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  #361  
Old 02-28-2018, 06:08 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
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I finally reread the manual for the areas I've been working on. Should have done that earlier, as it would have told me the correct way to assemble that spar bulkhead strip that I had to unrivet. The manual says "The rivet holes through the skins and the bottom flanges of bulkhead F-303 should not be drilled until both skins are in place."

I agree with this with one exception: if you drill through the bulkhead flanges first, then when the skins are in place, you can back-drill through the skins using a 12" bit, and there will be no difficulty locating the holes on the skins. Just watch out for edge distance when you're locating the holes on the flanges and when you set up the skins for drilling.

Also, note that some of the rivets are -4. When you're doing the drilling, if you don't go bigger than #40 at this time, you'll save yourself some time. You can drill those holes to #30 before dimpling. Just don't forget.

I glued the strip on to the flanges. That'll let me remove those clecos during the fitting of the forward belly skin.

A machinist friend made the button at the end of the manual flap handle and cut the slot. The bearing blocks for this are ready now, too. The plans don't show it but the manual correctly says to install nutplates under the bearing block mounting angle to facilitate easier maintenance. Since my seat rib flanges were running low on edge distance (the extruded angle is ample) I made a small plate to rivet the nutplates to, and then riveted the plate to the frame. The other side is complete too.



The photo also reveals that the exoskeleton angles for the seat pan skin are done. I had to use my shrinker/stretcher to get the correct curve in these.

Here's a bit of tape that I removed as part of the process when I glued the right side skin on. Clecos protruded through the holes and carried glue along with them. I pulled the tape off and the glue came along with it, nice. Since the clecos themselves would push the tape away, I poked slits through the tape in each of the cleco locations before gluing.



The alternate photo hosting site has these photos, too. The first one and the second one.

Dave
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  #362  
Old 03-29-2018, 04:54 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
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The left-hand belly skin under the seat is now glued on. Here it is with the glue curing, the exoskeleton in place, and the tape freshly off. Removing the tape is one of the first things to do after the clecos are in (the first ones are wiping off the cleco tips and filleting any joints).



Then I made the exoskeleton for the right-hand side and did all the prep. As of today, this skin, too, is glued on. This photo shows the same status as the first photo but on the right side. Note that some tape is still on, under the exoskeleton.



While I was close to the details, I resolved to correct a bad area on the very bottom-most longeron just aft of the firewall. I hadn't positioned these correctly on either side. Initially, I thought that shimming them would suffice, but the more I thought about it, the more I leaned towards simply replacing these. Haven't done that yet, but that's coming up on my list.

The arrow shows the gap. This is the left side; the right side is worse.



Alternate photo hosting, in case these photo have disappeared

Here's one,

Here's another,

And if I've done it right, here's the final one.

Dave
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  #363  
Old 04-24-2018, 07:13 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
Default Forward Belly Skin

Working on the forward belly skin, F-321. This one is the .040 piece that goes to the firewall.

The first bit of work I had to do was to correct the bottom edge of the forward lower longerons and the F-312 (mine aren't stock) ribs so that their aft edges fair to the seat-area belly skins. I'd made them too high. Fortunately I had enough material to do these things.

I put a description of this on the RV-3 Clarifications page.

After that, I had to bevel the forward edge of the forward belly skin to fit between the firewall bottom cross-piece and the firewall lower flange - wish that were wider, but it's not.

Then I could start clecoing the skin on. I worked from the going front aft and things went well enough until I got to the spar bulkhead. That has the wing dihedral angle in it so that the bottom of the skin isn't flat. Since the forward belly skin is one-piece, that meant that there's a compound curve going over the bulkhead flange.

I made a tooling piece and suppose I should call this a Howe fitting like the ones I used on the wing. Same sort of affair, held on and pulled tight with straps. Fortunately the .040 skin is relatively robust and it pulled down without trying to buckle.

Putting the carpet on the fitting, with a much-used roll of carpet on the right,



And then I added a post in the center area, where I wanted local pressure.



The skin overlap at the center of the spar bulkhead, where the seat belly skins overlap, left a bit of a gap under the F-321 forward belly skin. I glued on some shims and they're curing now. I can strap down the Howe fitting when they're set.

The photos are also at this place and this one too. Just in case.

Dave
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  #364  
Old 04-30-2018, 10:40 AM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
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I clecoed the forward belly skin back on and used straps to tighten the Howe Fitting in place over the spar bulkhead. That is, it's "over" because the fuselage is being built upside down, but as far as the airplane is concerned, it's under the belly.



