WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- In June, Air Force Research Laboratory and Lockheed Martin completed the first flight demonstration of the Advanced Composite Cargo Aircraft.  The success of this event prompted official Headquarters Air Force designation of the ACCA as the X-55A, effective in October. The initial flight focused on establishing basic handling qualities, as well as monitoring structural performance and response to load maneuvering--assessments relying on a network of approximately 600 sensors (strain gauges and accelerometers) integrated within the airframe. Following this preliminary demonstration, the aircraft flew twice more, in July and August flight events geared towards expanding the maneuvering envelope and recording external aerodynamic flow visualization.

The lab/industry team conducted the first flight demonstration out of AF Plant 42, located in Palmdale, California. After takeoff, the aircraft flew approximately 1.5 hrs, in Edwards Flight Test Center test range 2515 and with the National Aeronautics and Space Administration's Dryden Flight Research Center providing chase plane support. The aircraft landed safely, successfully completing all planned test points. With a contract awarded in September, Phase III of the program work will include full flight envelope aerostructural characterization, structural design reliability/longevity testing, and design archiving in order to fully baseline the X-55A as a test bed for other technologies.

As a critical-technology experiment, the ACCA program demonstrated the feasibility of designing and manufacturing large, bonded, unitized structures featuring low-temperature, out-of-autoclave curing. The aircraft fuselage consists of two large half-sections (upper and lower) comprising MTM-45 skins and a Nomex core. This sandwich construction employs adhesive and ply overlay bonding along the longitudinal seam, rather than relying on the multitude of frames, stiffeners, and metal fasteners common to traditional aircraft configurations. Meanwhile, the vertical tail design leverages tailored-stiffness technology. These unique components are joined with an existing Dornier 328J cockpit, wing, engines, and horizontal tail to create the novel aircraft. These innovative processes saved an order of magnitude (in both overall parts count and mechanical fasteners) relative to conventional metallic construction as a means of controlling cost. Compared to traditionally constructed configurations, the composite structure used approximately 300 structural parts (versus 3,000 metallic parts) and approximately 4,000 mechanical fasteners (compared to 40,000).

This milestone represents the payoff of years of effort and hundreds of researchers sponsored by AFRL through the Composites Affordability Initiative, a decade-long effort involving industry, NASA, and Department of Defense labs. The successful construction and subsequent flight of the ACCA (newly appointed X-55A) demonstrates not only the value of composite construction, but the ability to rapidly construct an aircraft from assembly to (manned) flight test. Design entailed a 5-month period; thereafter, the vehicle was built and flown 20 months after fabrication go-ahead--all for approximately half the cost of a conventionally designed craft of the same size--and thus met the program goal of exploiting composites to break the historic trend of aircraft cost as a function of weight.