Mark Dickens

Mark Dickens

Well Known Member
Patron
I've decided against the Sikaflex approach for my -8 canopy, so I've come up with the following mechanical attachment strategy and would like to get opinions from the knowledgeable:

1. Drill and tap canopy frame for #6 screws
2. Enlarge holes in canopy to accommodate movement (perhaps to 1/4"?)
3. Place a thin nylon or teflon washer between the canopy and canopy frame for each hole.
4. Fill canopy hole with a compatible RTV and install screw with a tinnerman washer. The idea being that once the RTV cures, it makes a shock absorbing spacer inside the hole.

Thoughts?
 
Seems like it should work. I've seen ones done with #6 screws, but couldn't tell the details from the outside if they had done any other special prep.

That's going to be lots of fun taping all those #6 holes! I broke a tap just doing the front windscreen as it is.
 
1. I don't know what your canopy frame is made of, but I doubt that it's thick enough to tap and get reliable seating for the threads.

2. Don't fill the holes with sealant. It's not shock that the holes are supposed to allow but thermal expansion and contraction, and an empty hole allows that.

Dave
 
David Paule said:
1. I don't know what your canopy frame is made of, but I doubt that it's thick enough to tap and get reliable seating for the threads.

2. Don't fill the holes with sealant. It's not shock that the holes are supposed to allow but thermal expansion and contraction, and an empty hole allows that.

Dave
Click to expand...

The tubing is 4130 steel...I know of other builders (Matt Dralle for one) who have tapped these tubes, so I'm not worried about that part of it. I'll research some more on the other issue.
 
Every hole you drill, there is a possible strees-crack point due to thurmal expansion-contraction. I have one hole in my canopy. how many holes are you going to drill?
 
Nomsilkaflex

I started on the canopy on my -8 today. Why no silkaflex? The positives seem to outweigh the negatives. Is there something I should reconsider?
Respectfully
Bob
 
bobmarkert said:
I started on the canopy on my -8 today. Why no silkaflex? The positives seem to outweigh the negatives. Is there something I should reconsider?
Respectfully
Bob
Click to expand...

If you're asking me why I am not going that direction, it's a combination of being more comfortable with a mechanical process, and less comfortable with the Sikaflex process. I am not aware of any reason not to use Sikaflex. My only intention was to get feedback on my potential approach to this. Like everything else in this hobby, there are many different ways to accomplish the same thing.
 
Hi Mark,

I am building a 7, but have seen a post by Ironflight and Danny King (for the 8) that proposing to use oversize holes with an insert of surgical tubing to fill that gap. This allows the plexi to float more to allow the thermal expansion to take place without self loading against the steel and create high stresses.

I will keep searching. Also I saw the same thing in 27 years of the RVator. I will amend this post when found.

OK: Here is the Paul Dye method link - http://www.vansairforce.com/community/showthread.php?t=87203

Edit-2: 7/98 RVator article used riv-nuts in the tube for the screws rather than the pull rivets.

There is a lot of good information on expansion and sealing of canopies in the digital version on the RVator. I can sent it in email but cut paste w/o pictures here is problematic.

Good Luck
 
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Planes like King Airs use a little piece of neoprene tubing over the screw in an over sized hole. A voice inside me says your method will crack before long. Maybe I'm wrong. Also, RTV is said to craze plexi.
 
Mark,
If this is true, it is a game changer.

aerhed said:
Planes like King Airs use a little piece of neoprene tubing over the screw in an over sized hole. A voice inside me says your method will crack before long. Maybe I'm wrong. Also, RTV is said to craze plexi.
Click to expand...
 
Tapping Holes in 4130 Tubing

I did some pull tests to failure on this very issue a while back for an RV-9 builder. I think we were both surprised at how high the force was required to make the joint fail - much higher than would be found in securing an acrylic canopy. He went ahead with that process and has had very good results so far.

David Howe
RV-4 S/N 1136 1700+ hrs. - Sold
HRII S/N 002 800+ hrs. - Flying
RV-3 S/N 11226 - Building
 
I considered both methods and ended up going with Sikaflex on the -8.

If I had gone with mechanical attachments, I was planning on drilling 1/4" holes and using silicone fuel line (for model aircraft) and attaching with #6 screws. This would allow some differential expansion.

Just the thought of drilling all those holes in the plexi scared the bejeebers out of me. I'm very happy with the Sika... Nice stuff to work with...

Good luck whichever method you choose!!
 
Ok all you SikaMaffia, you may love it, but some of us don't. I for one hate the thick black frame you get around the tubes in all the pictures and examples I've seen. But then you don't like all my pop rivets either, so let's let all three methods be an option! :)
 
Follow the plans

It can never hurt to simply follow the instructions. Which is what I did, and completed my entire slider in about four weekends. Why? Because I didn't have to research and deploy a method to sikaflex the dang thing. I like the look of sika flexed canopy.... Maybe on the next build:D
 
rockwoodrv9 said:
Mark,
If this is true, it is a game changer.
Click to expand...

Yes, there is research to do on this. If it turns out that using an RTV isn't a good idea, there's always the idea of using silicone fuel line or something like that. At this point, all this is, is an idea. Certainly not yet a fully fleshed out process.
 
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