Question on fluting tabs on Bulkheads and frames?

[PrescottB787]

Page 10-12 step 3 say to "Heavily flute the tabs of the bulkhead and frames which have two punch holes". Should I assume this is to make it more rounded for a bitter fit of the top skins?? If this is the case why didn't they have us flute the Bottom of F-1011 bulkhead? Or did anyone do that? I had a **** of a time getting it to fit properly.
Thanks again for all the help!

[flion]

There's no room to flute the tabs on the F-1011. Since they are tabs with single holes, it should have been fairly easy to adjust the tabs to fit. Fluting does not round the tabs. That's pretty much set by the form for the bulkhead. But because of springback, the tabs and flanges may not be at 90 degrees (or in this case, because of the conical section, a little less) to the bulkhead. Fluting along a flange shrinks the outer edge, pulling it in and making the angle more acute. This is most apparent on a long curved flange such as found on the nose section of the wing ribs.

What you could do for the single hole tabs, to help them conform to a curved skin better, is use seaming pliers lightly at the outer corners to help them match the curve at the base of the tab. However, I had not problem fitting my skins to the bulkheads, and riveting pulled the tabs tightly to the skin.

[SeanM]

I just completed this step last night. The middle bulkhead on the rear top skin was hard as I couldn't reach my hand around the inside to help align the holes. It did take a fair bit of work and time but it all pulled together perfectly.

[Thunderpig]

In the process of this myself today and it is not going well...I've fluted all of the available sections and there is still one side of the middle section that wants to bow out. About to try and remove all the blue stuff and see what that does for the fit.