Wood for box spars?

Discussion in 'Wood Construction' started by cdlwingnut, Sep 9, 2018.

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  1. Sep 9, 2018 #1

    cdlwingnut

    cdlwingnut

    cdlwingnut

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    I am afraid my source of douglas fir flooring has been cleaned out only a few boards left none of the ones long enough to use in spars are near good enough with grain and runouts. The yard does have some very nice board of white pine and poplar. So will one of those work if so which to choose. Do i pony up and get spruce from wicks or ACS which wil also take quite a while to ship. or keep on the quest for douglas fir?
     
  2. Sep 9, 2018 #2

    TFF

    TFF

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    As much as finding a cheap alternative is a worthy quest, how much is your life worth with respect to peace of mind. The extra cost of the real deal hurts, but falling out of the air from a bad substitute hurts more. Buy up the fur for other stuff buy real spars from ACS. I would never use anything less than aircraft quality wood for a spar. Where it comes from does not matter. Correct species and quality does.
     
  3. Sep 9, 2018 #3

    Aerowerx

    Aerowerx

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  4. Sep 10, 2018 #4

    Pete Plumb

    Pete Plumb

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    I've got a fair amount of nice 20 foot spruce boards in stock right now if you need it faster. I usually don't sell raw lumber but will help you this time. PM me your sizes if you want. You don't want doug fir anyway. Spruce or Hem fir is best.
     
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  5. Sep 11, 2018 #5

    cdlwingnut

    cdlwingnut

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    I found a source of good wood wing production will start soon
     
  6. Sep 11, 2018 #6

    TJay

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    You don't want doug fir anyway. Spruce or Hem fir is best.[/QUOTE]

    just out of curiosity why do you say that?
     
  7. Sep 12, 2018 #7

    Pete Plumb

    Pete Plumb

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    Personal preference based on 42 years of working with Sitka spruce I guess.
     
  8. Sep 12, 2018 #8

    TFF

    TFF

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    Not that I can take them off your hands, but 20' spruce would be hard to let go without a worthy project. Hard enough getting 12'.
     
  9. Sep 12, 2018 #9

    pictsidhe

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    I have an abundance of hardwood trees. Tulip poplar is therefore going to be my wood of choice. It's nearly as good as spruce and I have a LOT of it. Once I start building buildings from it, I'll be picking out the extra nice bits for aircraft. It's also commonly available at your local big box, along with white pine. Anything designed in poplar can use the 'proper' sitka spruce as a drop-in substitute. Doug fir has good strength to weight, but is denser, so it's not really a direct substitute unless the extra weight doesn't bother you. While purists insist on Sitka, that's because it has historically been the best available. But the large old growth trees are getting rarer and people are less willing to pay the increasing premium. Especially once outsize shipping cost across several states is factored in.
    I've gone into a big box to buy construction lumber and come out empty as I didn't like the crap that they had left. I really regret not buying and hoarding the really, really good spruce that I saw in Lowes 5 years ago. Yes, spar grade white spruce in a big box.

    Read up on the properties of various woods before deciding which to use.

    All aircraft wood is graded by a person, whether it be spruce, poplar, oak or balsa. If YOU don't want to be that person, you pay someone who does. That's YOUR decision. That doesn't mean that others here won't or can't do their own grading.
     
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  10. Sep 12, 2018 #10

    TFF

    TFF

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    The premium has always been there for true aircraft grade lumber. You use spruce and fur one for strength to weight. Good numbers. Not overall strength. You also pick it for how it breaks. All those pretty straight lines all in vertical rows break incrementally. Tulip poplar it shatters like glass when it breaks. All at once. No second chance. Vertical straight grain tulip poplar? It's like one grain per board. UL Wing ribs maybe, secondary wood, ok; spar, delusional. Not saying it can't fly, but every time it goes up, it's one less time its probably going to be as safe. Like Peter Stipol's first plane was not made to fly more than once and lots could have been done to keep it around. One was spars and their protection. His objective was different, buts lots of effort for shuch a short life.
     
  11. Sep 12, 2018 #11

    dcstrng

    dcstrng

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    From AC 43.13-1B I note that for the various firs, that gluing is “satisfactory” (the same said for most -- except White Cedar, Port Orford – which is “difficult”), while for spruce it simply says “Excellent for all uses. Considered as standard…” From those who know this stuff, what does that mean for gluing and airworthy joint – are there special precautions? I have some experience with marine woods, some fir (moe mahogany or teak), but we don’t use spruce much anymore (except for restorations and the like; masts, etc., have been aluminum for decades), so am wondering what I might be in for to get an airworthy joint using fir as a substitute for spruce.
     
  12. Sep 12, 2018 #12

    Pops

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    Local high end wood molding mill about 25 miles away. They will let you come in and go through their warehouse and spend all day if you want, picking out aircraft grade wood. The have Yellow Poplar, Oak, Walnut, Cherry, etc, in boards up to 24' long. Very good prices. This is all local grown wood. I bought all of my molding when building my house there. The lattice strips on the last 3 sets of Geodetic wings were sawed from the aircraft grade of yellow poplar.
     
  13. Sep 12, 2018 #13

    Pete Plumb

    Pete Plumb

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    20 to 23 feet is what my logger bucks the logs at. I take what he sends down and usually have to buck them further down wasting some wood at the ends. I also have to cut 30% of them down to 14 and 16 feet due to knots and other anomalies but I still end up with lots of 20s. Cub front spars are almost 18 feet long and by the time I work them down to size I'm usually grateful for the extra foot or 2 of length. Full disclosure here: finding perfect grain in a 20 foot by 8" wide board is almost impossible.
     
  14. Sep 16, 2018 #14

    ToddK

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    Those geodetic designs are pretty cool. What kind of wings?
    TK?
     
  15. Sep 16, 2018 #15

    Pops

    Pops

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    First set of wings for the SSSC with 2-- 4 gal wing fuel tanks for a total of 8 gal ( VW powered Single Seat Super Cub ) , then a second set of wings with long range wing fuel tanks of 8 gal each for a total of 16 gallon with a fuel burn of 3 gph. Then the wings of the JMR Special.
     

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