+ Reply to Thread
Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 41
Like Tree7Likes

Thread: sailplane spar joining methods

  1. #16
    Registered User handprop's Avatar
    Join Date
    Apr 2009
    Location
    wisconsin
    Posts
    158

    Re: sailplane spar joining methods

    Thanks Norman, I see what your saying.

    Now that I think about it, using no pins in the spar results in the box taking the stress whereas if overlapped and fastened, the loads are more concentrated into the spars themselves.

    Hmmm.... a lot to think about here.

    Mike
    Where am I? — Charles Lindbergh, upon arrival in Paris.

  2. #17
    Registered User Norman's Avatar
    Join Date
    Nov 2003
    Location
    Grand Junction, Colorado
    Posts
    1,877

    Re: sailplane spar joining methods

    Quote Originally Posted by George Sychrovsky View Post
    That is not true
    Thanks for the link. Another page on that site shows more pictures of the spar layup.


    Notice that I said "or nearly so". Ir27's drawing looked like it had too much taper to me. Structurally you don't really gain much, if anything, by tapering the root end of the spar but it does complicate the mold so if you don't have to why bother. Now bending the bottom cap would allow you to set a dihedral angle so that would be a good reason for taper but just a few degrees.
    Geek1945 likes this.
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

  3. #18
    Registered User
    Join Date
    Nov 2007
    Posts
    886

    Re: sailplane spar joining methods

    That picture was just conceptual. Th taper merely saves you some weight, I think, and some expensive material, perhaps.

    Just for yucks, I ran the crippled FEA that goes with the CAD, and it showed the max. stress down near the base of the stub. So if the taper is excessive, it's not by much.

    The FEA had some simplifying assumptions that make it less than definitive.
    Quote Originally Posted by Norman View Post
    Thanks for the link. Another page on that site shows more pictures of the spar layup.


    Notice that I said "or nearly so". Ir27's drawing looked like it had too much taper to me. Structurally you don't really gain much, if anything, by tapering the root end of the spar but it does complicate the mold so if you don't have to why bother. Now bending the bottom cap would allow you to set a dihedral angle so that would be a good reason for taper but just a few degrees.

  4. #19
    Registered User BBerson's Avatar
    Join Date
    Dec 2007
    Location
    Port Townsend WA
    Posts
    4,690

    Re: sailplane spar joining methods

    Here is a G109 motorglider spar stub photo.
    The Schweizer 1-26 or 1-23 is worth looking at for a metal spar stub end.
    BB
    Attached Thumbnails Attached Thumbnails sailplane spar joining methods-img_0107.jpg  

  5. #20
    Registered User handprop's Avatar
    Join Date
    Apr 2009
    Location
    wisconsin
    Posts
    158

    Re: sailplane spar joining methods

    The photos and links you guys posted are interesting. Here are two photos of a glider spar and pocket I found so far. Thanks for the tip BBerson. Mike
    Attached Thumbnails Attached Thumbnails sailplane spar joining methods-sch-spar1.jpg   sailplane spar joining methods-sch-spar-pocket1.jpg  
    Where am I? — Charles Lindbergh, upon arrival in Paris.

  6. #21
    Registered User BBerson's Avatar
    Join Date
    Dec 2007
    Location
    Port Townsend WA
    Posts
    4,690

    Re: sailplane spar joining methods

    That looks like a late model metal skinned Schweizer 1-26 wing photo. To get a good look, just help somebody assemble one sometime at the airport and see how it works. The Pilatus B4 metal glider has a real neat wing spar attach also.
    BB

  7. #22
    Registered User handprop's Avatar
    Join Date
    Apr 2009
    Location
    wisconsin
    Posts
    158

    Re: sailplane spar joining methods

    Thanks BB, I'm going to try and look up the Pilatus tonight and see what I come up with. There are some guys I know with gliders so I should be able to get a first hand look.

    Mike
    Where am I? — Charles Lindbergh, upon arrival in Paris.

