At 05:25 PM 9/27/2015, you wrote: > Larry Flesner wrote; "adding carbon fiber > to wood components can actually make them > weaker due to the different stiffness > characteristics of the two materials." We use > Styrofoam under fiberglass. ? How does this > work? ? Could I use 1/8 inch plywood > sandwiched between fiberglass for something > like extending my rudder or elevator? Joe Nunley ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I could have been more clear on the example. I'm speaking of when one material ( wood or any other material) is designed to be the primary load carrying structure and we hope to "beef it up" by adding a material with other strength characteristics. You can end up shifting the load path in the structure to the point of making it weaker, as in Jeff's prop example. In the case of foam under glass, the foam is not the load carrying material , the glass is. The foam simply maintains the shape of the load path which is in the glass and is primarily in tension. The glass has very little compression strength. Even in a very strong sandwich construction the foam does not carry tensions loads. In the case of extending your rudder or elevator, most are extended by making the spar (be it spruce, ply, or a combination) longer and using foam and glass to shape, as in the original construction of the KR. Be careful how you extend the spars, even of the same material, so you don't create any stress points. Gluing on additional length with a patch can cause a stress point at the patch, if not done properly. Larry Flesner
