fiberglass mesh in foam wings

[Wayne Galligan]

ED,

I can send you some photo's of how I do it when I get home tonight.
The spars, whether they are c.f  or glass, do provide a definite increase in strength.   It is important to have the upper and lower spars directly in line with each other top and bottom.   I also tie the aileron box together with a square of thin c.f. between the forward and aft spar top and bottom with negligible weight gain.    This has little effect on raising the balsa and what it does can be sanded smooth.  I use urethane glue and lay up the c.f. strips with the sheeting and cores at one time.  The urethane works great and your wing will be plenty strong.   There are several methods of sheeting and I am sure they all have their good points.

Wayne G.
  ----- Original Message ----- 
  From: Ed Alt 
  To: discussion at nsrca.org 
  Sent: Tuesday, December 21, 2004 6:39 AM
  Subject: fiberglass mesh in foam wings


  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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