RV-4 canopy/skin drilling
The canopy/skirt skins are probably the most difficult parts of the -4 to assemble....heres how I did mine. First make sure your "frame" fits the aircraft fuselage pretty well, and do most of the work with it in place, as it will become very rigid once you start attaching the skins and bubble. I had to cut the aft end of the tube support as do most builders, and shorten it slightly.I actually made a new end from a piece of tubing and inserted smaller tubing into it, fastening it with pop rivets along the inside radius of the tubing.Get the bubble trimmed to overlap the tubing by 1/2 inch or so, and make the cut then sand and polish the edge with 600 wet/dry paper or finer...this will prevent edge cracks.I marked the tubing contact line with a sharpie and pre-drilled the tubing so you can have a target to drill into.I re-sharpened my drill bit for plastic (kind of blunt and make the cutting edge angle approx. 90 degrees, so the bit "plows" instead of cuts). Now practice on a piece of the trimmed off plexi til your confident ! I then set the bubble in place, and secured it with tape all around leaving the holes accessable.Drill and cleco at each hole location, then remove, and oversize the bubble only with a unibit just over 1/8. Countersink the holes to accept a dimple from the skin.I then masked a line just above the drill line in the inside of the bubble, and applied a bead of proseal to the tubing and clecoed the whole thing together, with tape between the clecoes, essentially bonding the bubble to the frame...walk away and come back in a couple days.Now I can tell you from 27 years of working with pro-seal in the airline industry, that thing is on to stay! and its paintable, and wont hurt the plexi. Now, remove clecoes and tape, and start fitting the side skins.. I used a hole finder to pick up the holes in the plexi. After all is drilled and dimpled,another bead of pro-seal between skin and plexi as its assembled..no leaks and a nice paintable seal.
Good luck to all!
Bill E.