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  #21  
Old 01-22-2016, 12:29 PM
BonitaRV8 BonitaRV8 is offline
 
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Yes, CTE = Coefficient of Thermal Expansion. Might want to think about a couple of chicken fasteners at the root and tip to prevent peel, once it starts it unzips real quick.
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  #22  
Old 01-23-2016, 05:32 PM
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rvmills rvmills is offline
 
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Well as the fabrication apprentice and future test meat servo, I'll just say what a privilege it is to be in this project with Steve and Bob. The education and experience has been extraordinary! High-end scratch building (I reckon this is what you might call this) is gratifying work, and we're having fun too! Definitely stretching my knowledge and skills! Here are a few pics of some of the early stages:

CNC-cut foam mold assembly in the Bay Area


Bagging the mold to the working table


First mold out of the bag. Aluminum and mylar substrate was epoxied to the foam when bagged


Molds moved up to Bob's HP-24 shop in Arnold. One mold is bonded to each side of the metal table, and can be flipped on the wood table


Our rack of materials


Bob applying gelcoat, pre-layup


Foam core prep, edges beveled on a table sander


First carbon layup


Foam core layup


First skin bagged


More pics in next post...
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RV-6 "Rocket Six" N49VM
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President/Sport 47/49, Sport Class Air Racing
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  #23  
Old 01-23-2016, 05:32 PM
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rvmills rvmills is offline
 
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...continuing...

As skins come out of the mold, we had to start making cradles to store them, as the spar and rib work takes place. We used the mold plugs to layup some glass cradles...and got the kids involved in this part


Trimming raw edges from the skin as it came out of the mold. Final cuts well down the road


Steve inspecting the first of 8 skins




Meanwhile, back at the home drome, spar parts box ready to unpack


Unpacked and ready to prep, measure, mark, drill, debur and assemble, then rivet...piece o cake, right?! Good look at the sheer web and sheer doubler on the right, and the spar cap parts on the left


The hole layout and drilling schedule for spar assembly


I'm on layout and marking, but on hold as we reconsider a design alternative. Looking at pros and cons of moving to Bob K's concept of Al spar stubs that insert into my fuselage, and mate to carbon spars outside the fuselage. One thing I've been really pleased with is the collaborative effort and "best solution" approach. Steve's design foundation has been strength and safety...as well as performance!

As a teaser, here is the original drawing that Steve made when we began discussions on the project...


Cheers,
Bob
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Bob Mills
RV-6 "Rocket Six" N49VM
Reno-Stead, NV (KRTS)
President/Sport 47/49, Sport Class Air Racing
President, Formation Flying Inc (FFI)
Flight Lead, Lightning Formation Airshows

Last edited by rvmills : 01-23-2016 at 05:42 PM.
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  #24  
Old 01-23-2016, 08:13 PM
BillL BillL is offline
 
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Nice work there Bob. I was imagining a slick wing like the 787 - - just like your picture!

Hey, all is pretty much hand made, but that CNC foam mold core looked special!

Do ya'll do that "in house" or get it outsourced?

Keep the progress reports coming, it is great to see something besides the same standard rivets all the time.
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  #25  
Old 01-24-2016, 06:33 AM
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DanH DanH is offline
 
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You guys form a dream team, for sure. This is one of those rare times when I really wish I lived on the West Coast. I would cheerfully become your slave

Could you expand a bit on the mold-making process? Looks like you started by bonding an aluminum skin to both sides of a 2" pink foam board, which probably yields a very stiff panel?

Then you bonded a CNC'ed foam mold to that sandwich panel, upper skin mold on one side and lower skin mold on the other?

During that same session, you bonded an aluminum and mylar finished mold surface to the foam mold? Aluminum thickness? What sort of mylar? You can bond mylar?

What is the purpose of the aluminum edge rails?

Then you repeated the process to build molds for the other wing?

Details, please?
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  #26  
Old 01-24-2016, 07:50 AM
aerhed aerhed is offline
 
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Fascinating captain. A world and a half away from the wooden makeover I'm doing now. Do I dare ask what your cost estimates are (not counting infinite labor)?
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  #27  
Old 01-24-2016, 08:48 AM
David Paule David Paule is offline
 
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Dan, I've got some left-over Mylar drafting film that has a drawing surface on once side and is plain on the other. I've bonded the drawing surface to aluminum successfully with Pliobond. They've lasted more than 20 years on my Cessna, for about a dozen minor gap covers.

Probably not what you're hoping to learn, though.

This project is very interesting. I prefer working with composites to aluminum and chose an RV-3B project (wings nearly ready for close-out) with the idea that I might, at some point after the plane was done, build longer tapered composite wings. While that was mostly a mental bit of appeasement, I've been fascinated to learn how experts do it - keep this thread current! - and many of the choices you've made are things that I've at least thought about.

Please keep it coming.

Dave
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  #28  
Old 01-25-2016, 08:19 AM
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Av8torTom Av8torTom is offline
 
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Great photos on the mold and the lay-up.

I have a couple of technical questions:

How long do you wait between spraying the gelcoat layer and applying the cloth on top of it?

How much resin gets soaked-up by the foam? Does it get saturated?

Keep the photos coming.

T.
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  #29  
Old 01-25-2016, 10:56 AM
sthopkins sthopkins is offline
 
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I love this thread! I've considered doing a similar conversion for a constant-chord wing airframe (though it is strut-braced). I'm intrigued by the pultruded spars, have to learn more about that.

If you convert to the aluminum stub spars, how would you make the tapered carbon spars? Any thoughts on CNC-cut plate for the web and bonded caps? Finding the lengths required would be challenging.

Dan covered my questions about the mold. When I've done similar work I had access to more $$$ and more infrastructure, so it is good to see some practical DIY techniques.

How do you plan to control bond gap? And why is the core windowed?

For the curious, there's a recent 2-part Kitplanes article that has some good information on similar work.

Last edited by sthopkins : 01-25-2016 at 11:00 AM.
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  #30  
Old 01-25-2016, 11:28 AM
Autoreply Autoreply is offline
 
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Good to see those wings out in public. Great work guys!

Quote:
Originally Posted by Av8torTom View Post
How much resin gets soaked-up by the foam? Does it get saturated?
Most foams are closed-cell, since you wouldn't want them to soak tell they're saturated.

For the finer high-grade foams (Rohacell IG-F, Divinycell H/fine), typical resin intake is on the order of 200-280 gram/m2 per side. So say roughly a pound per square yard per sandwich panel on top of what the normal laminate would take in. Numbers are assuming double-sided vacuum-bagging, or at least good ventilation of the mold surface (holes in the foam core).

That's why for smaller skins other, saturating cores makes sense. I've posted a comparison of various options here:
http://www.homebuiltairplanes.com/fo...andwiches.html

(I don't have any commercial stakes in either of the mentioned products, but am a satisfied customer of all mentioned products)
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