Polycarbonate (Lexan) Skylight

[svyolo]

OK. Thanks.

[Battson]

The screws will seal up nicely if you use plastic washers.

[Nev]

There are already foam strips under the Lexan along the stringers. I’ll also put foam strips on the outside aluminium pieces that capture the sides. The only place I’m unsure about are around the screws themselves. I might do a test once the windshield is on with a hose or bucket of water

[robcaldwell]

Yes. Again, I wish I had taken pictures... It's basically the gap between the inboard wing edge and the lexan skylight and the windscreen. The gap is about 2 inches wide, and the tape is 3 inches. Totally seals out water and air.

[Battson]

I used oversized holes with bushings made from fuel line on my second skylight, same as Glenn suggested. I’ve added nylon washers under the machine screws and the screws are not tightened. So far so good. I’m getting additional aluminium side strips fabricated currently, I’ll post pictures when it’s finished. It should result in a good way to capture the sides of the Lexan as well as a surface to mate the wing trim strips to.

Will you put rubbed strips under the aluminium strips, and will there be strips along the stringers (so to speak)? Just thinking about waterproofing for parking outside in the rain.

[svyolo]

When you say foil to seal the gap, do you mean you cover the entire wing root to fuselage with foil tape first?

[Hewko]

Does Zenith use an avex rivet like Murphy? A 'pop rivet' and an avex rivet are two entirely different rivets. An avex rivet is an aircraft structural rivet designed in WWII for field repairs, while a hardware store pop rivet is not designed for aircraft structures. The steel head and mandrel design, and method of expansion to fill the hole makes the avex a structural rivet. The pop rivets will work on lexan windows though.

[jcowgar]

I have seen pop rivets on lexan covered doors and windows, with and without metal strips over them. I don't know if the rivets were AL or steel. I might try it on some scrap first.

Zenith uses AL pop rivets (body and stem). They make it very clear that these AL pop rivets should NOT be used elsewhere, only in the windows.

[robcaldwell]

Another look at my transition and gap cover from the wings to the skylight. The Lexan extends about 1.5" from the outside rivet line and the AL strip simply lays on top of the Lexan up to the rivet line and is secured to the wing edge with #6 PK screws. Before attaching the AL strip, I used foil tape to seal the gap, like Cessnas use. Forgot to get a pic of the foil tape. Very happy with the outcome.

F398E53C-AF03-4D53-B204-EEC6B17FB247.jpeg

[Nev]

I used oversized holes with bushings made from fuel line on my second skylight, same as Glenn suggested. I’ve added nylon washers under the machine screws and the screws are not tightened. So far so good. I’m getting additional aluminium side strips fabricated currently, I’ll post pictures when it’s finished. It should result in a good way to capture the sides of the Lexan as well as a surface to mate the wing trim strips to.

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[rodsmith]

I really like that idea!

[robcaldwell]

I drilled my 1/16" Lexan oversized with acrylic drill bits. I used these large head rivets to attach the Lexan to the stringers.

https://www.ebay.com/itm/330490032427

Under the rivets I used these neoprene washers as a cushion and a seal. No cracks in the Lexan yet.

https://www.mcmaster.com/catalog/90133a017

Here is my description for the skylight:

https://bearhawk4place.blogspot.com/2018/10/the-skylight.html

[Glenn Patterson]

We did not do the skylight however a Bearhawk builder ions ago recommended a good idea for fastening Lexan. The method may work for a skylight and is good in particular for the windshield. The builder recommended drilling the holes oversized then using poly fuel line for bushings in the Lexan holes. The poly bushings keep the screw threads from coming in contact with the sides of the holes to soften the attach points. We used the poly fuel line bushings on the windshield and side windows. The thought is that with the temperatures ranging from -40C(-40F) to +37C(98F) that the poly bushings may be good with the temperature swings. The Lexan would pull tight in the extreme cold and expand in the summer sun to push and pull on the screws.

[Sir Newton]

I you are capable of building a model. Vacuum forming thin plastics is very simple to do. Youtube the subject. I am of the same mindset for my doors.

[Bcone1381]

Does the four place plans call out any Material for the Lexan Cap Strip? The Patrol calls for a .500" wide strip over the lean 1/8" thick...quite a bit more robust than what is being discussed. ref Patrol Plans p.17 and p.25.

Another viewpoint on drilling Lexan/polycarbonate P. 18 of the pdf document above calls for
-standard twist drill bits and
-avoid heat build up with frequent clearing out the swarf....swarf increases friction & heat buildup....also frequently cooling the hole with compressed air.

The Lexan Sky Light from the Patrol Plans......
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