Finishing Kit

April 21, 2012

Canopy Installation - SikaFlex! - 6.0 hrs.

Today is the big day. I've been planning, prepping, and looking foward to this day for months. I've reached a point where I've done all I can to get ready. I wanted some help, so I enlisted the help of another local builder, my friend Bill DeLacey. Bill is building an RV-9A with a tipup, and he's at about the same stage I'm at. So we've been talking a lot over the last few months, sharing notes and ideas, and so on. He was eager to come help me, so he can see firsthand how it goes, and I'll go help him with his in return, a few weeks from now. I'm grateful to have another set of hands, and his ideas, here today.

First, after a lot of thought, I decided not to use the siderail clamps that my friend Bruce Hill sent to me, after all. The reason is, it would require two applications of Sika, instead of one. The first application would presumably be to the canopy frame sides, and the plexi clamped in place against the frame. Then later, after it sets up, the clamps would be removed and a second application on the outside surface of the plexi would be done, and the side skirts clecoed in place. You have to figure out a way to press the side skirts tightly up to the plexi if you don't want any ugly gaps in between the side skirts and the plexi. But you have to do this anyway, either way. You can't use these clamps with the side skirts in place because they fit under the 1/8" gap at the bottom of the canopy frame's side rails. With the skirts clecoed in place, there's no gap. I hope all that makes sense. It just seemed more efficient and better overall to do it all at once.

So first, we took the clamps off and clecoed the side skirts in place. Then, the canopy frame is carefully positioned in it's final place and clamped in place. You can see the yellow clamps holding the frame to the fuselage, and the clamps above on the curved upper frame, holding it to the roll bar (with spacers in between). Once it's clamped down, the skirts are removed so the Sika can be applied. Bill is pulling the clecos so the skirt can come off.

Now, the application of the Sika involves 3 different products. We started with the Sika Cleaner 226, which is a cleaner and activator. You use clean pads and wipe every bonding surface on the metal and on the plexi. It's supposed to clean and prep the surface for the primer that follows, leaving a dry film behind. It needs 10 minutes of drying time, then you apply the Sika Primer 209-D. This is a runny black liquid that you need to handle carefully. Don't spill it or allow it to run! At one point, the brush I was using was loaded up a bit too much, and as I started to brush it on across the front of the canopy frame, too much came out of the brush and it immediately ran down the side of the canopy frame onto the fuselage side skin below. I yelled, and Bill immediately grabbed a rag and some mineral spirits to clean it up. It's a good thing he was right there and acted fast! In just the few moments before he got it all cleaned off, it was bonding to the uncleaned metal so fast, I was really wondering if he was going to get it all off. Those last few moments, he was really rubbing and scrubbing, and his elbow grease finally took it all off. Bottom line... this stuff is amazing! It really seems to chemically bond very rapidly to the aluminum. Seen here, I'm brushing it on over the top of the bow on the canopy frame. It took me about 1/2 an hour, maybe 45 minutes to apply it to all the surfaces on the frame and on the canopy. That was just about right, because it's supposed to be left to dry for 30 minutes before you start applying the Sika.

After the 30-minute waiting period, you start applying the SikaFlex 295 UV. An ordinary caulking gun worked very nicely for this job. The material is low viscosity, so it's easier to work with than a lot of caulks and other adhesives that I've used over the years. You cut a V-notch in the tip, so that when it's held perpendicular to the surface as seen here, you pull it along and it leaves a perfect V-shaped bead, as recommended. I applied the Sika to the canopy frame only, not to the canopy itself.

I've had a number of people ask me if I made provisions for the 1/8" thickness of the material talked about in the Sika literature. Short answer, no. I did not. With one exception. I used some popsicle stick spacers across the front of the canopy as seen below, to lift the front of the canopy slightly, allowing a thicker bead across the front. The plexi comes into contact with the canopy frame here at an acute angle, and there's really nothing holding it there except this bead of material. A layer of fiberglass layups and filler will go over the front to make a nice smooth fairing later on, and that helps strengthen it too, I'm sure. But this is the decision I made after a lot of thought and study. I'm not recommending to anyone what they should do, just explaining my thinking on the matter.