  8. #23
    Registered User ultralajt's Avatar
    Join Date
    May 2009
    Location
    Slovenia
    Posts
    1,130

    Re: sailplane spar joining methods

    Pilatus B-4 wing yoint looks pretty similar as you show on your two photos above. Maybe a bit different look but the same principe.

    Mitja
    ____________________
    Never try, never fail.
    Ultralajt Website

  9. #24
    Banned George Sychrovsky's Avatar
    Join Date
    Jan 2003
    Location
    Shirley airport MA
    Posts
    450

    Re: sailplane spar joining methods

    This is what I’m talking about. Contrary to your statement “They should be full depth (or nearly so) all the way to the end” they taper down almost to one third, from 6 inches to 21/4 to be exact.
    Attached Thumbnails Attached Thumbnails sailplane spar joining methods-im000806.jpg  

  10. #25
    Registered User Norman's Avatar
    Join Date
    Nov 2003
    Location
    Grand Junction, Colorado
    Posts
    1,877

    Re: sailplane spar joining methods

    OK, George, it can be done either way. I would still rather keep the extreme fibers as far away from each other as possible.
    Geek1945 likes this.
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

  11. #26
    Registered User ultralajt's Avatar
    Join Date
    May 2009
    Location
    Slovenia
    Posts
    1,130

    Re: sailplane spar joining methods

    Well, I find the wing root atachment to the fuselage of Pilatus B4.

    Mitja
    Attached Thumbnails Attached Thumbnails sailplane spar joining methods-pilatus-b-4-wing-root.jpg  
    ____________________
    Never try, never fail.
    Ultralajt Website

  12. #27
    Super Moderator orion's Avatar
    Join Date
    Mar 2003
    Location
    Western Washington
    Posts
    5,945

    Re: sailplane spar joining methods

    Quote Originally Posted by Norman View Post
    OK, George, it can be done either way. I would still rather keep the extreme fibers as far away from each other as possible.
    You really don't need to nor, in some instances, is it even advised. If you draw yourself a free-body diagram of the loads and the resolution of same into the mounting pins, what you'll find is that the pin at the end is really only in shear. In other words, the only load on the inner-most pin is a vertical in-plane shear (no bending). As such, the material surrounding the pin must be able to take the localized vertical load and of course the resultant bearing stress caused by the pin and its bushing.

    Moving outboard from that "base" mounting point you then have the vertical shear load acting further and further away from the area of interest - as such, the vertical shear load times the distance then equals a moment and it is for that moment that you're trying to increase the distance between the spar caps. For that reason can the caps can be tapered down at the end (there's no moment there).

    And the maximum strength needs to be at the point of the other pin since that immediate area sees the maximum root bending moment of the wing.

    You can keep the caps apart as you say, but then you also need to design in the proper shear mechanism into the web since that too is a potential failure source.

    There's a few design variables to balance here so the end configuration will depend on a few specifics of the actual layout. For instance, if you have a very high bending moment it is unlikely that you want to put a kink in the spar cap that's usually under compression. But in an aerobatic application it may be beneficial to avoid the kink in both caps. But if you have a kink, then you also need to stabilize the cap there for the resultant out of plane load. This means more external structure capable of handling the proper amount of shear.

    Choices, choices.....
    "To live is to learn; to learn is to live" (author unknown)

  13. #28
    Registered User planebuilder's Avatar
    Join Date
    Jun 2010
    Location
    Midlothian Texas
    Posts
    228

