Originally Posted by k2k

Saroyan Hardwoods, San Marcos.

Thank you, I checked them out, looks good

Her's my .o2 worth. based upon 65 yrs modeling, 44 plus years as a profesional wood worker, 10 of those working in aircraft repair and restoration.
Comparison tests.
Obtain three sticks, 3/16" sq x 36" : One of bass, one balsa, and one spruce.. With naked eye, balsa and spruce can be IMEDIATELY and EASILY assessed for their grain properties, end to end. Near impossible with bass. It is extremely easy to miss bass slash grain, and other minute weaknesses, even with careful visual checks under magnification. Assuming all three are deemed adequate, pick up each stick at one end and do a wiggle test. Then a wave or even a whip test. Balsa and spruce will act more like a fishing rod tip. Bass will behave more like a garden hose.

My own feeling is that Balsa and Spruce are stronger in compression, thus generally make better spars and longerons, Being "bendy", bass makes good wing tip laminations etc. Possibly as an excellent thin doubler or caps to lighter soft balsa spars/ longerons. I think it a poor choice for typical use, such as a longeron or stringer, where it may have to resist deformation from shrinking covering materials, etc.

I personally wouldn't use it as a direct substitute for spruce, preferring pine and Western Hemlock. But then I am biased toward certain methods and practices. If you can live with it and use it, successfully, I'll let you.

Besides, if you use Sitka, you could sing along with ELO while building or especially, flying...

"Don't let me down, Spruce..."











sorry

The thing is, how much are you willing to spend if you decide to replace the basswood spars with Spruce?
And will you really notice the difference?
Unless you are flying 3D where the planes are reinforced with CF it won't make a beans worth of difference.
These are model planes and they have been built with balsa spars forever. The older kits had Spruce but the costs have become to great to continue using Spruce in kits.
Just make sure you know how to make good scarf joints and don't skimp on the glue quality.

Originally Posted by jollyroger

....................
And will you really notice the difference?
Unless you are flying 3d where the planes are reinforced with cf it won't make a beans worth of difference.
.....................................
Just make sure you know how to make good scarf joints and don't skimp on the glue quality................

+1!

Originally Posted by packardpursuit

Her's my .o2 worth. based upon 65 yrs modeling, 44 plus years as a profesional wood worker, 10 of those working in aircraft repair and restoration.
Comparison tests.
Obtain three sticks, 3/16" sq x 36" : One of bass, one balsa, and one spruce.. With naked eye, balsa and spruce can be IMEDIATELY and EASILY assessed for their grain properties, end to end. Near impossible with bass. It is extremely easy to miss bass slash grain, and other minute weaknesses, even with careful visual checks under magnification. Assuming all three are deemed adequate, pick up each stick at one end and do a wiggle test. Then a wave or even a whip test. Balsa and spruce will act more like a fishing rod tip. Bass will behave more like a garden hose.

My own feeling is that Balsa and Spruce are stronger in compression, thus generally make better spars and longerons, Being "bendy", bass makes good wing tip laminations etc. Possibly as an excellent thin doubler or caps to lighter soft balsa spars/ longerons. I think it a poor choice for typical use, such as a longeron or stringer, where it may have to resist deformation from shrinking covering materials, etc.

I personally wouldn't use it as a direct substitute for spruce, preferring pine and Western Hemlock. But then I am biased toward certain methods and practices. If you can live with it and use it, successfully, I'll let you.

I've built kits that came with bass spar caps. Combined with shear webs the completed spars were plenty strong as they didn't fail in flight. I like the resiliency of bass and would prefer bass to fast growth spruce with widely spaced growth rings. I would also prefer close grained pine to fast growth spruce.

Packard' makes a good point on the difficulty in seeing any grain issues. And in fact wood carvers prefer bass due to this consistency of grain and hardness across the growth rings for carving shapes without showing any grain effects. A trait that makes it very difficult to see any run out in a lot of pieces.

I suspect we model builders get away with using it and other options due a lot to the fact that many of our designs are overbuilt. But if I'm looking at a lighter construction which will load down smaller sections for wing spars and not using carbon then I'm going to want to go with good sitka spruce or close grained (as in minimum 18 rings per inch) pine.

After all, it's primarily the harder small thick ring layers that have the long strong fibers that makes the wood suitable for things like wing spars.

To be fair fast growth building spruce is horrible stuff. I'd rather trust hard density balsa. And for my own thinking I'd put garden variety basswood on par for spars with the hard balsa. Some selected examples of harder or more fibrous bass might rank higher. But the difficulty in seeing the grain in bass makes it hard to evaluate them. After that it would be high ring count cedar. But not the rather brittle redwood or western cedar. It would need to be something like yellow cedar. From there tight ring count pine and from there tight ring count sitka spruce. The last being generally what we'd get by ordering up a few boards to rip down from somewhere like Aircraft Spruce and Specialty.

I just remembered that when I first saw Balsa USA ads they used redwood for their sailplane spars. Seems like redwood was not strong enough and brittle. Sailplanes exert huge loads on the spars during the launch.

This should answer all of your questions
https://sigmfg.com/collections/basswood
Gene

Not to put too fine a point on it, but SIG may want to promote Bass over Spruce, because it has become their go to kit wood in place of Spruce?

If Bass was as strong and as utilitarian as Spruce, it would be an approved structural wood specie for aircraft repair. However, in U.S. regs it is specifically relegated for gluing blocks and certain rib repairs. It is also specifically listed as not being a suitable alternative to Spruce.

Originally Posted by packardpursuit

Not to put too fine a point on it, but SIG may want to promote Bass over Spruce, because it has become their go to kit wood in place of Spruce?

If Bass was as strong and as utilitarian as Spruce, it would be an approved structural wood specie for aircraft repair. However, in U.S. regs it is specifically relegated for gluing blocks and certain rib repairs. It is also specifically listed as not being a suitable alternative to Spruce.

I suppose if your building a man carrying vehicle more power to you. Sig's numbers are from testing many samples and are well documented. Judge for yourself.
Gene

And just where are these well documented tests and samples to be found ? Close grain Sitka spruce has been the choice of woods for over a hundred years for wood airplanes . Even Sig's so called spec's show that Sitka spruce is superior to bass . Use what you want or what you can get and afford , I'll still use the spruce .

Mike 1484

Experimental wood model maker, Lewis Research Center ( NASA )
1967 - 1994

Whatever spins yer prop. Spruce is expensive and there aren't that many outlets to buy it.
As for model planes, the difference is unnoticeable for the most part.
If someone wants to spend the extra money, more power to 'em.

Originally Posted by Mike1484

And just where are these well documented tests and samples to be found ? Close grain Sitka spruce has been the choice of woods for over a hundred years for wood airplanes . Even Sig's so called spec's show that Sitka spruce is superior to bass . Use what you want or what you can get and afford , I'll still use the spruce .

Mike 1484

Experimental wood model maker, Lewis Research Center ( NASA )
1967 - 1994

Books on strength of materials and especially engineering text books!

I guess I am the odd man out here. If a plan called foe a spruce spar i would laminate one from balsa and carbon tow. Lighter and Much stronger.

Scott