Bonding the windscreen is a critical milestone. It isn’t nearly as glamorous as mounting the engine or powering up the avionics, but it means a great deal to the overall aircraft structure and final outcome of the project. It’s a make or break moment.
Surface preparation of the bonding surfaces is very important. Various special primers promote adhesion. Accurately locating the about-to-be-bonded windscreen while things are battered with jet-black SikaFlex polyurethane marine adhesive, onto the frame and fuselage, is aided by reference holes and locating pins. Masking and protecting areas where adhesive does not belong, makes it just possible to get the assembly together without too much of a mess. Gentle, even clamping keeps the windscreen in place while the adhesive cures.
Minimum working temperature for the adhesive is 50ºF. At that temperature it will take up to 12 days to cure and it will be all I can do to keep my workshop warm enough though the winter days, here in Pacific Northwest Washington. Time will tell.
All in all, it seems like I’ve pulled it off! Looks like a good fit, no Plexiglass cracks and plenty of nice adhesive in the right places. Now I just hold my breath for a couple of weeks. Whew! Glad to have this step in my rearview mirror. What a relief.
Having put this off as long as I could, I’ve summoned the courage to trim the windscreen until it fits. I absolutely do not want to crack it and I cannot afford to over-trim. It has to be done, just so. If ever there was a time to apply, measure twice, cut once – this is it!
Along the way, I take comfort in and from small stress-reducing distractions. Testing out my fancy new lithium battery charger yields a few moments to gather myself. The charger has a feature that can supply up to 10A of current to power the avionics and allow for extended sessions of testing, configuration and familiarization – ok, play! There’s a lot to learn and it’s going to take quite a bit of play time.
The canopy latch is inset within an oval area that must be carved out of the top front of the canopy plexiglass and underlying composite frame and held in place with blind M5 rivnuts and screws. Let’s just say that this is a challenging and nerve racking set of tasks. And – that’s a major understatement. But, with patience and a good bit of careful work with my trusty Dremel tool, I was able to achieve what I deem, at this point anyway, a satisfactory result.
The latch mechanism is an over-center affair with a hook engaging a latch pin that mounts to the top underside of windscreen support arch. Four 3,2 x 10mm CSK rivets attach the pin and it’s mounting plate to the arch, along with whatever additional security is afforded by a dollop of JB Weld epoxy. Where exactly to position the pin is an exercise left entirely to the discretion of the builder. Good luck with that.
I think by the time I get the weather seal in place, the latch will pull the canopy closed – firmly and without gaps. We’ll see. All of this latch fitment has happened before having the windscreen and support arch bonded in their forever positions. I’ve got my fingers crossed. Time will tell.
The exhaust system has been languishing in a box and it seemed a good time to see how well (if) it fits with the engine and airframe. It looks… maybe not so bad. Good!
There’s going to be some work needed to get the cabin heat muffler shroud assembled, because I don’t have a part that actually fits. So far, I’ve gotten 2 different parts (and part numbers) from the factory, but neither part matches the mounting rings on muffler. Argh. I’ll have to adapt and/or fabricate something. But, at least it seems the exhaust pipes and muffler do fit. Hooray for that.
Rivets, wires and avionics are friendly territory for me, compared to where I’m headed now. Fitting the windscreen and getting it bonded in position are tasks I’ve been apprehensive about – extremely apprehensive.
Manipulating clear acrylic sheet – Plexiglass and Perspex are brand names – that’s been molded into compound curves of unusual size, is just asking for trouble. I don’t like trouble. Dealing with this stuff is tricky, all by itself. Don’t even get me started about cutting or drilling holes in it. Eventually, I’m going to add sticky gooey pitch black marine adhesive caulk to the mix. That could easily lead to – yes, you guessed it – super trouble!
The time has come. I can’t avoid it any longer.
Because I opted for a factory quick-build kit, it came with the main canopy already trimmed and bonded to its painted composite frame. That’s fortunate because it may well have spared my frazzled nerves just enough to be able to deal with the windscreen.
The initial canopy placement seemed easy enough. Screw holes in the frame aligned with the ones in the slide assemblies. Countersinking of the frame will be needed to correspond with the short M8 stainless steel CSK mounting screws.
The arched windscreen support frame was fitted and match-drilled to align with M5 rivnuts that were installed at the factory. I made cardboard templates for left and right sides because they’re different. (They shouldn’t be – but that’s how the factory built it.)
The trial fit reveals that the rear edge of the windscreen will have to be cut back by at least 4 or 5 cm to align with the arched support frame. The lower rear edges (corners) of the plexiglass will just barely be under the fuselage top skin when it’s riveted in place. Precise positioning of the windscreen is going to be extremely important to avoid any unsightly gaps between the aluminum skin and the plexiglass.
A latch mechanism has to be fitted into the canopy. I inventoried the latch parts when I received them, but I could not have detected that the supplied spring was not correctly formed. I checked with the factory and confirmed the situation. They’re going to send me a replacement spring.
Windscreen cutting, drilling and bonding comes next.