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Old Sep 16, 2012, 02:18 AM
I hate propellors
emufingers's Avatar
Australia, SA, Normanville
Joined May 2009
383 Posts
PTX, nice idea, there is stuff called rocket release that releases PU from silicon moulds and should work if melamine finished MDF is used. I was thinking one piece of mdf with 10mm holes drilled in several places might make handling easier. The PU releases tend to use an oil base so may be MDF soaked in Canola oil would release too. I have also found that foam releases from food grade polyethylene
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Old Sep 16, 2012, 06:44 AM
Needs brain lubrication
biber's Avatar
Aachen, very western Germany
Joined Dec 2004
1,391 Posts
I've been pondering the Drela way of building very light Apogee wings using XPS foam cores in negative molds.
Problem was, that Drelas method involves heating the molds and I don't have heat resistant molds.

Now, this stuff might eliminates the heating problem.
That's sort of cool.

biber
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Old Sep 16, 2012, 11:20 AM
Caution:Makes sharp left turns
Troy's Avatar
United States, CA, Lake Forest
Joined Feb 1999
6,015 Posts
Quote:
Originally Posted by ptxman View Post
What about this concept Troy: since you have a mold flange, clamp down a series of surfaced MDF planks just after the wet foam is applied. They are positioned with a small, consistent gap between their edges, acting kind of like vent holes. When foam is cured, pop off the boards & all you have to sand is a thin section that oozed in through the gap. Not sure what releases expanding foam though...always seems to stick to everything. Release treated mylar 3M'd to the MDF maybe?
Hey Peter, I have considered that to build better cell consistency and not have to sand the foam. I did it this way because it was quick and it was worse case scenario for the process. Now that my wing is out, I can look at making some lids with proper vents.

With regards to release, I typically wax a rigid surface like shelving board (melamine) and then spray a light coat of Rocket Release.
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Old Sep 17, 2012, 12:41 AM
BVM Viper Fever
pdawg's Avatar
United States, OH, Dayton
Joined Apr 2004
5,552 Posts
Sweet wing Troy! looks amazing! Would you use the wild control setup in the sloper model too?
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Old Sep 17, 2012, 01:18 AM
Composites guy
North OC, Ca.
Joined Jun 2005
1,187 Posts
Hey troy-
if it doesn't come out okay, use it for a boomerang!

Nice wing. How would you put a solid leading edge in this design( think 1/2" basswood with an upper and lower half.

Yes, we land in a the rock garden.
Scott
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Old Sep 24, 2012, 04:06 PM
He who dares ... repairs!
Hobster's Avatar
Joined Jun 2005
682 Posts
Perhaps not the correct thread, but I am interested in views on whether using expanding epoxy or PU to fill a D-box on a heavy carbon 2-pc wing is too risky (of distorting the profile). Being 2-pc, one end will be open (having dremelled out the root first)

But will foaming epoxy pour down a 1m long D-box or is it too thick? Guess I could coat a balsa stick with the epoxy (or PU) and push that in the D-box?
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Old Sep 24, 2012, 07:20 PM
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Australia, QLD, Woody Point
Joined Nov 2006
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It's not an easy answer Hobster. Not sure if it's been tried enough to give a definite answer. I'd be worried about using PU to fill the D-box. It would be OK if you only put enough in to partly fill the cavity. But if it fills the cavity and keeps expanding it can put a lot of pressure on the skin. I'd recommend putting a lesser amount in and let it run back and forth with the wing standing with LE down. The light PU isn't going to add a lot of strength in a small wedge however - you'd need to use a higher density foam.

I really like the idea of filling behind the LE with foaming epoxy but although I keep talking about it I've not yet done it. I have used it for repairs, where I've filled a part of the wing either side of the repair and it is great. I'd like to put enough in to fill several cm depth behind the LE. I'd like to get a hollow wing and drill holes every 8cm or so, and inject perhaps 10ml of Ampreg F230 or Sicomin PB 170 or PB 250 into each hole. However I'd be worried about filling the whole cavity as there's a chance the epoxy might shrink back a bit and distort the profile. Probably unlikely in a very thick carbon wing though. Someone needs to have a go and report the results. It's going to greatly increase the survival rate of DS wings.
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Old Sep 24, 2012, 10:08 PM
Caution:Makes sharp left turns
Troy's Avatar
United States, CA, Lake Forest
Joined Feb 1999
6,015 Posts
I wouldn't recommend doing something like that unless it was contained in a mold. Not only do you have the pressure from expansion, you have exotherm that can soften epoxy if it wasn't post cured to a decent temperature.

BTW, I've been working on my wing getting the control surfaces cut out. I should get some more done as the week progresses.
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Old Sep 25, 2012, 04:50 AM
R.I.P
josh18's Avatar
Australia, QLD, Toowoomba
Joined Jan 2010
3,506 Posts
Nice Troy! Are you using yorque rods for your flaps?
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Old Sep 25, 2012, 10:49 AM
Caution:Makes sharp left turns
Troy's Avatar
United States, CA, Lake Forest
Joined Feb 1999
6,015 Posts
Yes, the inner flaps will run from one servo and two sets of toque rods. For a full-house race plane I would go with 2 separate servos in the wings to save space in the fuse-pod.
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Old Sep 25, 2012, 02:51 PM
He who dares ... repairs!
Hobster's Avatar
Joined Jun 2005
682 Posts
Thanks AvB and Troy. I'll pass on the PU approach for LE fill then. May try the expanding epoxy using small quantity and try and get it back in the mould quick style. That's if I can manage to get some expanding epoxy, not found any one in the UK selling small quantities yet. I'll report back if I manage to source some.
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Old Sep 25, 2012, 03:03 PM
He who dares ... repairs!
Hobster's Avatar
Joined Jun 2005
682 Posts
Probably a waste of effort but wonder if back filling D-boxes with polystyrene balls mixed into epoxy and micro-balloon splooge would have any noticeable effect on strength. Wouldn't need to worry about expansion. Only one way to find out I guess.

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Old Sep 25, 2012, 05:52 PM
R.I.P
josh18's Avatar
Australia, QLD, Toowoomba
Joined Jan 2010
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Thanks Troy, thats a clever way of doing it.
Hobster, I once crushed up some polystyrene foam and mixed it with epoxy to fix a hole in an old foamy. It worked pretty well, better for a mouldy though. I even thought of using poraver/ epoxy mix like in a mould but never tried as its pretty crumbley.
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Old Sep 25, 2012, 06:39 PM
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
Australia, QLD, Woody Point
Joined Nov 2006
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Tony Fu managed to get hold of some Sicomin PB250 in small quantity - maybe ask him.
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Old Sep 25, 2012, 07:43 PM
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Ward Hagaman's Avatar
San Diego
Joined Mar 2003
2,315 Posts
Quote:
Originally Posted by Hobster View Post
Probably a waste of effort but wonder if back filling D-boxes with polystyrene balls mixed into epoxy and micro-balloon splooge would have any noticeable effect on strength. Wouldn't need to worry about expansion. Only one way to find out I guess.

I played around with the tiny beads from a stuffed animal, and I found that I could mix epoxy into a cup of it at a 1:1 ratio by weight, and then use a spatula for spreading it fairly easily. I was hoping that I could somehow pump the stuff, but the best I could get was the spatula method. For a D-box that would work fine!
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