Alternatives to spruce in wooden aircraft construction?

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Charles_says

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Perhaps I misled, or confused some. Let me clear that up.
It is the long lengths of Sitka Spruce, which are costly to ship.
Hell even the $38.00 Bargain boxes of Sitka from A/S, cost more to ship,
than the material costs Cost me $84.00 to ship from Atlanta.

I used the Ash only to laminate the Spars. Everything else, was fabricated from the Bargain box.
I cut my own 1/4" rib sticks, and cap strips from the Bargain Box material. And I have pieces left over for repair work, if it becomes necessary.View attachment 86071
I found this to be the most cost effective method., and I get to say:
" Yeah, I built it all, myself!" which for me is the fun part. I truly enjoy building things.

(edit) Oh.... my 12' wing weighs 28 pounds less fabric. ( end edit)
 

Charles_says

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Further... it is only my wings that are made of wood. Struts , and empennage, are 6061 T6 and the airframe is welded 4130 tube.
 
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If that is true, then somebody better let the Forest Products Laboratory know that they got it wrong.

They built lots of planes out of Ash prior to finding Sitka. Sitka is just easier to find A/C lumber then Ash. Meaning maybe 1 in 10 meet mil spec whereas 1 in 200 meet it with Ash. With all the Sitka resources dwindling down, Ash has now become a viable replacement.

True Replicas of the Curtis Jennys are still built of Ash.

Ref. NACA 354 report Aircraft woods: Their properties and selections. No 1079.

Published by "United States Department of Agriculture and Forest Services"
 

mcrae0104

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They built lots of planes out of Ash prior to finding Sitka. Sitka is just easier to find A/C lumber then Ash. Meaning maybe 1 in 10 meet mil spec whereas 1 in 200 meet it with Ash. With all the Sitka resources dwindling down, Ash has now become a viable replacement.

True Replicas of the Curtis Jennys are still built of Ash.

None of that is in question. What is in question is this...

Ash lumber is known to be the highest strength to weight ration of all the common lumbers.

...because the values listed in ANC-18 say the opposite about the relative strength-to-weight ratios of Ash and Sitka Spruce.

Ref. NACA 354 report Aircraft woods: Their properties and selections.

I read through this report but it does not contradict ANC-18. If I missed it and you would like to point out a particular section, I would be happy to take another look.
 

cdlwingnut

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sawmillpatric, your views and opinions of ash are appreciated and respected, but please stick to one thread. Your build looks cool, do a build log so we can see your airplane built from ash come together. I too like the idea of alternatives to spruce since the price is high and shipping to me is higher. the longer parts of my airplane are douglas fir with the shorter lengths specially the thinner parts are spruce from ACS. I did this for a couple of reasons one of which is that i didn't like the idea of trying to cut 1/4 by 1/4 pieces with a table saw. I like my fingers intact.
 

John wadman

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sawmillpatric, your views and opinions of ash are appreciated and respected, but please stick to one thread. Your build looks cool, do a build log so we can see your airplane built from ash come together. I too like the idea of alternatives to spruce since the price is high and shipping to me is higher. the longer parts of my airplane are douglas fir with the shorter lengths specially the thinner parts are spruce from ACS. I did this for a couple of reasons one of which is that i didn't like the idea of trying to cut 1/4 by 1/4 pieces with a table saw. I like my fingers intact.
Use a “push stick”, adjust your blade height properly and a tight kerf insert in your table saw and you’ll have your fingers you’re entire life!
 
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sawmillpatric, your views and opinions of ash are appreciated and respected, but please stick to one thread. Your build looks cool, do a build log so we can see your airplane built from ash come together. I too like the idea of alternatives to spruce since the price is high and shipping to me is higher. the longer parts of my airplane are douglas fir with the shorter lengths specially the thinner parts are spruce from ACS. I did this for a couple of reasons one of which is that i didn't like the idea of trying to cut 1/4 by 1/4 pieces with a table saw. I like my fingers intact.

Another way to cut it down so to say. I plan it 1/4" then run it threw my bandsaw. Lots safer!
 
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None of that is in question. What is in question is this...



