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RV-12 back window sealant

JRo

Well Known Member
I'm looking for a recommendation on sealant for the RV-12 back window. The large concern seems to be fuel seepage, but I'm concerned, as well, with appearance. This sealant can obviously be seen through the Lexan, and all fuel sealants I've encountered are black. My RV is white, so hoping for a product that might blend better.

Also, looking for hints on tightening the rear window hardware which will never cause crazing or cracking around the holes in Lexan.

JRo
 
Can't help you on the sealant. I've never found it necessary on any of my previous airplanes.

The most surefire way to avoid cracking involves a couple of steps during construction. First, always use a drill bit for plexiglass and go slow. Second, countersink with sufficient depth to ensure the skin will fully nestle down in the countersink without touching the plexi. Then third, overdrill the hole size to allow for a short piece of rubber tubing to fit over the screw shaft as it passes through the plexi. This seems to work for me and all my previous projects.
 
That fast set time (2 - 3 min) would worry me. It seems it would be hard to work with.

I've had my RV flying a little over a year and haven't had any of the fuel spillage issues. My painter used a thin bead of what appears to be grey RTV where the plex and skin meet. There is nothing applied between skin and plex overlap area. A lot of guys here on the forum think eventually I will have problems, but so far so good.

If it ever needs replacement I intend to buy a sheet of Lexan at Home Depot and use the old window as a template to cut another one.
 
If it ever needs replacement I intend to buy a sheet of Lexan at Home Depot and use the old window as a template to cut another one.

Wouldn't be hard to do but the Home Depot Lexan will be even more vulnerable to damage than what is supplied in the kit. The kit supplied window has a protective surface coating on it that common Lexan sheets don't have.
 
Scott, I never said it would work, just that I'll try it! :)

And I never said it wouldn't.

Just letting the masses know that the RV-12 rear window is not made out of the same material you would buy at Home Depot. It is actually a material used extensively by NASCAR.
 
Take a look at Dow 795, boat builders use this to install windows. I did. Its a urethane structural skyscraper window glue. Cheap too.
 
Thanks guys from thread starter. I already ordered Vans replacement window, so that's that. I like the idea of over-sizing the holes for short section of tube, as well as countersink.

As to the sealant, I think it may be an important factor on the 12 especially, 'cause of the fuel filler location just above the Lexan margin. Careful fueling to avoid splash-over, and immediate clean up of any drip(s) may be as important. For that matter, sealing the right side with tank sealant would be considerably more important than the left side, as the filler is on the right.

If the sealant used doesn't resist petroleum well, I'd just as soon skip the sealant step all together. It's a messy, time-consuming job, which really complicates any future window replacement, too. Finding a co-worker to fit comfortably in the baggage area of the '12 was a challenge, too!

Thanks folks!

JRo
 
Byron,

What color is Dow 795? Is it impervious to gasoline? I'm looking for something light in color. Was thinking of coming up with a fuel filler vent to prevent "burping" during fueling, and just skipping this sealant step.

JRo
 
Scott,

Was the Vans supplied window intended to have a specific service life (e.g. 5 years)? My thought is if I can get comparable life out of cheaper material it would be worth my while to make my own replacement if I ever need one.

Rich
 
Cut and drilled raw edges are the problem.

The Lexan has a special coating and is protected. The cut outer edge and the drilled holes are the problem. Oversize the holes a bit and coat the inside surface of the holes and the cut outer edge with laminating epoxy using a small brush and maybe a pipe cleaner for the holes.
 
I am at the point of sealing the rear window and also do not want the sealant to show through the window on the inside. Was considering painting the bottom half inch or so of the lexan the same color as the interior...which is self etching primer. Any reasons why this should not be tried?
 
I have fitted my rear window but have not permanently installed it yet. When I had it in for a test fit, I marked the outside of the window along the aluminum edge. When I removed the window, I trimmed away the protective coating, masked the edge, and painted the outside lower edge gloss black. I did this on my windshield on my Rocket and it turned out very nice. The sealant will be applied on top of the paint and thus, the inside will look the same all the way around.
 
Can't help you on the sealant. I've never found it necessary on any of my previous airplanes.

The most surefire way to avoid cracking involves a couple of steps during construction. First, always use a drill bit for plexiglass and go slow. Second, countersink with sufficient depth to ensure the skin will fully nestle down in the countersink without touching the plexi. Then third, overdrill the hole size to allow for a short piece of rubber tubing to fit over the screw shaft as it passes through the plexi. This seems to work for me and all my previous projects.

