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Fiberglass side and rear sliding canopy skirt ?

William

Well Known Member
Hello everyone I've decided to make my side skirts and rear skirts on my RV-6A out of fiberglass and carbon fiber. I went with the following layup; 3 layers of 6 ounce fiberglass cloth and 1 layer of 5.7 ounce carbon fiber cloth. Now my question is do you think this will be strong enough? It is quite rigid but not quite as rigid as the stock aluminum skirts. Next if you have used fiberglass skirts how did you attach them, glue or rivets. Lastly did you use the reinforcing C791? If so how did you attach this to the bottom of the inside of the fiberglass skirting, glue or rivets?

thanks guys,
William
 
Here's how I did

Hey Willam,
This is what I did. My skirts are thicker then most I think. I "think" I use 3 7oz. and 3 carbon. The last layer of carbon I put on after the first layers were sanded down, filled, and super smooth. Everything is screwed down. The reinforcements were made in carbon right off the aluminum ones.

1233200024.jpg
 
I made a fiberglass rear skirt but kept the aluminum side skirts. I attached the rear skirt with counter sunk screws along the rear roll bar and riveted/epoxied the rear skirt to the aluminum side skirts.

For the main attachment at the rear, I took the following approach:
1. Drilled the rear roll bar and plexi for screws focusing mainly on how best to attach the plexi to the frame. I drilled through the frame and used nuts on the interior
2. When I was ready to attach the fiberglass skirt, I removed every other screw from the canopy and put the rear skirt in place.
3. Back drilled the fiberglass where I had removed the screws.
4. Counter sunk the fiberglass so the heads sat below the surface.
5. Attached the skirt to the frame.
6. Worked on the side skirt
7. Did the final filling and shaping when I was sure that rear skirt was on to stay
 
One more note. My plexiglas is only mounted with screws on the sides and down the center. The front and rear are just siliconed.
 
Some research shows that Sikaflex is not only a good solution to bond the canopy to the frame but also the skirt to the canopy, not really sure what it would look like from the inside but as I am going to attempt to venture down this path in a few months.

-david
 
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I laid up a one piece skirt from 3 layers of glass & 2 layers of carbon. I used Sika to bond the canopy to the frame, no holes through the plexi other than for the latch on top. I attached the skirt to the frame & canopy with Sika 295, but also ran blind rivets into the outside surface of the side bows per plans. C791 reinforcements are blind-riveted to the inside of the side bow, again per plans, likewise riveted to the skirts with solid rivets.

Chris Frisella is an artist with carbon, mine is workable, but his looks so much better than mine that I'm going to decline posting photos :)

Like Chris's, mine is also a fair bit thicker (like maybe 3x) than the stock skirt material, but it's rock-solid, and you can't slide a business card between the skirt and the fuselage skin, anywhere.
 
Hey Willam,
This is what I did. My skirts are thicker then most I think. I "think" I use 3 7oz. and 3 carbon. The last layer of carbon I put on after the first layers were sanded down, filled, and super smooth. Everything is screwed down. The reinforcements were made in carbon right off the aluminum ones.

1233200024.jpg

Very interested how your windscreen layup is going to come together over the canopy.???? :)
 
Thanks everyone for the information, sounds like I'm on the right track. The main concern is how to secure the skirts to the frame and it appears I have 2 options. Either secure with screws/rivets, or glue on. I originally was going to go per the plans with rivets to attach the skirts and the c-791, but I'm very concerned with the possibility of the rivets pulling through the fiberglass/carbonfiber over time especially since these rivets will be countersunk into the skirt. Any thoughts on this?

thanks,
William
 
Yes... the aluminum skirts work the best and are really easy to install. :)

I suppose it depends on what you mean by "best".

I had the chance to study about a half dozen slider RVs last weekend. After seeing how most of the canopy skirts fit, I was reminded about how much I liked mine :)
 
I went with the following layup; 3 layers of 6 ounce fiberglass cloth and 1 layer of 5.7 ounce carbon fiber cloth.

Carbon used in an asymmetrical layup is usually just wasted money. Fiber properties and placement determine how the part will act under load. Random selection and placement nets a random result.

