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Jan 04, 2013, 03:16 PM
Registered User

Balsa or Foam?

A few years ago white foam was the hot ticket items for larger wings like 48" WS +. I got caught up in the surge and made a complex, swing arm, wing cutter from scratch . I covered with balsa sheet, obeichi , fiber glass etc. I even made one wing covered with foam and balsa and routed out spaces between the ribs . Ribs were about 3/8" wide and covered with balsa strips running length wise from the D tube. A lot of work but it was a very good wing.

So I started on a new design to day with a foam wing again. But I said to myself why not use balsa instead ? All my ARFs are balsa and well made, lighter and just as durable. Time to build with balsa is a lot faster and cheaper also. The swing arm cuter has a big foot print of about 30" by 60" built on a table. I can use the space in my shop for something else. I'm also thinking I could use it to make D tubes for molding wet balsa to match the balsa ribs.

Any reason why I just should forget foam? I know the small flyers use it but that's using flat sheets of Depron and is a whole different deal.
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Jan 04, 2013, 03:39 PM
Registered User
rcav8r2's Avatar
I think this is a personal decision. I've heard the pros/cons of each; and each make valid points to some extent. I've done each, and for most designs I prefer a good old balsa built up wing.
Jan 04, 2013, 04:27 PM
Registered User
I like balsa and scale models.However there are some subjects with higly tapered wigns (like Curtiss P-6E, etc), even some constant chord wings (RYAN NYP) that have very close rib spacing. In normal sheet balsa ribs that could be a ton of work and expense, especially in larger scales. I'm thinking about trying those types of subject with a foam wing . Balsa wrapped LE and strip balsa ribs in scale position glued directly to foam. This would keep the covering material and finish, away from the foam.
Jan 04, 2013, 04:54 PM
Bellanca Kruesair
epoxyearl's Avatar
I am a 'dyed in the wool,by gosh balsa and spruce builder',but there is a place for other materials too.
In a recent Estate closure,I happened upon a 1/4 scale Cessna 172 model.
It has a fiberglass fuselage,and is a well built very scale airplane.But there are no wings.
I've made a/c plywood patterns that I'll send to the AMA to use to cut some foam cores.....I can build the foam wings much faster than designing the wood ones,and the finished weight is close enough.
Foam cores don't weigh a lot more than air,and they're certainly more supportive !
Latest blog entry: I'm a 'whiner'
Jan 04, 2013, 10:03 PM
Build something.
Nodd's Avatar
Funny but I'm in the exact opposite situation. I've been building built-up balsa wings & to tell you the truth I'm wondering if switching to foam might be something to look into instead. Either technique can produce a good wing so as stated above, I think its a matter of preference.

By asking this question I think you've already answered it for your self. Try something different, why not?
Jan 04, 2013, 10:21 PM
Hope to get out of life alive
kenh3497's Avatar
When I crashed the CAP in my avatar I decided it needed a new wing. It WAS a H9 ARF. I built a new wing using foam and fully sheeted with balsa. The new foam wing came out 32 grams lighter than the original wood wing. I wound up scratching a new fuse for the plane as the old one was to far gone to salvage. The plane was glass and epoxy and painted. RTF weight is 7 1/2 pounds.

I did break the wing in flight though late this fall It broke at a high stress point. A new wing will have a light ply spar to shore up this high stress area.

The rebuild thread here and photos of the broken wing.

I guess what I'm saying, I have no preference to wood or foam. Both have there place, strengths and weaknesses. Both can build fast or slow depending on the complexity of the wing. Properly done both are plenty strong and weight IMO is a tossup.

Jan 05, 2013, 12:04 AM
Registered User
ForeverFlying's Avatar
Interesting thread! I am in the reverse mode also. I am just now learning how to cut foam cores using a single point attachment, one template, tapered core settup. It looks promising, and if successful, will be cheap, easy, and fast!
It might be largely a "the grass is always greener" proposition. Everybody is always looking for something better. That's one of the joys of the hobby, though. Always something new to try!
Jan 05, 2013, 06:01 AM
Bellanca Kruesair
epoxyearl's Avatar

Re: post #7

Exactly-we are always challenging ourselves in modelling.
The first cowl I built was for a 1/3 scale Piper Tripacer. We used white foam from floating docks, at a Marina where I worked. We carved it and sanded it to shape,then covered it with fiberglass.
After hogging out the foam form,an acetone soaked rag removed what was left.