As I understand it, the 1/8" recommended thickness is designed for marine applications where large sheets of plexi are installed. Sheets as large as 8' x 10' in size. Sheets that are square or rectangular. Flat, basically. The expansion/contraction of flat panels that large would require a thicker layer of material around the edges. That's easy to understand. But our canopies aren't nearly that big. And they are curved. Any expansion/contraction can go mostly up or down, like a balloon slightly inflating or deflating. These bonded edges aren't affected nearly as much as those on a flat panel would be. That's my reasoning, and my decision to build it this way. Plus, along the sides of the canopy, the plexi is sandwiched in between two sheets of aluminum, with Sika on both sides. This makes an incredibly strong joint. And over the curved bow on the aft end, there is a filet bead on both the front and back sides of the frame, adding a lot of Sika material and a great deal of strength to the structure. I'm not an engineer, and again, I'm not telling anyone what to do. But if I were betting money, I'd put the strength of this structure up against any riveted/bolted canopy out there. At least one builder, who went to great trouble making modifications to the canopy frame to allow for the 1/8" gap, has told me if he were to do it again, he wouldn't bother. Thinking about it... a riveted and bolted canopy is held to the frame by a finite number of points spaced along the way, through holes that weaken the strength of the plexi. You can easily count them. You have an attachment point where a rivet or a bolt goes, followed by the space to the next one where nothing is holding the canopy. Then another attachment point, and so on. But this canopy is held in a continuous bond, an infinite number of points, every square millimeter along the way held by the adhesion of the material. And no holes! Which sounds better?

I know, this can be argued and debated all day long, and I won't go into it any further. There's nothing wrong with doing it the conventional way. After all, thousands of RV's are flying with riveted/bolted canopies in place. I'm not saying that's a bad method. I just didn't want to drill any holes in my canopy. After I cracked my first one, I'm scared to! And then there's the story about the builder who was towing his finished airplane on a flatbed from his shop to the hanger. He forgot to latch the canopy shut and make sure the pins on the tipup's hinges were inserted. On the way to the airport, his canopy bounced loose, the wind caught it, and it flew off, crashing and tumbling down the highway. It shattered, of course, but he commented later that the Sika adhesive held! It did not fail him. That was the final thing that sold me on this method.

Okay... I'm off the soapbox now. Here you can see the spacers I used across the front, with the V-shaped Sika bead in between them. This ended up working just fine. My idea was to use just enough Sika to bond the canopy in place, and then come along later, remove these spacers, and fill it in and make nice filets along the edges. Kind of like a welder, who tacks or spot-welds a structure together. Once it's held firmly together, he goes along and fills in the weld with a nice bead. Same idea. If there's one thing I would recommend, after doing this, it would be to use less Sika rather than more for the first application. It's far less messy, looks better, and you can fill it all in later on. Even take the canopy off the plane and do the rest of it on the bench if you like.

Here's a closeup, showing the Sika bead in between the spacers. A sharp eye will notice that the gap between the white and black masking tapes has been primed with the black primer. But also, I laid the Sika bead down right next to the white tape. Not in the middle of the primed strip. Why? Because the canopy will lay down with the interior side right next to the white tape line. Due to the acute angle and tight space in there, I may find it very difficult to get in there later and apply more Sika, if I'm able to do it at all. So I want to make sure there's enough material that squeezes out into the interior when we lay the canopy down on here to give me a nice bead and good adhesion on the inside. I can always come along and add more to the outside. In fact, that's my plan. After the material sets up enough to allow me to pull the spacers, that's exactly what I'm going to do.

Here you can see how the bead continues all around the sides. This is the one area where I didn't hold back on the Sika. I won't be able to add more inside here once it's together. I want this channel filled with Sika, on both sides of the plexi. So my strategy, once the canopy is in place, is to put a bead on the side skirts, and then cleco them in place over the canopy, a cleco in every hole. I used a Q-tip for the "ears" at the front of the siderails, to push the material down into the gap and make sure the surfaces were completely covered inside there. The outside of the ears are masked off, as you can see here, so cleanup should be easy.

Here's the bead I laid over the aft end bow, with Bill looking on. The roll bar still has the masking tape on it that I applied a long time ago.