Note the fundamental layup schedule quoted by Chris and Lars; 3 glass and two carbon (Chris added one after the fact for purely cosmetic purposes). That would be a sandwich with 3 glass core plies and one ply of carbon on each outer surface. The idea is to place the carbon at maximum distance from the neutral axis (the center of the thickness), thus utilizing carbon's typically high modulus to actually get a stiff part.

Carbon has a downside; it acts like a highly dissimilar metal. Standard fasteners and aluminum in direct contact can develop severe corrosion. Frankly I see very little justification for carbon on an RV, but......
 
Hi Chris as others have said your skirting setup looks amazing! When you stated you made the reinforcements right off the aluminum ones are you saying you used the aluminum ones as a mold to pull the identical part out of carbon fiber? Then these reinforcements are held to the carbon fiber/ fiberglass skirt with screws?

thanks,
William



Hey Willam,
This is what I did. My skirts are thicker then most I think. I "think" I use 3 7oz. and 3 carbon. The last layer of carbon I put on after the first layers were sanded down, filled, and super smooth. Everything is screwed down. The reinforcements were made in carbon right off the aluminum ones.

1233200024.jpg
 
Yes... the aluminum skirts work the best and are really easy to install. :)


I really did want to use the aluminum skirting but my canopy frame didn't end up a uniformed distance inside the top of the longeron all the way around. When the aluminum skirts were fitted this caused large gaps that were unable to be closed up no matter how I manipulated the skirting. Figured fiberglass will follow any path you make for it. ;)

William
 
Hi Rick how are your fiberglass rear skirts holding up around the rivet heads? Did you countersink the fiberglass?

thanks,
William



I made a fiberglass rear skirt but kept the aluminum side skirts. I attached the rear skirt with counter sunk screws along the rear roll bar and riveted/epoxied the rear skirt to the aluminum side skirts.

For the main attachment at the rear, I took the following approach:
1. Drilled the rear roll bar and plexi for screws focusing mainly on how best to attach the plexi to the frame. I drilled through the frame and used nuts on the interior
2. When I was ready to attach the fiberglass skirt, I removed every other screw from the canopy and put the rear skirt in place.
3. Back drilled the fiberglass where I had removed the screws.
4. Counter sunk the fiberglass so the heads sat below the surface.
5. Attached the skirt to the frame.
6. Worked on the side skirt
7. Did the final filling and shaping when I was sure that rear skirt was on to stay
 
Hi Lars how are your fiberglass side skirts holding up around the rivet heads? Did you countersink the fiberglass?

thanks,
William






I laid up a one piece skirt from 3 layers of glass & 2 layers of carbon. I used Sika to bond the canopy to the frame, no holes through the plexi other than for the latch on top. I attached the skirt to the frame & canopy with Sika 295, but also ran blind rivets into the outside surface of the side bows per plans. C791 reinforcements are blind-riveted to the inside of the side bow, again per plans, likewise riveted to the skirts with solid rivets.

Chris Frisella is an artist with carbon, mine is workable, but his looks so much better than mine that I'm going to decline posting photos :)

Like Chris's, mine is also a fair bit thicker (like maybe 3x) than the stock skirt material, but it's rock-solid, and you can't slide a business card between the skirt and the fuselage skin, anywhere.
 
Why are some of you using carbon in the lay-up?

Is it for stiffness?

My concern is that while fiberglass has a thermal expansion that's reasonably close to aluminum, which is roughly 1/3 that of plexi, carbon has a near-zero thermal expansion and it's four to five times stiffer than the fiberglass.

This means that if there's any load on the plexi due to the thermal mismatch, having carbon in the lay-up will exacerbate the issue. The carbon, being stiffer, will determine the characteristic of the lay-up, and its thermal expansion is considerably worse for the plexi than aluminum or fiberglass. And its so stiff that the loads will be greater on the plexi.

Dave
 
DanH went into a big discussion once about thermal expansion and acrylic/sikaflex/bolts

the actual expansion value is very, very, very small for the typical temperature fluctuations seen by RV's
 
the actual expansion value is very, very, very small for the typical temperature fluctuations seen by RV's

Ummmm.....plexiglass has a huge coefficient of thermal expansion.

Listen to David.....he understands materials properties.
 
