Lockheed Martin X-55

The Lockheed Martin X-55 Advanced Composite Cargo Aircraft (ACCA) is an experimental twin jet engined transport aircraft. It is intended to demonstrate new cargo-carrier capabilities using advanced composites. A project of the United States Air Force's Air Force Research Laboratory, it was built by the international aerospace company Lockheed Martin, at its Advanced Development Programs (Skunk Works) facility in Palmdale, California.

Design and development
The X-55 is a one-off aircraft intended to demonstrate the use of advanced composite materials in the fuselage of an otherwise conventional high-wing transport aircraft. There are no plans to place the X-55 into production.

Lockheed Martin's design for Advanced Composite Cargo Aircraft (ACCA) was chosen over Aurora Flight Sciences' design based on the An-72 in 2007. The aircraft is powered by 2 Pratt & Whitney PW306B turbofans. The X-55 design is based on the existing Fairchild Dornier 328JET. The fuselage of that aircraft, which is constructed of aluminum alloys, was replaced aft of the entrance door with a newly designed fuselage. The new design makes extensive use of advanced composite materials, selected to allow out-of-autoclave curing at lower temperatures and pressures than previous materials. The new widened fuselage allows the loading of cargo through a rear ramp.

The new fuselage section is constructed as a single large component, including the vertical stabilizer. When attached to the existing nose section, the fuselage is 55 feet (16.8 m) long and 9 feet (2.74 m) diameter. The fuselage has upper and lower halves, each with a roughly-oval shape similar to a canoe. The halves are bonded to circular frames. The fuselage section ahead of the entrance door consists of the existing (metal) 328J component, with fasteners used to bring the forward and new aft sections together.

As of April 2008, the fuselage was being fabricated. The first flight of the modified aircraft was expected during the winter of 2008/2009. However, due to a "glitch" during fabricating the composite fuselage, that schedule slipped. The delay was caused by an unsatisfactory bond of the skin on the lower fuselage, which required a second fuselage to be fabricated.

The first flight was completed at Lockheed Martin's Advanced Development Programs facility (Air Force Plant 42) in Palmdale, California on June 2, 2009 by the Air Force Research Laboratory in conjunction with Lockheed Martin. In October 2009, the ACCA demonstrator was designated X-55A by the USAF. Over the course of the program, 15 to 20 flights were expected. Furthermore, it was estimated that the vehicle was built for half the cost of a conventional design for a similar aircraft.