Help? Home wing load testing

Discussion in 'Workshop Tips and Secrets / Tools' started by wingtesting, Feb 5, 2009.

Help Support HomeBuiltAirplanes Forum by donating:

  1. May 8, 2009 #21

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,216
    Likes Received:
    463
  2. Oct 17, 2009 #22

    Mac790

    Mac790

    Mac790

    Well-Known Member

    Joined:
    Jun 22, 2008
    Messages:
    1,529
    Likes Received:
    18
    Location:
    Poznan, Poland

    Attached Files:

    • wing.jpg
      wing.jpg
      File size:
      51.1 KB
      Views:
      3,761
    • fuse.jpg
      fuse.jpg
      File size:
      66.4 KB
      Views:
      1,100
    Last edited: Oct 17, 2009
  3. Nov 18, 2009 #23

    skier

    skier

    skier

    Well-Known Member

    Joined:
    Mar 5, 2008
    Messages:
    1,075
    Likes Received:
    327
    Location:
    CT
    I realize that people want to test their aircraft to 150% of limit load, just to be sure it can handle the loads in flight, but is it really a bright idea to be doing this with a structure you will be flying with? When aircraft manufacturers do structural testing, they have a purpose built aircraft for structural testing. Taking the aircraft to high loads multiple times (or even once) could damage the structure enough to where fatigue failure could become an issue.

    Or am I wrong in my assumption that a lot of homebuilders use a wing they're mounting on the plane to test the structure? Do most people build multiple of the same part for testing?
     
  4. Nov 18, 2009 #24

    wsimpso1

    wsimpso1

    wsimpso1

    Well-Known Member

    Joined:
    Oct 19, 2003
    Messages:
    5,627
    Likes Received:
    2,866
    Location:
    Saline Michigan
    Most of us never test. The designer may have tested to failure.

    The biggest reason to test above flight loads is that some parts are not being stressed as they are in flight, so some overload gives comfort that you are not near limits. And those of us that do test probably only go to a proof load a little above max flight loads.

    Fatigue experience says that at 90% of yield stress, fully reversed loading, you will have a life of about 1000 cycles, and life does not get much shorter unless you actually yield the part. At lower stresses, the life increases rapidly. The scales used to plot S-n curves are log stress and log cycles, and you usually get a straight line plotted this way.

    So, your static test is several half-cycles, with the most severe one at maybe 99% of yield (more likely less). You may use up 1/1000th of the life of the part this way... No, I would not be worried if the part comes right back when unloaded to its original position. Now if you see signs of distress, or it has changed shape, that is another deal...

    Billski
     
  5. Nov 18, 2009 #25

    Mac790

    Mac790

    Mac790

    Well-Known Member

    Joined:
    Jun 22, 2008
    Messages:
    1,529
    Likes Received:
    18
    Location:
    Poznan, Poland
    If I'm not mistaken in some European countries, static load test is required for the first example of a particular design, even if it's a proven design for example in the US. It also might be a good idea special for the composite planes, overall "strength" really depends from your technique, of course safety factor for composite structures is 2 instead mentioned by you 1,5 for an aluminum plane.

    Seb
     
  6. Nov 20, 2009 #26

    vortilon

    vortilon

    vortilon

    Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    453
    Likes Received:
    5
    Location:
    Marana AZ USA
    Dumb question here. Do you throw the wing away after the test or do you put it into service? I think manufacturers discard them even if they don't go to failure right?
     
  7. Nov 20, 2009 #27

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,801
    Likes Received:
    133
    Location:
    Western Washington
    It is generally accepted that once you do your static tests that you throw the wing away and yes, that also includes tests to limit load. Ideally you would actually take the wing apart and see what, if any, reactions the internal structure had to the test loads. But regardless whether you had failure or not, none of the components should be put into service.
     
  8. Nov 20, 2009 #28

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    5,992
    Likes Received:
    1,999
    Location:
    Rocky Mountains
    I gotta ask - 12G!?

    4200# is about right for 12 g on a Q rear wing but in the real world you will never come close to that load. Something on the order of 3.5G is all the airframe is capable of developing. Just not enough lift in the canard to do more. I've built one (wing that is, never finished the Q-2) and I doubt you are going to get close to 12G load before the 7 plys of UNI de-laminate from the core. I could be completely wrong, but I wouldn't be standing anywhere near by without some sand bags in front of me :para:

    Please let us know how the testing goes. I'm real interested in the outcome.
     
  9. Nov 20, 2009 #29

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,562
    Likes Received:
    4,584
    Location:
    Fresno, California
    With the OP's location, I suspect this is a college aero class experiment (or senior project) at Cal-Poly SLO.
     
  10. Feb 10, 2010 #30

    Mac790

    Mac790

    Mac790

    Well-Known Member

    Joined:
    Jun 22, 2008
    Messages:
    1,529
    Likes Received:
    18
    Location:
    Poznan, Poland

    Attached Files:

  11. May 7, 2010 #31

    Tom Kay

    Tom Kay

    Tom Kay

    Well-Known Member

    Joined:
    Aug 10, 2007
    Messages:
    398
    Likes Received:
    15
    Location:
    Ottawa Canada
    Hi Guys;

    I'm no ace on wing loading, but generally, shouldn't the cement bags be loaded in a tapered fashion, with most being at the root, and fewer of them toward the tip? Especially if the wing is fairly tapered? This to approximate actual wing loading?

