[ArVeeNiner]

I'm at the point where I'm re-examining how I'm going to secure my slider canopy. I had decided long ago that I would Sikaflex it. However, I just got back from the airport and looked at a friend's who, despite Sikaflex, still developed cracks at the rear of the slider. I still have to talk to him more about what happened. I think he's thinking that he just didn't have enough bond line back there. So naturally, I'm now looking at perhaps going the conventional route using screws.

My question is, does anybody know how the canopys on Van's demonstrators are holding up? I'm sure they are screwed on and they probably have been flown more than a lot of other RVs.

 

[Mel]

My -6, completed in '93, is done completely with aluminum pulled rivets. No cracks to date.

 

[Ironflight]

Louise's -6 (Mikey), kit number 20004, has been flying for about 19 years - original canopy, no cracks.

Paul

 

[N131RV]

Where exactly did it crack?

I'm at the point where I'm re-examining how I'm going to secure my slider canopy. I had decided long ago that I would Sikaflex it. However, I just got back from the airport and looked at a friend's who, despite Sikaflex, still developed cracks at the rear of the slider. I still have to talk to him more about what happened. I think he's thinking that he just didn't have enough bond line back there. So naturally, I'm now looking at perhaps going the conventional route using screws.

My question is, does anybody know how the canopys on Van's demonstrators are holding up? I'm sure they are screwed on and they probably have been flown more than a lot of other RVs.

Can you describe exactly where the exemplar canopy cracked? On the rear at the side rails? Was there any penetration of the canopy near the crack?

I just finished the sika treatment on my canopy/windscreen. I ended up doing the screws on the side skirts, but no other holes in canopy or windscreen. It's very, very strong stuff. In addtion, I laid up fiberglass skirts at the rear of the canopy. My previous canopy was done per plans, and had no cracks in 298 hours of operation (until asked to support the weight of the aircraft,that is).

 

[Skytrash]

Aft Canopy Cracks

Here are a couple of pictures of the cracks on my aft canopy. One looks to be originating from where the canopy frame has a slight kink from bending during fitting to the fuselage. The bond line should have been thicker between the frame and the plexi. The bond line should vary in thickness with the shape of the frame to allow for the as bent shape of the frame while allowing the plexi to be as stress free as possible.

I still think that bonding is the way to go and will do it again if I build again.

 

[N131RV]

Youch!

Here are a couple of pictures of the cracks on my aft canopy. One looks to be originating from where the canopy frame has a slight kink from bending during fitting to the fuselage. The bond line should have been thicker between the frame and the plexi. The bond line should vary in thickness with the shape of the frame to allow for the as bent shape of the frame while allowing the plexi to be as stress free as possible.

I still think that bonding is the way to go and will do it again if I build again.

Is the rear skirt riveted on? I can't really tell from the images.

 

[Captain Avgas]

In either case, cracks begin like any other fracture in an airframe---from what metallurgists and engineers refer to as stress risers. In this case, a stress riser at the edge of the plexi, originating from pehaps a tiny chip or an unburnished edge, gave birth to a crack that migrated to the extent that it did.

Maybe, but maybe not.

Acrylic as used in RV canopies is very prone to solvent attack leading to microscopic crazing and the subsequent forming of larger cracks therefrom as a result of work-of-fracture theory.

The Sika 209 adhesion promoter actually contains approx 25% MEK and approx 20% Ethyl Acetate. Both of these solvents are in the worst category for damage to acrylic.

Sikaflex is mainly used in marine applications where generally the small acrylic windows are not thermoformed. Severe double curvature thermoforming (such as in RV canopies) may give rise to instrinsic stresses remaining in the canopy after it cools which might make the canopy more prone to cracking from solvent attack.

This is not the first case of cracks being reported in a Sikaflex canopy. It is possible that these cracks are not formed by edge imperfections but by microscopic solvent breakdown of the acrylic polymer.

 

[rv7charlie]

Interesting. If you study the Sika literature, it says that it's specifically designed for bonding acrylic to other materials. I would think that the boating people would have serious problems since most boats are out in the weather 24/7 & the stresses are likely to make a/c loads look pretty tame. Has anyone heard of cracking problems from the boating crowd?

Charlie
(almost to the point of applying the Sika...)

 

[Mark Castle-Smith]

I have a small (22ft) mini tonner in which I bonded new windows about 10 years ago with Sikaflex, no problems at all.

I followed all the rules with my canopy, very hot when it was cut and drilled, used the recommended plexiglass drills etc. All looked good with the naked eye, no sign of cracks. I then decided to make doubly sure and used a magnifying glass all around the canopy with a strong light. All the cut edges were fine but I found two micro cracks emanating from 2 holes in the sliding section of the canopy which I would never have found by just examining by eye and would have definitely led to in flight cracks. I dressed out the micro-cracks with fine emery cloth on a small dowel. Checked the whole canopy again with a magnifying glass!

No problems with cracking so far.