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Old 03-29-2017, 07:11 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252
Default Skin in the Game

According to other builder reports, the aft-most bottom fuselage skin is especially difficult. It's thick at .040 and arrives poorly bent. Mine was no exception. I spent some time attempting to unbend the bends that were in the wrong place, and rebend the skin with bends in the right places.

One thing that makes the aft portion, around F-311, easier, I've read, is making the slot for the tailspring mount to protrude. Remember that mine is a bit higher than standard? In my case, it looks as if it'll be completely covered by the skin -- so no relief there. No access slot required.

Unfortunately I didn't take photos of the as-received condition.

After working at it a couple days, here is the skin resting on the F-309 bulkhead, the most forward bulkhead this skin covers.

Here is the skin resting on the F-311 bulkhead, the aft one with the tailspring mount.

It appears as if, with a bit of help, this connection will fit reasonably well.

Here are the tools I've been using to unbend and rebend the skin. The table is an essential part of the tool assortment.

I continued to work on it, and today I was able to make a first attempt at clamping the skin on.

Here's the F-309 bulkhead.

I moved my collection of aluminum angle so that I could get under the fuselage jig, poked my head into the innards (this is the first time the fuselage has had innards to poke my head into) and took a photo of the skin resting on bulkhead F-310. There's still work to be done.

At the back, though, it fits pretty decently.

The fit at F-310 needs some work. A friend suggested driving over it with my truck and after working on it for a few days, I believe that just might be necessary. But before I resort to something that extreme, I'll think about it for a while. Remember that so far I haven't added straps. They'll probably help, of course. I made a couple Howe Fittings (review the wing skin postings for those nifty strap partners) and have a couple more to make, and might think of something else.

Kind of hope so.

The pictures are also posted here, here, here, here, here, here and here.

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Old 03-29-2017, 08:13 PM
RussellT RussellT is offline
Join Date: May 2016
Location: Albany Western Australia
Posts: 101

Lots of fun to be had with the bottom skins Dave (especially the hard to work 40 thou), I struggled with mine too but it eventually concedes defeat and once riveted on looks quite OK. The large rear bottom skin also needed to be massaged similarly to improve the fit.
Get used to climbing in and out from under your jig....

Your under baggage floor cable clips are neat, did you consider using conduit under the floor which is called to be secured with pop rivets I think? Nice work Though.

My current status, If I get the canopy sorted be the end of this year it will have been a good year, I can see why most choose tip overs on the 3.

Cheers, Russell

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Old 03-29-2017, 09:06 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252

Russell, I did consider conduit a long time ago, and decided that since I have no plans for redoing the electronics every few years, bushings would suffice. In this case, I'll have the cable and pitot static lines in before the floor goes on.

There's no conduit on the plane.

Yours definitely looks like it's progressing - super!

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Old 04-07-2017, 12:25 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252
Default Bottom Aft Skin Games

While I was working with the aft bottom skin on my RV-3B's fuselage, I got to a point where I wanted to remove the blue vinyl.

So I did. Under it, the aluminum was translucent. It was a total surprise. I can't figure out how Van's did that. I've never seen aluminum do that before.

I kind of like it. What do you think?

Ok, I missed the first of April. Meant to post it then. What happened was that I bought a sheet of .020 polycarbinate and didn't bother to strip it's protective coating off, any more than I have the skin. I rough-trimmed it and clamped it in place so that I could easily assess the underlying fit of the bulkheads and longerons. It didn't work out so well, the polycarb being a bit too flexible for the job.

Incidentally, I bought sheets of .010, .015, .020 and .030. Of these, this was the closest thickness to optimal and I could cut it with scissors.

The main area that needed more bending was the bottom center at F-310, the second bulkhead from the tail. After a number of approaches that didn't work out, I found one that did, and succeeded in bending this area a bit more.

Here's the basic idea. I clamped pieces of 1/2" plywood to the sides to protect the skin, and used the darker steel clamp to mostly squeeze the sides of the skin. The steel clamp by itself didn't bend the skin much, plus as the sides bent in, the clamp started to wander closer to the edges. So I added the orange clamp closer to the area I needed to bend more. That did the job nicely.

At the F-310 bulkhead location, the dimension between the plywood pieces when the skin was maximally clamped was about 1.85 inches. This gave me a bend that closely matched the bulkhead. I'd previously tweaked the existing curves a bit, which definitely helped.

I didn't want to squeeze the aft end too much, so I placed this piece of dowel there, clamping it at the forward end of the skin. I should have also clamped it at the aft end but the fit at the tail is pretty good as it is now.

The short piece of plywood led to a skin ding. The plywood was simply too short and I should have caught that.

The ding is easily small enough to fill later. A wide friend of mine had a saying: "If you want it like downtown, take it downtown." So instead I took this skin to a local auto body shop, where they bumped it out for me.

