I’m working on fitting and trimming the canopy on my B model Sonex right now and wanted to reach out to everyone and see if the bulges on the sides are normal or if my fitment procedures are off. Following some blogs, I’ve decided to clamp the canopy frame in place to give the canopy a backer while I fit and trim it. Right now, the canopy fit on top looks pretty good but when I look down the sides, you can tell its bowed out. While I know the bow will decrease a little once the sides are “tucked in”, it still seems like the canopy will "bulge” on the sides and not really follow the line of the rest of the airframe. On one hand, I don’t think I mind a little extra shoulder room but I want to make sure that I’m not going to compromise a ton of performance or do something incorrectly. I’ve attached some pictures to show what I mean. I appreciate any advice. Thanks!
On the A model that is normal. We worked hard to get the canopy and windshield aligned at the top center, so in profile it looks like a smooth line vs the coke-bottle shape.
One of the biggest issues we had with the canopy was the latch was too hard to move. It would have been impractical and unsafe to leave it like that. The reason it was hard to move was because the canopy does not come down vertically on the side. It bows out, and this twists the latch in its slots. So, we needed to reshape the canopy. We did this with a board and a heat gun.
When done there was a bit of distortion, but it was all down low. It may be a problem if we evolve to have eyeballs in our shoulders. Totally worth it though – the latch works like a dream.
Thanks for the tip, Bryan. The heat gun and board is a great idea if I run into the same issue (I’ve done the alignment pins but not the latch yet). For a brief moment, I considered using heat to suck in the sides a bit but I’m sure that would be a disaster. Right now, its only noticeable looking straight at the plane from the front.
A second canopy from factory is expected this week; I have to redo since my first one has cracked (installed recently on my Sonex-B project, SNB0048). I’ve included some pics of the extensive cracking that has developed on the sides (right side in pics but both side areas are cracked horribly and even some cracking on bow areas). Suffice it to say I was not smart enough to keep thread cutting oil (used when threading for all machine screws) from getting on canopy, of course plans just say avoid Loctite but they would be better to say avoid anything! My own fault for not better testing prior to exposing plexiglass to the oil. Furthermore I’ve since done a more extensive test with scrap plexi under a bending pressure (with holes drilled similar to canopy) and have confidently concluded the cutting oil weakened the plexi which resulted in the prolific cracking. In my test, the plexi, with no oil exposure has never cracked to date while the oiled piece cracked, at a hole location, within a few hours. Cris at Sonex factory, recently told me factory gets no cracking, however they are adamant about keeping any thread cutting oil away from canopy during installation- sure would have been nice to know beforehand. Additionally , I also have always been concerned about the canopy sides bulging (initial discussion in this post). Sonex told me bulge is normal and that the sides should compress into the “sandwich” as depicted on the SNB-D01 drawing, sec E-E. This high pressure side area is what got me into trouble in the first place as I thought I’d need clecos to pull the sides into place (sandwich), thus I did the hole threading (using cutting oil) with the canopy in place - this would allow using clecos which were removed one at time as ea hole was threaded and a screw subsequently put in. BUT, I was wrong to use the oil and thread the holes in this manner, you MUST avoid any exposure to canopy, so whatever methodology is used, the machine screw holes must be threaded so canopy is not jeopardized with oil.
Hopefully everyone in the Sonex building world is smarter than me and knows all this somehow, but I’m passing along just in case. I’ve also confirmed with another Sonex-B builder/flyer that no cracking has occurred in his canopy (anywhere) and he did NOT allow cutting oil near canopy during construction. He did not mention using any special methods to compress canopy sides into place (that is, the sandwiching along side rails). Hope this info is beneficial.
Welcome to the forum and thanks for sharing your experience. That information is super helpful and you’re absolutely correct; the plans say nothing about thread oil, only loctite. I very much appreciate you sharing your experience.
My Canopy cracked, for no apparent reason, after 175 hrs/about 2 years of flight time.
Seems to me, that the creation of the “Sonex Canopy Crack Club”, is sufficient indication for Sonex to revise pretty much everything to do with canopy material specifications/supply/installation type & instruction.
Its just not good enough that the canopy, for most owners, has become a service consumable (regular fix/replacement) item.
Mine came pre-cracked, but tolerably so. After repairing landing gear, upgrading brakes, and updating avionics, I will see how much the cracks are bothering me.
BTW, it takes a lot of patience to buy parts for this thing. It’s my fault for going in to it with unrealistic expectations. I got used to waiting days instead of weeks or months for things to ship, but each small corner of industry has it’s own tempo.
The Sonex supplied canopy is a consumable item ie if not yet replaced, due to cracking, it almost certainly will be, long before the aircraft is unfit to fly. This is a poor design/concept, that should be addressed by the supplier.
