Originally Posted by Ward Hagaman

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!

Yep I like this idea!

I've put a post somewhere here on my experiments with foam beads, expo y and foaming agent.

It formed a very stable matrix that had similar density to blue foam. I agree it is an unwieldy mix to get into place

Todo..... Find link

Cheers Jeff

Glad you clocked in Jeff.....I still think it is a little brittle. As for filling a wing...put it through a normal silicon gun..no tip..
Maybe not this thread , but I've had some good success with ampreg and glass balloons , saving about 30% weight saving, and it is a stronger matrix because of the high compression modulus of the bubbles. Lighter and stronger

Tim

Originally Posted by jirvin_4505

Yep I like this idea!

...................., expo y and foaming agent.

...........................
Todo..... Find link

Cheers Jeff

I'm interested in the details Jeff. When you find the link post, will you post here?

Thanks,

Jim.

Originally Posted by jirvin_4505

I've put a post somewhere here on my experiments with foam beads, expo y and foaming agent.

Todo..... Find link

Cheers Jeff

Here you go ..... http://www.rcgroups.com/forums/showt...ght=foam+agent

After being inspired by this thread,Troy and Myself decided to do some experimenting of our own using some expanding foam products produced by BJB. We used a small existing wing mold (posted pics a few pages back) for my Electrolyte design. The experiment was very encouraging considering this completely different approach to molded wings. Compared to previous wings bagged with balsa this expanding wing set was lighter, faster, and easier to produce. There are still a few imperfections that need to be resolved but overall its a step in the right direction.

Electrolyte: molded wings using expanded foam part 1 (8 min 1 sec)

Electrolyte: molded wings using expanded foam part 2 (4 min 20 sec)

Electrolyte: molded wings using expanding foam part 3 (3 min 52 sec)

I also made a pilot for my new pylon plane this week using 6lb foam and a silicone mold. I've already between asked to write an article for the process once some folks saw it at the race yesterday.

Really great Troy and Pdawg. Very interesting. I loved the fuse filled with foam in the mould ... my Scratcho mould is made for use with the inflation bladder technique, which works excellently. So it has a hole only at the tail end, and I could therefore use the foam-in-the-mould idea - could be another step on my path of developing very crash resistant DS and slope planes. Definitely worth thinking about for simple versions, but for the full spec'd ones I'd need to route control snakes in there, and ballast tube etc. But I'm sure with some trial and error we'd work it out. I already use the cheap spray can foam to fill booms for durability once they're fitted out.

With the wing, yours is in 2 halves, open at the root, and very small so the free rise plus back pressure is perfect. But my Scratcho is a 64" span, fully closed one piece mould. Going back to my findings at the start of this thread, the technique of rapidly smearing the mixed PU liquid over the full surface area of both mould halves and then closing the mould, worked excellently. I haven't had time to do another one, but the first one was so quick and easy that I'm looking forward to doing the processt again and improving it. The main issue with a wing that size is having a few guys on hand to help cover the areas within the working time. Other than that, it's dead simple. As I reported earlier, in cutting the control surfaces I have not found one bubble and the foam is of amazingly nice consistency. I'm excited about the potential for the technique.

Fyi-
http://www.compositesworld.com/webinars

Stepan.com
pourable foams webinar:

Also:

http://www.stepan.com/Products/Polym...RZ-Series.aspx

Hi Pdawg,
Did u join the top & bottom fiberglass sheet with thickened epoxy or with fiberglass tape before pouring the foam? Or do you let the foam join the two halves together?

Thanks
Dave

Originally Posted by eaticus

Hi Pdawg,
Did u join the top & bottom fiberglass sheet with thickened epoxy or with fiberglass tape before pouring the foam? Or do you let the foam join the two halves together?

Thanks
Dave

Dave,
I tried it both ways but got the best results by laying a bead of thickened epoxy around the perimeter prior to pouring the expanding foam. The epoxy ensured an airtight seal around the perimeter which made the consistency of the expanding foam more reliable. In the non-epoxy perimeter I was suprised to see the ability of the expanding foam to migrate into parting plain fairly easily despite a tight fit...or at least what I thought was a tight fit....

Update: I've got back from my NZ DS Safari and have got back to the PU filled wing. I cut out the 4 servo pockets and am still impressed that I have not found one bubble or void and the foam is completely consistent all through. If I'd been told the core had been hot wire cut from a block, I'd believe it. Picking it up and handling it again I am still so impressed with the stiffness and light weight.

There are some definite differences in handling/ working with this stuff compared to the blue EPS foam. It's easier to cut pockets out of the PU foam than the EPS. But it crumbles when handled. By comparison the EPS is more like cheese - cuts smoothly, has some give, doesn't crumble. I think for long term durability, the EPS is the way to go.

I tried pushing tunnels through the foam with a wire rod, to run the servo wires. I read somewhere that it would be a problem, but it wasn't. It has a different feel, but to me it wasn't much different to doing it with EPS. I did it with ventilation and avoided breathing the fumes which are apparently quite toxic. I did breathe in a bit, but it didn't shleem toowoo eeeeffect meeeeeeee grrr-yiyi-woofwoof at all.

Pulling the wires through most graphically demonstrated the crumbliness of the foam. I took the easy way out and just left the JR plugs on rather than doing the whole soldering thing, so I was pulling the bulky plugs through (minus the outer case of the female plug). It was easier to pull the wires through compared to the blue foam, by far. Instead of being stopped by narrow sections in the tunnel, the plugs just crushed and crumbled the foam as I tugged them through, and piles of foam dust came out with the plugs. I'm not sure whether this crumbliness will have any major impact on the long term durability ... I suspect it will though. The blue foam has a lot more "integrity" and maintains its shape despite handling and impacts.

I hope to have it together and out for some flying soon, which after all is the main aim of all this!

Great report as usual Andrew. Great to read the success!

Oh, the other thing I meant to say is that tightening the wing down onto the fuse has created shallow dimples around the holes. And on the underside, the wing is slightly depressed around the holes too. Yes it's a very light layup skin, but I've made similar ones using the blue foam and never noticed it before. Not a deal breaker ... it wouldn't stop me using the method due to its simplicity and speed, but worth noting.

Was it carbon or glass skinned?

One layer 120gm plain weave carbon with one layer 100gm tight glass on top.