Composites

The advantages of high performance composites are many, including lighter weight, the ability to tailor lay-ups for optimum strength and stiffness, improved fatigue life, corrosion resistance, and, with good design practice, reduced assembly costs due to fewer detail parts and fasteners. The specific strength and

131 ft

Metallic 707

Fig. 1.6. Comparative Planform Areas7

131 ft

Metallic 707

Composite B-2 Bomber

Fig. 1.6. Comparative Planform Areas7

specific modulus of high strength fiber composites, especially carbon fibers, are higher than other comparable aerospace metallic alloys. This translates into greater weight savings resulting in improved performance, greater payloads, longer range and fuel savings.

The U.S. military was an early developer and adapter of composite materials. As mentioned earlier, the AV-8B aircraft had an airframe with 27% composite structure by the early 1980s. The first large scale usage of composites in commercial aircraft occurred in 1985, when the Airbus A320 first flew with composite horizontal and vertical stabilizers. Airbus has applied composites in up to 15% of the overall airframe weight for their A320, A330 and A340 family of aircraft.5 While the percentages are lower for commercial aircraft, the part sizes are much larger. For example, the Boeing 777 horizontal stabilizer has approximately the same surface area as a Boeing 737 wing. The B-2 bomber (Fig. 1.6) has the largest composite parts manufactured to date and is proof that at least some of the issues with fabricating large commercial structures have been addressed. Channel laminators and large tape laying machines, capable of making one piece skins in excess of 65 ft in length, demonstrated automated composite part fabrication in a large factory environment.6 However, to realize this type of structure in the commercial aircraft world, the cost of composite structure still needs to be reduced through innovative design and manufacturing technologies. The cost of composites is the number one deterrent to their broader application.7

Was this article helpful?

0 0

Post a comment