    Re: sailplane spar joining methods

    So the important thing to remember here is there must be a complete understanding of all the wing reactions. The design of this sailplane wing root is similar to the ASW 28. Notice the steel pin at the nose of the root rib? There is also a similar pin near the trailing edge. This wing joint is designed to react wing bending internally by pinning both spars together. This joint is made independant of the fuselage, in other words there is not a common bulkhead that this pin would pass through. The other wing load reactions that need to be considered are Vert and Fore/Aft shear, drag and accelerated stall condition. All of these latter conditions are reacted through the two wing root pins. Each pin has a receptor socket in the fuselage root rib, these sockets each have a compression tube that attaches to its opposite mate on the other side of the fuselage. All of the sockets are capable of reacting vert and fwd/aft shear. The drag and the accelerated lift loads are reacted as a couple between these two sockets. Look at the zero g dive condition, there is a drag load that is trying to bent the wing aft. This load is reacted by placing the rear sockets in compression. The aft shear, is again reacted by both pins and sockets. The much heaveir load that needs to be accounted for and reacted is due to the acceperated stall condition. During a sharp pull up at V Max, the wing lift vector changes direction and a componant of this vector is reacted by the wing trying to bend FWD, this load and shear again is reacted by placing the FWD pin in compression and again, both FWD and AFT pins react the shear. When you add self connecting controls, the brilliance of this design is really apparent. I really like this design because it only requires two pins to connect both wings. I am in the process of redesigning my Robin Robin Ultralight wing to this configuration. I am using a blade/fork design rather than two tapered spars. The redesign also allows me to correct an oversight on the prototype wing and that is the lack of a wing walk. I have to reinforce the root ribs to the point where a pilot walking on them is not a design load condition
    Last edited by planebuilder; March 13th, 2011 at 04:39 AM.
    Geek1945 likes this.

  14. #29
    Registered User Lucrum's Avatar
    Join Date
    Jun 2008
    Location
    Canton, GA
    Posts
    585

    Re: sailplane spar joining methods

    sailplane spar joining methods-pilatus-b-4-wing-root.jpg



    I am considering a wing attach method similar to the above diagram. Except the spar and caps will be one continuous piece (laminated wood) and the pins going through the upper and lower caps would 1) be in the same vertical plane and 2) would be located at the side of the fuselage. I had planned on a, as yet to be determined, welded and or bolted steel truss of sorts to pin the wing to.

    1) Am I in LA LA land? IOW would this be a generally accepted/satisfactory method?
    2) Is there a reason/benefit to having the upper and lower pins in different vertical planes, as in the diagram?
    3) I'm assuming this arrangement would be considered a "Pinned" wing?

  15. #30
    Moderator autoreply's Avatar
    Join Date
    Jul 2009
    Location
    Leiden, Netherlands
    Posts
    8,381

    Re: sailplane spar joining methods

    Quote Originally Posted by Lucrum View Post
    I am considering a wing attach method similar to the above diagram. Except the spar and caps will be one continuous piece (laminated wood) and the pins going through the upper and lower caps would 1) be in the same vertical plane and 2) would be located at the side of the fuselage. I had planned on a, as yet to be determined, welded and or bolted steel truss of sorts to pin the wing to.

    1) Am I in LA LA land? IOW would this be a generally accepted/satisfactory method?
    Everything can be made to work.
    2) Is there a reason/benefit to having the upper and lower pins in different vertical planes, as in the diagram?
    Not that I know, but there're a couple of good reasons not to do this. The bending moments are reacted to the fuselage in an almost scary way. Search for the Ka6 and Ka2, ASK 13 gliders. If I understand you correctly they have exactly the same method which works fine (same materials too).

    Why the asymetrical idea (pins on the side of the fuselage)?
    Kennis vermenigvuldig je door het te delen.
    (You multiply knowledge by dividing it)

+ Reply to Thread
Page 2 of 3 FirstFirst 123 LastLast

Similar Threads

  1. Ultralight Carbon Spar...
    By Senna in forum Composites
    Replies: 24
    Last Post: May 28th, 2013, 06:18 AM
  2. Pultruded Carbon Rod as Spar Material
    By Northman in forum Composites
    Replies: 31
    Last Post: May 3rd, 2011, 07:59 PM
  3. Joining wing spar sections
    By TravisD in forum Sheet Metal
    Replies: 14
    Last Post: July 9th, 2009, 12:30 PM
  4. wing spar design
    By jany77 in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 10
    Last Post: July 21st, 2008, 08:24 AM
  5. Spar Stiffner.... attn: Orion
    By BD5builder in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 9
    Last Post: November 17th, 2005, 11:57 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts