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RV-3: What Airplane Were These bulkheads For? Making New Flanges

Ironflight

VAF Moderator / Line Boy
Mentor
I stole that line from a famous Central Texas builder ? can?t take credit for it. But it is fairly truthful ? the bulkheads in the RV-3 kit are interesting to say the least. I am not sure that you can get a location for them where both the top and bottom fit precisely ? and in fact, the instructions clearly tell you that you can (and may have to) cut off the flanges and make new ones in order to get them to fit properly. Remember ? these kits were designed well before the age of CAD/CAM and match-holed technology. These are good old-fashioned drawings and parts. And when it comes to the curves and conics of an airplane fuselage ? well, let?s just say that a fair amount of art is involved.

So it was time to fit out aft top skin in place, and since we had already invested a lot of time into the seat back bulkhead, we decided to use it and the aft end bulkhead (F-309) to determine the shape of the skin. We would then adjust the 306 and 308 to fit. That meant cutting off the 306 and 308 flanges, which I did with the cut-off wheel, sanding disks, and scotchbrite disks. Meanwhile, Louise went to work fabricating some ?Flexi-flange? as I call it ? lengths of flange with notches cut in to allow it to conform to the curvature of the bulkhead and the conical nature of the skin. She predrilled the flanges on the bench ? that it made it much, much easier when crawling in to install tem, and assured straighter rivet lines on the outside skin.

Installation was actually pretty simple ? if you like working in enclosed spaces. Since Louise had spent an afternoon inside ?Fuselage Cave? to drill the turtle deck to the longerons, it was my turn to go in and fit these flanges. Rather than build plywood bridges that are supported on the bulkheads, we stuffed the spaces between the bulkheads with blankets, then put more blankets on top, making it a nice, soft play to lay with the loads spread broadly over the structure. I crawled in with a drill and a drop light ? a headlamp helps a lot as well. Before we put the top skin on we cut out plywood forms for each bulkhead, to keep them straight and stiff ? these were attached with C-clamps. Without them, you?ll never keep the things in a straight line while attaching the flanges.

IMG_4731.JPG


The sequence was easy ? hold the flange up to the skin and the bulkhead, make sure it was flush with both, and drill the skin holes. The outside person clecos as you go. Once the flange is fully drilled to the skin, swap drill bits and drill the flange to the bulkhead, clecoing as you go. It helps if the outside person feeds you clecos in the pliers, one at a time, like a surgical nurse handing the doctor sutures. We found that six inch drill bits were the perfect length ? with shorter bits, the drill chuck hit the bulkheads or skin, and longer ones just flat don?t fit inside a -3!

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After everything was drilled, we took off the skin, removed the flanges, primed and debured them ? then riveted them to the bulkheads. Now THESE bulkheads fit the airplane like a glove!

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Paul
 
Paul, Your efforts to share your learning curve are greatly appreciated. I will be following your path soon and it is comforting to have these references. I plan to use the QB wings just to speed things up. Any regrets on the QB wing choice? Does workmanship match yours ?
Larry D
 
Great post

Paul
Thanks for the great photos, I will be installing the turtle deck soon, really appreciate the information.
 
What Memories!

Ah Paul,

Looking at you laying in the tail area of the fuselage with such a tight fit and trying to work.

Mine was in the 8 so I had a liitle more room but what fun!

Don't get in that position with the tail down as you can get stuck! I don't think you need to ask me how I know this!

Keep up the good work.

Ted
 
Yes, heed this warning if you are building a 7 as well....Not that I know anyone that might have done this.....:eek:

Looks great Paul!

Don't get in that position with the tail down as you can get stuck! I don't think you need to ask me how I know this!
 
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Thanks guys - just rememebr that if you like the quality of the flanges - those are Louise's creation! All I did was crawl in and install them....
 
topskin

Paul;
I did mine exactly like you did, HOWEVER, when I re-installed the topskin for rivetting, it was amazingly difficult to get it back on. Things seem to grow.

Bill Newkirk
Prather, CA
 
Paul,
That is exactly what I did on my second RV4, the only difference, was that when I removed the turtle deck, I also unclecoed the flange and backriveted it to the turtle deck. Then I put the skin /flange back on the fuselage and then riveted the flange to the bulkheads.
Did I tell you how much I love building the RV12!:D:D:D
 
RV3 Tailcone bulkheads

One day, long ago, my dad was visiting and I needed something for him to do. One of my dad's jobs had been a loftsman at Douglas Aircraft Company.

I had heard about tailcone bulkhead fit problems, so I asked my dad to review the four tailcone bulkhead geometery.

He figured out pretty quickly that they did not fit together properly.
And he also figured out why they didn't fit.

All four bulkheads were drawn properly for them to be mounted vertically.
However, the seat back bulkhead is tilted 12 degrees aft at the top. and becomes too short. (I believe this is the same on the RV-4 tailcone bulkheads. Which is why a 1/4" is normally added to the height of the RV-4 seat back bulkhead at the horizontal split.)

Since the RV-3 seat back bulkhead had only a vertical split, it would have to be cut horizontally also to add the additional height.

Or if you were really lazy like me, you might notice that the top skin slopes back at 3 degrees, and the seat back bulkhead is the correct height if it is mounted at a 6 degrees angle.

Personally, I like John Harmon's solution for the RV-4 tail cone bulkheads.
The standard RV-4 tailcone bulkheads are installed per print making certain the bottom of the bulkheads line up properly.
The standard bulkheads are cut off at the top of the longeron.
John's HR2 tailcone bulkheads are added to the top of the longeron to get his fastback design.
The back threeupper bulkheads are installed. The seat back bulkhead is lined up with the angle of lower seat back bulkhead. However, the top angled section of this upper seat back bulkhead is left free.
The top skin is matched drilled to the bask three bulkheads and the lower sides of the seat back bulkhead.
But the secret to installation is that the top of the seat back bulkhead is simply pulled into place after the top skin is mounted.

I wonder how much time it would take to change the RV-3 top skin and modify the canopy?

Jim Ayers
RV-3 sn 50 - 650 hours
modified HR2 (RV-4 tailcone) - 37 hours
 
-3s seem to be quite different from -4s

As Paul has pointed out in another, earlier thread when someone suggested a -4's solution to the bulkhead problem, the problem is different on the -3. Shifting the top up will still not match up with the skin on the sides. The bulkhead just doesn't have the geometry of the skin. And, personally, I absolutely do NOT want a fastback (nor a slider). I'm very psyched to have the 3560 degree unobstructed view. (And, yes, my 50-somthing neck can turn to see 360 degrees with the shoulders locked.)
 
Looks Great!

IMHO, this should be the standard method of attaching the rear skin to the bulkheads. Having gone the standard route, I can say that your outer skin surface WILL look nicer if you take the time to fabricate new flanges. I spent a lot of time aligning the bulkheads and fabricating shims and its still not perfect. Nice job.
 
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