Sizing white pine...

Discussion in 'Wood Construction' started by MadProfessor8138, Sep 16, 2018.

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  1. Sep 16, 2018 #1

    MadProfessor8138

    MadProfessor8138

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    Since Wicks has decided to only carry plywood now I'm not willing to pay the outrageous prices that Aircraft Spruce wants for its wood.
    Longerons and spars will be spruce but I'm changing to white pine for the rest of my build.
    I can't find a formula to calculate the sizing of the white pine.
    If white pine is 85-95% the strength of spruce what is the formula to calculate the increase in size?
    Is it as simple as adding 5-15% to the size of the white pine to equal spruce strength?

    Kevin
     
  2. Sep 16, 2018 #2

    lr27

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    Depends on the failure mode. If it's buckling, the increase in size can probably be much smaller. Also, you have to know whether the part is designed for stiffness or strength. Or by standard size, which may mean you can use it without changing the size.

    I don't know what the price of douglas fir is these days, but it's a viable alternative to spruce. Somewhat heavier, but also somewhat stronger.
     
  3. Sep 16, 2018 #3

    plncraze

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    Find a copy of Drake's "Aircraft Woodwork" and go to bowersflybaby.com and look up wood testing techniques. I believe Drake's has some numbers and then you can test your materials to be sure.
     
  4. Sep 16, 2018 #4

    MadProfessor8138

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    I've read just about everything that has ever been written when it comes to wooden aircraft structures,including the sources you listed.
    One problem is that each report will contradict the other.
    A report will state that white pine is a direct substitute for sitka spruce and the next report will claim that it is only 85-95% as strong.
    One report will say that NORTHERN white pine is the best choice while the next report will state that EASTERN white pine is the strongest and lightest of the pines.
    Doing your own testing is not a fool proof way of achieving a consistant result either,unfortunately.
    I would dare say that you nor I have the millions of dollars worth of equipment or a sterile lab to scientifically compare two pieces of wood that look identical to the naked eye.
    One piece failed while the other didn't,yet to our eyes and grading they were identical.
    We do not have the ability to measure exact moisture content which changes constantly due to humidity and temperature of the surrounding environment.
    And without the ability to x-ray each piece to ensure the cellular makeup is identical between pieces,internal variations will have a dramatic effect on testing results.
    Building with ANY material is a crap shoot with hopes that unforeseen defects in the material don't creep up to bite us later.
    So basically you have to dumb things down and put your faith in things that have generally worked well in the past.....you role the dice and you take your chances.

    There has to be a standardized general practice for substituting white pine in place of spruce.
    Does anyone know the rule of thumb ?
     
  5. Sep 16, 2018 #5

    dougwanderson

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    i have and tested some white pine with tight grain and have some spruce from Aircraft Spruce grab bag cutoffs. tested both same size same length same grain direction white pine quality was better and stronger weight same or a little more. Spruce was inconsistent in weight and strength.
    clamped test pieces to table and used a pull scale till failures. also did compression test with shop press (not as accurate)

    so test against known specs and samples.
     
  6. Sep 16, 2018 #6

    MadProfessor8138

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    At hainesengineering.com he does tests on 3 samples of 4 different woods and the results were surprising.
    I will only list the sitka spruce and the white pine but as a note,all of the other wood samples beat the sitka spruce...the tests were add weight until destruction.
    Sitka spruce .... #1 27lbs,#2 32lbs,#3 29lbs
    White pine...... #1 45 lbs didnt break,#2 45lbs didnt break,#3 36lbs it failed.

    Your tests also show that white pine is more consistant and stronger that sitka spruce.

    White pine is looking pretty good actually.......its a fraction of the price of spruce,its locally available at any Lowes or Home Depot,I can pick my own material,I don't have to wait weeks for the order to arrive,and shipping costs are a few gallons of gas.

    Anyone else have test results to post on the topic ?
     
  7. Sep 17, 2018 #7

    TFF

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    Except for the ancient texts, there is no other information. No one commercially is looking for white pine to be aviation wood. Published results are only published because it is being used. If you are going to do it ,take the most conservative published info and go with it.
     
  8. Sep 17, 2018 #8

    plncraze

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    Find RS Hoover's blog. He played around with alternatives prior to his death and he was designing a plane using locally sourced wood.
     
  9. Sep 17, 2018 #9

    plncraze

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    When you are looking at "pine" at the store see if it is really SPF. That stands for spruce or pine or fir. Some folks are finding spruce for the price of pine.
     
  10. Sep 17, 2018 #10

    Pete Plumb

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    Well, simplified, if the parts in question are in bending use, allowable stress (psi), Fbp = MY/I . If they are in column (as in cap strip in a trussed rib) use, allowable stress (psi), Fce = pi^2 E/(L/rho)^2. The column calc will be conservative if you don't use a restraint coefficient (4 for fixed ends).

