Drilling canopy and Filler for canopy

What is the best process for drilling the canopy and producing matched holes in the canopy rail and the canopy skin? I know what Van's books says about drilling but maybe there has been some improvements in aligning the holes in the three pieces that have to be mated? Also, should the holes in the canopy should be slightly larger than those drilled in the canopy rail and skin to allow for expansion and contraction of the plexiglas?

Second, what are the best materials for filling and finishing the area between the canopy skin and the canopy? I see a mirad of materials in the Spruce catalog and trying to make a choice.

Bob Mears
RV-4

Bob,
I am just about at the same stage as you seem to be. I just finished bending and tweeking the canopy frame to fit just right. (not much bending was needed) I was thinking of following the instructions because it seemed to make sense in my mind. The instructions say to tack the canopy onto the frame with rivets spaced at 12 inches. Then drill through the three layers in assembly. I admit that hitting the middle of the canopy frame tube makes me a bit nervous. Is that your concern?

I spoke with one of Van's guys today. He had some good info. Seems he must have done it.
Start with a #40 drill, put masking tape on the canopy rail. When you push the plexiglas against it, it shows a dark line that is the apex of the curve of the rail. You drill the plexiglas along that line. When it comes the rear skin, it is not so clear. It is a matter measuring and trying to hit the same hole. Supposedly, you can get real close and when you drill all three out with a #30 drill you will take out the slop. The plexiglas is drill with a still larger drill to allow for expansion and contraction. One of my buddies who built a -4 in the 1980's reminded me that the plexigas is countersunk. I would like to think I would have remembered when the time came. Also he uses one of those skinny step drills that has a 1/8 inch starting diameter. He drills his plexiglas with it because it will fit the hole in the canopy rail and keep things in alignment. The 1/8 end is a little oversize for the #30 drill but works great with the blind rivet. Need to clean up the hole on the back side with a deburring tool. Do it lightly.

So I have been finding things out that I did not know. I will keep it up until I feel I am read to take the step. I am still trimming the lower edge of the canopy trying to get a good fit to the canopy rail.

Oh yes, the guy at Van's also said some folks cut the canopy rail at the rear of the frame so they can get a better fit of the rail to the plexiglas. They splice a 40 mil aluminim piece to span the gap. I will have to look at that.

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.

Glue it on?

Bob - you probably want to go the drilled route, but just in case you have not thought about it there is an alternative. Glue it on. See here.

I have not done it but plan to.

Cheers,

Glue is good!

Not a fan of drilling plexi, but to each his own.

Attaching Plexiglas

I know there is a Pro Seal gun to dispense the stuff but without it I have never seen a bead of Pro Seal. I have seen a smear, a glob, and a mess. I will have to get a gun I guess otherwise, I will have it from head to toe. Is that just me or what? I do like the idea of gluing to make it water and air tight and I am certain it will make a good seal. I guess I don't feel totally comfortable with just glue at 200 mph and that is primarily because I have not tried it. I suspect I will use a few rivets too.

I do appreciate all the input. It was very helpful.

Bob Mears

It's worth the extra $ to get the Sika. It come in a glue-gun tube and applies just as neat (or messy) as any multi-purpose silicone calk. It's not pro-seal, but for this application it may be better (known resistance to UV).

-Bruce

Bruce,
I will look that one up. I wonder if it is paintable? I will find that out when I research it.
Thanks.

Bob

Drilling the canopy

I think I have this process figured out. Now. I need a second opinion on trimming and drilling. Currently I have a little extra plexiglas hanging beneath the aluminum tubing along the side of the canopy frame. It seems prudent to drill with a little excess there and cut it off after drilling. You are not so near the edge when you drill and it could give some support and discourage cracking. Any thoughts on this?

Bob Mears

Cut ,drill,trim....

No problem to trim after drilling...just remember the smoother the finish of the trim line, the less chance of cracking. I am not sure if you fully understood my process described earlier, but the pro-seal is doing a two-fold function.It holds the canopy on the tubular bow for drilling the side skins, and also provides a tight seal.For those doing a "bond only", I am not sure how the metal side skins can be pulled down tight against the plexi without the row of rivets along the tube. I have no filler of any type on my side skins...they can be formed to fit nicely if you take your time. I scrapped the OEM ones, and made some a bit wider for more workability.

