Chapter 18 - Canopy

I'd planned to drive up to AeroCad and pick up a Cozy turtleback, but cashflow got the better of me and I decided to make it myself. I made the jig, then puzzeled through the plans trying to figure out how the foam lays down properly in the complex curve. The archives have an alternative method of laying the foam down horizontally instead of vertically. Can't see how that would work - looks like you'd loose much of the longitudinal curvature. I came up with my own way to hold the foam down. I nailed it. You might think this sounds nuts - nailing foam - but it's actually quite effective. I used 1/2 inch wire nails and a small hammer. Doesn't dent the foam at all and it holds it in place nicely. When I "pop" the turtleback out of the jig my tests show that the nail heads will pull through the foam leaving a tiny hole to fill with micro. We'll see. (later note - don't do this!).

Wicks was out of stock of last-a-foam so I called AC Spruce. I've avoided using AC Spruce since I had a couple of bad experiences with them early on. I decided to give them another chance. They said they had 8 sheets in stock so I ordered two and was promised same day shipment. Three weeks later I called to check on the order. After being on hold for 20 minutes they're phone system hung up on me. After two more attempts and listening to a clipped recording for another 20 minutes I got "customer service" who told me the order was on hold because they were out of stock - but they could get some foam shipped from the west coast at my expense. I told the to delete my order, then delete my customer record, address and phone number. I called Wicks again, got through first time, and ordered from them.

My experiment with nails was a total failure. In the end I removed all the foam, broke most of it at the nail holes, and started from scratch. You see, I didn't like the way the foam was sitting, and I definately didn't like the strips of AL under the joins. Wasnt working for me at all. I see from archives that it doesnt work for many builders. I had another idea. You'd think by now that I'd be getting cautious of my own ideas by now, but no. That's just not the way of experimental airplane building is it? . I'd been cutting up a roll of 10 inch al flashing as used in house building to make the little strips. Problem was I couldn't get the cuts to lie flat, so.... I decided - why cut it at all? Why not just line the whole jig with the stuff? I got another roll (about $5) and lined the entire jig with al flashing using spray contact cement to stick it in place. I just let it lie wherever it wanted so long as there was an overlap. The flashing flowed into the curves of the jig perfectly. It took about 30 feet of flashing, but placing the foam on a continuous surface was easy. I had the foam layed smooth in a hour or two with no gaps bigger than 1/16. (don't forget to carve each piece to a good fit. If you try to force it into place it will buckel). Next thing that didn't work for me was taping the joins with masking tape. Firstly, I had no joins worth worring about. Secondly, masking tape doesn't stay stuck to foam, and thirdly - why would I want 1/2 seams with masking tape under the glass. Ugh! Sounds like a recipe for delamination to me. So... I had another idea. I mixed up some fairly dry micro and filled all the joins with it, then microed the rest of the foam with wet micro. (later note: This worked well. I had no problems with micro or epoxy running out the other side. - but it won't work if you have big gaps). I layed a strip of 2 inch peel ply on the foam where the TB1 bulkhead would go. Why? Because I'd had yet another idea about how to dispense with that ugly "in the way" bulkhead - more about this later.

I layed the glass, peel plyed (on top this time) where the TB1 would go, and added my 4 mil plastic. After squeeging for a long time, I gave up with the plastic and removed it. It just wouldn't sit in the curves and air kept coming up through the gaps and making the layup go dry. After removing the plastic I added more epoxy to be sure they layup was good and wet. After cure I added the straight part of the D bulkhead. I used a 2 inch strip of 3/8 foam glassed with 2 ply BID and 2 ply UNI both sides. Instead of placing it vertically, as it would be in TB1 I placed it horizontally so that it will lay down over the rear two inches of the seatback. Later I added an inch to the back of this part so that it lined up with my spar cap and would complete the structure better. It hangs off the back of the seat back about an inch. I plan to add a vertical bar to give it a little more strength and make a less sharp surface infront of the rear passengers. I added two additional UNI plys going onto the canopy lip and two ply BID taped to the top. After this cured I lifted the canopy out of the jig. I should have been more careful and cut the 5 minute epoxy per plans. I was too anxious, and ripped out a few chuncks of foam close to the rim (mainly because I'd forgotten to put duct tape along the sides of the jig). No big deal. I'll fill these holes with more foam and sand to contour. They'll be under the fairings anyway. There were a few minor bumps, but in general I think my aluminum flashing idea worked out very well. I spline sanded the foam and was amazed at how quickly I was able to produce a perfectly smooth result. I only have one small kink, and that's right where one of the windows will go. My small kink was caused by a joint in the foam strips. The large end of the jig needs strips which are longer than the 4 foot foam length. The 5 minuted joint doesnt bend as well as plain foam. If I were doing this again I'd stagger the joins along the middle of the jig where the curvature is slight, rather than put the join at one end.

TB1 Bulkhead

So - what was my idea for replacing the structure? It was a really dumb one. Thanks to Wayne Hicks, I dumped the idea before getting too far down that pathway. I was going remove a channel of 1/4 foam and flox in a 2 inch * 1/8 strip of T4 AL all the way around. I'd even bent my trusty straight edge to the correct shape. Thankfully Wayne pointed out that this wouldn't do a good job and I dumped the idea. Unfortunately I'd already peel plyed under the glass. So after the inside skin cured I was wondering how to get the peel ply out when I spotted another idea in the archives. What about Roving Spar Cap Glass? I have some left over from the spar caps. Hmmm. 1/4 inch of Spar Cap Glass should do the job nicely, and I can smooth it to contour just before glassing the top. By chance, I just happen to have a strip of peel ply under the foam in the right place! I cut the foam strip and removed the peel ply. I figured out I'd need 10 yards of glass tape for the job, so I had to wait for a delivery. Once this came I masked off the area and layed the spar cap in my 2 inch channel. It took 7 plys to get flush with the foam. The only problem I had was getting the strands to turn onto the lip at the edge. The cap does a gentle turn there and leaves me a bit of a bump. I figure this area is going to be covered by a fairing anyway. I didnt want to terminate the cap at the corner. Seemed to me that it would be better to have it bend round so I could bond it with a few plys of UNI underneath and along the supporting part of the D. While the spar cap was still wet I layed the 2 ply UNI glass on the top of the turtleback and added my plastic peel ply. After cure the result was (to my standards) excellent. It will need very little filler and, I think, will be perfectly contoured. As for the spar cap - I hope we'll never know if it will support the weight of a fully laden Cozy. I can stand and jump on the top of the canopy without bothering it at all, but that's not much of a test. I'm not going to test it to destruction. I doubt that the D shaped bulkheads people are doing are as strong. I think they would snap at the top if subjected to a LOT of weight. Instead of breaking, my spar cap will bend like a spring. I figure that if I ever DO land inverted it will bounce me right back onto the wheels.

Windows

My 10 minute recipe for Cozy IV rear windows