If you are to save much weight, a composite spar with graphite rod caps (Marske Graphlite rods) is probably a good path.Īs someone who is well on his way with a self designed airplane, I urge you to review your goals, the materials you prefer to work in, and the available airplanes that suit your mission and regulatory environment, and then build that airplane to plans. In rag and tube airplanes, the base design is usually pretty hard to beat for weight. If you need to save weight, this is not usually a beneficial scheme. Trouble is that if the graphite is carrying much load, the wood becomes a heavy core. Consider yourselves warned.Ĭlick to expand.We have talked about the wooden spar with carbon reinforcements many times. One stack of light blue insulation board that I got as a gift is "tooling only" for poor adhesion. I have also tested Divinycel - no problems there. I have tested batches of flotation billet and insulation board before making airplane parts with it. If the resin comes off the foam clean anywhere on the test pieces, AVOID THAT FOAM. If it takes parent foam everywhere, good. Silicones and mold waxes that *might* be used in processing extruded foam can cause delamination and then other really-bad-day events.Ī good plan when preparing to use an unknown foam is to build some test pieces, laminate samples with your intended resin and cloth, cure it, post cure it, then peel the lamina from the foam. The issue is that foam has to stay well attached to the fiber-resin facings or it is not supporting the facings against buckling. Insulation board appears to be an unknown. Dow flotation billet (the large cell stuff) as used for airfoil cores was known back when Rutan was selling plans to not use any silicones. Scaling his fixes correctly will require that you know enough about beam design to do your own anyway.ĭoes the Skypup specify insulation board or flotation billet? The difference is significant. Drela's specific beef-ups to make up for his "surprise" failures may or may not be scalable from his RC models to your airplanes. Same thing with Hollmann's early test failures at Lancair. When I read his writeup, I was able to forecast that he was going to have "surprise" failures, which he did. Still very much at the outline design stage.Ĭlick to expand.Trust Drela on structures? Not me and for good reason. I'm also looking at a 3 piece wing, with the joint outboard of the undercarriage mount, to allow the outboards to fold and reduce hangar costs.
#FOAM BOARD AIRFOIL DESIGN FULL#
Full composite spars seem more difficult to build than a wood/carbon composite. My current scheme is a wooden spar with carbon uni reinforced caps, foam ribs and plywood skins, partly for the ease of construction. Is this an appropriate subject for this thread? Should I start a new thread? Is there a text book anyone can recommend? But the other less intuitive load cases, torsion, control surface loads, u/c loads and so on seem much more difficult to estimate. The basic bending & shear cases appear (to me at least) to be straight forward once the n-V diagram (with gust loads) is drawn and a lift distribution assumed. It occurs to me that loads estimation is important in designing an optimised structure and is something of a mystery for me. I need to save some weight to be sure of achieving 300kg TO weight with a useful payload. I'm an aero (handling qualities) guy who moved into autopilots and then systems development, so structures is something I last looked at when I graduated in the mid 80s! I'm now looking at building a 300kg single seater based on an existing wooden design. This is a great thread from my perspective.