The fellow that helped me with mine used a 1/8 thick honeycomb board and did the layups on top of that. Really worked slick. It is very strong and looks great.
 
Hi Lars how are your fiberglass side skirts holding up around the rivet heads? Did you countersink the fiberglass?

thanks,
William

I'm not flying yet (close, though) so I can't say for sure. The canopy has been opened and closed a bazillion times, but that's hardly the same as vibration due to engine and/or aerodynamic effects. That said, use AD4 rivets, not AD3. Bigger head, more bearing area. I squeezed the rivets; they didn't sink into the layup after squeezing.

Why are some of you using carbon in the lay-up?

Is it for stiffness?

My concern is that while fiberglass has a thermal expansion that's reasonably close to aluminum, which is roughly 1/3 that of plexi, carbon has a near-zero thermal expansion and it's four to five times stiffer than the fiberglass.

This means that if there's any load on the plexi due to the thermal mismatch, having carbon in the lay-up will exacerbate the issue. The carbon, being stiffer, will determine the characteristic of the lay-up, and its thermal expansion is considerably worse for the plexi than aluminum or fiberglass. And its so stiff that the loads will be greater on the plexi.

Dave

Yeah, I realize that you can actually create structures with a near-zero CLTE using carbon fiber- my recollection is that pure carbon fiber actually has a negative CLTE. In my case, I used carbon fiber for stiffness, but also because I happened to have a large piece of the stuff. I laid it up as Dan described, with material cut at 45°, and the resulting structure is really stiff.

In my case, the layup is bonded to the canopy and steel (not aluminum) canopy frame with Sikaflex, and riveted to the canopy frame only, with pulled rivets as called out in the plans. So the joint between the fairing and the canopy is somewhat elastic. The published elongation at failure for Sikaflex 295UV is >300%, so there is some give available. The aluminum stiffener with the large holes (C791?) is riveted between both the steel frame and the skirt, but it's pretty flexible.

We shall see if I made the right decision. I wouldn't necessarily recommend that others run out and lay up a glass (or carbon) canopy skirt. I did it because it was mentioned in the plans and it sounded like an interesting project. I learned a LOT.

Oh yeah; having been around a lot of carbon fiber bicycle frames over the years, I've had many opportunities to see the corrosion that happens to metal parts when they aren't isolated from direct contact with the carbon. When carbon was first becoming popular, one bike manufacturer built frames using round carbon/epoxy tubes bonded into steel lugs. The lugs corroded and the tubes pulled out. Those were bikes targeted at the high end of the market, for racers and hard core athletes that pushed the bikes; not fun to have your bike self-disassemble when at speed. Needless to say those frames weren't on the market very long.
 
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Hey William,
Yes, I molded right on top of the aluminum kit parts. I haven't had any issues caused by expansion. I also have half as many screws mounting the plexi to the frame and skirts. We shall see.
 
A variation of the theme

http://i456.photobucket.com/albums/qq282/whittfic/DSC02283a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02265a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02772a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02773a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02774a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02777a.jpg
http://i456.photobucket.com/albums/qq282/whittfic/DSC02778a.jpg

Photos above show how I made my rear canopy skirt.

A foam/fibreglass compsite was layed up over aluminium tape that was applied to temporarily fill the gap between the fuselage and canopy. Once this was cured more glass layed up on the inside up to and slightly overlapping the rear canopy frame tube. The raw skirt was then removed and cleaned up, trimmed to final shape and glued back in position on the frame using Sikaflex.

When glueing, I left the canopy very slightly open and postioned the rear skirt so that it would be a nice firm fit when fully closed.

I also riveted brackets inside the rear lower frame, sandwiching the fibreglass to the outer side fairing.

Not flying yet but feels very firm.

Clive Whittfield
Auckland
New Zealand
 
Hi Rick how are your fiberglass rear skirts holding up around the rivet heads? Did you countersink the fiberglass?

No problems after 3+ years of flying (about 350 hours). The rivets remain completely hidden with no signs of cracks.
 
looks great

Chris, I read this thread all the way through and since I am not that far along, most of it doesn't make much sense yet. Ond thing that does is how nice your canopy frame - plane transition is. WOW. Nice job.
 
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