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Composite canopy skirt?

L

Larry DeCamp

Well Known Member
I started on my canopy install today using a TODD'S CANOPY. It does not conform well to the vans aluminum frame structure, but that is not important to me. While pondering the task, I resolved that Van's design was developed to secure plexi canopy and ALUMINUM SHEET to a tube with rivets. Today most builders use composite material for the skirt.

Varieze, Longeze and Cozy have used the composite approach with acceptable results. Therefore, I plan to build the entire canopy skirt structure with E-glass and maybe some carbon. Please point out the errors in my logic....Larry
 
I am not commenting on your approach. However, if you've never studied it, you should looks at the properties and suitability of UNI-glass. It's used in the spars of composite designs. It's incrediblely strong.
 
I love mine!

Hey Larry, here's how I did it on 7A. Made of carbon/glass molded right the canopy and fuse. Everything is screwed on or clamped.


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Carbon fabric spec ?

Chris, yours is obviously elegant and I read the dialogue on a recent post. What carbon fabric did you use ? I understand the carbon is only valuable as a skin element where the tensile ( stiffness) is incrementally usefull.
 
I used a 3K 7.5 oz., plain weave fabric. You can make it either all carbon or a sandwich layup with carbon on the outside layers. I went the mixed route to save some money. If I went all carbon, same thickness ,the skirt would be much stiffer.
 
Carbon has an interesting property in that its expansion or contraction with temperature is near zero. While that depends partially on the fiber orientation, it can even be slightly negative. This requires that there be a suitable flexibility or compliance somewhere between the carbon and the aluminum or the carbon and the acrylic.

Unidirectional fabric is roughly twice as stiff as bidirectional fabric, but only in the direction of its fibers. Carbon is, very roughly, five or six times stiffer than glass. Certain forms of carbon, like Graphlite, are much stiffer than that if you need that stiffness.

Also, are you planning on abandoning the aluminum frame altogether and using a carbon one? I'd be interested in that since I might do that for my RV-3B, when I get that far along.

I'd expect that the composite section around the front of the canopy could replace the aluminum bow which, in the metal frame, goes in front of the instrument panel. But replacing the aft bow might be more difficult, depending upon the roll bar configuration. I'd want to make sure that when it was done, that the composite frame had at least as much stiffness in torsion as the aluminum one.

Dave
Still on the left elevator....
 
No Aluminum

David,
My concept is to use all glass and carbon..no aluminum. If the canopy does not function as well as the 3/4" square aluminum bows for flexure when the canopy is open , I will deal with it. 7" tall composite walls under the canopy will be significant when hinged and latched in position ! I plan to use classic "section depth" techniques ( foam and hat sections) to optimize the stiffness...Larry
 
Larry,

Keep us posted with what you design and how it works out - and thanks for leading the way!

I think that Showplanes has a composite canopy frame for their RV-8 fastback mod, might be worth checking out.

Dave
 
David Paule said:
Carbon has an interesting property in that its expansion or contraction with temperature is near zero. While that depends partially on the fiber orientation, it can even be slightly negative. This requires that there be a suitable flexibility or compliance somewhere between the carbon and the aluminum or the carbon and the acrylic.
Click to expand...

In particular the acrylic, which has a huge coefficient of thermal expansion. Beautiful carbon work, but fasteners suggest holes through the plexiglass. The difference in thermal expansion rates may create very large stresses in the plexiglass at those holes.
 
Eliminating rivets

Thanks David and Dan for your comments. The expansion issue causes me to 'theorize' a good mounting between fiberglass skirt and Plexi canopy is SikaFlex. I am only "reconning" ( no calculations ) that a 1" overlap of glass (inside and out) will be safe if others have proven a SikaFlex bead along the aluminum tubing has worked. The plexi could be scored with a cutting wheel to provide additional anchorage beyond rough sanding.

A second issue, how much should the canopy hinge pin line overhang the fuse skin. I figure the pin must be at least even with the boot cowl / turtle deck skin or the skirt will dig in when the canopy is raised???
 
Carbon skirt

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I love the utilitarian look of Chris' carbon fiber skirt and would consider using 'as is' in a military-type paint scheme. Would this be possible/pactical using a clear finish over the carbon?

I'm thinking all carbon skirt over the stock alum slider frame on my RV8A project.
 
