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Canopy Fitting RV4 Rear Part

T

ThorLasVegas

Member
We are carefully trimming and fitting a replacement canopy. Long process but going well. Question for this group. It looks like we need to pull the canopy sides in towards the bar quite a bit the further we go back. Is that normal and will it not create stress in the plexiglass as we pull in to rivet?
 
ThorLasVegas said:
We are carefully trimming and fitting a replacement canopy. Long process but going well. Question for this group. It looks like we need to pull the canopy sides in towards the bar quite a bit the further we go back. Is that normal and will it not create stress in the plexiglass as we pull in to rivet?
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We found the same thing when we did our canopy this past October. There was a full 3/4 to 1 inch that the plexiglass was going to have to movein to meet the metal rail. In our opinion, that put too much stress on the plexiglass bubble. We solved the problem by cutting the canopy tube and welding in a spacer on each side of the hoop. This made the lower edge of the canopy wider and the plexiglass didn't have to pull in as much in that area. Another thing you may want to consider, is to NOT rivet the plexiglass to the frame. We only drilled a few holes through the plexiglass into the metal frame for clecoes to hole the bubble in place. The plexiglass was then glued to the frame with sicaflex . This method greatly reduces the chances of cracks developing down the road. I used the same method on my RV8 and it lasted for 20+ years with no problems.
 
Just did my 3rd one this weekend and did what Mark did and widened out that tube by cutting it off the U frame at the back seat. I just happened to have a TIG welder from a former line of work. I didn't widen it out so it'll touch, just gave it an extra 3/8" or so on each side. Also lifted it so it wouldn't rub on the aft skin when closed.
This is my first try with no holes, no Clecos all Sikaflex with about 12 clamps and 1/8" strips of aluminum as spacers. It's still drying so we'll see.
DO NOT rivet the plexiglass to the frame.
 
Totally understand. On the Sikaflex, I see how you glue it to the frame. Do you glue the skins on too at the same time or in a second go?
 
ThorLasVegas said:
Totally understand. On the Sikaflex, I see how you glue it to the frame. Do you glue the skins on too at the same time or in a second go?
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If you use Clecos you probably could. I wouldn't if you just used clamps like I did as it has the potential to move before the Sikaflex sets.
 
Another basic question. Do you clamp the plexiglass to frame first and then a bead of Sika on top and bottom of the frame rail where it meets the plexiglass. Or do I put a bead on the frame first and press the glass to the frame. Never done this before.
 
Clamp first. I clamped everything up on the fuselage so everything was in its correct position, then flipped it over and set it on a table with a moving blanket as a cushion. If you're using Clecos starting at the table is fine. You need a gap between the plexiglass and the frame for the Sikaflex to work, it can't be direct contact, that's what the spacers are for. Use as many spacers as you need to keep an even gap around the sides, don't try to stretch the front and the back to force an opening, just do the best you can, it'll hold. Wherever you have a spacer, clamp or Cleco, just leave that space empty and come back after everything has set. I did mine Sunday and it's still all clamped up, figuring another day or two. I hope you're using the primer and activator. Careful with that stuff, if it gets on bare plexiglass where you don't want it, it's a bear to get back off, make sure your masking tape is tight.
 
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I just finished my fastback canopy and did more or less the same thing. I drilled 3 holes through the plexi and the frame rails per side with clecoes purely for keeping it in the same spot, then I used something like 3/16 thickness fuel hose cut up into spacers and clamped the canopy every 12-18 inches or so at the spacers. Then Sikaflex, let cure and remove everything. I also attached and latched the frame back to the fuselage after application so it would cure closer to the final shape. I still need to fill the gaps from the spacers, but am going to handle it later.

For the skins, I got everything rough fit as best I could, drilled and clecoed, adjusted fit many many times more, then glued with sika to the plexi and riveted after cure. I did end up with one strange spot that I either missed pushing some glue out or dried strange so I'll need to fix that, but nothing major.

And I think my largest gap I had to clamp closed was less than 1/2 inch, but I spent dozens of hours bending, cutting and welding the frame to be very close.
 
Thanks all for you help. How much outward flex from the plexi can the SIka hold. I am doing a replacement and we need to clamp in some parts of the plexi to touch the rail.
 
