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

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The transition to hybrid-electric propulsion for short-haul aircraft has been has been energised by two milestone developments involving engine manufacturers Pratt & Whitney Canada and Rolls-Royce. The former, which produces engines for medium-to-large turboprop aircraft, has partnered with GKN Aerospace in the Netherlands to develop a high voltage, high power wiring system for a new hybrid-electric powertrain, which is targeting lower CO2 emissions and 30% more efficiency than today’s most advanced turboprop engines. Flight testing is expected to begin in 2024. Meanwhile, Rolls-Royce has just completed the first fuel burn of a gas-powered small turbine for use in the Advanced Air Mobility (AAM) sector and hybrid-electric commuter aircraft seating up to 19 passengers. The new turbogenerator system is designed to provide scalable power offerings for hybrid-electric aircraft, enabling pilots to extend flight range by switching between electric power and either sustainable aviation fuel or hydrogen combustion.

Pratt & Whitney Canada is progressing its expansion into hybrid-electric aero propulsion in partnership with Collins Aerospace, a sibling company within the aerotech conglomerate RTX, and UK-headquartered GKN Aerospace. 

Having integrated a lightweight 1-megawatt electric motor developed by Collins into a high-efficiency fuel-burning engine, Pratt & Whitney Canada is now partnering with GKN Aerospace to develop the high voltage, high power electrical wiring interconnector system (EWIS) for the RTX hybrid-electric flight demonstrator project.

The companies will collaborate on the development, construction and installation of the electrical wiring system on the demonstrator, which Pratt & Whitney Canada expects to achieve a 30% improvement in fuel efficiency and lower CO2 emissions than the most efficient turboprop engines currently in use, delivering better performance during take-off, climb and cruise.

Collins says its 1MW motor is half the weight of the most advanced electric motors now flying, but will deliver four times the power and double the voltage, with half the heat loss. The unit is being developed by the company at its Solihull, UK, facility and tested at the University of Nottingham’s Institute for Aerospace Technology.

Supported by the governments of Canada and Quebec, flight testing of the new powertrain will begin next year on Pratt & Whitney Canada’s Dash 8-100 experimental aircraft.  

The Netherlands division of GKN Aerospace will lead development and design of the EWIS for the hybrid-electric propulsion system, as well a producing and installing the hardware on the demonstrator aircraft.

“Hybrid-electric propulsion technology has the potential to improve efficiency for a wide range of future aircraft applications, supporting the industry-wide goal of achieving net zero CO2 emissions for aviation by 2050,” said Jean Thomassin, Pratt & Whitney Canada’s Executive Director for new products and services. “Our collaboration with GKN Aerospace brings extensive expertise to the project, which will help integrate high voltage electrical systems on our experimental aircraft, as we target flight testing to begin in 2024.”

John Pritchard, President of Civil Airframe at GKN Aerospace, welcomed the new partnership, which follows the company’s design and manufacture of EWIS systems for the all-electric Vertical Aerospace VX4 air taxi and the Eviation Alice passenger and freight planes.      

“This project extends our teamwork in hybrid-electric propulsion technology, which also encompasses the SWITCH project, which is backed by the Clean Aviation Joint Undertaking of the European Union,” he said. 

The Rolls-Royce turbogenerator system, which is part-funded by the German Ministry for Economic Affairs and Climate Action, will allow power to be scaled between 500kW and 1,200kW, enabling hybrid-powered aircraft to fly longer routes or carry greater payloads than all-electric battery powered models. As well as delivering energy to electrical propulsion units, it can recharge batteries in hybrid-electric powertrains.

“The development of the turbogenerator solution brings together Rolls-Royce’s capabilities in designing compact and lightweight high-speed rotating electric machines and highly efficient gas turbines, combined with the expertise to integrate them on a system and platform level,” said Matheu Parr, the engine maker’s Customer Director, Electrical.

In addition to providing more operating flexibility, Parr explained the engine had been designed using novel combustion technology to minimise emissions, not just in the evolving AAM market, which includes electric vertical take-off and landing (eVTOL), electric short take-off and landing (eSTOL), but also potentially for helicopters and auxiliary power units on larger aircraft.

“This significant achievement confirms the effectiveness of the compact, power-dense turbine that will be integrated into a lightweight turbogenerator system,” he said.

“The turbogenerator system will enable our customers to extend the routes that electric flight can support and means more passengers will be able to travel further on low and potentially net zero emissions aircraft. It is well suited to recharge batteries as well as provide energy to electrical propulsion units directly and therefore enables aircraft to switch between power sources in flight.”

He added that since the product had been defined, it had taken just two years to develop then test the new gas turbine. 

“This significant achievement follows the fast-paced development time of the new gas turbine from concept freeze to ‘pass to test’ in under two years,” he said. “Test facilities and equipment, comprising 14 sub-systems in total, were designed, procured, and built – or adapted – by a global team in a record time of just under a year.

