Extra stringers to stiffen the aft bottom skin?
There have been a number of mentions here about belly skins oil canning and 'popping' in and out in flight (damned if I can find any of them now that I look).
I have been considering putting in some extra J-stringers in this area to prevent the problem. I'm thinking perhaps two J-stringers between the F-706 and F-707 bulkheads, evenly spaced either side of the belcrank rib and one on the centreline between the F-707 and the F-708 bulkhead. I have plenty of J-stringer stock left over from the wing kit to do this.
Firstly, I am interested in what people think of the concept in general. My worry is that I might be creating areas of rapid transition from supported skin to unsupported skin, which is a bad thing apparently because it localises stresses in that area.
Secondly, I am interested in opinions about the method of attachment. I see two options:
A) Cut into the bulkhead flanges to create new tabs, mimicing the existing tabs on the F-706 bulkhead that let the trimmed end of the J-stringers underneath. Then drill a new line of holes to rivet the skin to the new stringers, i.e. exactly like the standard side/top J-stringers are done. A slight problem here is that if I use the location of an existing bulkhead flange hole, it will no longer match exactly with the corresponding skin hole when the tab is made.
B) No attachment to the bukheads and simply pro-seal the stringers to the inside of the skin, stopping them just short of the bulkheads at the ends.
Forgive me if this has been discussed before but I did try to search and couldn't get a search string that pulled up any relevant information.
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Loman O'Byrne
RV9 TU. O-320-E2D. Engine hung, working on FWF, Arklow, Ireland
=VAF= dues paid through Dec 2020
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