Balsa vs. Papered Balsa vs. Basswood

[neil_w]

But by using Basswood, would you not then be able to use thinner stock than balsa?
Even back a few years I was getting some low power kits whose balsa fins were practically unusable unless they were papered and even then attempting to put an airfoil on the edges was a nightmare, the stuff didn't "Sand" it just fell apart, kind of like sanding burnt toast.

The thing I like best about basswood is that it doesn't require delicate handling like balsa. I find I can be quite rough with it when sanding, and rarely damage anything, including sharp edges. Of course, it is also quite a bit harder to sand than balsa.

 

[boomtube-mk2]

The thing I like best about basswood is that it doesn't require delicate handling like balsa. I find I can be quite rough with it when sanding, and rarely damage anything, including sharp edges. Of course, it is also quite a bit harder to sand than balsa.

That afore mentioned kit with the soft balsa, I could leave dents in them just by picking them up.

 

[icyclops]

I think you mean 0.010" or 0.020". With 0.10" on each side the fin would be about a quarter inch thick or more.

You are correct….forgot the 0 in front….

thank you

 

[DaHabes]

No need to guess. Below are the material properties of Balsa vs. Basswood. Basswood is 2 to 2.5 x the weight of balsa, but is 3 times stronger in almost all parameters. You can easily substitute Basswood at 1/2 the thickness of balsa with only a slight weight penalty and an improvement in overall strength. No brainer....

 

[BigMacDaddy]

No need to guess. Below are the material properties of Balsa vs. Basswood. Basswood is 2 to 2.5 x the weight of balsa, but is 3 times stronger in almost all parameters. You can easily substitute Basswood at 1/2 the thickness of balsa with only a slight weight penalty and an improvement in overall strength. No brainer....
View attachment 486553

Thanks this is great information.

Now I need to figure out what my misnamed plywood comes out to...

 

[Joshua Smith]

Probably an age-old debate but I am really surprised that more people do not use basswood plywood given the cost / challenge of finding balsa.

Has anyone done a weight comparison of 2mm balsa vs. papered 2mm balsa vs. 1.5mm basswood plywood vs. 2mm basswood? I bet that basswood is negligibly heavier than papered balsa (especially if you compare to the thinner basswood that is similar strength to thicker balsa - basswood might even win out on weight here). I am not going for any altitude records or anything so maybe I am not appreciating the impact of small differences in weight.

Basswood is so much more durable, you do not need to worry about direction of grain as much, can make more complex fin shapes that will not snap, can make massive fins/wings out of a single piece of basswood, etc... On the negative side, basswood is definitely harder to cut (I forget how easy it is to cut balsa till I get back to a kit). Also, I am by no means great at finishing / painting, but it seems that the tighter grain of the basswood with a bit of sanding makes it really similar to papered fins for finishing (especially if you are using a filler-primer as a first coat).

The determining factor for me is that I can get 200mmx300mm sheets of 2mm basswood for like $1 a sheet (20 sheet order from Amazon).

I would not both to upgrade a kit and swap out all the balsa for basswood, but in scratch-building I am using all 2mm basswood (1.5mm is more expensive for some reason).

Lite Ply is handy as well (apologies if it was already mentioned)

 

[BigMacDaddy]

Lite Ply is handy as well (apologies if it was already mentioned)

Some people stated that is likely what I have... I bought it on Amazon -- both 1.5mm and 2mm basswood (that is actually plywood)...

The listing changed since I ordered since this was the 2mm listing but just so folks can see the language --

https://www.amazon.com/gp/product/B08RJ2LRWQ/

 

[heada]

It does look like a "plywood" made up from at least 2 veneers of basswood. I can't see a 3rd veneer but a good plywood should have odd number of veneers. It should warp less than a single ply of basswood. Should be stronger too. If it is only 2 plys rather than 3, it won't be nearly as good.

 

[BigMacDaddy]

It does look like a "plywood" made up from at least 2 veneers of basswood. I can't see a 3rd veneer but a good plywood should have odd number of veneers. It should warp less than a single ply of basswood. Should be stronger too. If it is only 2 plys rather than 3, it won't be nearly as good.

It does have 3 layers but honestly it seems like the middle layer is not nearly as solid as the outside two (at least for the 2mm stuff I got). The 1.5mm stuff is also a 3-layer plywood but I cannot recall what the middle layer is like. I wound up with 40 sheets of the 2mm and 10 sheets of the 1.5mm so I wind up using 2mm all the time.

 

[neil_w]

Then again, you could super-harden the basswood: https://arstechnica.com/science/202...tlessly-through-juicy-medium-well-done-steak/

 

[jqavins]

In using thinner stock of stronger wood, do keep stiffness in mind. The stiffness of an object like a fin goes with the third power of the thickness. From the table that Mike provided in Post #34 (thanks, Mike) you might think that you can go with half or less of the thickness you'd need with balsa. And you probably can. But the stiffness will be less. With the elastic modulus of the basswood about three times greater than that of the balsa, and the thickness halved, the basswood fin would have only 3/8 the stiffness.

You might even want to go thinner, since the basswood is a good three times stronger, or thereabouts. But then stiffness would be 1/9 that of the balsa. If you get to speeds where you even have to begin thinking about thinking about flutter, keep this in mind.

