jhitesma's Danaus style thing?

[LitterBug]

However he's really unimpressed with DTFB and is disgusted that I'm "wasting my talents" with FG on such a crummy core material. I'm not as worried...at least not for this particular application. Yeah, it's not going to compare to higher quality stiffer foam - but for a low cost alternative to sheets of G10 or CF for this frame I still think it has potential.

My pilot buddy thought the same thing about DTFB till he saw how well they actually fly. Especially after we went to some of the local shred fest indoor flys. It's really silly to take anything of any value to those crash fests. He really liked the craziness of the flying battles at FFE last year too.

Cheers!
LitterBug

 

[jhitesma]

My pilot buddy thought the same thing about DTFB till he saw how well they actually fly. Especially after we went to some of the local shred fest indoor flys. It's really silly to take anything of any value to those crash fests. He really liked the craziness of the flying battles at FFE last year too.

When I handed him the long-EZ I tossed together Friday night he was convinced it was a different foam

He couldn't believe how stiff the wings were compared to the piece of foam with the paper removed I showed him. He was mostly just surprised that despite my FG work looking better than his (in his opinion - I'm still not very happy with my own work and his didn't look that bad when I saw it) the panels were still as squishy as they are.

I was looking at DragonPlate's table of composite CF panel options though: http://www.dragonplate.com/ecart/categories.asp?cID=262

And noted that depron (the closest option to DTFB) was similar to the two foams he likes (last-a-foam and divinycell) for stiffness to weight. But it's the crushability (I prefer the term squishability) that had him host concerned...and those two are both better for that.

Except...I looked up pricing on them. And while DTFB runs about $0.25 per sq.ft both of those foams are $2.50-$3 per sq.ft without shipping - and shipping pretty much doubles them because of the size (they come in 4' lengths.) Which is still cheaper than even G10 sheets of a similar thickness and would probably still be lighter...but...I think the DTFB has a chance of being usable.

The birch core from dragon is rated best for crushability and toughness - but I've tried quad arms out of it before and was not impressed with their durability. UFOdziner is using some kind of foam/CF composite arms right now though and really happy with them...I'm not sure what kind of foam is in his though or where he's getting the source material.

I'm still thinking my DTFB with FG plates are going to be better than plywood or lexan or the PVC sheets I've tried on this design. Will they be as good as CF or G10 or something with a higher quality foam? Nah. But I'm not looking for best. I'm looking for something affordable I can actually get in big enough pieces to make this frame somewhat viable.

 

[jhitesma]

Oh yeah...also...those more expensive foams? They're heavier. If I did the math right then DTFB without the paper is ~2lb/cu.ft. (I weighed a 14"x14" piece with no paper at 21g and then calculated the rest from there - would love to have someone do the calcs themselves and confirm I didn't mess it up.)

The divinycell is 3lb/cu.ft and the last-a-foam is 4.5lb/cu.ft.

But the last-a-foam that dragonplate uses is even heavier at 6lb/cu.ft.

Also those foams are only available in 1/4" thick sheets (well, the last-a-foam also comes in 1/8" but that's too thin) so they're a bit thicker than the DTFB. Which does mean a bit more strength in the final composite...but also means I'd need longer screws adding more weight....

I'm really curious to see how my homemade composite weighs in compared to the ply and pvc and lexan once it's cut....

 

[jhitesma]

And looks like I'll be trying the expensive foam core options. My friend called last night saying he was placing and order at Aircraft Spruce for some stuff he needs for his Velocity and he was going to get a sheet of divinycell and last-a-foam for me to try. Only catch is he wants to be here when I do some destructive testing of the resulting panels

 

[jhitesma]

Starting to think I should split these composites experiments off to a new thread in the Workshop section or something...they're kind of growing beyond this project...(which is funny because this thread started as one I asked Balu to split off of a prior discussion itself...this Danus thing is just great at taking discussions off course apparently!)

Anyway - Last night my friend stopped by with some aerospace quality foam! I didn't have a chance to get any photos yet but there are currently one sheet each of 1/4" thick last-a-foam and divinycell foam. I thought I had shared the gory details of these materials already in this thread...but looks like I forgot to so:

LAST-A-FOAM: "Rigid, Polyether Polyurethane foam with fine closed-cell structure, light cream-yellow color." They have 1/4" thick sheets available in 24"x48" size...it's 4.5Lb/Cu.Ft. and $20 a sheet. At 24"x48" 1152 sq inches or 8 sqft and costing $20 that makes it $2.50 per sqft for 1/4" thick 4.5lb/cu.ft. foam.

DIVINYCELL FOAM PVC: "A closed cell medium to high density foam which has high compression strength, durability, and excellent fire resistance". This is also available in 1/4" thick (as well as 1/8" but that's probably too thin.) this comes in 32"x48" sheets...it's 3 Lb/Cu. Ft. and is $28.90 per sheet.
At 32"x48" 1536sq inches or about 10 sqft. and costing $29 it comes out as $2.90 per sqft for 1/4" thick 3lb/cu.ft. foam.

DTFB foam by comparision comes in 20"x30" sheets...so 600sq inches or about 4 sqft. It costs $1 so that's about $0.25 per sqft for 5mm thick 2.12 lb/cu.ft foam.

So DTFB is by far the cheapest and easiest to find as well as the lightest.


My initial impressions of the Last-A-Foam and Divinycell are that they're both very similar. The Last-A-Foam seems to be "dustier" as it leaves crumbs on my fingers while the Divinycell doesn't. But they both have similar textures - kind of like a stiffer version of styrofoam (the open cell stuff like you see in craft stores for flower arrangements and making wreaths and such.)

They're also very different than the DTFB foam. They're an open cell foam so the surface is much rougher. It's suggested to give them a sealer coat (usually epoxy and microbeads) to give the cloth and resin something better to stick to. They're also much less squishable. You can squish them...but it takes a LOT more effort.

They're also much tougher. Which I'm not sure if it's going to be a good thing or not. I haven't done any rigorous testing yet - just cut off a few small pieces and broke them in various ways to get a rough feel for the materials. My gut is saying that their overall yield strength isn't that much different than DTFB. But because they're stiffer they don't bend and flex like DTFB foam does. Instead they just suddenly snap. If DTFB was mild steel these would be hardened steel.

It will be interesting to see how they compare. My plan is to make some 14" x 2" test pieces out of the DTFB and both of these aerospace foams. I'll do one piece "bare", one with 2 layers of 6oz cloth, and one with 2 layers of 1.43oz cloth. Then we'll do some tests on them. Based on that I'll decide what I want to do for some full 14" panels to finally cut the frame for this thing out of

Oh - also yesterday I picked up a roll of red rosin paper to play with based on Hillaflyers experiments with DTFB. I laminated it onto some bare DTFB foam but apparently didn't use enough resin because it didn't fully soak into the paper. It did stiffen up the DTFB but I found it trickier to work with than cloth. I'm also not sure just what happened for weight. The rosin paper was 20g per piece. My foam is 21g. And I mixed up 22g of resin for each 20g sheet of foam. So that should be 40g of resin + 40g of paper + 20g of foam = 100g final piece. Except when I weighed the final piece it came in at 86g?!? Really not sure how that was even possible. I did use peel ply again but since the resin didn't fully saturate the paper the peel ply didn't really absorb any resin. And I didn't use 100% of the resin but there wasn't much (maybe 1/8") left in the mixing cups.

Oh wait...one thing I just realized....I did trim off the excess paper before weighing. Doh. That probably explains it....