Canopy Attachment Strategy

[Mark Dickens]

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?

[akarmy]

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.

[Mark Dickens]

Originally Posted by akarmy

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.

All that's needed is patience and if there's one thing I've learned in this odyssey, it's patience!

[David Paule]

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

[Mark Dickens]

Originally Posted by David Paule

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

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.

[bret]

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?

[bobmarkert]

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

[Mark Dickens]

Originally Posted by bobmarkert

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

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.

[BillL]

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/communit...ad.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

[aerhed]

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.