“With this achievement, we have proven we can apply our expertise to novel designs and are able to test them on a very quick timescale. This capability will help Rolls-Royce to deliver the products that will help us on our path to net-zero within the ambitious industry timelines of the Advanced Air Mobility market.” 

Image: The RTX hybrid-electric flight demonstrator

Tony Harrington

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The unprecedented heatwave sweeping the UK during the 2022 Farnborough International Airshow was a timely, if unwelcome, prod to the aviation sector that it must continue raising its game in the collective fight to mitigate the growing impact of global warming. Established and emerging aerospace players, from Airbus to ZeroAvia, used the biggest air show since the start of the pandemic to promote and progress deals, partnerships and initiatives designed to help deliver net zero emissions by 2050. In addition to more than 300 orders for new-technology aircraft, Farnborough showcased a range of developments on new propulsion systems and fuels, the growing trend to convert fossil-fuelled aircraft to zero emission power and continued strong growth in the urban air mobility sector, reports Tony Harrington. As countries met in Montreal to discuss a long-term target to reduce emissions from international aviation, the UK government released at the air show its eagerly-awaited Jet Zero Strategy to decarbonise the British aviation sector.

Having recently unveiled plans to use an A380 superjumbo as a testbed for its ZEROe hydrogen propulsion programme, Airbus announced it would convert a second A380, this time to be used in a collaboration with engine manufacturer CFM International to test new open-architecture powerplants. This engine technology, known as RISE (Revolutionary Innovation for Sustainable Engines), features large external fans which are expected to drive significant operating efficiencies and cut emissions by 20%.

Airbus UpNext, a subsidiary of the airframer, also announced a partnership with the German Aerospace Center (DLR) to study contrails created by hydrogen-powered engines. Through a new project called Blue Condor, two modified Arcus gliders will be deployed, one powered by a conventional kerosene combustion engine, the other hydrogen combustion. A chase aircraft will follow each of these craft to assess and compare their contrails at high altitude, in what will be the first in-flight tests by Airbus using a hydrogen engine.

To further support its hydrogen ambitions, Airbus has invested an undisclosed amount in Hy24, described as the world’s largest clean hydrogen infrastructure investment fund, focused on supporting large-scale green hydrogen infrastructure projects. “Since 2020, Airbus has partnered with numerous airlines, airports, energy providers and industry partners to develop a stepped approach to global hydrogen availability,” said Karine Guenan, VP ZEROe Ecosystem, Airbus. “Joining a fund of this magnitude demonstrates Airbus’ continuously active role in infrastructure investments for the production, storage and distribution of clean hydrogen worldwide.” 

Rolls-Royce and European low-cost airline easyJet also announced a hydrogen propulsion programme, the H2Zero Partnership, to jointly pioneer the development of hydrogen combustion engine technology suitable for a range of aircraft, including narrowbody airliners, from the mid-2030s. This collaboration, which combines Rolls-Royce’s engine expertise and easyJet’s operational experience, will start later this year with engine tests on the ground and ambitions by both companies to also progress to flight tests.

“In order to achieve net zero by 2050, we have always said that radical action is needed to address aviation’s climate impact,” said Johan Lundgren, CEO of easyJet. “The technology that emerges from this programme has the potential to power easyJet-size aircraft, which is why we will also be making a multi-million-pound investment into this programme. In order to achieve decarbonisation at scale, progress on the development of zero-emission technology for narrowbody aircraft is crucial. Together with Rolls-Royce, we look forward to leading the industry to tackle this challenge head-on.”

Boeing, which announced more than 200 aircraft orders at the show, has become a founding member of the University of Sheffield Energy Innovation Centre to explore various methods of producing sustainable aviation fuel, and bringing it to market. During the air show, the aircraft OEM revealed it was advancing its partnership with the University of Cambridge on the Aviation Impact Accelerator (AIA), an international group of practitioners and academics convened by the university. AIA develops interactive evidence-based models, simulations and visualisation tools for decision-makers and the wider engaged public to understand the pathways to net zero flight. The outcomes and key learnings will eventually be integrated into Boeing’s Cascade data modelling tool, which provides real-time visualisation of carbon emission reductions in aviation, and also announced during the show. The model assesses the full lifecycle impacts of renewable energy by accounting for the emissions required to produce, distribute and use alternative energy carriers such as hydrogen, electricity and SAF. Boeing said it plans to utilise the tool with airline operators, industry partners and policymakers to inform when, where and how different fuel sources intersect with new airplane designs.

The company also expanded a long-standing collaboration with Japan’s Mitsubishi Heavy industries to study electric and hydrogen propulsion, development of green hydrogen, new feedstocks and technologies for development of SAF, carbon capture and conversion, sustainable materials and new aircraft design concepts. As well, Boeing announced a $50 million investment in AEI HorizonX, a partnership it established with private equity group AE Industrial Partners to support transformative aerospace technologies.

