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Author Topic: Foam wings  (Read 2040 times)

Offline John KruziK

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Foam wings
« on: November 22, 2009, 03:00:12 PM »
Would there be any benfit or detriment from cutting out blocks of foam and balsa from a sheeted foam wing. To more or less look like a conventionaly built up wing. Just a thought.   Thanks John
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Offline Howard Rush

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Re: Foam wings
« Reply #1 on: November 22, 2009, 03:15:33 PM »
Consider the grain in the wood. 
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Offline Balsa Butcher

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Re: Foam wings
« Reply #2 on: November 22, 2009, 04:02:53 PM »
The "Kept Foam" tecnique as popularized by Tom Dixon among others will allow you to replicate the look of a built up wing using a foam core. Foam isn't removed but may be sanded down between the rib bays to compenstate for the sag in the covering material between the ribs. Tom's web site is one place where the technique is explained.  8)
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Offline phil c

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Re: Foam wings
« Reply #3 on: November 22, 2009, 07:02:50 PM »
You can do Tom Dixon's kept foam, use 3/8 in. wide cap strips, and cut the foam out of the bays.  Be sure to leave at least a 1/2 in. thick strip of foam between the cap strips.  Foam isn't quite as stiff as balsa and needs to be proportionately thicker for strength.  I've done it on sport/combat style planes.  Unfortunately, the balsa and glue add almost as much weight as the foam removed.  Does look nice though, since it looks like standard rib construction
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phil Cartier

Offline jfv

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Re: Foam wings
« Reply #4 on: November 22, 2009, 07:40:57 PM »
Works great.  Here's some pics of a wing I did for an RC plane.  Sheeted LE & TE, cap strips, covered with polyspan.
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Jim Vigani

Offline John KruziK

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Re: Foam wings
« Reply #5 on: November 22, 2009, 08:04:23 PM »
what JFV did is what I was thinking about. Is their a spar?  I would like to do this to a sig mustang to lose some weight. Just didn't know if it was a good idea or not. Thanks John
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Offline John KruziK

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Re: Foam wings
« Reply #6 on: November 23, 2009, 05:33:21 PM »
I remember reading an article ,Ithink by Tom Dixon about doing something similar on a Pegasis.
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Offline Alan Buck

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Re: Foam wings
« Reply #7 on: November 24, 2009, 04:24:59 PM »
Tom Dixon  did cut out the bays with a soldering iron at an  angle the melted foam is stronger than cut foam
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ALAN E BUCK

Offline jfv

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Re: Foam wings
« Reply #8 on: November 24, 2009, 05:40:30 PM »
I use spars inset into a groove in the foam.  I sand the groove with a simple tool made up from balsa and 80 grit sand paper.
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Jim Vigani

Offline John KruziK

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Re: Foam wings
« Reply #9 on: November 24, 2009, 06:08:35 PM »
Thanks for all replys. I'm redoing a sig mustang, already built, removing monokote all plastic and suspending bellcrank. Balsa sheeting has delaminated on one wing panel. I figured it would be easier to repair if I cut out bad section and put on cap strips to look like ribs. Then I could remove foam, Tom Dixon style. But I dont know how I would be able to insert a spar. Was there a spar on the Pegasas? Thanks John
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Offline Bob Furr

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Re: Foam wings
« Reply #10 on: November 24, 2009, 07:36:08 PM »
John, just do not remove foam or sheeting forward of the high point of the wing and it should be strong enough without putting a spar in.   If you really must have a spar take the wing out of the fuselage and slot it from tip to tip with a table saw (you will probably need to make a disposeable jig to keep it straight) along the high point of the wing about 1/4" deep.   Glue in a balsa spar of whatever thickness the table saw blade cuts and sand it down to the existing sheeting carefully so you do not gouge the existing sheeting.    (Honestly this is too much work for too little gain)  Do this one side at a time as you will really weaken the wing when you slot it and the spar will be needed to add back strength you lost.   
Heck how about just buying a new foam wing already cored and start from there?   That will save you as much weight and probably be half the work I just suggested... there are some excellent foam wings available commercially or you can cut your own.   For suggestions on cutting your own google up "foam wing cutting" and have fun!
Bob Furr
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Online Brett Buck

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Re: Foam wings
« Reply #11 on: November 26, 2009, 01:33:21 PM »
Quote from: phil c on November 22, 2009, 07:02:50 PM
You can do Tom Dixon's kept foam, use 3/8 in. wide cap strips, and cut the foam out of the bays.  Be sure to leave at least a 1/2 in. thick strip of foam between the cap strips.  Foam isn't quite as stiff as balsa and needs to be proportionately thicker for strength.  I've done it on sport/combat style planes.  Unfortunately, the balsa and glue add almost as much weight as the foam removed.  Does look nice though, since it looks like standard rib construction

   This approach is notorious for the aft part of the wing collapsing. Todd Lee's older silver Mustang/Mustang had this problem as did Ted's "Russian" airplane, and a bunch of others locally. It doesn't make much difference in the performance. Todd and his collapsing airfoil beat me and my not-collapsing airfoil handily, and was very close to winning the entire thing, at the 2000 NATS and qualified easily for the 2001 WC Team.

    Last time this came up, and I told people not to do it that way, I got a nasty-gram from Tom saying that he *does not* recommend cutting out the foam in the bays - which is certainly going to help the "collapsing aft airfoil" problem. It does have a potential problem with the tissue or covering getting stuck to the foam in between the capstrips but I would expect that just being careful would solve that problem.

    I might also note that this is not a new idea. I have an old issue of AAM from maybe about 1972 that shows an advertisement for a Nobler wing built very similarly.

     Brett
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