Complete
Hi Dave/Brad and the 50,000 or so other VAF geeks,
So I finally finished the canopy. Talk about one monster of a project. No wonder it had an entire section of the instruction manual dedicated to it. I started work on March 8th, and finished a day ago, working on it almost every day. Admittedly some days were only a couple of hours of work, because I'd have to wait a full 24hrs before I could sand the West 407 filler back due to the low temperatures (even with 205 fast hardener).
So the canopy skirt (or rear roll bar as Brad refers to it) came in at 1.8kg total after surface filling then priming the interior with Wattyl (Valspar) UC230 high build primer, and top coating with a couple of coats of Colourthane Polyurethane. Heavier than I would have liked, but crikey it is stiff. I had just bridged between the canopy and the fuselage with packing tape, so like others, I experienced a bit of sagging when the layup cured, so I had to use more fill than I would have liked, which I suspect lead to the higher than calculated weight, although I still don't know a better way of bridging this gap. I used the proscribed MK319-BS rivets to attach the fairing to the canopy frame, so I had to countersink pretty deep, then filled over the top with West 407. I went with the monel rivets instead of the longer aluminum CS4-4 due to Dan Horton's concerns about corrosion with the carbon fiber. I suspect given that these will be completely sealed, then the risk of corrosion should be very low. The canopy skirt brace is riveted to the skirt using soft -A instead of -AD rivets, and on the inside of the steel canopy frame using the regular LP4-3 rivets. The top slider dog house was laid up over the supplied aluminium part (it was taped down to the aft fuselage when the packing tape was laid as the release agent) then much later in the fabrication the C-679 slider seal was shaped, then taped with packing tape so a tighter mould could be taken to ensure an airtight seal. The skirt was attached to the perspex using Sikaflex 295UV (and 209 primer of course). 0.75mm spacers were fabricated from layers of black electrical tape and places at 2-3" intervals When the original layup was completed, 0.75mm thick layers of electrical tape were run all the way around to simulate the future sikaflex layer. The big issue faced when bonding the skirt to the canopy was getting the sikaflex to squeeze out of the layer. The problem was the sikaflex was so thick and I didn't have clamps deep enough to clear the aft of the skirt, so I had to squeeze using my hands as hard as I could and progressively work from one side ot the other. It came up fine, but in hindsight I was just lucky I got it down before things cured with an overly large gap. I probably should have fabricated some deep clamps for this purpose.
Once the canopy was complete, I then laid up a coating of West G-Flex epoxy and West 407 filler and placed it around the windscreen. My windscreen is also a bit non conventional. The windscreen was originally bonded to the fuselage using West G-Flex and flox, on both the inside and outside, with Sikaflex 295UV around the roll bar portion. I then I added more flox and G-Flex around the front of the windscreen and sanded this into a smooth transition, before laying up just one layer of 12 oz double bias glass cloth. This glass was laid onto a coat of G-Flex but was wetted out using West 105 resin, as G-Flex isn't much good for wetting out (but bonds well to Aluminium and Perspex). A couple of final layers of West 407 filler was progressively laid down and sanded accordingly. Around the roll bar I laid a transitionary coat of G-Flex mixed with 407 filler so I could have a smooth aerodynamic flow from the windscreen to the canopy. My canopy didn't match the windscreen perfectly, as I had clamped the windscreen down a little hard in places when the sikaflex was setting, so this 407 filler masked my incompetence. The gap between the windscreen and the canopy is very consistent (I spent a day and a half sanding it, so I guess it should be) thus I have decided to do without the 1" lip that normally extends from the windscreen over the canopy, and instead will just add a foam seal, as it the practice on aircraft like the Grumman Tiger. I can always add something in the future should I deem it necessary, however this got around the problem of people leaning on the strip when entering and exiting the aircraft and potentially causing cracks, or making something so stiff (carbon) that it causes thermal coefficient of expansion problems and subsequent perspex cracking. It also buys back some of the weight I added with my overly massive canopy skirt! Anyway, I'm glad that's a chapter of this build completed, and I'm definitely looking forward to the engine installation as a change of pace from sanding fiberglass.
Tom.
PS. Having trouble uploading pics, so will try to add more tomorrow.