    Tom.
     
  12. Jun 9, 2010 #32

    M61A!

    M61A!

    M61A!

    Member

    Joined:
    Jun 1, 2010
    Messages:
    23
    Likes Received:
    0
    Location:
    QLD, Australia
    I have a little experience in proof loading, generally there are calculations to be made that will tell you exactly where to put the load and how it is distributed. You will need to make a jig to hold the fuselage/wings at appropriate angle to simulate the load correctly. Bags work well, as they spread the load on the skin without damaging it, although I have seen bricks used, neither should be interlocked as this prevents correct load distribution.As long as you wing does not exceed it's limit load and has no permanent set/deformation, with an inspection, it should be fine to fly.
     
  13. Aug 15, 2010 #33

    millerdvr

    millerdvr

    millerdvr

    Active Member

    Joined:
    Aug 14, 2010
    Messages:
    29
    Likes Received:
    1
    Location:
    Missoula, MT
    I don't see much point in building a whole wing, then testing it. it would make more sense to just order a front spar and test the breaking strength or that.
     
  14. Aug 15, 2010 #34

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    5,992
    Likes Received:
    1,999
    Location:
    Rocky Mountains
    There is a lot more to it then just seeing if the spar breaks at a particular load. During a proof load you should also be looking for things like, but not limited to, skin buckling and control system bind. You really need the whole structure:para:
     
  15. Aug 15, 2010 #35

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,738
    Likes Received:
    2,537
    Location:
    Rotterdam, Netherlands
    That's kind of like a guarantee to build infinitely on your established design in most countries... since the airframes have to be tested for each particular aircraft. With a well-designed design (of which another one is tested) I don't see any problem in testing to the limit load?

    As for interesting test reports:
    Jonker Sailplanes

    And also have a look at the flutter part:
    Jonker Sailplanes
     
  16. Aug 17, 2010 #36

    deskpilot

    deskpilot

    deskpilot

    Well-Known Member

    Joined:
    Jun 30, 2009
    Messages:
    1,081
    Likes Received:
    180
    Location:
    Morphett Vale, South Australia. Just south of Adel
    All of this is very interesting but one aspect not covered is the cord wise spread of the load. How much of the surface area is covered, middle third? What area would I have to use on my 'double delta', 'truncated taper' what ever you want to call it.
     
  17. Aug 17, 2010 #37

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,738
    Likes Received:
    2,537
    Location:
    Rotterdam, Netherlands
    It's always an approximation.
    [​IMG]

    Most engineers approximate this by laying all mass roughly around one point (the neutral point, usually 25% chord), also close to the spar.

    On a delta this is a bit harder. I would take 2/3rd of the mass in the first half of the chord and 1/3rd in the last part. Maybe some calculations on the pressure difference the skin sees?
     
  18. Aug 18, 2010 #38

    wsimpso1

    wsimpso1

    wsimpso1

    Well-Known Member

    Joined:
    Oct 19, 2003
    Messages:
    5,627
    Likes Received:
    2,866
    Location:
    Saline Michigan
    Ideally, the process looks like this.

    First step, Calculate your envelope. You need to know your V, Cl, and AOA over the max positive g range.

    Next step, look at the v/V or (v/V)^2 diagram for your airfoil. It will usually be shown for Cl=0 and Cl equals some cruise level. You need to interpolate it to the Cl's that you figured above. The wing load is the difference between (v/V)^2 for the top minus (v/V)^2 for the bottom. The most severe case structurally is the Dive Speed. You may find that the pattern looks a lot like what has already been described here(!). Or you might find that you will do well just to get all of the weight on the wing at all.

    Billski
     
  19. Aug 23, 2010 #39

    danishrehman

    danishrehman

    danishrehman

    Member

    Joined:
    Aug 19, 2010
    Messages:
    10
    Likes Received:
    0
    Location:
    Pakistan
    I m gona ask a stupid question. . So be patient!!

    What if, we do not use sand bags or whiffler tree (beams) and instead use an airbag filled with a pressurized air. I mean its just an idea that is popping up in my mind that calculate the pressure from your loading and then attach a bag shaped like the wing's planform beneath the wing and a rigid support at the other end so that when it would expand, pressure will be applied on the wing's surface.
    As far as I could learn from this thread and some other that finding out the load is not an issue (Please Correct me if I am wrong). Weight of the bird is let's say 500kg. You ve ultimate load factor of 2gs, apply a safety factor of 1.5 to it and the net '+y' g loading will be 3gs. Now assuming that all the weight will be supported by the wing's lift, So L=500*10*3=15000N. For single wing it becomes 7500N.
    As force varies across the span due to change in planform. If a constant pressure of (7500/Planform area) Pa is applied from the bottom then force will automatically be distributed like max. at root and min at the tip.
    Can this be a wing loading test?? :s
     
  20. Aug 23, 2010 #40

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,738
    Likes Received:
    2,537
    Location:
    Rotterdam, Netherlands
    Interesting remarks. I see a couple of problems:
    *Even distribution of the force. Since you use a highly-pressurized airbag a slight shift of it might torsion away your whole wing.
    *Even distribution of spanwise force. While bending of the wing goes with the square of the span, loading usually approaches an elliptic function of the span. Since those 2 aren't proportional I guess it's quite hard to achieve a realistic lift/force distribution.
     

Share This Page

arrow_white