Here's a view of the F-310 bulkhead with the skin clamped in place. We're looking at the forward bulkhead, since I've paired two of the bulkheads (the plans only specify one of the pair and I put two there, back to back). There's a substantial gap which I get to deal with. The aft flanges (the flanges at the rear of the pair face aft) actually fit reasonably well.

The photos are also hosted here, here, here, and here.

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Old 04-19-2017, 07:42 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252

The aft bottom skin passed a small milestone last night. The clamps came off.

Remembering that the aft two bulkheads are doubled up, you'll realize that I've only drilled and clecoed one for each pair. So far. What's going on is that there are some gaps between the flanges for the forward of both the two bulkheads and the skin, and I don't want to drill those until I've got shims in there.

Since the bulkhead pairs are glued to each other, front to back, I can't simply take the flanges off and rivet new ones on. I'd ordered several F-803CPP for just that eventuality and they were on hand. These are the strips that make a perimeter flange for the RV-8 instrument panel; they'll probably do the same job for mine. I'll actually need to shim these gaps.

It's a subtle thing, but the tailspring mount is not attached at the moment. The way I located the skin/flange holes was to first drill the bulkhead and longeron flanges and then back-drill through the skin. That wasn't much fun. I needed both a right-angle drill and separately, a 12" bit for my regular drill, to get most of the holes. Four were blocked by the tailspring mount, so I removed it.

Note that after the skin is riveted on, the tailspring mount isn't removable without replacing the skin - it's got to be right when it's finally bolted in place.

After the mount was gone, it was possible to drill those holes. Since I expect to use Cherrymax blind rivets here, setting them should not present a problem; there's room to get them in.

Also, there's a hole in the skin that I still need to drill for access to the tailspring attachment bolt's nut. And lots of trimming, of course.

That photo is also located here.

As I mentioned on Vlad's thread about getting a new camera, I did too. The new one has an articulating screen, and while it's not absolutely necessary if you're young and flexible, I've got to say that it's a nice luxury to have now. I took a set of photos showing the various flanges and their gaps, and as I measure the gaps, I'll note them on some prints I made.

Worth mentioning is that I didn't need to strap down this skin, just plenty of time working at it. I was so sure I would, I'd even made a set of Howe Fittings to do that.


Last edited by David Paule : 04-19-2017 at 07:45 PM.
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Old 04-25-2017, 08:17 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252

I measured the flange spots where I needed shims and made the shims. Then I gathered together my tools: plastic ups for clean water and soapy water, plenty of small squares of paper towels, Scotchbrite pad, some cards for mixing epoxy and a bunch of popsicle sticks. Oh, yeah, and the West Systems thickened G/flex epoxy and the aluminum powder.

I mixed up some of the epoxy and mixed in some of the aluminum powder. The epoxy was already, without the powder, thick enough so it wouldn't flow - but it will creep before curing. Adding the aluminum powder made the cured epoxy stiffer and the wet epoxy thicker. THis shows my mixing cards after the job was done.

I glued the shims to the flanges of the F-310 and F-311 bulkheads in two passes, because I didn't know how long it would take. The first pass was the aft four shims. This took right around an hour. First I cleaned and abraded all the shims and then the flanges. After that was done, I mixed up the epoxy, applied it, and clamped the shims in place. I wasn't too worried about squeezing out all the epoxy because I knew that the powder would give me a minimum thickness, plus some unavoidable mismatches in the flanges and shims (most of them slightly curved) would cause thicker sections of epoxy too.

Later I went back to do the front-most shims on the F-310 bulkhead. Same affair except that some of these took two pieces of aluminum to build up the thickness, resulting in more time for this job. The cleaning is good for two hours, and I was easily inside that. The pot life of the epoxy is 45 minutes and that was close. One of these little shins, a piece roughly 9/16 inch square, jumped out of my hand and escaped. It's probably south of the border right now; it sure doesn't seem to be in the shop. I made a replacement that was more cooperative.

Here are the F-310 shims. The ones on the right side of the bulkhead in the photo were done in this pass. You can pretty clearly see a couple of instances of places where the shims are doubled.

On the left side of the bulkhead, the aft side, at the bottom, the one shim that's visible is from the previous pass at this. The glue had cured enough that I could release the clamp. Q-tips, a generous amount of them, did a reasonably decent job removing squeeze-out and smears.

I anticipate that I might need to file down some of these if they end up too thick. I don't have a good idea of what the final glue line will turn out to be.

The photos are also hosted here, here, here and here.

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Old 05-07-2017, 08:57 AM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252

Marked and trimmed the F-326 aft bottom fuselage skin so that I can start fitting the larger tailcone bottom skin F-325.

