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  1. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    That's interesting regarding the phenolic bushings to increase the bearing load. Thats's my limiting factor as well given the bearing load de-rating due to the length/dia ratio of the strap bolts. On the KR2 newsletter archive I came across a post from someone that had done something similar but...
  2. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    Thanks Heliano, Yes galvanic corrosion was one of my concerns. That was what initially made me wonder if turned 7075 end threaded studs as strap mounting bolts along with 7075 straps might be a good solution, although you still have the problem if the strap join bolts are steel of course. Noted...
  3. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    In your designs have you used any hardwood or alu bushes around the strap mounting bolts or did you just go for bare AN bolts through the capstrips?
  4. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    Ah maybe there’s been a misunderstanding then. I probably should have made it clearer in my earlier post. For the aluminium based design, I was only proposing that the straps and the strap mounting bolts (that mount the strap to the wooden spar cap) be aluminium, the joining bolts that bolt the...
  5. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    Ok so Billski's comments prompted me to re-visit my spreadsheet with the approximate values for a KR2 main spar as a sanity check. Note that these are based on some simplifications, not Schrenk, not using MOI, etc and apologies for any errors or omissions. Some values are approximate but should...
  6. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    I hear you and it scares me too! What started off as a "I wonder why I can't do this" has led me down an interesting rat hole but it's probably best to revert to a more conventional solution.
  7. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    Billski, I take your points regarding the fasteners and I certainly want there to be a considerable safety margin. In my example that equates to: 43000/23000 = 1.87 Safety Factor @ ultimate (compression failure at upper surface of spar assuming ultimate compressive strength of spruce @ 4700psi...
  8. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    OK so I've made some progress on this. I've done a spar stress analysis based on the Schrenk approximation. Verifed my calcs against a known good example and am confident that the spar loads are reasonable. From there I've done a stress analysis of proposed wing attach fittings. The dimensions...
  9. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    Those examples were exactly what I was looking for, thank you. That KR-2s solution is the first one I’ve seen where the upper and lower tie bars are joined together. I like the simplicity and the assuredness of alignment between the two it provides. I take your point Hot Wings regarding the...
  10. buckie555

    3 Piece Box Spar Wing Modification For Single Seater SSDR

    I'm in the process of building a wood and fabric single seater of an established design that currently has a 1 piece cantilevered wing of box spar contruction. I am keen to modify this to be a 3 piece construction with a fixed centre section and two outboard sections, each approximately 2.5m...
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