1970 7GCBC Restoration with Milman Spars

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Kmcaero

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Hello all!
I am in the process of replacing my wood spars wings with the Milman aluminum spars. Presently working on the right wing first, all wing parts are cleaned, ribs straightened, holes drilled and deburred. Before primer I wanted the check the fit of the rib spar windows to the new spars for any clearance issues, the Milman main and rear spar caps measure .812" +/- .002" in width, the rib spar windows measure .805" +/- .005" in width for the main (front) spar and .800" in width for the rear spar. Will be a snug fit if I cannot do a little rework to open those up. The big issue: 3 of the ribs, p/n 5-274, located in the flap bay have a rear spar window width of only .770" +0.000"/-.002" definitly not going to let that aluminum spar cap through, was fine for the .755" wood spar width. Has anyone run into this issue. Maybe its an issue for that era of rib stampings?? would hate to order 6 new ribs from Univair and have the same results.
Todd Kendall
 
Hi Todd,
Good luck with the conversion. When I did mine I used a hand seamer to flatten the rib flanges so they would slide more easily onto the spars but they were still tight. I don't think new ribs would change that.


let us know if you have any other questions, there are a few of us here that have done the conversion and we're happy to help. keep us posted with pics, I am curious to see how the flaps are mounted and actuated.

Bart
 
Mine were the same as yours, smaller spar windows. Milman has this in their instructions.... File the hole bigger using a round file so you don't make a stress riser where a crack can form from later.
 
I think he is talking about the width of the openings. milman's instructions refer to the height, no?
 
Correct Bartman, the Milman instructions refer to the height of the front rib window for the main spar to fit through. Opening up the width of the rib windows .002" to .005" can easily be done to fit the spar cap, however, I have to open up the "flap ribs only" rear spar window width by .044" for them to be able to fit the spar through. Maybe this vintage of construction from Champion they decided to tighten up this window to the wood spar?. I was hoping to hear from someone with a newer 7GCBC that has done the aluminum spar conversion if their flap ribs fit onto the rear spar without too much rib flange work.
 
In that case I'd call Milman and ask them what they'd recommend. They are easy enough to get in touch with and were mostly helpful when I called them.
 
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