Aircraft designers have gone from wood and fabric to metal and composites in the last 100 years.
This second installment of a three-part look at the first 100 years of powered flight focuses on the materials used by aircraft pioneers and manufacturers. As always in engineering, the drive has been to lighter, stronger materials that are easily machined, assembled, and repaired.
Currently, metal is king, having inherited the crown from wood and fabric, but composites seem to be the "next big thing" waiting in the wings. Technologists and futurists assure us composites will dominate the industry by the end of the next decade, but no one can point to solid evidence that composites are any better than metal, or wood and fabric, for that matter. They might be stronger or lighter, but they're more expensive to make, more difficult to inspect, and trickier to repair.
Composites: Materials for the future?
Composites are the newest and possibly most-important aviation material since aluminum alloys were developed in the 1920s. They consist of a matrix or resins, such as epoxies and polyamides, embedded with reinforcements, including glass, boron, and carbon fibers. Although the finished materials are strong and lightweight, engineers are still trying to master the manufacturing, machining, and repair techniques that will make them less costly. Composite parts are also hard to repair and difficult to inspect.
Airliners and military planes rely on composites to cut weight and meet otherwise impossible design goals. The new F-22 Raptor fighter aircraft, for example, uses composites for a third of its structure, and some experts predict future warplanes will be more than two-thirds composites.
The Beech Starship, however, illustrates the difficulty in getting new materials from the drawing board to the flight line. Designed with help from Burt Rutan, an expert in composite aircraft, the Starship is powered by two rear-mounted Pratt & Whitney turboprops and uses tip-sails on the wingtips rather than conventional rudders.
Though Beech had no experience in composites, nor any data on resins, fibers, and other technologies needed to assemble the plane, it went ahead. And after spending $300 million and millions of man-hours, the company had the first all-composite, pressurized business plane. To earn FAA certification, however, engineers had to add more than a ton of structural composites and cut seating from eight to seven passengers. It first flew in 1986 and in 1988 went on sale for $5 million, more than the price for a similarly sized but faster jet plane.
The high price and maintenance costs hurt sales, and the company shut down production in 1994 after building only 53 Starships. The good news is that Beech gained invaluable experience in composites, letting it develop the Hawker Horizon and Premier I, both of which have composite fuselages.