The U.S. Air Force Research Laboratory's Advanced Composite Cargo Aircraft (ACCA) is fully assembled and in subsystem testing at Lockheed Martin's Skunk Works, with a first flight expected by June. ACCA, which AFRL hopes will be soon be assigned a coveted X-plane designation, is intended to demonstrate dramatic cost reductions through using advanced materials and manufacturing technologies.
Conventional composites are cured under elevated temperatures and pressures in an autoclave, which increases costs and imposes size limits on components. ACCA's large integrated composite primary structures were vacuum-bagged and bonded on the factory floor, in modular ovens built around the parts then disassembled.
And the parts are big - the upper and lower fuselage halves (seen above) are single pieces 30-40ft long. There are no stringers - the half-hulls are sandwich structures - and the relatively few bulkheads and frames are slotted into simple "tongue-in-groove" pi-joints, shaped like the Greek letter π, that are bonded to the skins.
ACCA is based on a Dornier 328JET regional airliner. The original metal fuselage has been removed aft of the flightdeck and replaced with the new, wider cargo fuselage with rear loading ramp. The composite vertical tail is also new, but the 328JET's original wing and tailplane, engines and systems are retained.
The original goal was to go from program launch to first flight in just 17 months. But the lower fuselage did not bond properly and a second one had to be made, delaying the program. Lockheed Martin is now aiming for a first flight just over 24 months from contract award, which AFRL argues is still pretty quick for designing, fabricating, certificating (FAA Experimental) and flying an aircraft.
Simply stated, the program's objective is to break the paradigm that an aircraft's cost is a function of its weight. AFRL says that goal is being achieved, and that cost is more a function of parts count with the processes and technologies used to design and build ACCA - the new composite fuselage and tail having just 300 parts compared with 3,000 in the original 328JET metallic structures.
Phase 2 of the ACCA program will end with the first flight, but AFRL plans to use the X-plane as a research asset, based at NASA Dryden on Edwards AFB. The composites technology, meanwhile, could find its way into the Joint Future Theater Lift, a potential STOL or VTOL replacement for the C-130 tactical airlifter.