Randy,
I'm at the point of permanently mounting my rear window. Are you going to use your idea (above) of the rubber tubing through the holes?
Helped some friends strip down their -12 last night for annual, and they are seeing some crazing, eminating outward from some of the rear holes. I'm liking your tubing idea.
Are you still going to use the tubing on your aircraft?
Thank you-
 
Randy,
I'm at the point of permanently mounting my rear window. Are you going to use your idea (above) of the rubber tubing through the holes?
Helped some friends strip down their -12 last night for annual, and they are seeing some crazing, eminating outward from some of the rear holes. I'm liking your tubing idea.
Are you still going to use the tubing on your aircraft?
Thank you-

Can't help you on the sealant. I've never found it necessary on any of my previous airplanes.

The most surefire way to avoid cracking involves a couple of steps during construction. First, always use a drill bit for plexiglass and go slow. Second, countersink with sufficient depth to ensure the skin will fully nestle down in the countersink without touching the plexi. Then third, overdrill the hole size to allow for a short piece of rubber tubing to fit over the screw shaft as it passes through the plexi. This seems to work for me and all my previous projects.


****Edit: the crazing I mentioned above, small 'spider cracks' around the screw hole(s) was WAY over on the pilot side. Far beyond the reach of any fuel possibly ever reaching it!
Thank you-
 
Gary,

Yes I am. You and I are neck and neck in the building. We seem to hit the same steps at the same time. I just finished up painting the interior this weekend and plan to install the window early next week.

I will buy some flexible rubber tubing that fits the screw shank and then drill up the window to the OD of the tubing. I'll cut little inserts the thickness of the plexi and use them as bushings.
 
Gary,

Yes I am. You and I are neck and neck in the building. We seem to hit the same steps at the same time. I just finished up painting the interior this weekend and plan to install the window early next week.

I will buy some flexible rubber tubing that fits the screw shank and then drill up the window to the OD of the tubing. I'll cut little inserts the thickness of the plexi and use them as bushings.

Excellent, Randy. Thanks! I believe I'll follow suit and do the same. Like you mentioned earlier, if it has worked well for you in the past on many-many builds, it's sure worth trying again on these -12's.
I appreciate the tips!
 
Spilling fuel

Seems to be a common problem. I have a Goat-throat pump for 3 x 25 litre (6.6 gal) Scepter Containers on order for that very reason - to avoid spills.
I have also thought that maybe a 10mm wide 1.5mm thick (or less) adhesive (on one side) closed cell foam tape stuck to the fuse around the window would provide some elasticity, a weather seal and remove the need for tight screws.
Anyone out there ready to shoot me down for these ideas - fire away please.
John
Oz.
 
I installed my rear window yesterday and I enlarged the mounting holes and used rubber spacers as described in my previous post. I found some Bing fuel line that fit the #6 screw shanks perfectly and the OD was 1/4", which matched a plexi drill bit I had. After mounting the window, I can see why there are cracks and crazing around the screw holes. The window is a perfect fit but getting it installed all the way tends to put some stress on the screws and the holes.

I mounting all the screws loosely at first until I got them all started in the inserts. Then I pushed the window around to get all the bushings seated and aligned, then tightened down the screws. Worked perfectly.

I still need to go back and loosen up one side at a time and apply the fuel tank sealant. I'll do that once I get the canopy fitted.
 
Recent update

According to manufacturer, gasoline will dissolve the polymers in Lexel. Not a wise choice for the 12

While searching for a sealant to install my Makrolon rear window in my RV-12, I was looking for good sealant and came across this thread. Considering that Lexel is recommended for sealing both acrylic and polycarbonate, I was interested until I saw this posting. So, I read the SDS, the tech data, the brochure and found nothing from the manufacturer that states this. I also noted that the product is 15-40% naphtha (petroleum) and toluene.

I then contacted Sascho, who makes Lexel Clear, and they said that while they would not recommend it for sealing a fuel tank, as extended contact will soften the polymer strings, however incidental contact by fuel (such as splashed fuel) should not be a problem.

The advantage of this product over Fuel Tank Sealant is that it’s much easier to remove should the day arise the window needs replacing.

I used Lexel Clear to seal my rear window and was easy to use and looks great.
 
I don?t know what you guys are planning to do with the sealant, but consider what a problem it might be if you ever have to replace the rear window. I didn?t put any sealant on the contact urface between plex and aluminum. Instead I masked a line 1/8? from the aluminum edge and applied clear RTV. I pulled the tape up before the RTV set and got a great inconspicuous seal at the edge. When I replaced my flat lexan window with the new molded one it came out with no problems. I sealed the new one with the same method.
 
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