Wingtip flexing

[Electrogunner]

I finished one of my wingtips and was a little concerned about the flexibility of the large surface. I could see a flutter possibility there ie: oil canning type action. Has anyone added support inside via maybe glassing some foam ribs in maybe? Thoughts?

[ppilotmike]

I have seen some people's build logs where they install foam ribs to strengthen the FG tips. However, it seems like most were doing something else too, like installing auxiliary fuel tanks or something. I did not install anything and my tips seem fine. Check with Vans, but I don't think a little stiffening would hurt.

[erich weaver]

I have a -7A but had the same concern, as the tips are pretty flimsy and folks walking by often put a hand on the wing tip, resulting in oil-canning and hairline paint cracks. I removed the wing tips and applied a single ply of 8.8 oz bidirectional fiberglass in the area of most concern. Worked great at improving the stiffness; wish I had done it sooner.

erich

[wera710]

By all means, reinforce this area. My wing tip top is cracked from someone leaning on it at an airshows. Its gotten worse once started, by flight loads. Been waiting for warmer weather to fix. My buddy reinforced his on his initial build and his does not suffer the oil canning effect. One hopes some schmuck at an airshow will not lean their fat appendages on it hard enough to crack like mine.

[BillL]

You can use 2mm Soric, a core material with a layer of 8 oz cloth over top. After sanding, just wet the inside lay the soric on, and cover with pre wet cloth. It is best to overlap an inch w/o the core, but I tested pieces that indicated little structural benefit. Make a test piece using your process first. Let me know if you need more details.

The gel coat is about half of the thickness of the 7-8 tips, don't know about the 10. quite fragile.

Use the link above, and sign up at fiberglass and you will get more discounts. They need them.

It will reduce deflection by about 8x for the same load.

Edit: Here is the test article with the 2mm core. The test piece without the core touched the bench with the same weight.

[Dbro172]

I never thought of doing the wing tips but i did reinforce the inside of my wheel pants and filtered air box with additional layers of epoxy, basically to fill in the weave until it was smooth.

[wirejock]

There's a great set of tips in the "Articles" section.
Opening VAF page.
Go to the left column of links.
Click on "Articles"
Download all the "Tips for Tips"

[Carl Froehlich]

Originally Posted by Dbro172

I never thought of doing the wing tips but i did reinforce the inside of my wheel pants and filtered air box with additional layers of epoxy, basically to fill in the weave until it was smooth.

Not to flame, but epoxy alone adds no strength, just weight. If you just want to fill in weave, use micro. If you want to reinforce, add glass.

Carl

[Kyle Boatright]

Originally Posted by Electrogunner

I finished one of my wingtips and was a little concerned about the flexibility of the large surface. I could see a flutter possibility there ie: oil canning type action. Has anyone added support inside via maybe glassing some foam ribs in maybe? Thoughts?

Have you screwed it to the wing? IMO, oil canning isn't a worry with it attached. The convex shape helps.

[Electrogunner]

Originally Posted by Kyle Boatright

Have you screwed it to the wing? IMO, oil canning isn't a worry with it attached. The convex shape helps.

It is attached with hinges. Per the advice I think I will do a layup on the inside across the widest area to stiffen it up a bit. Thanks all for the advice and ideas.