Advice on conical bend rivets?

[mattasmith12]

Happy 4th all,

Hoping for some advice. How did you tackle the transition where the conical bend from the forward side skin matches with the aft side skin. These two skins don't transition smoothly and there is a wedge-shaped gap between them.

The build manual is lacking in detail. I've scoured builder threads and haven't really seen how to handle this. I know just driving rivets will cause pretty large dimples. I could fabricate wedge-shaped shims to take up the space... Any tips?


Here's a view looking aft.


This view is more from the centerline.

[Kyle Boatright]

I made large wedge shaped shims back in the day. Others notched the skins to create tabs which would lay flat. There are several ways to approach it.

[David Paule]

Can you rebend the outer skin to match the correct contour? I did that in a few places, mostly on the belly skins, of my RV-3B. Of course this is best done before doing any drilling.



I used a long pipe, a long heavy angle, and numerous wooden planks and clamps.

Dave

[PaulvS]

The Frank Justice manual says to make tabs in the F-673 skins to match those in the F-606 bulkhead.

Another way may be to use liquid shim i.e. epoxy, rather than to cut individual wedges, but I haven't tried that in this situation.

A builder here stretched the F-670 skin in that location, using a tool made from a pair of bearings mounted on a handle.

I'm slightly behind you now Matt, so am very interested in what you do!

[mattasmith12]

David, I had to do that in a few areas too. Unfortunately, this is less of an issue with the curvature. It's more of an issue with the two sheets of aluminum meeting at different angles to each other.

Kyle, I'm glad to learn the wedge approach isn't too far fetched. It may be my best option in this situation.

Paul, If you are slightly behind me, let me hope that I can save you a mistake I made. One of the reasons this transition is even more difficult for me is that I trimmed off the aft 1.75 inches from the F-670 prior to making the conical bend. To my dismay I found that this prevents me from matching the line of the F-606. So, I'd advise that you make sure things line up before trimming of the aft of the F-670.

You can maybe see here what I'm referring to. The dots line up with the F-606 flange. The angled line is where the aft edge of the (now trimmed) F-606 lies.

[PaulvS]

Thanks Matt, I haven't yet trimmed the F-670, other than the slot to fit around the wing spar rear attachment, so I will hold off. But I did already drill those holes in the F-606/F-673 where you have red dots, and hopefully that will not be a regret.

There is another challenge at the forward edge of the F-670 at the firewall. Apart from the jig being in the way for drilling and riveting, the cowl hinges cannot sit flush against the firewall flanges because of the fluting in the flanges. Did you encounter and resolve this issue?

[mattasmith12]

Originally Posted by PaulvS

There is another challenge at the forward edge of the F-670 at the firewall. Apart from the jig being in the way for drilling and riveting, the cowl hinges cannot sit flush against the firewall flanges because of the fluting in the flanges. Did you encounter and resolve this issue?

I haven't gotten to that point quite yet. But it looks like I have something to look forward to. Haha. I've decided I am going cut off the upper half of the 2x6 jig members to allow better access. So maybe that will help a bit.

[PaulvS]

Originally Posted by mattasmith12

I haven't gotten to that point quite yet. But it looks like I have something to look forward to. Haha. I've decided I am going cut off the upper half of the 2x6 jig members to allow better access. So maybe that will help a bit.

I think the fuselage should be rigid enough at that stage so the firewall doesn't need the jig support anymore. I am probably going to need to do the same, although it is a steel jig.

Re. the conical bend area where your sheets have been trimmed short of the F-606 rivet line, is that going to mean new F-670 skins? Or rivet on an extension so you can get the intersection? Luckily the F-670 skins are just flat so would not be too costly to replace if that is what's needed.

I'm finding plenty of challenges in this dang thing, everythings gotta be measured three times, on different days, before cutting and drilling!

[airtractor8]

There was an article in "14 years of the RVator" on notching the skin and bending it and the bulkhead out to improve the fit up between everything. That's how I did it on my 6 there. It was easy and worked well. Here is a link to a pic I took of the old article for you
https://photos.app.goo.gl/dppCayS8cTKReztg9

[johnbright]

My interpretation/implementation of Frank Justice's Bunny's Guide and RVator is shown in the following two photos plus an RVator photo and a Bunny's/Matronics photo.

F-673 is cylindrical and F670 is conical so they can't overlap without compound forming (stretching) or tabs. As you can see in the exterior photo, I relieved the F670 to make it work (you can see this relief in the RVator photo also). The interior photo shows the tabs of the F-606 and F-673 are bent to meet the conical shape of the F-670.





A photo from RVator:



A photo from Bunny's Guide at Matronics:



BTW, since you're working on the fuselage, something another builder suggested, leave the doubler out for the rear inspection plate at the elevator bellcrank, makes the hole bigger, the cover plate will not be flush.