As soon as the aft skin was trimmed, I remembered that the F-325 skin had a reputation for being slightly short. Mine is no exception. And if I'd left the F-326 aft skin longer in front, and there was room for that, I could have attached the F-325 to the extended part of F-326 -- and now I can't. It'll have to share the F-309 bulkhead rivets and somehow work with the too-short F-325.

Here's a photo marking the aft edge of the aft skin. I used a laser torpedo level on my camera's tripod to locate the cut line. I left it slightly long so that I could do a final trim later after the side skins are on and the vertical stabilizer is on.

I got a new Aerolab gascolator yesterday. Here's what the filter looks like, on the left, compared to the Andair, on the right. The shells are included too so you can get in idea of the overall size.

On the Aerolab one, the filter and filter housing shown closer to the camera drop down out of the belly of the airplane. There are no service items inside the airplane, and since the gascolator has that red locking feature, no safety wire is needed.

On the Andair one, the part fixed to the airplane is near the camera and the small housing shown farther drops down. You have to unfasten the safety wire that secures the threaded ring, black, and unscrew the ring to remove the bowl. Then you can reach back up and remove the filter for cleaning. Upon reassembly, you have to rethread and tie new safety wire to that ring.

The Aerolab one is 113 grams heavier, but I finally decided that's a good trade-off for the easier servicing.

Here's the aft bottom skin with all the clecos in. I back-drilled through the added bulkheads, through the new shims, and through the skin.

The F-325 tailcone skin that goes on ahead of this aft bottom skin isn't bent properly, besides being a bit short. Fortunately, since it's .025, I think I can wrestle it into place, even though it's bigger (but not heavier) than I am.

It's misbent on the forward end as well, but this isn't as obvious. Same problem, the bends are too far apart. There, it's trivial.

I used some straps while trimming the forward end. It's apparent that I'll need to use more tooling to force it to maintain the correct shape.

Here's a photo of one of the methods I used to increase the bend. This only works near the edge, as the 1" x 2" x .120" aluminum tube (available from Wick's Aircraft, 6061-T6) needs a flat spot. Bending it by hand is too localized; use a stick or something to distribute the bend, and work down the length as needed. It's likely that the whole length won't need tweaking.

The photos are also here, here, here, here, here, and here.

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Old 05-20-2017, 07:21 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,252

With the long F-325 tailcone belly skin in place, I started strapping it down. It was quickly clear that I'd have to either make a set of Howe Fittings or figure something else out. Here's a first pass at the F-306 bulkhead straps.

One thing that was necessary to continue was to get the tailspring mount back so that I could cleco the aft tailcone belly skin in place. Here it is, nicely cadmium plated. The plating was because this thing is exposed and difficult to remove (impossible, I think) and I didn't want corrosion problems.

After strapping down this long belly skin I realized that the tailcone bulkheads were warping under the strap's tension. So that's why other people have made wooden bulkhead stiffeners! After removing the skin yet again, I made this set and have to apologize for the crudeness of the woodwork - especially compared to some of my other woodwork. Crude it is, and functional, too. Functional wins. The stiffeners are screwed to tooling holes I drilled in the bulkheads using #6 x 5/8" wood screws that I had on hand, and some #6 AN960 washers that I'm borrowing from future use.

The F-306 stiffener can't extend the full height of the bulkhead since the jig's in the way, but I'll eventually need to have it do so.

One that was installed, I strapped down the skin again using this arrangement. Note that it's slightly different than the earlier set-up. It works and that's about all I can say for it.

And after some work, I have a lot of clecos installed. Working by myself, I found myself drilling a couple holes, getting up and installing two clecos, kneeling back down and drilling two more. It was slow-going. At one point, three consecutive holes needed three drills, one a 90 degree drill, one with a jobber's length bit, and one with a 12" bit, all one after the other.

The aft-most bay remains undrilled pending the next stage of the job. And I can see that I'll probably need to shim the F-306 bulkhead bottom flange, too. The next one aft, F-308, already has a shim and seems fair.

The photos are also hosted here, here, here, here, and need I say, here.

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Old 05-20-2017, 11:10 PM
dlomheim dlomheim is offline
Join Date: Sep 2006
Location: (2OK2) OK City, OK
Posts: 391
Default Dave's RV-3B Progress

Great progress Dave! I know it can be slow going without a helper to cleco as you go; but you're still getting it done!


RV-3A sold
RV-9A Mazda 13B (FWF)
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Old 05-21-2017, 04:19 PM
Capt Capt is offline
Join Date: Feb 2017
Location: Australia
Posts: 722

Have just read this thread, man you sure have patients there ! Well done. I'd prefer to fly, don't think I'd have have the tenacity you have to do a full build
Shall watch this thread with interest from now on, good work, keep at it:-)
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