TTBW
SAN DIEGO—NASA’s Sustainable Flight Demonstrator (SFD), a full-scale transonic truss braced wing (TTBW) design in development by Boeing for flight tests later this decade, has been designated the X-66A by the U.S. Air Force.
The latest X-plane, the X-66A is the first in the almost 80-year experimental aircraft series specifically focused on achieving the goal of net-zero aviation greenhouse gas emissions, according to NASA, which unveiled the designation at the American Institute of Aeronautics and Astronautics (AIAA) Aviation forum here.
The X-66A designation comes less than a month after the Air Force announced a new DARPA aircraft designed by Aurora Flight Sciences to test active flow control technology will be dubbed the X-65. Also known as the control of revolutionary aircraft with novel effectors (CRANE), the Aurora project was the first new X-plane to be publicly revealed since the Air Force Test Pilot School’s F-16 Variable In-Flight Stability Test Aircraft was redesignated the X-62 in 2021. The identities of the missing X-63/64 designations are unknown.
Bob Pearce, associate administrator for NASA’s Aeronautics Research Mission Directorate, says “to reach our goal of net zero aviation emissions by 2050, we need transformative aircraft concepts like the ones we’re flying on the X-66A. With this experimental aircraft, we’re aiming high to demonstrate the kinds of energy-saving, emissions-reducing technologies the aviation industry needs.”
NASA Administrator Bill Nelson adds the X-66A “will help shape the future of aviation, a new era where aircraft are greener, cleaner, and quieter, and create new possibilities for the flying public and American industry alike.”
The agency selected the TTBW for the SFD in January under a funded Space Act Agreement with Boeing. Under the agreement, NASA will provide $425 million in funding through milestone payments, while Boeing and its industry partners contribute $725 million. A yearlong flight-test campaign is planned to begin at NASA Armstrong Flight Research Center, California, in 2028.
The TTBW is a long, slender wing structurally braced by trusses that also generate lift. Increasing span reduces lift-induced drag. The design, which is optimized for cruising at the typical Mach 0.8 speed of current single-aisle airliners, has a span about 50% longer than the cantilever wing on an equivalent conventional aircraft. The SFD will be based on the fuselage of a heavily modified McDonnell Douglas-designed MD-90.
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 successor to the 737 family next decade.
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