Side-by-side Airframe Prep for Sika

I've decided that I want to use the Sika process for installing the tip-up canopy for my RV-7A.

I'm at the point where I need to build the "roll bar". This piece must be trimmed in the center, before assembling, so that it fits the fuselage side-to-side.

I know that the Sika process requires 1/4" Sika to glue the rear fixed portion of the canopy onto the roll bar. My question is, does this imply that I should build the roll bar 1/2" narrower than the fuselage, to make room for the additional 1/4" thickness of the Sika on either side (vs what would normally be the width if I went the screw/rivet route)?

For those that have gone before me with this process, can you comment?

that's what I get out of that

I wish I knew then what I know now
I did both roll-over bars (canopy and frame) at the same time.
We'll see how it turns out with sika.

When I did mine last summer, I built the rollbar 1/4" narrower than the fuselage width, to allow an 1/8" bead of Sikaflex. It turned out well, and it very sturdy with the 1/8" bond width (which I also used on the canopy). Check the width against the fuselage, rather than using dims from the plans, as variation in longeron bending may have it slightly off the plans.

Further on in the process, I made some wedge spacers to go on the outside of the rollbar mounting angles, rather than filing a taper into the mounting angle. This will maintain the top skin in the proper place WRT the fuselage side skin, even though the rollbar (and mounting angles) are shifted inboard by the 1/8" per side.

Wedge spacers:


I never did figure out a good way to do the aft side of the rear window and maintain a proper bond thickness without a big draggy "step" from the plexi to the skin, so I did use screws there, with a thin bead of Sika to seal against water.

Rollbar & canopy build log for more photos and commentary.

I built mine to plans. When I applied the Sika, I used ~1/8" thick shims across the top of both the roll bar & canopy bow, & allowed the plexi-rollbar/bow gap at sides of the canopy & back glass to taper to nothing a the bottom. Part of the decision process was figuring out the trailing edge of the back glass; I couldn't see any way to install it with a thick layer of Sika & have it look/work 'right'. I just buttered a thin layer of Sika on the plexi & the inside of the skin, & forced a tight fit. After the initial cure, I pulled the shims, filled those gaps, & then applied a fillet from plexi edge to aluminum.

I used basically the same technique on the canopy sides, adding a fillet from bottom edge to the side rails. Seriously creative clamping methods were required to make that work. If I'd seen the idea of shimming the side rails in slightly before I'd already built the frame, I might have done that, but mine turned out pretty well with everything built to plans.

The Sika is *very* strong. I'd bet that just a 1/4" fillet on the edges & front/back of the roll bar would hold the back glass in place, & not much more would be needed on the canopy.

I used Sika for the windshield fairing, & that worked pretty well, also (no final finishing/paint yet).

Dig through all the info you can find before even ordering the Sika. I tried to, but still missed some good ideas until after the fact.

Charlie

dont forget to use their primer prior to the sika flex

Sika

I trimmed for about a 1/4" bead. Don't forget to trim height as well.
When building the frame, I offset the inside rail with a 1/8" spacer at the front.
For the aft window, I used a wide overlap (like 1.5 to 2") and sanded agressively to give the bond some thickness. No holes in any of my plexi.
Search the archives - there is a lot there.
The most important thing to do is apply the Sika within 2 hours of priming.

Today is my 3 year anniversary of 1st flight I live in Michigan, so it's seen a wide range of temps, and the canopy bonds look brand new.

Well, the "consensus" (of 4) seems to be that, either allowance was made or, if it wasn't, they wished they had.

In either case, all were able to "make it work", in some fashion or another.

Are there differing opinions out there? Any reason NOT to allow the additional 1/8" "all around"?