“In order for the aviation industry to meet its net zero carbon emissions commitment by 2050 it will take all of us collaborating and investing in scientific research and testing,” said Boeing’s VP of Global Sustainability Policy, Brian Moran.

Boeing also announced a new partnership with Alder Fuels to expand production of SAF around the world. Using Boeing aircraft, the companies will test and qualify Alder-derived SAF, advance policies to expedite aviation’s energy transition.

Meanwhile, Virgin Atlantic, Corendon Dutch Airlines and Albawings have selected Boeing’s Jeppesen FliteDeck Advisor to optimise operational efficiency and reduce fuel consumption across their fleets of Boeing aircraft. During a three-month trial on its 787 Dreamliners, Virgin Atlantic found the digital solution delivered cruise fuel savings of 1.7%, saving around 1,900kg of CO2 per flight.

Hydrogen propulsion pioneer ZeroAvia secured an additional $30 million from new investors including Barclays Sustainable Impact Capital, NEOM, a sustainable regional development in Saudi Arabia, and the impact technology fund AENU, as well as additional capital from International Airlines Group, an existing investor and parent of airlines including British Airways, Iberia, Aer Lingus, Vueling and LEVEL. “Our new investors are each looking at our journey through a different lens,” said Val Miftakhov, founder and CEO of ZeroAvia, “but all energised by our mission to enable zero-emission flight using hydrogen-electric engines.”

ZeroAvia, Universal Hydrogen and Ampaire announced during the air show a total of 55 firm orders for kits to convert commuter or turboprop aircraft from fossil fuels to zero-emission electric or hydrogen propulsion, while Swiss aero-battery manufacturer H55 launched a partnership with Canadian training group CAE and Piper Aircraft to convert to battery-electric power two-thirds of CAE’s fleet of Piper Archer training aircraft. Ampaire also flagged in excess of 200 orders on the horizon for its Eco Caravan and Eco Otter aircraft, re-engined variants of the Cessna Caravan and De Havilland Twin Otter regional aircraft.

GKN Aerospace revealed during the show that advances in fuel cell technology could enable hydrogen-electric propulsion to be scaled up more quickly than previously thought. The company had assumed that hydrogen propulsion was easiest to introduce for aircraft seating around 19 passengers, but now believes the use of cryogenic cooling technology can expedite deployment of the technology to power aircraft seating 96 or even more passengers, and reducing both CO2 and non-CO2 emissions.

Norway’s Widerøe Zero, the sustainability arm of regional airline Widerøe, signed a MoU with Embraer to help develop the airframer’s new Energia family of zero emission aircraft, with four variants ranging from 19 to 50 seats, while Collins Aerospace has completed the preliminary design of a 1-megawatt motor and controller to power a hybrid-electric demonstrator aircraft for the engine manufacturer Pratt & Whitney Canada.

Collins and Pratt & Whitney also launched a new electric propulsion concept, the Scaleable Turboelectric Powertrain Technology demonstrator (STEP-tech), to power novel aircraft including high-speed electric vertical take-off or landing craft (eVTOL), unmanned aerial vehicles (UAV) and small-to-medium commercial aircraft, while new deals, developments and partnerships were announced in the eVTOL segment by companies including Germany’s Lilium, Embraer’s Eve, UK-based Vertical Aerospace, French start-up Ascendance Flight Technologies and a tie up between Rolls Royce and Hyundai Motor Group’s air taxi division, Supernal.

GE Aviation announced a milestone for its own electric engine programme, conducting the world’s first test of a hybrid-electric propulsion system in simulated high-altitude conditions. Using NASA’s Electric Aircraft Testbed (NEAT) in Sandusky, Ohio, GE assessed a pair of hybrid electric systems, one to simulate an aircraft’s left engine, the other its right engine, in conditions expected when flying at 45,000 feet. The test simulated the electrical loads needed to optimise engine performance, while propelling and powering an aircraft at that altitude.   

Mohamed Ali, VP and GM of Engineering for GE Aerospace, said: “We’re making aviation history by developing the technology to help make hybrid electric flight possible for everyday commercial air travel. We just passed a key milestone by successfully concluding the world’s first test of a high power, high voltage electric system at altitude conditions. This is one of many milestones in our journey with NASA towards demonstrating a hybrid electric aircraft engine system for a more sustainable future of flight.”

A small Spanish airline, AlbaStar, was identified at Farnborough as the European launch customer for the US-made WheelTug electric taxiing system, which enables aircraft to be manoeuvred around airports without using external tractors or their own engines. Using a small electric motor installed within the nosewheel, pilots can control all ground movements by their aircraft, including reversing from airport aerobridges. AlbaStar, which operates six Boeing 737 jets, estimates that in a year the WheelTug system could eliminate 1 million kilograms of CO2 and nitrogen oxide emissions from the airline’s operations. The WheelTug system is due to be introduced into service in mid-2023.

Image (Embraer): Norwegian airline Widerøe has signed a MoU with Embraer to help develop the airframer’s new Energia family of zero emission aircraft