Bill E

Canopy side skin

Bill,
There was someone recently advocating glue only on the canopy. But you are right, what to do about the side skins. Rivets are good. Now, to make that side skin fit and not have to fill. Now that will be a trick for me. Thanks for the input.

Bob Mears

Canopy Drilling - Rear Skin

Someone tell me how the two skins are overlapped and attached at the back of the canopy. I see a row of holes in the plexiglas in that area an invitation to a crack. I don't know what the standard procedure is. From all pictures, etc., I am not supposed to trim the canopy to match the tubing on the canopy frame rear of the back seat. Tell me if I am wrong. Thanks.

Bob Mears

Hi Bob
Here is how I did mine link to canopy page I hope this will answer some of your questions

Canopy Drilling a Trimming.

I guess I am not being clear about the issue I have. And The people at Van's can't seem to get it either. I am going to try again. So here it is.

The plexiglas canopy plexiglas extends beyond the alum. bow (round alum. tubing) at the rear of the canopy frame. In fact it extends about 3 -4 inches beyond the canopy bow(round alum. tubing) toward the rear all the way to the fuselage skin. Do I cut that part of the canopy off back to the round alum. tube portion of the canopy frame or let it be as is? If I leave it then I need to know how to manage the overlapped portion of rear canopy skin that must be riveted together starting at the canopy bow (round alum. tubing) to the point where the canopy skin comes in contact with the fuselage skin at the rear of the canopy.

I don't know if that helped or not. I guess I could send a picture. Let me know someone out there. I am frustrated here.

Bob,
I have been cutting and fitting my canopy for the last week. Actually cutting and fitting a little at a time, and then thinking about it while I work on something else. Right now my canopy touches (rests) on just the small few inches in front of the bow (top of instrument panel). My forward canopy skin is fitted but I have not drilled any holes yet to cleco it on. I am going to cut the canopy up just a little above the forward canopy skin. Too much sanding and fussing to get a perfect fit against the skin. I don't think it is necessary to sit on the skin.

In the rear it touches for about ten inches (measured around the edge). That means it touches the fuselage about five inches forward of the very end of the plexi. My canopy bow at the rear is an inch or two forward. When I get done the bow will sit up off the fuselage skin by about .5 inches at the very end. This is how I have seen others do it. The canopy bow is well above the edge of the plexi. The bottom canopy edge sweeps up and is not going to rest on the fuselage.

The problem I have is the canopy is too wide in the back. I have to pinch the tail of the plexi bubble together in order to make contact with the bow. When I put heat lamps on it the canopy bubble tail is easier to bend. I am worried about drilling holes in the area where it wants to pull away from the tube (canopy bow). It seems to me the tail of the canopy bow should have about one inch added in the area of the sharp bend. Again, I have stopped working on the bubble while I ponder my next steps. Send me a private email with your phone number and we can talk about it if you like. I'm on the west coast (Pacific time).

Riveting the Canopy Skin

I have decided to use the pop rivet approach to holding the canopy in place while I fit the skin. Since I cut the tubing at the back of the canopy frame, I can take the splice out and get the ends of the rivets out of the tubing by letting them dribble out the cut end. It should make fitting of the skin easier. Also, try this approach to riveting the overlap of the canopy skins at the back of the canopy. Drill the line of rivets that will join the two skins (exception being at the tubing if you have a rivet in the very rear of the tubing. Dimple both skins at that point but in opposite directions. Drive the rivets and you should get a countersunk surface on the top and bottom side at the overlap. Try it on a piece of scrap and see how it works for you. That should solve the problem with having the shop head resting against the plexiglas.

Bob

Bob,
Sounds like a good plan. I am planning a similar path.

I was having trouble fitting the canopy aft of the rear bow so I made a simple set of clamps out of scrap 1/2" plywood. I didn't feel like cutting the tube so I had to come up with a way to pinch the canopy tail. The clamps rest on 1/4" thick wood strips that bend enough to follow the canopy contour. The wood strips have 1/16" thick foam tape on the side against the plexi (no scratching). The foam tape has adhesive only on the wood side. The tape holds the strips nice and secure against the plexi. I can move the strips up just above the tube so drilling and skirt fitting can take place while clamped. Heat lamps help to soften the plexi just enough to reduce the clamping pressure. See photo

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Clamping Canopy to frame

Looks like it works. That is what counts. How will you hold the plexiglas to the frame (tube) while you fit the skin to it? I think you mentioned tape or a strap earlier.

Bob