Hi Paul

Another suggestion of a nice product that can be used for the I-beam
construction as well as for the spar

The attached photos are for two cool products made by nida-core

These are foam products one really dense and the second a little less
dense and less stiff

What's neat about this core material is that they have glass fibers
going though it and on the sides. As the second photo shows, the glass
can be pulled back a bit so you can cut the foam back such that you can
wrap the glass on all sides (double thick on the edges which is like
instant reinforcement

For the ribs I would first cut the airfoil shape in the foam with the
glass sides extending 2 or 3 inches beyond the foam

Then light epoxy the sides of the ribs but only to an inch away from the
edges and allow to harden

Then when you are ready to add the skin, on the wing, you epoxy the edge
(i.e. The last inch of the airfoil) plus the edge facing the skin (it
will be double layer since you have fiber matting on both sides) and
then put the skin on

I included the product name and company address. They used to be super
responsive but a few years ago were bought out by 3M so may be harder to
reach now

I believe the above described method will result in a super strong light
weight structure (caveat : I never tested this but have good confidence
in it). What this combo enables is the spreading of the forces across
the entire rib all the way to the bottom of the rib as well as both sides

Ps if someone wants to partner on this and pay for materials. I am
willing to make a few I beams and ribs over a couple of weekends as time
allows

Simon Saba

Do you think the foam would be affected by gasoline as in a wet wing?

What does it cost?


Paul Lamar


Not sure about the wet resistance to gasoline.

Regarding cost. If memory serves me right, it was about $200 to $300 per 4 x 8 ft sheet but that was 5 years ago before NIDA was acquired by 3M. 3M is an amazing company with top of the line products, but they always get a premium for their products. I would not be surprised if the price increased 2 or 3X after the acquisition. Still I am guessing only 3 sheets would be needed so it should be reasonable even if the price shot up drastically

In any case, this would not be difficult to replicate, using foam, chopped strand matting (can be S glass or carbon fiber) and some 3K or 12K carbon fiber string

All the materials for making your own should be readily available (try www.fibreglast.com) <http://www.fibreglast.com%29/>  or Tap Plastics (Not sure you have Tap Plastics stores in your neck of the woods, up here there are several walk-in stores). I am sure Tap Plastics can order whatever you need if they don't have it on the shelf.

Regards
Simon Saba

The ribs are not highly stressed. Consequently they are rarely heavy.
The wing skin provides most of the cap material  for the rib beam (if you will).
The rib itself supplies mostly the shear material

What is most important is to make them rapidly.

The other factor is one must be able to make the shear connection
to the skin. That implies a significant stiffness in the rib flanges.
If the glass is bent over the top of a one inch thick rib that is sufficient.
An epoxy bond is 3000  pounds PIS.

Paul Lamar

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