Tip: RV-7A Sika Flex canopy attachment

[dhall_polo]

I've read some of the writeups on the matronics site and other places. I'm still left with a few questions.

The Tipup is glued/attached to the canopy bow, but also rests unglued on the canopy frame.
How did you go about applying Sika across the full width of the canopy frame (seems you need this so there's a seal)?

Did you apply a mold release agent to the tipup plexi, then glue the forward half of the canopy frame with the tipup firmly in locked position? Then you remove the tipup and go through the process of gluing the rear half of the shell? (Or maybe do the rear canopy first, and come back and add the front seal as final step?)

[Rene Bubberman]

You'll find a description of how we did it on: http://websites.expercraft.com/PHVII...ry&log_id=6287 and on the pages beyond.

All the best,

[flyvans.com]

And here's what we did,
RV-7A tip-up, result looking great!

we did a few mods to the frame to prepare for the sikaflex:
and basically cou can finish the frame including the rear latches and weatherstripping before ever putting on / trimming the plexi as opposed to van's instructions where you'd wait e.g. with drilling the rear top center splice plate.

first, the "canopy stop" idea that has been floating around here is highly recommended, otherwise installing the gas struts will skew everything:


then we did some custom weatherstripping, which is awesome:



now to the actual mods on the frame:
- the siderails are mounted to the inside instead of the outside (plans) of the weldment, essentially resulting in an offset to the inside of .125". between the weldment and the bracket attaching the siderails are small spacers.




then there are 2 .063 strips with lightening holes clecoed to the siderails. on that the canopy will rest/can be clamped while the default top bend of the siderail will allow for a very nice bead on the inside of the canopy, giving enough sikaflex to hold on to. The sideskirts are later installed only with the rivets through the siderails and sikaflex between the canopy and the skirt, we have 0 holes in our plexi :-) also the rear canopy frame rib was built slightly undersize to give the canopy a nice sikaflex bead while resting flush on the rollover bar. also, no need to wait with installing the canopy frame top skin as per van's. when you're at the point, just rivet it on before plexi work.



and the actual gluing:
http://www.flyvans.com/log/2008_04_0...ex_canopy.html
http://www.flyvans.com/log/2008_04_1...x_canopy2.html

we made one mistake:
with the big cut, thought it was a good idea to move that away from the centerline of the rollover bar forward onto the flange of the forward rib. the idea being, that the rear canopy will have a stronger bond plus that ridge between the ribs where you can see the straps would be covered.
problem it turns out was, the forward canopy was now sitting flush while the rear canopy was "trumpeting" over the rollbar and the big cut didn't look good any more. we fixed it by trimming the rear canopy as well and filling the void with a solid sikaflex bead. that used about another cartridge but the end result looks good and we have a 0/0 sealed canopy :-)

observations:
-get enough helpers
-anywhere where there's no sika primer, sikaflex won't stick and can be easily removed by rubbing it off. best done about a day after while it's still relatively soft. use that to your advantage.
- get good quality electrical tape that doesn't leave too much residue.
- the quality of the joint is awesome, sample pieces (with adverse conditions, no cleaning, no scuffing) had the plexi break before anything would let loose.
- also the tip with sanding the sika with 120grit works perfectly. just make sure you "plaster" enough sikaflex on so you can sand it down and aren't left with any voids.
- get enough sikaflex. most descriptions mentioned about 2 cartridges, we had to order more, certainly used 3 for the "regular" front and rear canopy and used a fourth (but that was used to cover our big cut building mistake)
one gets probably sanded away again when you shape the fairings ;-)

kind regards,
bernie

[flion]

I'm partway through the process with my tip-up. I fitted the canopy without making 'the big cut'. I then glued the canopy to the front frame; it looks pretty much like the pictures in the previous post except I still have the rear section attached. Then the weather turned cold, so I've waited to finish. In the meantime, I've noticed that the Sika has hardened a great deal. My fillet around the front of the canopy worried me a bit but now I see that it's solid (like hard rubber).

