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Old 01-12-2018, 08:48 AM
Rupester Rupester is offline
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,196

Great post, Scott. A practical and innovative solution to a relatively common problem that doesn't offer a lot of fix options. If I were faced with the same problem, I'd go the same way. No way do I want to look at all those hours for building a second canopy in its entirety.
Terry Ruprecht
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Old 01-12-2018, 11:57 AM
RV7ForMe RV7ForMe is offline
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Default Thank you!

Hope I never need this but I have downloaded it with pictures and put into my folder for future reference if the pictures were to disappear!

Thank you for writing it up.
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Old 01-12-2018, 12:07 PM
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mfleming mfleming is offline
Join Date: Sep 2016
Location: Joseph, Oregon
Posts: 279
Thumbs up

What a great write up. I've saved this post as a webarchive for the future.

This should be a sticky!
Michael Fleming
Joseph, OR
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Old 01-12-2018, 02:20 PM
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goatflieg goatflieg is offline
Join Date: Jul 2013
Location: Clarkston, MI
Posts: 401

As I come closer to building up my own RV-8 canopy, this thread answered one important question I had: would bonding with only Sikaflex (no rivets) eliminate the chance of developing a crack later? The answer here is, no. Although you flew for many hours, it eventually happened... and since I live in Michigan and face some daunting temperature extremes, I can't help wondering if a canopy crack is likely (or perhaps unavoidable) in my future, however distant. I will build with the mind of making sure there is no built-in stress during fabrication, and the question of whether or not to use the suspenders-and-belt method of blind rivets and Sikaflex remains unresolved. I'm very glad you shared the details of your experience... I also agree that this post should be saved as a sticky in the RV-8 archives. It certainly is helpful information.
Martin J Filiatrault
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Last edited by goatflieg : 01-12-2018 at 02:23 PM.
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Old 01-12-2018, 03:56 PM
scsmith scsmith is offline
Join Date: Jan 2008
Location: Ashland, OR
Posts: 1,881

Thanks Scott, great informative write-up.

As I read along, I kept hoping for the big surprise that the filler material would in fact become transparent. I wonder if there is a product that would be more clear?

One question I have on your Sikaflex installation. One variable in various people's use is how thick a layer of Sikaflex they create between the frame and the canopy acrylic. I used garden-hose spacers that created a gap of almost 3/16" that got filled with Sikaflex. The hope was/is that this would provide enough expansion flexibility to allow the canopy to grow or shrink without (or with less) stress.

So-how thick is your Sikaflex layer between the frame and canopy?
Steve Smith
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Old 01-12-2018, 05:38 PM
Captain Avgas Captain Avgas is offline
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,659

Originally Posted by scsmith View Post

One question I have on your Sikaflex installation. One variable in various people's use is how thick a layer of Sikaflex they create between the frame and the canopy acrylic.
The thickness of the sealant will indeed be crucial. But there will be other important factors as well. In a post on VansAirforce dated 5/8/2008 I stated the following:

In actual fact polymethyl methacrylate (PMMA) or "acrylic" as it is commonly known is notoriously difficult to obtain a good bond to. Sikaflex itself will not bond to PMMA. An interlayer (or adhesion promoter) needs to be used. In the case of Sikaflex its 209 primer contains 25% MEK and 20% Ethyl Acetate. Both of these are solvents known to break down the cross links of the long chain molecules in PMMA. In the longer term that might very well lead to edge cracking (one case already reported).... the very thing builders were anxious to avoid.

My opinion is that the ongoing reports of cracks in Sikaflex canopies result from the following factors:

a) Vans canopies are either vacuum or pressure formed and will contain locked-in internal stresses.
b) Builders do not properly treat cut edges to fully remove microscopic imperfections/discontinuities.
c) The aggressive solvents in Sikaflex 209 primer will attack the acrylic, particularly at edges where there are discontinuities.
d) Builders are not using the recommended thickness of Sikaflex sealant.

Once small cracks form at the edges of the canopy they will continue to run due to an engineering phenomenon known as "work of fracture".

However despite all of the above, the main reason I would be very cautious about using the Sikaflex approach is because it may be bonded to Vans powder coating which itself has no known quality control and therefore provides no guarantee of adhesion.
Bob Barrow
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Old 01-13-2018, 08:18 AM
Captain Avgas Captain Avgas is offline
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,659

Originally Posted by Scott Chastain View Post
From the PGG DX-Series Data Sheet: "PPG DX Cleaners are specifically designed to remove waxes, grease, silicones, road tar, engine oil, overspray, adhesives and other contaminants. They can be used on bare metal, primers, automotive finishes or to clean plastic parts <emphasis mine>.
Hi Scott, PPG DX330 cleaner is a general purpose auto refinish wax and grease remover. It may be safe to use on some auto plastics such as thermoplastic olefins etc as used in bumper bars and other trims but I wouldn't use it on an acrylic aircraft canopy. I suspect that the fact that your gas inclusions are occurring mainly along the interface of the acrylic and the Plasti-Fix adhesive points to a problem with the cleaner.

But I'm also amazed that the Plasti-Fix instructions called for the use of denatured alcohol as a cleaner. To me, denatured alcohol is methylated spirits which generally contains products that are certain to cause stress cracking.
Bob Barrow

Last edited by Captain Avgas : 01-13-2018 at 08:25 AM.
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Old 01-13-2018, 02:57 PM
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snopercod snopercod is offline
Join Date: Aug 2016
Location: Asheville, NC
Posts: 1,358

Awesome job, Scott, and a very helpful writeup. It gave me chills looking at you gouging out the crack with a Dremel tool. I could just see the tool skittering across the canopy I don't know if this information will be of any benefit to the RV Community but on my Lancair, I used Hysol structural adhesive to bond the acrylic canopy to the fiberglass frame. IIRC, I cleaned both pieces with automotive wax and silicone remover, and lightly sanded the canopy in the joint area. On the inside, I reinforced the joint with BID tapes. No cracks in 220 hrs. (knock on acrylic). I have nightmares about cracks in my canopy...
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Old 01-16-2018, 05:45 AM
Tooch Tooch is offline
Join Date: Nov 2011
Location: Amelia, Va
Posts: 195
Default Heat Pad?

Hey Scott,
In the third picture down, what is that orange pad with the 2 wires going to it?
Looks like some kind of heat pad
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Old 01-16-2018, 08:09 AM
RV8 Tom RV8 Tom is offline
Join Date: Nov 2005
Location: New lenox , Illinois
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I'm guessing light strip for the panel.
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