Windscreen though bolts?

[Pbruce]

I recall airplanes with squeaks and rattles from the windscreen jiggling laterally across the cabin top and boot cowl. It was most noticeable on engine start and shutdown.

I have five 6-32 bolts holding the windscreen tightly against each vertical aluminum former at the rear of the windscreen, each bolted through an exterior trim, the window (with grommets) the former and/or steel mounting tabs, and a nut plate on the inside

. It feels like the top of the windscreen is inclined to “rack” side to side slightly in the double u-channel. Just a slight wiggle. I haven’t yet put acrylic sealant in to waterproof the joint, but I wonder if anyone has thru-bolted across the top of the windscreen, or the skylight for that matter too? How about the base of the windscreen?

On another matter, my boot cowl sides are detachable from the top, below the windscreen corners. I see no reason not to permanently attach the INNER windscreen flange to the boot cowl. Am I missing something?

Thanks.

[DBeaulieu]

On my first project (Zenith 750) The top of the windscreen was screwed into the top cross member of the cabin frame. Like you did on the verticals, there was a aluminum trim strip overlapping the skylight and windscreen at the cross member and the screws went thru the strip and oversized holes with silicon grommets into the cabin frame. Bottom of frame was not fastened to boot cowl. There was movement noted across the bottom, but only while cleaning the windscreen at the lower edge. I didn't consider it a problem in flight, but the 750 flies a lot slower than a Patrol. Maybe some thin cork strips in the u-channel would take care of your "wiggle if a concern. I like the idea of permanently attaching inner flange to boot.

Why bolts versus screws to hold the windscreen?

Disclaimer: Just starting my Patrol QB build - not even completely unpacked

[Pbruce]

Bolts vs screws: Well, actually, I think they they are 6-32 screws. I used the term “bolt” because they aren’t tapered, don’t have a pointed end, and they terminate in nutplates, rather than into sheet metal. The main thing besides waterproofing, is I want a sealant that is soft enough to allow removal of the acrylic without damaging anything. I’m not sure what that is.

I took a look and the u-channel separating the skylight from the windscreen is quite loose. You are probably right in thinking that filling the gap will help. I might be able to squeeze it too, and ultimately it will get acrylic sealant.

Maybe sealant up against th e inner flange is needed too. I haven’t seen any direction on this matter anywhere

[jaredyates]

The way Bob originally did things was to fold fabric into that channel, then push the windscreen into the channel. So in a skylight application with no fabric, the channel will probably be a little loose. Some ideas come to mind such as using some adhesive felt on the windshield plus generous application of Lexel upon final assembly, or perhaps carefully closing the channel a little. The second option is scary in that if you rush it and stretch the steel it will become wavy.

You'll want some kind of sealant to keep the rain out. I'd think that sealant is going to help limit the lateral movement.

The general idea is that the plastic is going to move due to thermal expansion and contraction, so if the airframe doesn't allow for movement and it gets bad enough, you can get cracks. I used oversize holes at the corner posts and deburred carefully.

As for the permanent attachment if the bottom angles, I'd just rivet them. If you need to remove them for repaint in 20 years, drill the rivets.

[Pbruce]

Thanks as always Jared, for your assistance. I have found Lexel at Lowes. I’m assuming this is the product you referenced? In your experience with this product, you think it would remain soft enough over time to allow removal with the aid of a tool like a razor knife? (Hopefully it wouldn’t. E neccessary, but…)

[jaredyates]

It would be a job to remove it. I wouldn't characterize it as hard or soft, and it sticks very well. I had a tube handy and used it to seal around the fuel filler neck, and the fuel softened it over a few years.