Boeing has formed a sustainability coalition of leading U.S. airlines to advise on the design and testing of the X-66A Sustainable Flight Demonstrator (SFD) project in development with NASA.
The group includes Alaska Airlines, American Airlines, Delta Air Lines, Southwest Airlines, and United Airlines—all which Boeing says will provide input on operational efficiencies, maintenance, handling characteristics, and airport compatibility.
The X-66A Transonic Truss-Braced Wing (TTBW) research aircraft will be built from a heavily modified ex-Delta MD-90 at Boeing’s Palmdale, California, site and will feature a high aspect ratio, 145-ft. span wing. Boeing says airline participants “will share feedback on sustainable operations and airport compatibility.”
Despite the large span—which is much greater than usual for a single aisle aircraft of its size—the company adds that “the TTBW design could be used by airplanes of different sizes and missions and may benefit from folding wing tips to accommodate existing airport infrastructure.”
The slender wing design is expected to reduce fuel burn by 9-10% compared with current best-in-class airliners and, when combined with advanced propulsion and lighter composite structures, could reduce fuel consumption and emissions by at least 30% for an aircraft entering service in the 2030s, NASA says. The goal of the SFD program is to validate the benefits of the TTBW concept at the aircraft level and could lead to the follow-on development of a 737 family successor next decade.
As well as providing guidance on airport operations, Boeing says “airline pilots will have a chance to experience the X-66A through a flight simulator and assess the vehicle’s handling characteristics.” During flight tests, which are slated for 2028 and 2029 out of NASA’s Armstrong Flight Research Center at Edwards Air Force Base, the aircraft manufacturer adds airline operations and maintenance teams will assess the X-66A as modifications are made to the aircraft.
Two MD-90s will be used for the X-66A program with one providing a source of spares. Work on the first aircraft—which according to the Air Current recently arrived at Palmdale after a short ferry flight from storage in nearby Victorville—will see the removal of the existing tail-mounted International Aero Engines V2500s. The forward fuselage will then be shortened by around 14 frames to balance it around the new center of gravity.
The all-new thin wing will be added to a new strengthened center fuselage crown section. The wing also presents a challenge from a systems installation and fuel storage perspective, and to simplify the program the demonstrator is not expected to feature the wing fold system that is being studied to enable the production TTBW to fit into 737-sized gates. The X-66A will be powered initially by a pair of Pratt & Whitney PW1100G geared turbofans and, for later tests, is expected to be re-engined with the CFM Open Fan—now in development under the GE Aerospace-Safran RISE program.
When selected by NASA for the SFD project, Boeing’s proposal outlined a possible future family of single-aisle TTBW aircraft, the VS-1 and VS-2 (for Vision System). Based on the MD-90 fuselage, the smaller VS-1 seats 130-160 passengers while the 180-210-seat VS-2 has a bigger wing and engines. Boeing says using one wing and engine size for both variants would have unacceptably penalized the smaller aircraft.
Related Content
