On its roadmap to the next generation of US single-aisle commercial airliners that should become available by the early 2030s, the National Aeronautics and Space Administration (NASA) wants to have a full-scale technology demonstrator ready for the first flight in FY26. The program called Sustainable Flight National Partnership (SFNP) has been included in NASA’s FY22 budget request to the Biden Administration on May 28. Simply stated, NASA paves the way for a 737 successor.

The Sustainable Flight Demonstrator be “a game-changing, ultra-efficient, and low-carbon emitting design at least 25 percent more fuel-efficient than today. The SFNP will demonstrate the first-ever high-power hybrid-electric propulsion system for transport aircraft, ultra-high-efficiency long and slender wings, advanced composite structures and advanced engine technologies developed from NASA-industry innovation”, the NASA Congressional Justification document says.
“The SFNP is NASA’s response to increasing challenges from entities to the Nation’s long-term leadership in commercial aircraft manufacturing and strengthen U.S. industry’s ability to take the lead in developing the next generation sustainable subsonic transport.”

The program be established under NASA’s Aeronautics Research Mission Directorate (ARMD) and falls under the Advanced Air Vehicles Program with a $243.7 million FY22 budget and the Integrated Aviation Systems Program with a $301.5 million FY22 budget. Budgets are expected to grow to $269.5 and $349.9 million respectively in FY26. NASA’s total aeronautics budget request for FY22 is $914.8 million set to grow to $996.8 million in FY26.

Two engine demonstrator programs

SFNP consists of a number of sub-technology programs, of which hybrid-electric propulsion under the Electrified Powertrain Flight Demonstrator (EPFD) is one of the most important. The administration plans “to award at least two contracts to demonstrate in-flight one-megawatt class electric powertrain systems necessary to achieve hybrid-electric propulsion systems for use in the design of propulsion systems for single-aisle transports. These first-generation hybrid-electric propulsion systems can increase propulsion efficiency by five percent while also substantially reducing maintenance costs.” These public-private contracts be awarded later in 2021. EPFD has an FY91.2 million budget for FY22. The complete SFD contract award is expected to be awarded in September. The lead center and performing centers still have to be confirmed.

Aerodynamics favor truss-braced wing

Under the Advanced Air Vehicles Program, NASA develop key subsonic technologies. They include hybrid thermally efficient core engines and high rate composite manufacturing that can be produced four to six times faster than now. On aerodynamics, the administration favors the transonic truss-braced wing design (TTBW) that has been studied before. In 2019, NASA and Boeing completed high-speed tests and initiated low-speed and high-lift tests of an advanced TTBW design for higher cruise speeds incorporating an integrated high-lift system. These tests confirmed a nine percent fuel burn benefit for the technology.

NASA has continued research on structural weight reduction, in with Aurora Flight Sciences and the University of Michigan. At Boeing, the truss-braced design was part of its Future Small Aircraft-design before it was mothballed by David Calhoun in January 2020.  As NASA paves the way for a 737 successor, it remains to be seen how Boeing commit to the demonstrator program. It has little choice, as rival Airbus has placed its full weight behind its own next-generation hydrogen-based airliners.

The Airspace Operations and Safety Program with a proposed $104.5 million budget will look at activities to improve aircraft operations. “These new activities will build upon NASA-developed trajectory management capabilities to provide integrated trajectories and operations tailored to minimize fuel burn, noise, and emissions for reduced environmental impact. This effort will also define requirements for advanced flight deck capabilities to improve system predictability and trajectory compliance. By expanding these activities, NASA will ensure that the technologies will be ready to support the integration of U.S. industry’s next-generation single-aisle transport aircraft.”

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