RV-6 carbon fiber surround

Merry Xmas, I fly an RV-6 built by Garry Legare in 2001. I have owned it since 2007. The canopy surround is carbon fiber with a latch system of Garry's design. There is now about 462 hours on it, I've flown in Reno heat and down to -15 C here in Alberta, no issues with canopy cracking, beautiful workmanship, no outside latches, smooth, light and fast! Love it! I would post an attachment, but it says I can't?
 
arunnells said:
...The canopy surround is carbon fiber with a latch system of Garry's design. There is now about 462 hours on it, I've flown in Reno heat and down to -15 C here in Alberta, no issues with canopy cracking....
Click to expand...

Al, is it all-carbon, or fiberglass with a decorative carbon cover sheet? If solid carbon, is it attached to the plexi with fasteners or is it bonded?

Chris, how about yours, the pretty one in the photo? Glass core?
 
metal canopy skirt

I am not good with composites and badly flubbed my first attempt at the canopy skirt. Then I tried using .025 2024-T3 sheet alum, making cardboard patterns, and doing some simple sheet-forming, with the results shown in the photo. There are six pieces to this skirt: the bow fwd of the instrument panel; the bow aft of the cockpit (a single piece which wraps all the way around), and the side skirts, two pieces each on each side. The fwd and aft bows are single-degree curves, and did not require stretching the metal. The side skirts were the tricky part, each consisting of a large sheet that has a single degree of curvature (no stretching needed here either), and a long, 2x2" compound-curved angle that will overlap the canopy on the frame tubing, then bends outward to rivet to the curved sheet below it. I had to stretch the edges of the 2x2 angles to match the curve of the canopy frame tubing it attaches to. I used a simple hammer and anvil (actually, just a bucking bar in a vise): hammer a little, hold the angle up to the canopy frame to check the fit; hammer a little more, hold it up to check the fit, etc. Rivet the six-piece skirt together onto the frame, attach the canopy with #6 screws, glue on the rubber moldings, and voila: a metal canopy skirt, ready for paint, no sanding or filling necessary. Zoom on the photo to see how I overlapped the fwd and aft bows to the side skirts. You have to enjoy making compound curves in metal to do it this way - an English Wheel would be the perfect tool, but I didn't have one. Canopy is attached with #6 screws through oversize holes in the plexiglass, each hole containing a little slice of clear plastic tubing, like a tiny donut. Each little donut is held in place by the frame tubing on the inside, and the metal skirt on the outside - the entire canopy effectively floats on a bed of slices of plastic tubing. Fifteen years of ops in temperatures from the teens to the 100's, no problem with cracks whatever.

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- Steven
700+ RV3 hours
(another one last weekend!)
 
DanH said:
Al, is it all-carbon, or fiberglass with a decorative carbon cover sheet? If solid carbon, is it attached to the plexi with fasteners or is it bonded?
It's all carbon Dan, bonded. Say, do you know how to post pics, or why the "You may not post attachments" is bolded?
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1 inch aluminum strip

Tony Spicer, I was looking at your canopy photos. Is the aluminum 1" strip glued to the plexiglass to keep the prexy from cracking? Is the full width of the strip glued to the plexiglass, or just a portion of It?

Bill Newkirk
 
Plexi protection

Hi Chris -

Just curious what you are using to protect the Plexi while working on the windscreen? (The white stuff)
 
N13BN said:
Tony Spicer, I was looking at your canopy photos. Is the aluminum 1" strip glued to the plexiglass to keep the prexy from cracking? Is the full width of the strip glued to the plexiglass, or just a portion of It?

Bill Newkirk
Click to expand...

Hi Bill,

Strip was put there to strengthen the canopy edge. Full width of strip is attached to canopy. No problems for 450 hours. Then the airplane got on its back. Now that was problem!

Tony
 
Tony Spicer said:
Hi Bill,

Strip was put there to strengthen the canopy edge. Full width of strip is attached to canopy. No problems for 450 hours. Then the airplane got on its back. Now that was problem!

Tony
Click to expand...

I guess you needed a bigger strip! :p
 
What about corrosion issues between the carbon fiber and aluminum, is a coat of paint enough of an insulator or is it done another way.


Glenn Wilkinson
 
Protecting the windscreen.

I just used the adhesive paper sticker companies use for transferring peel and rub decals.

My canopy is only screwed down on the sides using every other hole. Those holes were then over sized.
 
Larry DeCamp said:
...I plan to build the entire canopy skirt structure with E-glass and maybe some carbon. Please point out the errors in my logic....Larry
Click to expand...
Larry,
Your logic is sound, I went that route with my -3B, details can be found by scrolling down a bit on THIS page. Why would you want to use carbon fiber though? The canopy skirt is not under much stress so wouldn't benefit from the additional stiffness of carbon fiber. It is much harder to work with and finish, my advice would be to stick with e-glass, it will do the job nicely.
 
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