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Center fuselage construction

LettersFromFlyoverCountry

LettersFromFlyoverCountry

Well Known Member
've stared at the plans and viewed the Web sites and I'm not convinced I'm seeing things right on trimming the corner rib (I think it's F-723) forward part where it mates with the 705 bulkhead.

On the drawings, it appears to show that both forward flanges are trimmed maybe 3/4 of an inch or so and tapered aft. This would appear to include the little joggle section of the outboard flange. However the fact there's a joggle there tells me that it's there for a reason and that reason is not to cut it off.

However, in fitting the rib to be flush with the outboard edge of the bottom skin, that flange -- whether it gets tucked inside the 705L flange or put to the outside of that 705L flange (which I assume it doesn't because that would put a nice bump in the skin), pushes the rib inboard from the corner edge of the bottom skin slightly. You couldn't get it flush.

So the instruction say get it flush with the botom skin, best done if that front of the flange of the corner rib is gone.

However I've seen at least one Web site in which it was the inboard side of the flange that got cut away (and not tapered, either) while the outboard side (with the joggle) stayed as presented. And THAT confuses me too, because that flange doesn't appear to be interfering with anything.

As many have noted, the plans are very vague here, and I'm sitting here with a drill and snips ready to go.

so hurry up and put me on the right track ! (g)



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Ok, let me answer my own question here for purposes of the archives. Maybe it'll help someone else. After looking at the plans again and after fitting the piece (the corner rib), it is clear that what the plans are showing is correct. BOTH the web of the corner rib (at least the front portion and I suspect the aft portion too) and the inside flange of the corner rib have to get cut off. This is counter to some of the stuff I read on a few builders sites. (I actually took the second flange off too, but I think that (especially with the joggle) could've been left on. I don't see it as a big issue)

Here's why:

It's obvious when you fit the piece that this is done for two reasons. First, if you don't cut flange off, you can't align the edge of the corner rib to be properly flush with the edge on the bottom center section skin. What's more, if you leave the flange on, you cannot properly fit the F-723A piece onto the Web of the corner rib. there is a joggle there and you can try to make it work, but it won't. It's still going to push the edge of the corner rib inboard and you don't be flush with the skin all the way to the bulkhead and it'll push your aft end out of alignment.

Now the web portion gets cut off because if you don't, it will go up and over the flange on the bulkhead, leaving a small gap between the skin and the bottom of the corner rib. And if you look at the other ribs next to it, you can see how they've addressed that. Then, using the F23A allows a flush mating with the corner rib and the bulkhead here, allowing the skin to rest evenly across the bulkhead and the corner rib.

Many have noted -- correctly -- that the plans aren't very clear in this regard. First, they show up and forward, but they don't show inboard and outboard. Secondly, a top view of this piece would've eliminated any confusion.

But maybe nobody else was confused in the first place. (g)
 
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