Combining Balsa and Foam for Unique Aircraft Models

[Thomas_Brown]

Hey everyone

I've been toying with a project idea. I thought this would be a great place to share and gather some insights. I'm considering the idea of combining wood and foam to create a one of a kind model aircraft. Has anyone here ever experimented with mixing these materials?

I've always been fond of the nature and ease of shaping foam while balsa wood adds that touch and durability. However I'm uncertain, about the way to strike a balance between these two materials. Would it be better to use wood for the structure and reinforce it with foam or perhaps the other way around?

Any advice or personal experiences would be greatly appreciated. Additionally if anyone has any recommendations, for glue or techniques to bond these materials together please don't hesitate to share!

Thanks!

UPD

By the way, I came across an interesting discussion on this topic here is a link https://www.rcgroups.com/forums/showthread.php?2696719-Foam-vs-Balsa-model.

 

[Hondo76251]

I generally find that I can modify foam models with small amounts of balsa in the right places for the best results. I haven't built as many balsa planes but I don't see that foam would help them much.

 

[Flying Monkey fab]

There is nothing saying that you can’t mix and match building technices all you want. 3d printed planes don’t make sense to me but more and more small parts that I use are 3d printed. Balsa, ply, DTFB, carbon fiber, mix and match to your hearts content.

 

[mayan]

No harm in mixing the two however don’t really see why to do this. Balsa isn’t too strong at least not much more than foamboard is. I could see a solution where you would make spars out of foamboard and sheet them over with this balsa and that could possibly make you aircraft lighter.

 

[Tench745]

Balsa and foam have been mixing in one way or another since at least the 1980s and probably earlier. Some of the earliest involved hot-wire cut foam wings that were skinned with balsa sheeting.
Foam is great for complex shapes but is kinda floppy and weak by itself. Balsa's big strength is the amount of stiffness it has for its weight.

When I build de-papered foamboard planes I use balsa along the hinge lines of the control surfaces to stiffen them and give the hinges something solid to mount to. It also works well along leading and trailing edges of foam wings to stiffen the wing and help prevent hangar rash to the soft foam.
I have seen planes like the FT Scout built mostly from foamboard but with a built-up balsa fuselage from the cockpit back for that early aviation look.

In general, foam works well for monocoque style construction (think aluminum aircraft) and balsa works well for open truss structures. Play to the strengths of each material and use what works best for that specific task.

Hai-Lee on the forums here was playing with sandwiching foam and balsa at one point. Found the thread: https://forum.flitetest.com/index.php?threads/balsa-foamboard-test-build-ft-spitfire.32734/

As for glues to stick foam and balsa together, I like BSI Foam Cure for quick assembly. (Beacon Foam Tac is similar but more expensive). This is plenty strong for most things, but if I feel like I need slightly more strength I use 5-minute epoxy.

Also, check out NumaVIG on YouTube https://www.youtube.com/@NumaVIG for some really nice foam and balsa builds.

 

[L Edge]

Yes, especially if you are using foam as the major component. Planes should be light to give good performance especially if you use EDF's. If you are using material such as Adams Redi-board, a length of 36 inch balsa can really strengthen 2 segments glued together and also serves as a re-enforcement for a nose gear. Use 30 min epoxy. Nice way to prevent nose crumpling(orange area). Used this on my DarkStar and after 17 flights, when I hit clumps of grass, nose wheel tears off, straighten wire with plies and glue back on and ready to go.

Another interesting product is very thin basswood(1/64") , use it under the gear area to prevent gear from going thru foam and very lightweight. Join wings together (top and bottom) and really prevents twist. Use hot glue and then mono-cote iron heated, it will even out the glue and remove it from the foam to be used again!!

Another material you should look at is carbon rods and carbon strips. For instance, to reduce twist and bending of a wing, carbon strips glued all around the edges work well and add very little weight. Carbon rods glued to a groove area in the wing add quite a bit of stiffness to the wing.
With foam, anything goes.

 

[Captain Dunsel]

Balsa and foam have been mixing in one way or another since at least the 1980s and probably earlier. Some of the earliest involved hot-wire cut foam wings that were skinned with balsa sheeting.
Foam is great for complex shapes but is kinda floppy and weak by itself. Balsa's big strength is the amount of stiffness it has for its weight.

When I build de-papered foamboard planes I use balsa along the hinge lines of the control surfaces to stiffen them and give the hinges something solid to mount to. It also works well along leading and trailing edges of foam wings to stiffen the wing and help prevent hangar rash to the soft foam.
I have seen planes like the FT Scout built mostly from foamboard but with a built-up balsa fuselage from the cockpit back for that early aviation look.

In general, foam works well for monocoque style construction (think aluminum aircraft) and balsa works well for open truss structures. Play to the strengths of each material and use what works best for that specific task.

Hai-Lee on the forums here was playing with sandwiching foam and balsa at one point. Found the thread: https://forum.flitetest.com/index.php?threads/balsa-foamboard-test-build-ft-spitfire.32734/

As for glues to stick foam and balsa together, I like BSI Foam Cure for quick assembly. (Beacon Foam Tac is similar but more expensive). This is plenty strong for most things, but if I feel like I need slightly more strength I use 5-minute epoxy.

Also, check out NumaVIG on YouTube https://www.youtube.com/@NumaVIG for some really nice foam and balsa builds.

It takes a bit longer to cure, but I've had good luck with clear Gorilla glue (NOT the amber stuff).

 

[Burnhard]

I am using balsa for leading edges as it can be sanded to round edges rather than the pretty sharp foam board on the leading edges. This particularly works for the MS designs where the wings usually consist of two sheets of foam board. Also did this on the leading edges of my Viggen. This very much adds to durability.

Also agree on the use of carbon fiber. I use carbon tubes for stability in the wings (I do not trust the plywood spars) and never had a folding wing where I used a carbon tube.

 

[Tench745]

Also agree on the use of carbon fiber. I use carbon tubes for stability in the wings (I do not trust the plywood spars) and never had a folding wing where I used a carbon tube.

Out of curiosity, have you ever had a wing fold with a plywood spar?

 

[Burnhard]

Out of curiosity, have you ever had a wing fold with a plywood spar?

No, but there are some reports on the ME 262 on that and I had one incident with a folding wing on my tiny trainer. Also from a weight perspective, the carbon tube seems to be the better option.

 

[Merv]

Out of curiosity, have you ever had a wing fold with a plywood spar?

I use bamboo skewers as spars. They are incredibly strong. I imbeded them into the foam, above & below the typical foam spar. The idea is to make an I beam with the skewers at the top and bottom of the beam.