When the bead was applied all around, Bill helped me lift the canopy and very carefully lay it in place. We started here on the aft end, butting it up against the block I had clamped on earlier, lining up the centerlines. Then we carefully lowered it onto the Sika. I went to the front, and lined up the centerline there as well. This was really very easy. Making sure the canopy was down inside the ears at the front, next we put a bead of Sika on the side skirts, and clecoed them in place, sandwiching the plexi in between. Use a cleco in every hole. This was essentially it, at least for now. The canopy was now in place! The next immediate task, though, was to use my ratcheting tie-down straps. I had a pair of these on hand (no pictures apparently, sorry). They were simply laid down over the top of the canopy and looped underneath the fuselage, hooked up and tightened. Some wood blocks on the sides were put under the straps, onto the side skirts. The idea was to push the side skirts in close to the canopy and eliminate any gap or outward buldging. I wanted a nice tight fit all along the sides.

Now that the canopy was all in place, the next immediate task is to smooth out the material into a nice filet, while the Sika is still soft. One of the things I like most about this product is that you have a good amount of working time before it "skins over". So I started examining the edges all around the outside, smoothing the Sika here and there where it had oozed out. Pay particular attention to the side skirts, I made sure they were pushed into place and the filet smoothed out. I think it was at this point I decided, maybe I should put on a glove! I love this product. There's very little smell or odor. It's pleasant to work with. And if you get it on you, it is easily cleaned off.

Now, what about the interior? It was time to climb inside and check everything, smooth out the Sika wherever I could, and pull the masking tape before it sets up. I had rehearsed this earlier, so I knew I could do it. I climbed in through the rear window opening and carefully slid underneath the seatback bulkhead bar into the cabin. I had taken out the right seat earlier. Here's the view from inside. I basically did the same thing here, smoothing the Sika along the sides where it can be reached. I examined the aft end over the bow of the frame, no Sika was oozing out here. Perfect! I'll fill this in later and make a nice filet. You can't really reach up under the front of the canopy unless you have very small hands. I was glad I positioned the Sika bead to favor the interior. Especially across the front. It worked out very well. So I went to work and pulled off all the white masking tape and plastic covering from the glare shield vinyl. It was very easy and only took a few minutes.

Here's the view from the left seat, looking down the centerline. I had pulled all the masking tapes off in the interior at this point. I think it's critical to get this done, at least on the inside, while the material is still soft. The amount of masking I had done was way overkill, but I have no regrets. No harm in that. You can see my popsicle stick spacers sticking through under the front of the canopy. It's hard to see, but there's a nice bead of Sika that oozed under the canopy into the cabin in between the sticks. Perfect! I can't reach it, it's too narrow in there, to smooth it out into a nice filet, but it doesn't look bad, and I can always cover it with something later if I choose to. It also might be easier in a day or so when I can take it off and work with the canopy on the bench.

Here's the view looking toward the right side. It all looks good. Unfortunately, when I pulled off the black masking tape on the side of the canopy frame, it lifted up some patches of my interior JetFlex paint along the side frame. I'll have to touch this up later. The main thing is, the Sika looks really good. I have a nice tight fit all along here. No gaps or uneven places.

Looking aft, I shot this picture of the canopy going over the bow of the frame. I didn't pull the masking tapes here, because the Sika didn't ooze all the way out to the edge of the tape. Perfect! You can see the Sika underneath in there, where it smooshed out. I mainly wanted to make sure I had good contact under there, so it makes a good bond. When this sets up, I'll pull the canopy off the plane, and work with it on the bench to add more Sika, fill this in and smooth out a nice filet. Then I'll pull the masking tape. You can also see the yellow ratcheting tie-down strap going over the top of the canopy, to hold it down in place.

At this point, I carefully wiggled my way out of the cabin. Not much to do now but wait. I checked on everything periodically throughout the evening. I wanted to make sure the blocks under the tie-down straps continued to hold the side skirts in tight, especially the ears at the front. Late at night, just before I went to bed, I came out and checked it one more time. It had set up enough to hold up, so I pulled the popsicle stick spacers out from around the front of the canopy. As I relaxed throughout the evening, it gradually set in... my canopy is finally in place! I have been working toward this day for so long, it took a while to relax and let my excitement loose. I'm so glad to have this done, I can hardly contain myself. It was really an enjoyable day, no major buggaboos or problems. I think good preparation and a lot of thought that went into this made the difference.

I want to take another moment and really thank my friend, Bill DeLacey. I can't tell you how much I appreciate him for spending most of a day with me. His knowledge, experience, and helping hands proved to be very valuable. We both learned a lot, and I'm anxious to return the favor and go help him with his. Thanks so much, Bill!

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