Table of Contents

Materials and Structure




Humanpowered-Plane Spars

The diagram shows two spar structures in a human-powered plane. The tailplane is carried on a spar cantilevered from the cockpit area, and the wing-spars define the wing structure. Both these components must be resistant to bending and torsional deflection if the aerodynamic integrity of the plane is to be preserved. The shape independent performance index required is
(E/r2), as minimizing bending is the goal. Candidate materials are wood (spruce), aluminum alloy tubing, and carbon fiber reinforced polymer (CFRP). The order represents the historic order of material selection for these tasks. It is the ability to form shapes that have attractive "shape factors" that make metals and CFRP the more interesting candidates. Thin walled tubes can be formed from aluminum alloys and the associated shape factor can be as high as 25 before buckling during flight becomes a potential problem. This makes the material competitive with wood! CFRP spars may also be formed into hollow sections and can have shape factors of about 10. This value makes these sections better for spar use than either solid spruce or aluminum tubes.

From: Ashby, Materials Selection,
Pergamon (1993)