wing core foam source?

[bob branch]

Could someone tell me where I can order the 1 pound foam folks are using for wing cores?

Thanks,
bob

[Leester]

Go to the vendors corner The Control Line Guy  Crist Rigotti makes foam wings.

[Bill Little]

Could someone tell me where I can order the 1 pound foam folks are using for wing cores?

Thanks,
bob

Hi Bob,

I don't know a source for the foam, but I believe Crist can tell you where he gets his. (I think the others guys must have thought you wanted wings!  )

[L0U CRANE]

Bob,

If I'm not mistaken, most (much?) of the common, insulation type white styrofoam available from serious lumber yard type sources is 1 lb/cu ft. You can recognize it easily, as it tears out popcorn-like chunks when you try to sand it two ways... From what I've seen, this stuff is available from 3/4" to over 2" thick. ...should serve most purposes...

This stuff has NO inherent strength of itself, but makes a good 'form' for holding surface sheeting to shape and for occasional surface spars and reinforced 'clips' (Bob Hunt's term for "ribs" for such things as wing-mounted landing gear hardwood carriers), center sections and tip attachments.

Cuts nicely with a hot wire, and sands well  with fairly coarse paper - in one direction! - to get the shape. Finer grade paper, down to say 150 grit - in one direction - refines it to be ready for surface sheeting. Vacuum the crumbs out before attaching sheeting, whether with a THIN wipe of slow epoxy, or contact cement, or 2-sided tape, Gorilla, or whatever.

[Bob Hunt]

Hi guys:

I've been cutting "foam" wings commercially since 1969, so I guess I've learned a bit about the stuff. What we are using is generally 3/4 to 1 pound per cubic foot expanded polystyrene. It is not "Styrofoam." That is a brand name of another expanded polystyrene material that is manufactured by the Dow Chemical Corporation. The dialite beads that our foam is made from come for the most part from Europe.

The beads of polystyrene are poured into a stainless steel mold that has a cavity surrounding it. That cavity is called a "jacket." The stainless steel mold has very small holes drilled in it about every 1 inch. The foam I get comes in "billets" that are 35 inches thick by 48 inches wide and 16 feet long. Yes, I wrote 16 feet! If you do the math (and I'm not inclined to...) that adds up to quite a few holes drilled into the mold at 1 inch squares. Anyhoo, the beads are "ionized" before they are poured into the mold so that they will repel each other. Then live steam is injected through the many holes by filling the jacket with said steam. The steam makes the hard little beads of polystyrene expand (hence the name) and while they are "molten" they meld together as they expand. The amount of beads placed in the mold before the expansion process begins determines the density.

If you purchase direct from the blow molder you can ask for custom densities. Of course you have to purchase the entire billet if you go this route. And that's what I have done off and on for many years. Yes, I have a large shed in which I can store my foam... Fortunately, my supplier makes a 1 pound density foam that is actually just a bit under 1 pound. I have found 3/4 pound to be just too light for good cutting properties with a hot wire. Somewhere between 3/4 and 1 pound density foam is "just right" as one of the three bears might say. I also use a bunch of 2 pound density foam for my Lost-Foam Wing Building System sets. Since none of the foam is actually going to be a part of the wing I use the 2 pound here because it holds up much better and lets me make several wings from one LF set (I've built as many as 15 wings off one set and am still counting...).

One thing is very important here: USE ONLY VIRGIN BEAD FOAM! Some blow molders will put a considerable amount of "re-grind" into their foam billets thus cutting their costs. This foam is usually used as insulation in places where the ragged surface cut that results is not a problem. For us re-grind is awful. The lines in the surface of a core cut from re-grind makes them virtually unusable for our purposes. Also the re-grind has lots of hard spots in it that will hang up the wire when cutting, yielding some pretty interesting airfoils. I once got a billet of re-grind after having asked for virgin bead foam and had to explain to the manufacturer whey I couldn't use it. From that point on there was some hesitancy on that manufacturers part to sell me foam. I guess the liability factor came into play... I would suggest not telling any manufacturer you find what you are using the foam for.