(How thick would a piece of aluminum have to be to have the same strength as 1/8" balsa? It'd probably be as stiff as a wet noodle.)

Then again, you could super-harden the basswood: https://arstechnica.com/science/202...tlessly-through-juicy-medium-well-done-steak/

OK, now that is cool. But they really should have serrated the steak knife.

What becomes of the removed lignin, I wonder? Is it dissolved, or chemically destroyed, i.e. changed into some other substance. In talk of reusing the chemical bath, the lignin or lignin remains would have to be removed, and then what becomes of it? If I recall correctly, lignin removed from wood by steaming can be made into glue. Where did I read that? I don't remember. And if steam can do it, why the lye and sulfate? Maybe they do it better. Oh well, lots of questions, but it's still really cool.

 

[BigMacDaddy]

Found this interesting blog post that compares the weight of fins after finishing in a variety of ways we were discussing here. http://rocketn00b.blogspot.com/2018/05/balsa-grain-fillers-and-added-weight.html

FWIW: They found that papering fins added 72% of the weight of the original balsa. The earlier weights shared in this thread showed the the plywood was around 60% heavier than the balsa.

 

[Daddyisabar]

I'm with Old Chuck Heston. YOU WILL HAVE TO TAKE MY BALSA AND BUTYRATE DOPE FROM MY COLD DEAD HANDS!

Old school rules! Sanding sealer forever. Ain't no dopey old fart.

 

[lakeroadster]

Probably an age-old debate but I am really surprised that more people do not use basswood plywood given the cost / challenge of finding balsa.

Has anyone done a weight comparison of 2mm balsa vs. papered 2mm balsa vs. 1.5mm basswood plywood vs. 2mm basswood? I bet that basswood is negligibly heavier than papered balsa (especially if you compare to the thinner basswood that is similar strength to thicker balsa - basswood might even win out on weight here). I am not going for any altitude records or anything so maybe I am not appreciating the impact of small differences in weight.

Basswood is so much more durable, you do not need to worry about direction of grain as much, can make more complex fin shapes that will not snap, can make massive fins/wings out of a single piece of basswood, etc... On the negative side, basswood is definitely harder to cut (I forget how easy it is to cut balsa till I get back to a kit). Also, I am by no means great at finishing / painting, but it seems that the tighter grain of the basswood with a bit of sanding makes it really similar to papered fins for finishing (especially if you are using a filler-primer as a first coat).

The determining factor for me is that I can get 200mmx300mm sheets of 2mm basswood for like $1 a sheet (20 sheet order from Amazon).

I would not both to upgrade a kit and swap out all the balsa for basswood, but in scratch-building I am using all 2mm basswood (1.5mm is more expensive for some reason).

Fire up Open Rocket.... weights of all those materials are there. Make a fin, change the material type, write down the weights, and compare.

The only unknowns are how much weight the glue adds and how much strength papering adds.

Basswood is my favorite, I'm not doing any altitude contests, so why not build for durability. And making your own basswood ply allows you to make the basswood even stronger due to wood grain orientation.

 

[Lord Rory Gin]

No need to guess. Below are the material properties of Balsa vs. Basswood. Basswood is 2 to 2.5 x the weight of balsa, but is 3 times stronger in almost all parameters. You can easily substitute Basswood at 1/2 the thickness of balsa with only a slight weight penalty and an improvement in overall strength. No brainer....
View attachment 486553

And with a thinner fin you are going to lower the CD as well giving you additional altitude for the same form factor.

 

[bjphoenix]

Balsa can vary a lot. If you build a lot of Estes style kits you notice that some of them you can cut the fins out easily but others it is really difficult.
I've been papering my balsa fins recently using normal printer paper. I've wondered if there is a commonly available paper that is stronger. I had the idea one time to use Tyvek but then I discovered that it is hard to glue to and it is not very resistant to heat. It's probably too heavy for small rockets. I've read threads that mentioned vellum drafting paper so I might try that.

 

[BigMacDaddy]

Balsa can vary a lot. If you build a lot of Estes style kits you notice that some of them you can cut the fins out easily but others it is really difficult.
I've been papering my balsa fins recently using normal printer paper. I've wondered if there is a commonly available paper that is stronger. I had the idea one time to use Tyvek but then I discovered that it is hard to glue to and it is not very resistant to heat. It's probably too heavy for small rockets. I've read threads that mentioned vellum drafting paper so I might try that.

You may want to try basswood plywood. You can get it for around $1.25 per 8.5"x11"x1/16" sheet if you buy 20 sheets. It is so much stronger than balsa (not nearly as much of a "weak direction") and it does not require nearly as much work to finish since it has a much finer grain.

 

[naslrogues]

Usually just a reader of posts but thought I would add my papering method for balsa fins. After sanding and shaping the fins, I coat both sides of the fins with a light coat of spray adhesive. Nothing heavy duty, I usually use the Elmer's brand. Next I spray one side of a sheet of cheap copy paper and apply the fins to it, cut them out with a sharp X-acto blade, turn the fins over, and repeat. After cutting them out I place the fins under a weight (a couple of heavy books) and leave them for about 24 hours. Last steps are to use a Q tip and coat the fins with super thin CA. After it dries I sand the fins smooth and apply Fill and Finish to the edges. Sand and done. Stronger fins and not that time consuming. Just my method, not saying it is the best, just that it works for me.