Air Transport World

Composites vs. aluminum alloys: 'it's a horserace'.

Composites vs. aluminum alloys: "It's a horserace'

The laws of physics are simple and clear on this point--heavier objects are harder to fly than lighter objects. Heavy objects can be made to fly, of course, but at a greater cost. The history of flight has been a continuing story of efforts to lighten the vehicle of flight.

Mother nature's best solution to weight in birds was to make their bones hollow, shedding weight while retaining structural strength. Mankind's earliest flying machines depended upon nature for weight reduction in its use of wood. But wood, a material resistant to fatigue, is highly subject to weathering problems. Eventually aluminum took over from wood for most aircraft applications.

A competitive edge

For the past decade or so it seemed as if composite materials would, in turn, supersede aluminum as the material of choice in new aircraft designs. But a new aluminumlithium alloy has turned the materials competition into "a real horserace,' says one Boeing engineer, as Alcoa fights to keep airplanes largely metal. Barring suprises, it appears that the alloy will hold a competitive edge over composites in the near term. However, composite technologies keep advancing and applications keep expanding to the point that an all-composite transport aircraft now is a very real possibility in the long run.

Fiberglass was the first composite widely used in aircraft construction. Recently the use of graphite (carbon) and Kevlar composites has been expanding. All three are available in two basic forms--tape, in which fiber bundles of the base material are laid parallel to each other; or fabric, in which fiber bundles are interwoven. The bundles in both the tape and fabric forms are suspended in an epoxy resin matrix that is maleable until hardened during the cruing process.

The 23-30% weight savings composites offer over aluminum construction, plus a substantial reduction in the numbers of parts required for each application, have been a major attraction of these plastics. …

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