I have lurked here for years and finally feel the need to ask everyone's opinion of my project. I own the Jodel D-18 and D-9 plans and am a long time admirer of the elegance of the big box spar that handles all the torsion, air, and landing loads. It is an enigmatic single entity that everything hangs on. I believe that I can make a carbon fiber and Graphflite spar the does the same thing and is lighter. Delemontez acknowledged this in a recent interview. What He DIDN'T say, was whether he believed the the 200mm by 167mm box spar was the optimized format for composite construction.
My thinking was to use thin foam sandwich for the shear web with multiple layers inside and out all wrapping around the pultrusion stacks at the top and bottom. This is laid up in a female Marske type mold and then assembled with flanged diaphragms at each rib and thin foam sandwich tops and bottoms. The foam in the four shear webs would be missing at the intersection of the diaphragm flanges. Fluent large radii for the rods into the dihedral section. Two bolts into the fuselage with hard points and phenolic tube pass-throughs. Gear attachment similar to the original with concessions to appropriate hard point design. No D tube, just enough wrap to start the air around the 43015 airfoil and the whole enchilada Oracover wrapped.
I have learned from my reading here, that simply substituting carbon for the original material in a proven design is often inappropriate. That composite deserves its own clean sheet of paper. My question is whether this applies in this case. Are the dimensions of this spar appropriate for reacting torsional and flight loads when switching to composites or is there a better approach.
Thoughts?
My thinking was to use thin foam sandwich for the shear web with multiple layers inside and out all wrapping around the pultrusion stacks at the top and bottom. This is laid up in a female Marske type mold and then assembled with flanged diaphragms at each rib and thin foam sandwich tops and bottoms. The foam in the four shear webs would be missing at the intersection of the diaphragm flanges. Fluent large radii for the rods into the dihedral section. Two bolts into the fuselage with hard points and phenolic tube pass-throughs. Gear attachment similar to the original with concessions to appropriate hard point design. No D tube, just enough wrap to start the air around the 43015 airfoil and the whole enchilada Oracover wrapped.
I have learned from my reading here, that simply substituting carbon for the original material in a proven design is often inappropriate. That composite deserves its own clean sheet of paper. My question is whether this applies in this case. Are the dimensions of this spar appropriate for reacting torsional and flight loads when switching to composites or is there a better approach.
Thoughts?