I have recently found a great supplier that doesn't ask what I'm doing with the considerable amount of foam that I purchase. Even the name on my check - Robin's View Productions - doesn't seem to make them curious.   

Look in a Thomas Register for foam manufacturers in your area. Again, ask for Virgin Bead 3/4 to 1 pound (stress no more than one pound, but slightly more than 3/4 pound) expanded polystyrene foam.

The foam you get at Lowe's and Home Depot is actually Dow Styrofoam. It is not produced in the blow molding technique described above. This blue or pink colored foam is extruded in a chemical process that fills a cavity. This foam is what is called "Closed Cell" foam and it is extremely easy to cut and carve (making it ideal for producing mold bucks for molded fuselage shells). It is not available in less than 2-pound density (At least not any that I've ever seen...) and it is more costly to produce than the open cell foam that we use for foam core wings.

One more very important thing: Some colored extruded type foams are not polystyrene based. Some are polyurethane and when hot wire cut I'm told they give off a cyanide gas. Not good... I understand that when hot wire cut the polystyrene foam (our type) gives off a formaldehyde gas (Not too harmful I understand, although those who know me will say it's had an effect...).

Hopefully the above information is helpful. If there is enough of a call for it, I will consider shipping pieces of expanded polystyrene foam to modelers who wish to try cutting their own wings. The cost of shipping may be a factor as the blocks will be light but large.

Here's a teaser: I use a piece of 6-inch thick 2-pound foam as an alignment table for my models. I have developed a method of cutting extremely accurate pieces of foam from the large billets I purchase and the foam is inert. It will not be affected by weather changes as a wooden bench might and often is. I am guaranteed a perfectly flat surface on which to assemble my airframes. Since I've been doing this I have had no incidence problems with my models. Again, to ship blocks this large might be a logistical and financial problem, but I would be willing to try.

Attached (hopefully) are a couple of photos of my Classic Stunt design Caprice being assembled on the 6-inch thick foam alignment table.

Later - Bob Hunt

[Dwayne]

This is why I love this forum 
Thanks Bob
Dwayne
 
    

[Keith Spriggs]

Hi guys:

 If you do the math (and I'm not inclined to...) that adds up to quite a few holes drilled into the mold at 1 inch squares. Later - Bob Hunt

If they are 1/2 inch from the ends I get 35,232 holes.  Very interesting information. Thanks for passing it on.

[phil c]

Just an addendum to Bob's thorough disscussion of foam.
Almost all of the foam we use(1 lb. bead board) is produced for building EIFS(External Insulation Foam System) siding on high end houses.  All the fancy stucco effects you see are done this way.  The official spec is very stringent as to solid bonding of the beads to each other , the density, the aging, and the cutting of sheets.  It also allows a range of .9-1.0 on the density, so naturally almost all the foam comes at .9-.91 to save the foam producer 10% on materials costs.  The age of the foam is very important.  It takes 6-8 weeks to stabilize after molding.  If you try and cut a wing from really fresh material, which they aren't supposed to sell as EIFS, it will bend, warp, melt funny, and cause all sorts of problems.

[Ron Merrill]

WOW, would you look at Bob's shop, you can eat off the building surfaces. I have to wear a dust mask to go into mine. Thanks for the info. Ron 

[Paul Smith]

Back when I was in Wichita, there was a local "foam farm" where they grew 8-foot cubes of generic white foam.   They have a 10-foot square cast iron cutter frame with holes on 1" increments.

For a modest fee, they would slice & dice a cube any way you want it.

I expect you should be able to find similar ops in most major cities.

[L0U CRANE]

Thanks, Bob!

Almost more than we really wanted to know, but it turns out we want and need it...

Merry Christmas and Happy New Year!