyway). But, making that extra cross section continuous from the strut bolt on one side to the strut bolt on the other is important. Otherwise, you may be adding extra weight for no benefit. Kind of like the chain is only as strong as it's weakest link idea.

 

I'm also increasing my spar carrythrough tubes to the size used in the KF-4 1200, and increasing strut tube sizes as well. The wing and it's supporting structure will be pretty much the same as a 4-1200. When I get a chance to get out to my garage, I could take a picture of the strut carrythrough mod. I haven't touched the airplane for many months. Good luck with your mods.

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Posted (edited)

Well here is a picture of the lift strut attach point. The fuse is upside down. I could only weld a strap about 1" away from the bolt as the strut goes over top and bottom of this cluster. This tube is 3/4" x .035". Wing attach tubes are 3/4 x.035 front and 7/8 x .035 rear...had to replace that one. Keep in mind my MTOW is less than 600lds.

post-341-0-21154700-1435275097_thumb.jpg

Edited by Tree top pilot

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Posted (edited)

The photo you show is like an Avid structure - My Kitfox type is only a 5/16" thick plate with an angle under it to attach transport braces to - Don't have a photo handy to show you.

I thought you were talking about the top crosstubes - Suberavid put some reinforcement on the ends there. 

Don't think you should have a problem with this lower strut attach point - the cross tube was made heavier on the 1200 models.

The lower fitting is in tension 99% of the time when flying - The upper crosstubes are in compression.

My upper crosstubes are 1 1/8 x .049 wall, and the bottom was strengthened too - making new 1" x .058 wall struts.

I will probably have the heaviest short Kitfox clone 2/3/4/?, with flaps and about 20 more SF wings, 

Soob, nosedragger, built at 1320 gw - and hoping under 800 ew...

EDMO

Edited by Ed In Missouri

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