Paris Air Show

Advanced composites take to the air

 - June 16, 2009, 2:11 AM

Two weeks ago Lockheed Martin flew its Advanced Composite Cargo Aircraft (ACCA) testbed from Palmdale, California. Test pilots Rob Rowe and Joe Biviano took the ACCA through a series of airspeed, stability and control tests to bring Phase II of the program to a successful conclusion. ACCA is one of the programs that will feed technology into the Air Force’s next- generation airlifter, but also has much wider implications for the whole aviation industry.

ACCA is led by the U.S. Air Force Research Laboratory, and has its roots in the Composites Affordability Initiative (CAI) begun more than a decade ago. Under CAI, government and industry laboratories studied materials and manufacturing techniques with the aim of greatly reducing the design and manufacturing costs associated with traditional (metal) aircraft construction.

CAI looked at the dramatic reduction in parts and fastener counts, tooling and construction man-hours, and also examined factors such as floor-space efficiency and quality control. CAI evolved into ACCA.

Lockheed Martin beat Aurora Flight Sciences to the contract for Phase II. The company used its advanced construction knowledge, in part based on that developed for the Polecat UAV, and applied rapid prototyping techniques to build the ACCA in months. Large unitized structures were built up from materials heat-treated without the need for autoclaves, and assembled on low-cost “soft” tooling.

From the outside, the ACCA testbed looks nothing special, but it promises to be a landmark in the development of aircraft construction. Lockheed’s Skunk Works took a Dornier 328 regional jet and replaced the center and rear fuselages, plus vertical tail, with new composite structures. The front fuselage, wings and Pratt & Whitney Canada PW305 engines are retained from the original aircraft.

The rear fuselage is about 30 inches wider than that of the 328. It has a cargo floor and can accommodate two standard U.S. Air Force cargo pallets, with a rear ramp for loading. The Do 328’s domestic maintainer, Avcraft, provided vital assistance with the program, as did NASA’s Dryden Flight Research Facility, which helped with the flight test preparations.

ACCA’s first flight provided significant data to allow the analysis of the behavior of the composites structure. Further phases of ACCA are in the planning stage, and the testbed is likely to be used for other technology demonstrations and experiments.
The testbed was designed so that wings or landing gear could be changed at a later date, and a number of areas could be explored in future trials, including advanced wing design and powered-lift concepts, among others.