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X-55 Advanced Composite Cargo Aircraft (ACCA) - Program

The design and technology that comes out of the Advanced Composite Cargo Aircraft was intended for future Air Force programs, including successors to the C-130 Hercules beyond 2015. Future aircraft would include the Advanced Joint Air Combat System, a C-130 replacement formerly called AMC-X, as well as M-X, envisioned as a successor to the MC-130 Combat Talon.

The Air Force Research Laboratory Air Vehicles Directorate acquired the design, development, and manufacture of a technology demonstration aircraft that feature advanced structural design and manufacturing techniques integrated with advanced aerodynamic design. The purpose of this aircraft was to demonstrate the application of structural design and manufacturing technologies that can significantly reduce the structural weight and cost of future military transport type aircraft. The demonstration plane’s cargo bay was to have roll-on/roll-off capability and accommodate three standard pallets or 20 combat-equipped troops or one up-armored HMMWV.

On 15 December 2006 The Air Force Research Laboratory Air Vehicles Directorate (AFRL/VA) announced plans [BAA-Det1-AFRLPKV-07-02, cancelled 26 December 2006, and re-issued as BAA-Det1-AFRLPKV-07-04 on 22 January 2007] for the design, development, and manufacture of a technology demonstration aircraft that features advanced structural design and manufacturing techniques integrated with advanced aerodynamic design. The purpose of this aircraft was to demonstrate the integration of structural technologies to implement structural design concepts that will break current paradigms of vehicle cost as related to weight. The proposed demonstrator was visualized as an X-type aircraft with an emphasis on innovative structural configurations and concepts. It was to be sufficiently large to realistically represent the capabilities of next generation tactical cargo aircraft to meet critical military needs.

This effort emphasizes construction of a flying demonstrator validating lighter weight and lower cost structural concepts configured to meet the needs of future military transports. This demonstrator aircraft was designed to be manufactured primarily from advanced materials for weight reduction and surface smoothness, corrosion and fatigue elimination. It was designed to be manufactured rapidly using production-ready techniques and affordably in low unit rate and low total unit production. Its structural design (at a minimum) reflected provisions/considerations for rapid loading and unloading of cargo (including airdrop). As much as possible, engines, avionics, flight control equipment, were ready, in production, “off the shelf” technology. The aircraft was intended to be flown under an FAA experimental aircraft airworthiness certificate.

The envisioned program was budgeted at approximately $51M for aircraft design, development, manufacture and initial demonstration. This activity was intended to span a 17 month technical effort. The period of performance for the Phase 1 design effort was 5 months and the period of performance for the Phase 2 build and flight test was 12 months. The detailed design was to be delivered at the end of Phase 1 and the Flight Demonstrator Vehicle to be delivered at the end of Phase 2.

Particular emphasis was given to the need to have a flight worthy, innovative aircraft manufactured predominantly from composite material. This specific aircraft was intended to be operated as an experimental aircraft, and therefore, full production ready materials and manufacturing processes were not required. For realistic appraisal of future military capability, design concepts and methods, along with structural materials and fabrication methods would be close to production ready.

Teaming of traditional military prime contractors with non-military contractors to achieve a mix of experience in advanced aero-configuration design, lean programs and rapid airframe development and manufacturing was appropriate, and encouraged, but not mandatory. Solicitations began January 2007 and negotiations were complete April 2007. Companies that registered interest in bidding for the demonstrator contract include Alenia North America, Lockheed, Piasecki Aircraft and Voyager Aerospace, formed by Dick Rutan [brother of Burt Rutan]. AFRL received nine proposals for ACCA, representing a cross-section of the U.S. aerospace industry.

Of the nine, AFRL selected two, one submitted by Aurora Flight Sciences (Manassas, Va.) and the other by Lockheed Martin (Palmdale, Calif.). On 20 April 2007 Lockheed Martin Corp., Fort Worth, Texas, was awarded a $49,097,981 cooperative agreement contract (FA8650-07-2-3745) and Aurora Flight Sciences Corp., Manassas, Va., was awarded a $46,856,095 cost-plus-fixed-fee contract (FA8650-07-C-3700) to provide for Advanced Composite Cargo Aircraft (ACCA) flight demonstrators. Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, was the contracting activity. The first phase covered the design of a next generation tactical cargo airplane, while the second phase included the actual fabrication and manufacture of the design. Upon conclusion of the second phase there will be a first flight of the aircraft.

Both submitted a detailed plan for Phase 1 in which a donor aircraft would receive new composite fuselage and tail components to enable larger cargo transport volume, but the power plants, avionics, etc. would be reused, providing considerable cost savings because new subsystems would not have to be proven. Aurora Flight Sciences proposed that an Antonov An-72 military be outfitted with a new composite fuselage, wing and empennage, making use of segmented, hat-stiffened skins spliced with metallic bands and compression-molded plastic frames. Lockheed Martin proposed the use of a Dornier Do-328J high-wing regional jet, remanufactured with a composite fuselage and empennage. Although both concepts were deemed feasible, the latter was selected as the less risky concept. Lockheed Martin, therefore, was authorized to proceed to Phase 2 to fabricate, assemble and fly a demonstrator by Sept. 30, 2008.

