Discussion in 'Wood Construction' started by cluttonfred, Mar 4, 2018.
Further... it is only my wings that are made of wood. Struts , and empennage, are 6061 T6 and the airframe is welded 4130 tube.
So here are some great videos of Ash lumber being compared to Sitka Spruce. Ash lumber is known to be the highest strength to weight ration of all the common lumbers.
http://www.woodenaviation.com/aviation material info.html
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"
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.
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!
Amen to using a push stick
We used mahogany on the fuselage stringers, the window sills and other various pieces in the fuselage.
Another way to cut it down so to say. I plan it 1/4" then run it threw my bandsaw. Lots safer!
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
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.
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.
THE most important consideration when using commercial white ash is sealing it.
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.
I tested poplar quite a bit (referencing NACA report 354) and found it was very similar to sitka and better in some modulus'.
The Jenny...I agree, it's virtually all I use in solid wood parts.
Yep...it's shrinkage rate is so similar to spruce, I use it in all my restorations
The best place is NACA report 354, charts after pg 2 (raw data from testing) and after pg 26 (this one is weighted for manufacturing/production purposes)
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