Making a foam cored wing using 2-part rigid polyurethane foam in the mould. - Page 12 - RC Groups
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Oct 31, 2012, 11:03 PM
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Well AvB is looking at DS and Slope flying where crashing is inevitable

Mick
Last edited by AUSELECTRIC; Nov 02, 2012 at 04:20 AM.
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Nov 01, 2012, 03:43 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Agreed Razortoe, those are wise words. But John's point is correct ... my passion is building tough planes. I doubt that anything much I do is going to get "out there" because I'm finding the building process incredibly difficult and I can't see myself keeping it up with the amount of energy I've put in in the last year or 2! But if in the future anybody ever had anything nice to say about my planes, I'd like it to be "man those planes were tough!"

I was just saying to Asto today that designing and building the Scratchos was the thing that took my DS skills up quite a few notches over the last year and a bit ... just being able to put in so many hours flying, crash landing into the lantana etc, with little or no repair work.

Every SCratcho wing made so far is still intact and flying! (except the light PU one). Well, 6 of them are flying and 2 have yet to be flown. Several of them have survived big crashes and got back in the air with very little work. Hard foam cores, fibreglass rod leading edges, Innegra hinges and expanding epoxy foams (in various combinations), and PU foam filled fuselage booms are the way to go!
Nov 01, 2012, 04:43 AM
608 km/h!
josh18's Avatar
Hey Andrew I agree with you too. Even though I dont build full cores like you, all my layups are pretty beefy, and like you all my wings are still intact. Nearly all have been crashed and a couple really bad. A tough plane is worth two I reckon because you can just keep flying them when normal ones would be busted- Along with your wallet!
Nov 08, 2012, 07:22 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
More on the goodness of the expanded-in-mould PU core.

I reported recently that I'd busted the wing on the light PU wing Scratcho, and that the weak link in the construction was that the edges are not locked together. The PU is not a strong bond. This was proven in that crash when the skin really opened up and peeled off like a banana skin from the wingtip.

Anyway … I thought the busted wing was a throwaway, but Rhys looked at it and said “so why don’t you just cut both wingtips shorter ?” So I did, very roughly and quickly, using an old Caracho tip as a template for tapered tips, hacking and gouging and just taping the skins together. The damn thing flew brilliantly – that’s another story … https://www.rcgroups.com/forums/show...09787&page=873

What I wanted to show here is how good the cut off tip is. This piece was just hacked off quickly with multiple slices of a Dremel disc, so there’s black carbon dust in the surface. You can also see in cross section the 2 x 1.3mm thin f/glass kite spars stuck under the skin.

I wish you guys could pick this piece up and feel it, because it is just totally stiff. If that was blue foam, you’d be able to twist it a bit. This piece is amazingly light and stiff. I am really impressed. Remember, the skin is one layer of 120gm carbon and one layer 100gm glass. The skin in the other photo is a piece from the busted side.

I am sure that this method has great potential. Such a fast method, so much stiffness for a light layup and light weight. No need for a spar. But we have to lock the edges together. When I get the time I’m planning to do the following:
Lay up and cure skins. Trim and put mixed PU in both sides (this step needs a few guys on hand to get coverage within 40 seconds or so from mix) then put a waxed mylar splitter plate over one half, put the other half on top, and clamp together. Unclamp in an hour or 2, peel off the mylar, and you'll have 2 flush fitting sides fully solidly pressure-filled with PU foam. Then scrape the foam back a few mm from the edges all around. Dribble a bead of Sicomin 170 around the edges. Join the mould again and I’m sure the final result will be one of the strongest light wings ever made
Nov 08, 2012, 11:41 PM
Not landing late ever again
threcixty's Avatar
Could you mist the skins with epoxy, or something compatable with PU, to make the bond stronger?
Nov 09, 2012, 12:33 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
The PU is adhered to the skins OK. It's the bond between the top and bottom skins, where they are butted up next to each other at the mould join, that needs to be made strong. Normally in a hollow mould method you'd put splooge around the edges and have it hold the 2 halves together, but the pressure of the PU expanding in this method will just push any such goo out of thru the join and into the flange area.
Nov 09, 2012, 08:46 PM
Life begins at transition
I've seen a build where a small strip of depron is used to hold the splooge in place. Maybe it'll act as a plug to stop the PU pushing and splooge out?
Nov 10, 2012, 12:26 AM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Actually that's a good thought. You could use a thin socked foam rod, wet out and place behind the LE.
Nov 10, 2012, 12:42 AM
Life begins at transition
Yup, who am I to argue with Herr Huf?
http://www.su27.de/seite30.htm

He's not pumping it full of foam, but the idea's pretty similar...
Nov 10, 2012, 02:11 AM
Auzzie built planks
timbuck's Avatar
Now that's alot of work.. amazing.
Latest blog entry: More colours
Nov 12, 2012, 10:39 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Well Rob found a great product here recently. Its called Endurathane.

It holds together very well and hasn't got the brittle characteristics of other 2 part PU foams I have seen. It comes out a cross between high density EPS and EPP. But super light.

Oh and nice tight beads. The warmer you cure it, the closer the cell structure

I'm going to use it for my RT42s
Nov 12, 2012, 10:42 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by Odysis
Yup, who am I to argue with Herr Huf?
http://www.su27.de/seite30.htm

He's not pumping it full of foam, but the idea's pretty similar...
What impressive work!
Nov 12, 2012, 10:58 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Alex, checking out the tech pdf sheet, Endurathane looks exactly the same as the Erapol GP330 I used.
Nov 12, 2012, 11:00 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Here are the tech sheets:
Nov 12, 2012, 11:11 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Just put some into my first RT42 fuse, and mixed up another batch, curing at 38 degrees C.

Wondering if there is a magic temp to cure at...


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