The ACCA was built in Aurora's newly opened facility at the Golden Triangle Regional Airport in Columbus, Mississippi. Aurora's other facilities in Virginia, West Virginia, and Massachusetts would all support the project. Aurora Flight Sciences develops and provides robotic aircraft and other advanced aerospace vehicles for scientific and military applications. Aurora is headquartered in Manassas, VA and operates production plants in Clarksburg, WV and Columbus, MS and a Research and Development Center in Cambridge, MA. In 1995, Aurora became a key member of the Global Hawk team when it won the contract to build the V-tails for the RQ-4A Global Hawk. Since then, Aurora has steadily increased the scope of its Global Hawk work, which now includes almost one-third of each RQ-4A, and all of the aircraft's composite components except those found in the wing and radome areas.

The ACCA was conceived by AFRL as a fast-track, low-cost development effort. Working with Lockheed Martin's Skunk Works, it was designed in 5 months, then built and flown 20 months after the go-ahead. It was built at half the estimated cost of a conventional design of the same size.

The successful initial demonstration flight of the Advanced Composite Cargo Aircraft took place 02 June 2009 at Air Force Plant 42 in Palmdale, Calif. Duration for the first flight was about 87 minutes. 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.

The ACCA test aircraft was laden with more than 600 sensors and accelerometers to measure stresses on its structure. Later tests will focused on establishing the flight envelope of the ACCA to baseline its flight performance and validate predicted structural performance. Test flights on July 13 and August 8 expanded the aircraft's maneuver envelope and recorded external aerodynamic flow data.

Phase III of the program was awarded on 17 September 2009, to Lockheed Martin and planned to include fully expand the flight envelope and characterize the structure, examine reliability and longevity of the design, and baseline the X-55A as a test-bed for other technologies.

Air Force officials approved X-55A as the new designation for the Advanced Composite Cargo Aircraft as of 19 October 2009.

The X-55A program demonstrated the feasibility of designing and manufacturing large, bonded unitized structures featuring low-temperature, out-of-autoclave curing. The fuselage was constructed in two large half-sections (upper-lower) featuring sandwich construction with MTM-45 skins and Nomex core, bonded together with adhesive and ply overlays along the longitudinal seam rather than numerous frames, stiffeners and metal fasteners used commonly in traditional aircraft. The vertical tail was designed using tailored stiffness technology. These were joined with an existing Dornier 328J cockpit, wing, engines and horizontal tail. Compared to the original metallic components, the composite structure used approximately 300 structural parts versus 3,000 metallic parts for the original components and approximately 4,000 mechanical fasteners compared to 40,000.

The X-55 Advanced Composite Cargo Aircraft wing was used in 2011 to demonstrate the damage tolerance of Glass-Reinforced Aluminum Laminate (GLARE), which was an advanced hybrid material with outstanding fatigue and impact resistance, as well as high static strength. Three-dimensional woven fiberglass Pi-Preforms were used to joint the members together as a unitized structure. Advanced composite components were able to be combined with the metallic structure through the use of the Pi-Preform joints without the galvanization issue associated with composite-metallic bonded structure. A weight savings of 35% was shown for the outboard wing leading edge assembly compared with the existing X-55 ACCA wing leading edge. In Phase II Aurora proposes to develop a structural component, such as the outboard leading edge of the X-55 ACCA Demonstrator Vehicle, to demonstrate the benefits of GLARE unitized structure through manufacturing and testing of a representative article. UCLA will extend their multi-scale constitutive model to predict damage tolerance within the GLARE panels and metallic-composite bonded Pi-Preform joints.

Moving to a unitized GLARE structure on the X-55 ACCA Demonstrator Vehicle will provide a roughly 35% weight reduction in the outboard leading edge due to the improved damage tolerance of GLARE material. Reductions in weight and maintenance costs associated with fatigued and damaged components are possible throughout an aircraft using GLARE material in unitized structural configurations with fiberglass Pi-Preforms. Potential applications include the leading edge of the wing, lower wing skin, cargo doors, and access panels onboard the Air Force Next Generation Transport as well as many other platforms. Aurora envisions applications after demonstration on the X-55 ACCA Demonstrator Vehicle to initially include the Northrop Grumman GlobalHawk and Sikorsky CH-53K S-92 platforms, for which Aurora currently fabricates metallic and composite components. Additionally, the multi-scale constitutive models developed will allow for the publication of new damage tolerant design techniques for use by government and industry.

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Page last modified: 08-02-2014 18:50:54 ZULU