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Composite fuselage truss structure design

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jimbox

Member
Joined
Mar 6, 2010
Messages
6
Location
Philadelphia, PA
Hello everyone.
I am a new member. EAA member since 1977. Presented forum talk on sandwich composites at EAA Oshkosh 1988.
I am designing a single place low wing aircraft designed for 60-100 HP. The concept is based on a large-scale electric powered RC model I designed and built/flew in 1996, and a much larger fuselage for a half scale model that did not fly. Both incorporate a composite beam truss structure design that resulted in a light, robust structure.

I am focusing on fuselage structure right now.
The fuselage design has a Warren truss structure utilizing four foam/graphite/e-glass/epoxy composite longerons with a non-load bearing lightweight skin and turtle deck to provide streamlining.
Each longeron is rectangular in shape with a foam core, carbon rods at each corner, a carbon rod warren truss with e-glass/epoxy gussets joining truss to carbon rod caps. E-glass/epoxy covers core and carbon rods. Everything is vacuum bagged.

I am planning to test the column in axial compression up to 4,000 pounds with hopefully no permanent deformation. (This design is a refinement of a column that weighed 509 grams and held a 4,000-pound axial compressive load without buckling.) The test column is 47" long and weighs 13.78 ounces (391 grams).
For comparison, a 1-1/8 inch, .028-wall 4130 Cond N steel tube that weighs 1 pound, 4.64 ounces (586 grams) will begin buckling at relatively low loads.

This prototype longeron design appears to be relatively efficient and more than competitive for strength and weight with a steel tube structure. I can of course resize this basic concept, using larger or smaller rods, changing glass weaves, foam core dimensions, etc. My goal is to give the very slender, light carbon rods the support they need to keep them from buckling while producing a light structure.
Each longeron in the design will be part of a Warren truss aft fuselage structure using similarly designed components.
Have begun construction of test section of fuselage truss structure on which I will test my joint concept between longerons and Warren truss bracing.

Would appreciate your comments. I am a big fan of sandwich structures, and so I am going down a different path here. I think I may be onto something, but am trying not to fall completely in love with the idea—yet.


 
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