The compound curve due to the overall geometry still produced a ripply in the skin. I could not find a way to position the Howe Fitting to avoid that, even using shims. This shows the ripple.



With no other alternative, I consulted my mentor, who said that he'd cut the skin to relive the ripple. I decided to try it. A colleague in Australia had sent me a photo showing that he'd done it too; plus the RV-4 plans show something similar in the same location.

The cut was made using a Dremel cut-off disk and took a very short time. It's about .050 to .060 wide and 1.72 long. The hole at the end is for stress relief and is reamed to #30.



Here it is in place. Bottom line, it works. The ripple disappeared.



Now I wish that I hadn't thrown out the nicely drilled exoskeleton for the spar bulkhead after gluing on the seat belly skins. But it's a small workshop and alas, I did that.

The pictures might also be found here, here, here and here.

Dave
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  #365  
Old 05-16-2018, 12:36 PM
Garwin Garwin is offline
 
Join Date: Mar 2018
Location: Roswell NM
Posts: 19
Smile RV-3 building

Wow, what a great documentary on building the kit. I have picked up a kit ( SN 10006) with a lot of the work already done. But reading about your building helps me understand what all goes into one of these. I am a couple of years away from having a place to finish building the kit, (if I do) and will continue to review your building to learn more. I am also looking at possibly selling the kit but want to pass on as much information as I can. My wife(as do I) filp/flops on sit on it versus sell it. Storage may become a problem.
I will be researching the RV-3 more anyway. I would be a first time builder and need to move to an area with a good building chapter for help. Right now I am working towards the CFI rating as I enjoy sharing the sky’s and teaching/coaching people.
Thanks for sharing all your work on this with us.
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  #366  
Old 05-16-2018, 03:44 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
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Garwin, I tend to be slower than a lot of builders, so don't get the impression that an RV-3 is a huge amount of work, as it might not be for someone else. It's entirely doable and it's been an enjoyable process. I started this kit more for the project than for a flyable airplane and that might tend to draw the project out a bit, too.

You're right about documenting the construction of it. I hope to do that just to show how I've approached certain tasks and some of the RV-3 hidden gotchas.

Lately I've been working on the tunnel and that's been one of the more fun little jobs. I'm still figuring out how to add some Fiberfrax and titanium to the belly for insulation and as a firewall. I just need to settle on a construction sequence but there are no real stumbling blocks with it. I'll discuss that when I have some more time as the April - June period tends to be my busy season.

Regards,
Dave
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  #367  
Old 05-19-2018, 11:57 AM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,407
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With the tunnel shells and bulkheads drilled and fit, it was time to consider the belly insulation and fire protection. The insulation is 1/16" Fiberfrax and the fire protection is .020 Titanium. I chose that because the FAA recognizes .016 Ti as acceptable for firewalls and .020 was available from McMaster at a reasonable price.

Most people who do this use stainless steel foil. KatieB used that foil, for example.



But I got to thinking that the protection is more than from heat; it's to guard against actual fire under the belly behind the engine hot air outlet. The belly is aluminum, .040 thick to be sure, but still aluminum. I decided that primary firewall protection should be added. Hence the .020 Titanium.

At one point, it looked as if the Fiberfrax and Titanium sandwich would both go between the tunnel shell inner flange and the belly skin, and made this test piece to see how much the Fiberfrax compresses after being riveted with LP4-3 rivets. The side view shows minimal compression.



When looked at in the right light at the right angle, though, some dimpling is visible in the simulated belly skin.



Later, I riveted an AN470AD4 rivet in one end and that seriously did compress the Fiberfrax.

Therefore: the Fiberfrax should not be part of the structural connection between the skin and the tunnel. I decided to stop the Fiberfrax by the inboard edge of the tunnel shell. This led to some rivets on the belly going through the Titanium and others not. It appeared easy to screw up (still does) so I made this guide.



One issue is that with the Fiberfrax stopping at the inboard side of the tunnel shell, and the rudder pedals above the tunnel shells, what about insulation there? But I think that the tunnel shells themselves will give me some insulation, and if I add a bit of the Titanium to the inner wall, it'll be somewhat protected, for a short while anyway, against flame. With no Fiberfrax on the inner walls, heat on the Titanium can work through to the aluminum tunnel shell. No problem for normal flying but in a real fire situation, they could melt. Still, that'll give me some protection for a while.

The photos can also be found -
here,
here,
here
and
here.

Dave
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