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Drag/Anti drag struts

4 posts in this topic

Posted (edited)

Just wondering if any have founds small cracks...not all the way through, but more like the surface of the rounded edge of where the tube has been compressed flat . The manuals states......

STEP 1

Re-inspect all the drag tubes and tip braces . There should be no indication of cracking at any of the bend areas perpendicular to the axis of the tube.

No mention of cracks on the edge of the crimped area on the sides...see very crude drawing.

If it is not a problem....onward I go. This has been found on 3 of the drag tubes....the others are OK. Maybe the drag loads on the wing are not as severe as I am thinking. After all these wings are flying with Jabirus on a few of them. I think the covering helps to also bias against the drag of the wing and help to maintain strength.

Sorry for the strange questions....back to prepping ribs.....

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Edited by Tree top pilot

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Posted

From my Avid Mk-IV manual:

All of the tubes should be inspected for any cracks by carefully observing the areas where the tube has been flattened at the factory. There should be no indication of cracking at any of the bent areas perpendicular to the axis of the tube. Scratches running parallel to the axis of the tube are a result of manufacture and are permissible.

While this does not specifically address cracks in the crimped edges running parallel to the axis of the tube, I do seem to recollect my KF3 manual says these cracks are ok. I think this is normal and you are good to go but perhaps some one else can confirm. Cracks perpendicular to the tube axis at the point of flattening and bending, not safe in any instance.

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Posted

I just want to thank all you guys for helping me out....I am taking notes and making memories.... One more for ya....the pop rivets as supplied, the stainless ones, are they going to hold up to the loads on them? Most of the riveting I have done that involved shear stresses were Cherrymax rivets and the standard bucking block and airhammer type rivets. Just wondering if I need to get a small parcel of Cherrymax for the bulk of the wing structure. Your thoughts here?

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Posted (edited)

Well, I just used the SS rivets supplied. Of course, the drag tube ends are glued as well as riveted, but I also glued gussets between the drag and spar tubes. I figure the epoxy and gussets keep the parts from moving relative to each other (shear) which might weaken the rivet holes. The rivets keep the parts from peeling apart, which would eventually break the epoxy bond. Used together, this combination seems to be sufficiently strong as I've yet to see any reported Avid or Kitfox drag tube failures even without the gussets. I have seen pics where the drag tubes broke someplace other than their end attach points in a crash that totaled the wings. I wouldn't worry too much about the design or SS rivets.

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Edited by dholly

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