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hershey bar wings

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Posted

Good Afternoon,

I just damaged my fiberglass wing tip on the original Avid C wing.  I want to square the wing tips and install an air dam.  Wondering if you guys know of any pre-made kits for that?  How should I go about this?  Also what is the maximum safe length I can extend from existing wing spar.

Thanks

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Posted

I have had a hell of a time trying to find the original HH spar material.  I would not have a problem using the kitfox spars (.063" tubing) and splicing on 18" and squaring the tips.  Most of the forces are applied at the strut fitting and wing root and very little force at the tip.  Adding length to the tips with wings that have too much washout in them anyway will really only add to the problem though in my eyes.  If I was you I would just square off the tips and call it good on your bird or have someone do the glass work to fix what you have.  Its pretty easy to shape foam and make a new tip or repair the one you have

:BC:

 

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Posted (edited)

If you look at the picture of the wing sandbag load test in the original brochure, you'll see that the cantelevered part of the wing outboard of the strut attachment shows the greatest bending deflection, and clearly the highest spar-bending stress is right at the strut attachment.  If you have the wooden "spar stiffeners"  I wouldn't extend the span, since these only prevent the spar tube from crimp failure.  If you have the aluminum tube internal stiffeners with the vertical web, you have a spar stiffener and strengthener, so should be able to carry more bending load.  In this latter case, by how much you can safely extend the span should be the subject of an engineering stress analysis.  With an extended span, maximum loads will be higher in other places in the airframe as well.  To first order, the max bending moment (and bending stress) at the strut attachment point varies as the cantelevered span squared.

Edited by Turbo

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Posted

Didn't Chris B have extended wings on his Avid plus, and had to shorten them because of binding in the flaperons?  On the other hand, seems that Suberavid had longer wings as well, and didn't have binding.  Wonder what the difference was?? JImChuk

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Posted

On Randys wings he moved the strut attach point further out and I welded up new struts for him to make them longer.  He also increased the size of the spar stiffeners if I remember correctly.

:BC: 

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Posted

Leni is right, when Chris described his problems I was still building my extended wings, so I extended the lift struts out an additional bay and increased the spar insert from 18" to 36" by laminating an 18" microlam section to a 36" microlam section and then laminated and riveted 1/8 X 3/4 aluminum strips along the top and bottom of the 36" section to make a composite I beam out of it.  I don't have any problem with the wings or flaperons flexing too much thanks to Chris posting his issues with his extended wings.

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