I have trouble accepting foam as a true building material, but, there you are.

I sent patterns to AMA this morning, for the Cessna wings.
I have a router bit for the Dremel tool. I fasten a couple of straight edges to the cores, to fit spars and control runs. Use a vacuum while you're cutting,and plenty of epoxy, when you're gluing.

Good luck...
Latest blog entry: I'm a 'whiner'
Jan 05, 2013, 07:08 AM
Registered User
Originally Posted by epoxyearl
I have trouble accepting foam as a true building material, but, there you are.
And yet the vast majority of models available today are made of foam....often with no wood involved anywhere. I like foam and use it extensively even on my "balsa" models. E.g. I've pretty much given up the complexities of planking in favour of carved foam for turtle decks etc.

But for some reason I still prefer built-up wings. In some cases that's the models we build....many of mine are sort-of-scale and the original would have had the ribs showing so a wood sheeted foam wing just looks wrong. Still, there's room for all of us in this grand old hobby .

Jan 05, 2013, 09:20 AM
Registered User
LesUyeda's Avatar
Foam does have its place; and that is in flotation chambers of boats:-)))))))))))))

Jan 06, 2013, 08:45 AM
An itch?. Scratch build.
eflightray's Avatar
Well there's nothing wrong with trying built up foam wings as well as hot wired cores. You just design them to suit the load, same as any other material.
Jan 06, 2013, 08:49 AM
An itch?. Scratch build.
eflightray's Avatar
Originally Posted by LesUyeda
Foam does have its place; and that is in flotation chambers of boats:-)))))))))))))

You mean you don't use foam in a plane ?

Don't you worry your flying brick-outhouse models will sink if they land in a puddle ?
Jan 08, 2013, 12:49 AM
KE your cub.
Curare's Avatar
I like balsa.

I like foam too.

The overarching thing though is that I like building, but I'm lazy.

These days, I'll use whatever is going to get me what I need with the most minimal amount of effort.

If it's a constant chord wing, I cant be bothered setting up the rig to cut a constant chord wing, and with a set of templates I can knock out a pile of ribs in an hour or so. After that it's a cakewalk, and I get to play with balsa.

If it's a tapered wing, with very specific airfoils, I know that the effor to cut out a pile of perfect ribs is far too much for my liking, but spending some time setting up the foam cutter is less, so I'll knock our some cores. If I'm feeling really saucy or anal about weight, I'll honeycomb the wing.

Either way, the wings are sheeted in balsa as is my want, so that's a non. I hate open bays!
Jan 08, 2013, 02:32 PM
Registered User
I use both, but I do prefer foam for larger models with tapered planforms. I'm in the process of doing a foam-winged model with straight LE and a tapered TE, 1/8" of washout, and a percentage-wise change in airfoil thickness from root to chord. Very easy to do with foam, but with wood I'd have had to do a bunch of calculations, plus figured in different size feet to hold the ribs as the rest was added on.

I cut my cores with a corer I bought in the mid-1980's, then use slow-cure epoxy to sheet the wings with balsa. It does take a while to do the finicky setting up, and I do waste a few cores, but I can produce a finished wing within a few days. That's much faster than I can do with wood, especially since I use aliphatic glues instead of CA.

Bottom line, though, is you use what you like. This is a hobby.

Jan 09, 2013, 05:52 PM
Registered User
Here's foam model I built for a WWII themed museum in 2008 . No balsa but a lot of 3/4 sq pine and 1/8" doorskins. Hanging hardware is pure aircraft grade shackles and spade bolts. Exterior is FG cloth/epoxy over two pound foam. Not designed to fly but could with 65 hp engine (it's not quite the size of a real Mooney Mite) and suitable beefing up.

I liked working with 2lb foam. It would work well for flying models. Has much more strngth and stiffness than the 1lb. In many cases it wouldn't need to be sheeted and when hollowed out and in conjunction with outside surfaces, the hotwire leaves a smooth skin, providing sandwich type construction that is light and stiff. We were kicking around the idea of building a set of wings for a Smith Miniplane project. Very do-able, very quick ,relatively cheap and strong, in lieu of standard Spruce/fabric construction. In the end we should have as I threw more than enough foam away after the Mustang was finished. Can't get any cheaper than free!

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