Modern Composite Airplane

Stephen Trimble

Structures and structural materials have undergone progressive refine­ment. Originally, aircraft were fabricated much like ships and complex wooden musical instruments: of wood, wire, and cloth. Then, metal gradually supplanted these materials. Now, high-strength compos­ite materials have become the next generation, allowing for synthetic structures with even better structural properties for much less weight. NASA has assiduously pursued development of composite structures.

HEN THE LOCKHEED MARTIN X-55 advanced composite cargo aircraft (ACCA) took flight early on the morning of June 2, 2009,[642] it marked a watershed moment in a century-long quest to marry the high-strength yet lightweight properties of plastics with the structure required to support a heavily loaded flying vehicle. As the X-55, a greatly modified Dornier 328Jet, headed east from the runway at the U. S. Air Force’s Plant 42 outside Palmdale, CA, it gave the appear­ance of a conventional cargo aircraft. But the X-55’s fuselage structure aft of the fuselage represented perhaps the promising breakthrough in four decades of composite technology development.

The single barrel, measuring 55 feet long by 9 feet wide,[643] revolu­tionizes expectations for structural performance at the same time that it proposes to dramatically reduce manufacturing costs. In the long his­tory of applying composites to aircraft structures, the former seemed always to come at the expense of the latter, or vice versa. Yet the X-55 defies experience, with both aluminum skins and traditional compos­ites. To distinguish it from the aluminum skin of the 328Jet, Lockheed used fewer than 4,000 fasteners to assemble the aircraft with the single­

piece fuselage barrel. The metal 328Jet requires nearly 30,000 fasteners for all the pieces to fit together.[644] Unlike traditional composites, the X-55 did not require hours of time baking in a complex and costly industrial oven called an autoclave. Neither was the X-55 skin fashioned from tex­tile preforms with resins requiring a strictly controlled climate that can be manipulated only within a precise window of time. Instead, Lockheed relied on an advanced composite resin called MTM45-1, an "out – of-autoclave” material flexible enough to assemble on a production line yet strong enough to support the X-55’s normal aerodynamic loads and payload of three 463L-standard cargo pallets.[645]

Lockheed attributed the program’s success to the fruits of a 10-year program sponsored by the Air Force Research Laboratory called the composites affordability initiative.[646] In truth, the X-55 bears the legacy of nearly a century’s effort to make plastic suitable in terms of both per­formance and cost for serving as a load-bearing structure for large mil­itary and commercial aircraft.

It was an effort that began almost as soon as a method to mass – produce plastic became viable within 4 years after the Wright brothers’ first flight in 1903. In aviation’s formative years, plastics spread from cockpit dials to propellers to the laminated wood that formed the fuse­lage structure for small aircraft. Several decades would pass, however, before the properties of all but the most advanced plastics could be con­sidered for mainstream aerospace applications. The spike in fuel prices of the early 1970s accelerated the search for a basic construction mate­rial for aircraft more efficient than aluminum, and composites finally moved to the forefront. Just as the National Advisory Committee for Aeronautics (NACA) fueled the industry’s transition from spruce to metal in the early 1930s, the National Aeronautics and Space Administration (NASA) would pioneer the progression from all-metal airframes to all­composite material over four decades.

The first flight of the X-55 moved the progression of composite tech­nology one step further. As a reward, the Air Force Research Laboratory announced 4 months later that it would continue to support the X-55
program, injecting more funding to continue a series of flight tests.[647] Where the X-55 technology goes from here can only be guessed.