Wing weight

Discussion in 'General Experimental Aviation Questions' started by Dave Hodges, May 17, 2019.

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  1. May 24, 2019 #21

    Hot Wings

    Hot Wings

    Hot Wings

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    Maybe not all that hard. A light (454) part 103 with just enough wing to be legal at 80 mph = a little over 6G .... with a very efficient wing.

    Factor in the wing mass, a real world 3D CL and weight above the FAA minimum of 454# and the forces on the center section are probably on the order of 4G times the gross.

    Add the 1.5 FOS............
     
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  2. May 25, 2019 #22

    pictsidhe

    pictsidhe

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    VB, I ballparked an aluminium centre section spar for my project a month or so ago. I looked at strip caps with a sheet web on a 12" deep spar. The sheet web needed a lot of stiffening to prevent shear buckling, so I have ditched it. You may want to investigate that first... Plan B is to use strip caps riveted to a C channel. I then build up a truss web using the channel as one big gusset. The C channel also stabilises the strip cap vertically.
    I haven't done numbers on plan B yet.
    I have found affordable 7075 strip in 6' lengths, which is all I need with my foldable or removeable wings. That saves several lb over 6061 caps. I'll have to form the C channel from 7075 sheet. I'll probably use 6061 tubing as stronger tubing is significantly pricier.
    My centre section will be a lot like the full size Hurricane, but in aluminium. I'm still moving things around, so it isn't designed yet.
     
  3. Jun 17, 2019 #23

    Dave Hodges

    Dave Hodges

    Dave Hodges

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    Structural components fail due to buckling. The formulas for determining strength of columns are unreliable. I usually make a mock-up and test it to destruction. I wish you well. It's good to see a true experimenter.
     
  4. Jun 17, 2019 #24

    BJC

    BJC

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    Some do.
    Really? Which ones are unreliable?


    BJC
     
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  5. Jun 17, 2019 #25

    Dave Hodges

    Dave Hodges

    Dave Hodges

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    The ones you trust your life to. Here's where you can get started finding out about it. I made these videos just for people like you:

     
  6. Jun 17, 2019 #26

    BJC

    BJC

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    People like me? What does that mean?


    BJC
     
  7. Jun 17, 2019 #27

    wsimpso1

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    I watched your video, saw that you had buckled a truss element, and the video ended with you talking about the math for Euler's method. With you citing the unreliability of column failure prediction, I was expecting a refutation of Euler's method, but saw none. I am still curious about which relationships are unreliable...

    If you witnessed failure at lower loads than you might have forecast using Euler's method, have you eliminated other issues that are also known to trip an early failure of elements in compression? Among others there is wall crippling, section distortion, curvature in the element, and corrosion and/or impact damage to the tube. These known reducers of column strength would have to have been eliminated to refute standard methods for predicting these failures...

    Billski
     
  8. Jun 17, 2019 #28

    saini flyer

    saini flyer

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    Each metal wing of RV12 ELSA is 88lbs for a total of 176 lbs and a gross weight of 1320 lbs.
    This is ~13% of gross........ pretty good for a cantilevered and sailplane style removable wing!
     
  9. Jun 17, 2019 #29

    Dave Hodges

    Dave Hodges

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    People who want to know the right answers. That's what you expect when you ask me a question, isn't it?
     
  10. Jun 17, 2019 #30

    Dave Hodges

    Dave Hodges

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    That was part 1 of the Columns section. Here in part 9 we see that the assakkaf.com formula was closest to the actual results of an experiment. The Euler and Cornell calculator were also compared. Different formulas give far different answers. That's why I build mock-ups.

     
  11. Jun 17, 2019 #31

    BJC

    BJC

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    I expected you to answer my question. Still waiting.


    BJC
     
  12. Jun 17, 2019 #32

    Dave Hodges

    Dave Hodges

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    Did you see the part 9 video? The Euler equation predicted more than twice what the assakkaf.com equation predicted. My empirical testing agreed with the assakkaf.com equation. When several formulas give varying predictions, at best, one will be right and the others will give you a structure that is either too heavy or too weak.
     
  13. Jun 17, 2019 #33

    pictsidhe

    pictsidhe

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    Do you have a citation for those of us who don't like sitting through videos? I had a look around assakkaf.com but couldn't find anything on buckling. I'm with Billski on this, if Euler gave incorrect answers, you gave it incorrect inputs.
     
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  14. Jun 18, 2019 #34

    Mad MAC

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    Not noted so far is that Euler as applied to column buckling applies to a narrow range of load cases / geometry. Beam columns tended to far more common and are often in-correctly analysed as column buckling problem.
     
  15. Jun 18, 2019 #35

    Dave Hodges

    Dave Hodges

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  16. Jun 18, 2019 #36

    Dave Hodges

    Dave Hodges

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  17. Jun 18, 2019 #37

    Dave Hodges

    Dave Hodges

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  18. Jun 18, 2019 #38

    Dave Hodges

    Dave Hodges

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  19. Jun 18, 2019 #39

    Dave Hodges

    Dave Hodges

    Dave Hodges

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    I wasn't allowed to upload the whole lesson. The last page shows how Euler's equation gives 2,650 pounds for the strength of a column that only withstood 1,022 pounds. It was determined on page 19 of this lesson that the radius of gyration of the failed component of my mock-up tailboom is 0.0995 inch. Its cross-sectional area is 0.0382 inches∆2.
     
  20. Jun 18, 2019 #40

    Dave Hodges

    Dave Hodges

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    I'll be glad to email the entire 26 pages of this lesson to anyone who can't stand to just watch the videos instead. It details how the cross-sectional area of the test column was determined and how the radius of gyration was determined. Euler's equation may be fine for big beams. But you better put more confidence in proven mock-up testing for smaller cross-sections.
     

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