My next step will be to glue the canopy to the roll bar. I've masked the outside of the canopy to mark the big cut and I've masked the inside so that Sika on the rollbar only sticks aft of the cut (and I've left a little room aft of the rollbar for a fillet). Because I didn't think the process through and drilled the aft-canopy-to-skin holes oversized already, I will have to be inside to cleco the skin on. So I will clean, paint, and apply Sika generously to the rollbar and then lower the canopy onto it. Then a helper will cleco the top skin on while I cleco the canopy to the skin and complete the aft fillet. I'll then spend the next couple of hours working on cockpit wiring runs and catching up on my reading until my helper comes back and we remove the skin. I'll have to crawl out aft of the baggage compartment. We'll then put the skin back on (reaching in and putting a few clecoes at the top of the canopy should be enough to hold it at that point). When the canopy has had a few days to cure, I will make the big cut. That should leave a shelf of Sika for the front canopy to rest on; I'll dress any damage I do to that making the cut buy applying some Sika by finger. I'll finish up the canopy by using a thin layer of Sika and riveting the side skirts and top skin on. Finally, I'll wax the aft canopy around the big cut and lay up a fiberglass strip to cover the joint.

Like I said, the bubble is already glued to the frame and it is *soliid*. I've had the frame up and down working on the latch, struts, and some clearance issues, and it doesn't give way at all. For those familiar with how twisty at tip-up canopy can be, especially before the struts are on, you'll understand when I say that I think that gives it more stress than I think flight loads will. My only concern will be sanding out that big fillet at the front; try as I might I could not get it perfectly smooth when forming it and there's a healthy edge at the masked lines.

[Greg Arehart]

Hard to see in the photo. How did you transition from the extra .063 on the side rails to the welded front canopy frame? Did these just taper or did you offset the side rails toward the inside (obviously requiring longer rivets)?

Thanks. Great that you posted this stuff for those of us considering sikaflex to see!

cheers,
greg

[flyvans.com]

it's actually 2 strips of .63 (by the way, lent from another 7a kit, rollover bar strips) on each side for a total of about .125".

the intersection is achieved by simply making 2 spacers, .063 each and only half the width of the splice plate. going between the weldment and the siderail splice plate. longer rivets of course. the top "lid" is as per plans except for the lid now being on the outside.

here's another pic where you can kind of see the spacers.


also note the slightly different mounting of the lift struts. might be a result of the inboard offset of the siderails. actually more rigid as with the spacers per plans.



and another closeup of the weatherstripping



bernie

[Rupester]

This is a great thread ... thanks again to you brave souls who led the way. This is wonderfully instructive to those of us ready to start the canopy.

[dhall_polo]

Ah, that weatherseal was the missing detail I'm still pondering on. I'm curious to see if others did something similar.

Since the rear canopy section floats on a 1/8" layer of glue at the roll bar, there should be a 1/8" gap where the front canopy comes down to the roll bar, not really touching the roll bar, right? I was wondering if folks left the gap, or installed some weather seal (d-channel or whatever), or maybe allowed a little sika build up on the front half of the rollbar for a seal.

[Noah]

Originally Posted by dhall_polo

Ah, that weatherseal was the missing detail I'm still pondering on. I'm curious to see if others did something similar.

Since the rear canopy section floats on a 1/8" layer of glue at the roll bar, there should be a 1/8" gap where the front canopy comes down to the roll bar, not really touching the roll bar, right? I was wondering if folks left the gap, or installed some weather seal (d-channel or whatever), or maybe allowed a little sika build up on the front half of the rollbar for a seal.

Don, did you ever get an answer to this question? This is what I'm hung up on too.

Did you reduce the width of your rollbar? My latest thinking is to move my side frames in by .25, and the aft canopy channels in by .125" to account for the Sika bond thickness (skirts are 2x), and just fasten the rear window instead of using Sika. This allows no mods to my stock rollbar and also does not make the canopy stick out past the fuse side skins as it would if I sika'd the rear window and matched the canopy to it. This way the canopy and the rear window both sit flush all around the rollbar. I already have a good spare window from the 1st canopy which was cracked by the previous builder I bought the project from. So if I cracked the rear window, it wouldn't be the end of the world...

Can anybody comment on this approach? Anybody else done it this way??

[flion]

I tried letting the Sika flow forward to act as a seal under the canopy; I was not very happy with the results. You have no control over the forward edge and it looks pretty bad. I tried cleaning it up and filling but I'm still not happy. I'd say trim it flush with the aft canopy and install weather seal under the forward canopy. A targa strip over the canopy gap finishes the deal.