    I suggest using proportional limit to be conservative. As for Fbp values, I use ANC-18 (sticky note at the top of the Wood Construction thread, you can download ANC-18), pg 22, table 2-6. It is for 15% moisture so it, too, will be conservative if your moisture is less than 15 (table 2-2, pg 13 to adjust for different moisture).

    NOTE: You might find it easier for you to "see" the difference between the 2 species if you calculate the allowable load for identical cross sections instead of allowable stress. Allowable load (lbs), P = EIpi^2/L^2. ANC-18 lists E of spruce @ 1,380,000 psi and western white pine @ 1,280,000 psi.

    Personally, I like western white pine for a substitute for spruce. The numbers are so close you are bound to see crossover, i.e. some white pine samples will be stronger than spruce and some will be weaker. Wood strength is not an exact science. There are many variables that affect strength so just go a little conservative. It is the Home Improvement "sugar pine" you have to avoid!

    P.S. if you need spruce, I've got some in stock.
     
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  11. Sep 17, 2018 #11

    dougwanderson

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    if you test and weigh whatever wood you have with good grain and grain slope then you dont have to guess cut a 3/4 samples out and brake them with pull scale or weighted buckets.
     
  12. Sep 17, 2018 #12

    pictsidhe

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    Construction SPF lumber is mostly spruce in NC. I have seen some really nice batches. The bigger sizes tend to be the best quality, 8x2, sometimes 10x2. The largest construction lumber is often SYP though, which isn't very good for aircraft.
     
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  13. Sep 18, 2018 #13

    MadProfessor8138

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    I thought the Northern white pine was the accepted substitute for spruce not Western white pine.
    Is there a reason you like the Western white pine,Pete Plumb?
    Everything I've read says the Northern is stronger than the Western.

    It's funny that I live in a state that is listed as having Northern white pine growing here but after MANY phone calls today,nobody can supply it.

    Kevin
     
  14. Sep 18, 2018 #14

    proppastie

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    Stupid question...how do you tell the difference?
     
  15. Sep 18, 2018 #15

    MadProfessor8138

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    As far as the SPF and SYP goes.......if you go to Lowes or Home Depot the little white tag stapled to the end of the board will specify which one it is.

    Kevin
     
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  16. Sep 18, 2018 #16

    fly2kads

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    There are several regional forest products trade groups that publish specs for grading. Their members will stamp or tag their products with the species and grade. The one I am familiar with is the Western Wood Products Association, as they have rules covering several woods of interest to me: douglas fir, larch, hemlock, western red cedar, etc. You can probably find at least one trade group for each species of wood you're interested in, and learn how to decode their stamps.
     
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  17. Sep 18, 2018 #17

    pictsidhe

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    If it is there. SYP is a variety of pine, so the tag may say SPF for SYP..
    SYP is heavier and has a much more clearly defined grain. It's also kinda yellow. Spruce is much paler, almost white when fresh.
    I have a 'pair' of loading ramps for my truck. One is spruce, one is SYP. The spruce one is noticeably lighter AND stiffer.
     
  18. Sep 18, 2018 #18

    proppastie

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    SYP Southern Yellow Pine, Spruce-Yellow-Pine,?
     
  19. Sep 18, 2018 #19

    pictsidhe

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    SYP: southern yellow pine. Being a pine, it may be included in SPF: spruce-pine-fir. I confess that I don't pay much attention to the labels...
    If you want to build a plane with bigbox construction lumber, you need to look very, very closely at it. The SYP is easy to spot from the middle of the aisle for me. The small 'nice' PAR wood section is much easier to find decent white pine and poplar. But, no 16' pieces.
     
  20. Sep 19, 2018 #20

    MadProfessor8138

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    Soooo........after much frustration I have a few questions that I need someone to answer.
    I have a building supply company that I have done business with for years which are 10 minutes from me across the bridge into Indiana....wonderful people.
    They carry SPF material and will let me dig through their stock to pick and choose what I want.
    My questions are these.......
    1. How do you identify a spruce board from the rest? Sounds easy but it's not to me. I looked through their stock this morning and the majority of it looked the same,with a few oddball boards here and there.
    2. Is this spruce material adequate to use in plane construction as long as its graded properly? Come to find out their are about 25 different spruce species out there.

    I was going to use white pine but it seems that it's as unavailable as sitka spruce is around here.
    I live in a state that grows northern white pine but I can't get it...yeah,that sounds about right.

    Have I ever mentioned how much I totally hate Kentucky and wish someone would nuke it off the continent?!
    It's impossible to get ANYTHING done in this state !!!!!!!!

    Kevin
     

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