fiberglass mesh in foam wings

Tue Dec 21 06:06:01 AKST 2004

What is the balsa density you use?

Rcmaster199 at aol.com wrote:The mesh they recommend is the wallboard seam sealer/reinforcer material. The problem I have with this type material is in the fact that it's pre cured and will not conform very well when compessed using standard technique. If you have access to a vacuum bag set-up, thats a different story. 

Any epoxy or other glue used will not penetrate and wet this stuff and you may wind up using too much glue thinking it isn't secure.Material sounds good in theory but not as good in practice.  Sanding a groove into the foam is another solution, but to me, an undesireable one. A better solution is to use 2-3 oz glass cloth strips taken out 2/3rds span, starting at the root. you can squeegee as much epoxy as you can and still have enough bond

I use minimal glass under the skins of my wings, in areas of high stress. EG- I use short subspars to secure the tube socket and extend these 3" past the end of the socket; a 4" circular piece of glass is used around the end of the sub spars. Subspar material  is simple 1/8" medium balsa pro-bonded in place. It starts at the top and bottom panel surfaces, stops at the socket. The servo cut out and aileron cut out are well within this area so the stress risers induced by the cutouts are better distributed. I also extend the aileron cutout facing in the wing beyond the root of the cut out, to better disrtibute stress at the wing-aileron juncture. Hope this helps

MattK

In a message dated 12/21/2004 7:47:01 AM Eastern Standard Time, Ed_Alt at hotmail.com writes:
I'm getting ready to sheet a pair of Temptation wings and have questions about using the fiberglass screen mesh reinforcement strips they call for.  First, how necessary is it to even use any?  I can see where it obviously adds strength and stiffness in those sections directly under the mesh, but at the same time, it will also create a raised-up section of sheeting directly adjacent to the mesh strip.  It seems possible that there would be no bonding of sheeting to foam for about 1/4" to 1/2" wide all along those seems, at least not if a thin layer of epoxy is used.  It also seems that at the point where the sheeting does begin to bond with the foam again, it would be subject to shearing forces that might tend to pop the foam beads out over time due to bending loads on the panel.  Maybe not? I have no experience with this method, so it's all speculation.  It seems that a fairly heavy application of epoxy would be needed to bond foam to mesh, mesh to sheeting.  Is it possible that the
 same or better strength result could be accomplished with a slightly heavier wood selection and still be as light or lighter than adding mesh and extra glue?

Asuming the mesh is really necessary:  The 2nd question is about the adhesive to use if the mesh is used.  I normally use either Pro Bond or Elmers polyurethane glue, which does a terrific job of bonding several bead layers deep into the core.  I think it probably stiffens the structure alot as a result.  However, it's not clear to me if this would be a good adhesive with the mesh applied.  In theory, it would do a good job of filling that gap I'm worried about along the mesh edges.  Has anyone tried this and are you happy with the results?

The last question is about how far to run the aft reinforcement strip.  Do you really need to run it all the way to the tip?  At some point, you really get diminishing returns as you get further out in the panel. Sorry for so many questions!

Ed

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