fiberglass mesh in foam wings

[Rcmaster199 at aol.com]

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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