Boeing has selected engine maker Pratt & Whitney and its sibling company Collins Aerospace as partners in its groundbreaking X-66A sustainable aircraft programme, in which a former passenger jet will be converted to test the airframer’s futuristic Transonic Truss-Braced Wing (TTBW). The transformation of the 1995-built MD-90 twinjet is part of NASA’s Sustainable Flight Demonstrator Project, which is tasked with trialling a range of new technologies to increase aircraft efficiency and reduce carbon emissions. In a radical retrofit, Boeing will remove the plane’s low, rear-swept wings and instal high-mounted, long, thin wings, supported by diagonal trusses. The new, forward-swept wings are designed to reduce aerodynamic drag, improving fuel efficiency by up to 10%, while the addition of Pratt & Whitney’s GTF (geared turbofan) engines, and new nacelles and engine accessories from Collins, together with other initiatives, could improve total efficiency by as much as 30%. Both companies, part of the RTX aerospace group, will also support ground and flight tests of the experimental plane, which are scheduled to commence in 2028.    

The Transonic Truss-Braced Wing programme is a key element of broader US efforts to decarbonise emissions from commercial aircraft, and will help inform the design of future narrowbody airliners. The former Delta Airlines MD-90 to be used in the programme recently flew from Victorville, California, where it was stored, to nearby Palmdale for modification.

NASA estimates that single-aisle airliners generate more than 50% of global emissions from aircraft, but says technical and economic risks often prevent promising technologies from proceeding to production. It is partnering with the aerospace industry on the X-66A programme to help develop and flight test an advanced airframe and new technologies to improve fuel efficiency while reducing emissions, and to gather ground and flight test data to validate the outcomes.

“We are excited to be working with Boeing on the X-66A Sustainable Flight Demonstrator, making critical contributions to accelerate aviation towards its 2050 net-zero greenhouse gas emission goal,” said Ed Waggoner, Deputy Associate Administrator for Programs in the NASA Aeronautics Research Mission Directorate.

The agency said the research results would help the aerospace industry to progress development of next-generation single-aisle aircraft which meet the goals of the US Aviation Climate Action Plan.   

“This marks an important step in the Sustainable Flight Demonstrator project, advances Boeing’s commitment to sustainability and brings us closer to testing and validating the TTBW design,” said Dr Todd Citron, Boeing’s Chief Technology Officer.

“The X-66A is NASA’s first experimental plane focused on helping the US achieve its goal of net-zero aviation greenhouse gas emissions,” he said. “The learnings from the Sustainable Flight Demonstrator and the partnership with NASA are important elements in the industry’s efforts to decarbonise aviation. We’re grateful for the support from RTX on this critical effort.”  

Geoff Hunt, Pratt & Whitney’s SVP Engineering and Technology, said NASA’s Sustainable Flight Demonstrator programme highlighted how collaboration across the aerospace sector could help expedite the transition to net zero emission flight.

“We’ll work with Boeing to apply GTF engines to the X-66A and help demonstrate the potential of its pioneering truss-braced wing design,” he said. Pratt & Whitney’s geared fan engines, introduced into service in 2016, are designed to offer up to 20% better fuel efficiency than conventional powerplants and certified to operate with sustainable aviation fuel.

Further improving the efficiency of the testbed aircraft will be lightweight engine nacelles, produced by Collins using durable composite and metallic materials. It will also provide control system components for the GTF engines to be used on the testbed aircraft, including their heat exchangers, integrated fuel pump and starter, and air turbine starter and electronic controls.

“Collins has as long history of successful partnerships with NASA, Boeing and Pratt & Whitney, with decades of experience pushing the boundaries of innovation in aerospace,” said the company’s SVP Engineering and Technology, Dr Mauro Atalla. “Now, as part of the Sustainable Flight Demonstrator programme, we will work together to demonstrate new technologies and systems to support the next generation of low-emission single-aisle aircraft that will play an integral role in reducing the environmental footprint of the aviation industry.”    

RTX is also collaborating with NASA on other sustainable aviation projects, including Hybrid Thermally Efficient Core (HyTEC) and Hi-Rate Composite Aircraft Manufacturing (HiCAM), as well as progressing its engines to operate with 100% unblended SAF, hybrid-electric power and hydrogen fuel.

Image (Boeing): A render of the X-66A

Tony Harrington

Correspondent

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