Foam wings vs. balsa built - weight

[Barry McGrady]

As a general rule, which is heavier... a solid foam wing, or a built up
balsa wing (ribs, leading and trailing edges sheeted). I know that's a
loaded question, based on how much sheeting, which density and size balsa,
etc.... all I'm looking for is the general rule of thumb.

tia
-Barry

[Dr1Driver]

>As a general rule, which is heavier... a solid foam wing, or a built up
>balsa wing

In general, a fully sheeted solid foam wing is slightly heavier than built up
balsa. Of course, this depends, as you say, on the type of balsa, method of
contsruction, etc. However, a fully sheeted foam wing is TREMENDOUSLY strong,
much more so than a balsa built up.
Dr.1 Driver
"There's a Hun in the sun!"

[Mike Wizynajtys]

Yep, it's a loaded question all right.

If the wing has a thick airfoil then usually the built-up version is
lighter. If the airfoil is average to thin then it's a toss up. Nice light
wood, good quality white polystyrene and a light hand on the glue are key
elements to achieving a light weight solid foam wing.

Wiz

Barry McGrady wrote in message <7cc6o6$r3c$1...@paxfeed.eni.net>...

>As a general rule, which is heavier... a solid foam wing, or a built up

[bmwebb]

OK, you want a light foam wing? Glass it and vacuum bag. After that, stand it
on end, heat a rod, push it though at the l/e and middle. Cut templates, feed
wire thru the holes, and core the wing. Leave a spar at the thickest point,
about 1/2 inch wide. Removes alot of weight, retains the strength.

Bradley

[Slopemeno]

The lightest plane Ive ever handled was a Maple Leaf handlaunch (the flatwing
thermal duration one) at 10 oz all up Its like holding nothing in your hand.
Its contruction is blue foam 'glassed with light kevlar with the weave on a
bias (bias ply?) . You dont see many competitive builtup handlaunches
anymore,though the mini bird of time still hangs on.

[Ib Therkelsen]

Barry McGrady wrote:
>
> As a general rule, which is heavier... a solid foam wing, or a built up
> balsa wing (ribs, leading and trailing edges sheeted). I know that's a
> loaded question, based on how much sheeting, which density and size balsa,
> etc.... all I'm looking for is the general rule of thumb.
>

No general rule, so sorry. All depends on the actual design and the
final strength you want. But let me give you a hint: White foam, the
variety used universally for emballage boxes, may be sliced up. A 5 mm
thick slice of this material will, area to area, have the same weight as
1 mm balsa sheet.

Regards
Ib Therkelsen

[Ocram]

OK, right, but it only got the strength when bonding that same sheet of
balsa to it !!, so why not leaving the foam ?!.

That is what you basically do when building a convential balsa wing.

However a balsa sheeted foam core is most of the time just a little heavier,
it also is much stronger and stiffer, simply because the stresses are spread
over the complete surface of the wing.

So when building a high performance aerobatic plane like a 30% Extra300
likely to face verrrry high stresses, it is better to go just a bit heavier
and make a foam core wing. But when building a gentle, low and slow flyer,
like a piper cub, it is better to save some weight and make a convential
build-up rib/spar wing.

Marco

[Ib Therkelsen]

Ocram wrote:
>
> OK, right, but it only got the strength when bonding that same sheet of
> balsa to it !!, so why not leaving the foam ?!.

There are a few good reasons for that.

Foam is not necessarily much weaker than balsa, if you have a good
construction technique. The fact that foam is about 5 times lighter than
balsa, volume to volume, means that you can build quite compact
structures without getting near any weight penalty. Critical areas may
be strengthened with balsa spars or balsa sheeting, quite right, but on
the other hand, a lighter plane is less damaged in the event of a crash
(and not likely to kill anyone).
Foam is easier (and faster) to shape (strongly curved fuselages, etc).
Foam can often be found for free around garbage containers.

This being said, I must admit that personlly I prefer the looks (and the
smell) of a balsa plane :-)

Best regards
Ib Therkelsen

[Dan D]

Ocram wrote in message <7cmqq9$p2t$1...@news.worldonline.nl>...
:Bare foam is not suitable for wings, A foam wing ALWAYS should have somthing
:added to make it a sound construction, that means sheeting (balsa or
:glass/epoxy sheeting) or strong spars, or a combination of those two. I have
:seen bare foam fuses, but that were very stubby, thick things (ME163). I
:Know only one bare foam wing: the foam delta (slope glider), but that is
:also a very stubby construction, not very aerodynamic.
:
:

The Byrons 1/4 scale Pitts had a foam fuselage...

Dan

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[Jerry Brian]

Usually solid foam is heavyer than built up. I did long ago have an ugly
stick .40 size with a foam wing. It had square pockets molded in top and
bottom, making it a non solid, semi boxed construction. Add fiber
filament tape or spars or whatever, and you have a good wing.

Also seen where you take a foam wing and cut open bays only behind the
main spar all capped and lined with balsa.

Jerry