Weight of foam board vs. balsa

[trey]

Last night, I was watching a Peter Sripol video on YouTube. He was using foam as wing ribs, which I had never given much thought to. However, I am getting a laser cutter, so I did give it thought this time.

Has anyone measured the weight difference between foam and balsa in the same intended application? I don't have any balsa around, so I can't try it at home. I don't plan on buying any either, not in the near future.

 

[JasonK]

balsa normally uses truss based structures vs foamboard's solid.

so are you wanting to compare raw density differences or 'as likely constructed' differences?

Also note that foamboard is rather low cost and readily available at FF and is typical material choices given the venue, so even if balsa would have made a better material [on a mechanical/structural level], the foamboard has other things going for it beyond just weight to strength.

 

[trey]

balsa normally uses truss based structures vs foamboard's solid.

so are you wanting to compare raw density differences or 'as likely constructed' differences?

Also note that foamboard is rather low cost and readily available at FF and is typical material choices given the venue, so even if balsa would have made a better material [on a mechanical/structural level], the foamboard has other things going for it beyond just weight to strength.

I was hoping we could eventually have a conversation about strength to weight ratio.

I the idea of foam board for uses in larger scale planes is pretty interesting. It's considerably cheaper and easier to work with.

And it's more that I'm new to the foam board scene, and trying to figure out where the limits are.

 

[JasonK]

I have some balsa sitting here because I had a few ideas I wanted to try with it.

22g for a 1/16" x 4" x 36" piece

a fullsheet of adam ready board is ~3/16th thick [5mm is not quite that] and 20x30

so 3x for foamboard thickness and 600/144 for area means balsa the same size as one sheet of DTFB would mass about 275g vs DTFB's 115g. Which means the foamboard is less dense.

I don't have any good way to do a strength test on the balsa without breaking it, which I don't want to do.

 

[JasonK]

however, do note, that balsa stuff tends to not be built the same way, it is a stick truss setup with coverings, which means it could well be a less dense material in its compost configuration.

 

[JasonK]

On limits - Based on the 'why it didn't fly' comments, it sounds like Peter's plane didn't have sufficient twist resistance in the wing and needed some design changes to be able to work (or another possibility was more dihdral and make it a elevator/rudder only setup and no ailerons)

 

[trey]

I have some balsa sitting here because I had a few ideas I wanted to try with it.

22g for a 1/16" x 4" x 36" piece

a fullsheet of adam ready board is ~3/16th thick [5mm is not quite that] and 20x30

so 3x for foamboard thickness and 600/144 for area means balsa the same size as one sheet of DTFB would mass about 275g vs DTFB's 115g. Which means the foamboard is less dense.

I don't have any good way to do a strength test on the balsa without breaking it, which I don't want to do.

Break the balsa! Lol.

I think I might order some and cut a rib out of balsa, foam, and print one from LW PLA or carbon PLA. Then I could do some messing around and see the differences. I think it would be interesting to see the different properties.

 

[Bricks]

Balsa you will have different weights and stiffness depending on where the Balsa was cut from the tree, and where it was originally grown for the same size sheets. That is why when building with balsa you pick the sheets for the desired use light weight or high stress.

 

[Merv]

I agree with Bricks, there is a large range of strength and weight within the balsa world.

I’ve not done any testing, but I suspect balsa will win the day in a strength to weigh test.

There is another factor to consider, resilience. Foam board planes are far more resilient, than balsa. A foam board plane will survive a crash that would destroy a balsa plane.

 

[foamboardflyer]

I agree with Bricks, there is a large range of strength and weight within the balsa world.

I’ve not done any testing, but I suspect balsa will win the day in a strength to weigh test.

There is another factor to consider, resilience. Foam board planes are far more resilient, than balsa. A foam board plane will survive a crash that would destroy a balsa plane.

That is very true, foam board IS very resilient, I had a ft Corsair and a friend of mine had a balsa one, only one crash and the balsa one exploded but the Flite test one survived 9 crashes. Most of them harder than the one the balsa one had.

This is Stefan, me and my Corsair.

And this is a Corsair of similar size of my friend’s one.

 

[kilroy07]

I have seen people "glass" foam (that is add a thin layer of fiberglass cloth & epoxy resin) the FT guys even did foamboard once.

I suspect this would be heaver but orders of magnitude stronger than balsa.

 

[foamboardflyer]

I have seen people "glass" foam (that is add a thin layer of fiberglass cloth & epoxy resin) the FT guys even did foamboard once.

I suspect this would be heaver but orders of magnitude stronger than balsa.

I’e been wanting to “glass” a ft goblin.

 

[trey]

I have seen people "glass" foam (that is add a thin layer of fiberglass cloth & epoxy resin) the FT guys even did foamboard once.

I suspect this would be heaver but orders of magnitude stronger than balsa.

I built a flying wing for a friend years ago. It was basswood ribs, spars and LE were carbon. It was covered in fiberglass and was pretty light. I don't remember the AUW, but it was very surprising. It felt pretty strong, I'm not sure if he ever flew it though.

 

[trey]

however, do note, that balsa stuff tends to not be built the same way, it is a stick truss setup with coverings, which means it could well be a less dense material in its compost configuration.

What about foamboard built in a traditional truss style? I imagine it would be very weak, but all assembled, maybe not as bad as I think?

 

[JasonK]

What about foamboard built in a traditional truss style? I imagine it would be very weak, but all assembled, maybe not as bad as I think?

Go ahead and try it.

 

[trey]

Go ahead and try it.

I think I will, even though I likely know the result. Just have to wait for the laser cutter to get delivered.

 

[kilroy07]

I think I will, even though I likely know the result. Just have to wait for the laser cutter to get delivered.

What kind of laser cutter do you have? (I've got a 60W CO2 setup, 700x500 working area.)
Didn't buy it for planes, actually one of my (hundred) other hobbies...

I suspect shortly after getting your laser setup you'll be complaining about space to store all your new airframes!

 

[trey]

What kind of laser cutter do you have? (I've got a 60W CO2 setup, 700x500 working area.)
Didn't buy it for planes, actually one of my (hundred) other hobbies...

I suspect shortly after getting your laser setup you'll be complaining about space to store all your new airframes!

My wife decided she needed one for her business, with no outside interference from me. HAHA.

80watt, 20"x28" working area. I'm looking forward to it. I have a lot of things I'd like to do with it.

 

[Baron VonHelton]

I was hoping we could eventually have a conversation about strength to weight ratio.

I the idea of foam board for uses in larger scale planes is pretty interesting. It's considerably cheaper and easier to work with.

And it's more that I'm new to the foam board scene, and trying to figure out where the limits are.

Funny you should mention this! I was actually thinking of making a frame from foamboard, rigging it with fishing line & covering it with cling wrap!

......Bear in mind I have NO IDEA if it would even work.

 

[trey]

Funny you should mention this! I was actually thinking of making a frame from foamboard, rigging it with fishing line & covering it with cling wrap!

......Bear in mind I have NO IDEA if it would even work.

That's the point! It's much better to say you don't know if it will work, opposed to it won't work.