...because the values listed in ANC-18 say the opposite about the relative strength-to-weight ratios of Ash and Sitka Spruce.



I read through this report but it does not contradict ANC-18. If I missed it and you would like to point out a particular section, I would be happy to take another look.


Ref Table 1 of Naca 354
Commercial Ash Compression perpendicular to the grain is 2,250#/Sq inch
Sitka is 840#/Sq inch

Commercial Ash Sheering Strength Parallel to the grain is 1,380#/ Sq inch
Sitka is 750#/ Sq inch

Ash Weighs 41#s Cubic foot
Sitka Weighs 27#s Cubic foot
 

mcrae0104

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Compression perpendicular to grain and shear parallel to grain are not the figures of merit for airplane parts. Bending stress, stiffness, and compression parallel to grain are much more significant for things like spars, longerons, ring frames, trusses, and the like. Ash may have advantages in some applications (e.g. bolt tearout where shear parallel to grain comes into play) but having the highest strength-to-weight ratio is not one of them.

I do think ash is a legitimate alternative, but those considering using it must read and understand the NACA/ANC/FPL literature.
 
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Aircraft plywood seems like it will be around for a long time, if nothing else the Finnish birch type from sustainably managed forests, but spar quality spruce seems to be getting harder and harder to find. Yes, there are solutions like laminated spars, but at some point even that will be problematic. What if we want to keep building little airplanes largely of wood/plywood and fabric but without the spruce? I see at least four approaches, there are probably more:

1) Use other woods and take the weight penalty

2) Build up plywood laminations into substitute spars, longerons, etc.

3) Use hybrid plywood/aluminum construction with aluminum spars, longerons, etc. and plywood ribs, bulkheads, etc.

4) Use selective composite reinforcement to give the required strength to an otherwise all-plywood design.​

Yes, I know that there are also the alternatives of going all-aluminum or all-composite, but let's keep this thread on topic for the "Wood Construction" section.

Cheers,

Matthew
After reading many of the publications on aircraft woods I used NACA report 354 to do my own tests.
I have settled on using Commercial White Ash. It's approximately 1.4 x the weight, but it's about 4-6 x stronger in most modulus' and that's after being reduced in size to match the weight of Sitka. But ashes modulus of elasticity is very near to that of Sitka spruce, as well as it's shrinkage (very important).
I also use my very thin scrap to cross glue small gussets. The strengths and glue ability comparison is extremely in favor of ash.
If you didn't reduce the size of Ash to match the weight of Sitka spruce, it would add about 20 lb to an LSA.
 
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Compression perpendicular to grain and shear parallel to grain are not the figures of merit for airplane parts. Bending stress, stiffness, and compression parallel to grain are much more significant for things like spars, longerons, ring frames, trusses, and the like. Ash may have advantages in some applications (e.g. bolt tearout where shear parallel to grain comes into play) but having the highest strength-to-weight ratio is not one of them.

I do think ash is a legitimate alternative, but those considering using it must read and understand the NACA/ANC/FPL literature.
THE most important consideration when using commercial white ash is sealing it.
 
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Molded angle longerons and spars could be made of veneers. I think the Spruce Goose is mostly molded birch plywood, not spruce. It has molded angle stringers.
Spruce Goose was nearly 90% poplar...but that may exclude what plywood was used...not sure...just happened to read about it a couple days ago.
 
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If you redesign, there are other woods that can be used. If I build from wood, I'll use tulip poplar. Properties are similar to spruce, large one tend to be knotless. Most importantly, I have thousands of them... I also have oaks, mostly red, but some white. They may be good for props?
I tested poplar quite a bit (referencing NACA report 354) and found it was very similar to sitka and better in some modulus'.
 
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Ash is good for highly loaded parts but not for long stiffeners. It is especially very good in compression across the grain and in bearing (so ideal for a bolt going through).

It was used on the Stampe for the front of the fuselage longerons, scarfed with spruce at the back. I think this was done to have higher strength with the same dimensions to make assembly simpler.
Yep...it's shrinkage rate is so similar to spruce, I use it in all my restorations
 
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