Rear topskin

I have stalled for as long as I dare, but I guess it is time to fit the rear topskin. Does anyone have any words of wisdom regarding how to attack this job. Specifically, is it best to start at the top of each bulkhead and work down each side? Or is it best to start to start on one side and drill and fasten all along that longeron and then start going up each bulkhead? Also, I have read and have seen pictures where the skin does not readily conform to one or more of the bulkheads. Tony Spicer has an excellent photo showing how he cut off a bulkhead flange and made a new one. Question: should I try to drill and fit the skin to the bulkheads first, or is it best to assume the worst and to cut off the flanges and fit new ones?
I hope this makes some sense.

Bill Newkirk

Bill - not sure many folks have had problems here. It was an easy fit to install (clecoes only - I'm not riveting until the last moment) by starting at the tops of the bulkheads and working down evenly. Then find a skinny/small bucking partner to go in after laying some boards on the bulkhead bottoms and have at it.

If it's like the...

...non pre-punched 6 fuselage - you could stiffen the bulkheads with temporary plywood, and pre-drill the holes in the bulkhead flanges to #50 (1/16).

Strap down the top skin and pull it tight against the bulkheads (thats why you need to stiffen the bulkheads) and then back drill the skin from the inside.

If access is difficult, then you can back drill #50 with a long 12 inch drill bit, and have a helper drill #40 from the outside and cleco.

Work from the top down, but use duct tape to ensure that the skins don't bulge at the longerons between the bulkheads.

To drill the longerons, mark a straight line on the skin and put the first cleco at a point midway between the bulkheads, then just keep splitting the gap between clecoes...

As long as the bulkheads don't move, this method should work well.

Couple of things....

It may be too late as it sounds like your bulkheads are already fixed. I know that Randy Lervold positioned his by sighting down the span. He then tilted some of the bulkheads fore or aft to make them line up. Better info on his site.
http://www.romeolima.com/RV3works/Airframe/airframe.html
Regardless, follow Gil's advice and fix the bulkheads stiff so they can not move.
I came across a great invention for locating holes in hidden flanges. It was invented by my neighbor and he calls it a Mag Kit. The kit contains about 50 small round magnets and a "viewer". Using model airplane glue, you fix the small magnets on the flange centered in the location you wish to drill. The viewer uses a film that is sensitive to magentic flux with a small hole in it for marking the center point. When you place the viewer on the skin you can "see" the magnet attached to the flange through the skin. Mark the center then drill through and the drill bit pops the magnet off.
I am not sure if he is still making these kits but if anyone is interested I can ask him.
I am not sure there is enough room in the 3 to fit my body in to back drill so this Mag Kit idea sounds like the ticket for me when I get that far.

The RV-3 will be non-prepunched, like the RV-6A rear topskin that I recently installed (twice).
Tw key points:
1. the bulkheads must be in line so the skin lies perfect - doing a non-prepunched build requires thinking from the inside out - so, run a string across the flanges of all the bulkheads (front to back) that lie under the skin to confirm that they all line up. Do this at various places. If you cannot move a bulkhead forward or back at this point, and one is out, it can be cut and the height adjusted, and splice plates installed. I had to do this on one bulkhead. See Sam Buchanan's site for a picture of how he did just that.
2. Reinforce the bulkheads with wood sheet. I cut 1/4" plywood to shape, and clecoed the sheets to the bulkheads, particularly close to the flange. A few extra holes in the bulkhead will not matter (I deburred them). Also, run 1 x 2 pieces of wood between the bulkheads at various points to keep them exactly in position relative to each other - you can tape or screw these to the bulkheads. This is why I had to do the skin a second time - I reinforced the bulkheads, but failed to put the pieces of wood between them, with the result that when the strps pulled the skin down, the bulkheads shifted (fore or aft) resulting in misplaced bulkheads and a bent rivet line.

I predrilled the holes in the bulkhead flanges, much easier than marking and drilling the skin, and drilled the skin from the inside, with a helper and a block of wood on the outside puttin in clecos as I drilled. I found that I don't need shims, but thought that I might near the longeron between the skin and the bulkhead flange. If I had needed to shim, I was considering using a "liquid shim" technique, possibly Loctite "Liquid Steel" or something light that. I haven't tried that, but maybe others who have can weigh in. There is some info in the RV-List archives about that.
Bill Brooks
Ottawa, Canada
RV-6A
fuselage in progress

The RV3 is not a precision fitting kit. On my first 3 I strapped the skin down drilled and riveted. With clecos it looked pretty good but after riveting there were lots of indentations where the rivets were. Used lots of bondo to fill and smooth for a fair to good finish. Second time around I made a false bulkhed or two and it went together much better. Some of the super anal guys on the early 4s used 2216 on the bulkheads, masked the top inner skin, clecoed in place and then let the 2216 set up forming a perfect surface for the skin to attach to.
As always YMMV
Tom
RV3 x 2

I used the elevator push tube to make sure the bulkheads were all at correct elevation. I also had a friend push a long 2x4 from the outside against the side longerons, clamping the skin tight against the longerons, while I was drilling the skin to the longerons from the inside. Be sure to bend the bulkhead flanges to the proper angle so they are parallel to the skin.

Topskin

Thanks for the replies. I did the reinforcing thing and it seems to be working well. By tilting the seatback bulkhead, I was able to get the alignment to match the topskin pretty well.
Thanks, again.

Bill Newkirk