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Balsa wood properties

Balsa wood properties

(OP)
Low, Medium or High density, Which types of balsa wood is most cost effective and Structurally efficient and available in market?

Is it possible to have a balsa wood block of 5ft long and 3x3" cross sectional area in market?

As this wood beam will be subjected to bending, to make it highly efficient I like to make two types of wood blocks.
At tension region Wood with strong axial fiber (A grain)
And at compression region C grain.
Then glue will be used to join them together and make them act as one single beam.

Is it a good idea?

RE: Balsa wood properties

I've never seen balsa wood used for a structural application.

Wood is rarely mixed the way you describe. And I say rarely because although I've never seen it I can only assume one or two of the engineered lumber companies have tried something like it.

Generally you use a full spanning piece (or pieces grouped together ) and just design the length of bearing as required.

RE: Balsa wood properties

Wrapped balsa was used often - but a long while back. Not so much any more. Filled balsa now is more common foam polystyrene packed even for insulation..

So, why do you want to use something every else even in aero fields has abandoned in favor of other material? For example, balsa wrapped wood was not often used even by WWI: Wood frames with metal clamps and fasteners and highly-doped lightweight cloth covers were more common even then.

RE: Balsa wood properties

Still works for airplane models though... Perhaps even larger ones.

As for the specific structural properties and types of Balsa, I would have to Google it. Even older copies of the AITC do not list it to my knowledge.

Mike McCann, PE, SE (WA)


RE: Balsa wood properties

Balsa....not good for serious structural applications

RE: Balsa wood properties

Agreed.

Mike McCann, PE, SE (WA)


RE: Balsa wood properties

(OP)
Thanks everyone. smile Sorry for being offline for days.

I will use it for a homemade aircraft actually.

Your comments are really helpful, I like to switch myself from balsa wood to another material. Ill look for a better one. Suggestion will be greatly appreciated. bigsmile

RE: Balsa wood properties

The de Havilland Mosquito used balsa wood very extensively in its construction and I think its fair to say it was a very successful aircraft. Have a look on Wikipedia for some details.

RE: Balsa wood properties

(OP)
Thanks. smile I see, even wing spars are built with Balsa wood blocks! It sounds interesting. I have to rethink of material selection.

RE: Balsa wood properties

Be very careful selecting balsa wood, it can vary in grade and strength even across the length of the same piece.
If you are building Model aircraft go to your local hobby shop and check out their stock. Talk with some of the modelers that hang out there , especially the one that build 1/4 size models.
The application used in the De Havilland mosquito was to separate plywood skins by varying degrees by stacking the wood in an end grain fashion. Balsa is quite strong in compression compared to its weight. This technique was used after the 2nd world war to build high strength to weight ratio wings for sailplanes. Later plywood skins were superseded by fiberglass skins then carbon fiber, eventually the balsa cores were replaced by foamed PVC or honeycomb. You can still buy end grain balsa block pre fitted to a very fine woven scrim from companies like Fiberlay, or Baltek , Google them. The latest modeling methods are to cut parts from foam, then cover them with a high strength material such as fiberglass or carbon fiber.
B,E.

You are judged not by what you know, but by what you can do.

RE: Balsa wood properties

I know nothing about Balsa. But, Glulam beams use different grades of wood for different layers. The concept of laminating layers with different grades is sound.

RE: Balsa wood properties

That's what I was saying: Single wood "planks" of balsa are a very, very poor choice. Wrapping it, or building up plywood layers with good glue and even professionally laid plies professionally squeezed in large jogs ensuring professionally measured even pressures across the whole playwood span "might" work, and can be somewhat reasonable if you try and test and try and test. But today's home-built planes don't use balsa by itself.

Get a Rutan Vari-eze book and study what does work. The Mosquito was built by pro's after many years of failures and excess weight.

RE: Balsa wood properties

(OP)
Thanks everyone. smile

Then sandwich structure with balsa core sounds best.

Glulam beam also sounds very good.

RE: Balsa wood properties

Balsa is used sometimes as a core for fiberglass.

RE: Balsa wood properties

Quote (glass99)

Balsa is used sometimes as a core for fiberglass.

And notably classy and expensive surfboards...

RE: Balsa wood properties

(OP)
Thanks glass99 Ingenuity

Yes I know, sandwich structure. Btw will you please suggest me any solid wood other than balsa?

RE: Balsa wood properties

How about spruce? They used alot of it back in Biplane days!

RE: Balsa wood properties

The Spruce Goose was overweight and underpowered.

Mike McCann, PE, SE (WA)


RE: Balsa wood properties

Balsa is also used in the marine industry, as core and for the Flame, Smoke and Toxicity requirements of the U.S. Navy. There is a significant difference in the cost over structural foams.

RE: Balsa wood properties

Quote from a web site "the press insisted on calling it the “Spruce Goose” despite the fact that the plane is made almost entirely of birch."

My guess is that engine technology was to blame on the lack of power side. The engines look pretty small compared with the size of the airplane, even though they are huge when seen separate. The B-36 had the same problem and had jet engines placed near the wing tips in later versions.

My sailboat has 1/2" balsa cored hull. The bending strength is in the fiberglass inner and outer skins, the balsa serves as the spacer between the skins and takes some shear stress. The balsa is in mats, cut across the grain like a checker board. In that way it can be laid up to conform to the curved shapes of the hull.

RE: Balsa wood properties

the cross grain cut reduces chance for water absortion

RE: Balsa wood properties

True! Through penetrations should be routed oversized, then filled with epoxy. Then the hole is drilled, leaving a donut of epoxy around the hole to prevent moisture intrusion.
Since the core is primarily loaded in shear, the butcher block arrangement also loads the balsa in the cross-grain direction, which has a greater capacity in shear.

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