ThorLasVegas said:
Thanks all for you help. How much outward flex from the plexi can the SIka hold. I am doing a replacement and we need to clamp in some parts of the plexi to touch the rail.
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I don't know the actual numbers and I didn't prepare a test piece, but I have heard it's stronger than the plexi itself once fully cured. And when clamping, just make sure you have at least an 1/8" gap between the rail and plexi. That's the minimum thickness of the sika for full strength. I didn't do that for the skins, but that was more for sealing and finish than attachment.
 
I used a long piece of safety wire to pull both sides in onto the frame tubes.
I would definitely not try that when temps are below 80. I think I worked on it when it was nice and warm (90ies).
I used countersunk pull rivets. But rather that just drilling bigger holes I elongated the holes (dremel) -- longer and longer slots the further back.
So far so good.
Edit: I should mention that I had to split the canopy frame center piece so as to make the side angles flush with the longerons.

CanopyPull.jpg
 

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climbak said:
I don't know the actual numbers and I didn't prepare a test piece, but I have heard it's stronger than the plexi itself once fully cured. And when clamping, just make sure you have at least an 1/8" gap between the rail and plexi. That's the minimum thickness of the sika for full strength. I didn't do that for the skins, but that was more for sealing and finish than attachment.
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Great. Thanks. How did you clamp the skins on? I am having a hard time visualizing how to get the skins clamped to the plexi
 
ThorLasVegas said:
Great. Thanks. How did you clamp the skins on? I am having a hard time visualizing how to get the skins clamped to the plexi
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I just used harbor freight clamps. Here's the post from my build thread that shows some photos. https://vansairforce.net/threads/rv-4-4175-fastback-conversion.224269/post-1890181

I also ran beads top and bottom to make sure it was well filled. Someone else mentioned they split the center bulkhead, I did as well. Honestly I don't see how you could do the canopy well at all without splitting the frame. It just doesn't fit to the fuselage. I kind of wish I had split the front bow too. The rear I don't know since I had to chop it up for the fastback anyway.
 
Got it glued and now drying. Looking good.. Just trying to figure out how to clamp the outside skins to the canopy when gluing those... any hints?
 
ThorLasVegas said:
Got it glued and now drying. Looking good.. Just trying to figure out how to clamp the outside skins to the canopy when gluing those... any hints?
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I just clecoed it all together after applying a bead of sika to the skins. I just used a bunch of random boards wedged in between the skins and heavy objects around the plane to kind of clamp them down in the areas they weren't sitting flat on their own. Kinda pressed the skins against the plexi gently too to get the glue to flow and thin out.
 
I'm kinda late in the conversation, but I built my -4 long ago, and the canopy to most, is the hardest part of the build. I fitted the frame up per plans, found the front bow fit fine, the rear, I split at the center, trimmed out enough to bring it together a bit, and instead of welding, I used a piece of aluminum tube a couple inches long, curved to match, that fit inside the bow, and blind riveted it in. I then trimmed and drilled the canopy to the bow, oversized the holes in the canopy only so the rivets wouldn't crack the canopy. with everything gap checked while 100% clecoed (still no side skins) , I disassembled, countersunk the canopy for the future skin dimples, and then bonded the canopy to the bow with Proseal (Im not a Sika guy), clecoed 100% and let it cure. After that, I formed/fitted the side skins and picked up all the holes in the canopy with hole finders, and then installed the skirt skins with Proseal and pop riveted installing rivets dipped in sealant. I final filet sealed the tube upper and lower sides with Proseal. The canopy is essentially bonded in place, pop rivets are in oversized holes. I'm not sure how Sika accepts paint, but Proseal is 100% paintable.
 
How much gap do you want between the canopy's aluminum skirt and fuselage skin behind the back seat? What kind of weather stripping do you use to fill the gap?
 
My AFT "Skirt" is trimmed to very close fit with near zero gap. It takes some time to get that just right. The canopy position is held by the R/H hinge and the FWD/AFT pins in the lock position. At the very AFT end of the skirt centerline, I have a thin rubber "bumper pad" that lightly contacts the skin, otherwise, there is no contact. At the AFT sides, there is a slight gap that works as the cabin air exit rather than be a tight seal. Ignore the flight crew !, zoom in and you will see no gap at the skirt. It's just clear of the paint. I didn't have any other pics on my phone that show it better.
 

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