Designing with Advanced Fibrous Composites

Abstract

The design of advanced composite structures is explained via historical data from past projects. Valuable lessons are drawn from the all-wood de Havilland Mosquito and the all-composite Lear Fan aircraft. The influence on design of minimizing the overall costs by appropriate selection of tooling techniques and manufacturing breaks between detail parts and subassemblies is highlighted. The popular approach of large integrally stiffened co-cured structures is shown to be appropriate only for extremely low production rates, for research and development projects, or for applications with no need for in-service repairs. The impact on overall costs of a company's organizational structure is explained. Several reasons for using fibrous composite rather than metal structures are summarized. The relative weights of composite and metal structures are discussed from the point of view of how the materials would be used in real structures rather than in simple material test coupons. The role of joints and cutouts in limiting structural efficiency is explained. Mechanical fastening and adhesive bonding are discussed, for both lightly loaded and heavily loaded joints. Techniques are included for achieving ultra-high weight savings in those applications for which there is no need to provide for repair or damage tolerance. How best to proceed in applying advanced composites to commercial aircraft control surfaces and fairings is also discussed. The paper concludes by reviewing some do's and don'ts learned in past programs.