A Gulfstream G600 business jet has become the first aircraft to undertake a transatlantic flight using 100% sustainable aviation fuel. The flight on November 19 departed Gulfstream Aerospace’s headquarters in Savannah, Georgia, landing at Farnborough Airport in the UK six hours and 56 minutes later. The Pratt & Whitney Canada PW815GA twin engines were powered by 100% HEFA-based SAF produced by World Energy and delivered by World Fuel Services. Other partners in the flight collaboration included Honeywell, Safran and Eaton. The fuel was notable for a complete absence of aromatic content, normally considered essential for engine performance and safety. World Energy supplied HEFA SAF, which included synthetic aromatics supplied by Virent, for Gulfstream’s first 100% SAF flight of a Rolls-Royce powered G650 in December 2022. Virgin Atlantic is making the first transatlantic flight of a commercial airliner to use 100% SAF in the reverse direction on November 28.

The data collected from the Gulfstream transatlantic flight will help the OEM and its suppliers gauge aircraft compatibility with future low-aromatic renewable fuels, particularly under cold temperatures for extended flight durations, said the company.

“Gulfstream is innovating for a sustainable future,” said Mark Burns, President. “One of the keys to reaching business aviation’s long-term decarbonisation goals is the broad use of SAF in place of fossil-based jet fuel. The completion of this world-class flight helps to advance business aviation’s overarching sustainability mission and create positive environmental impacts for future generations.”

The lack of aromatics in the fuel mix allows for a reduced impact on local air quality, with lower particulate emissions and very low sulphur content, so reducing non-CO2 environmental impacts. To allow the fuel on the transatlantic flight to fly without an aromatics content, Gulfstream obtained an Experimental Airworthiness Certificate from the FAA and the flight was preceded by ground engine tests.

“With this flight, Gulfstream was willing to push the envelope to show what’s possible. They mobilised resources and personnel to demonstrate the future of sustainable aviation fuel,” commented Adam Klauber, VP Sustainability and Digital Supply Chain at World Energy.

The company said the SAF produced for the G600 flight reduces flight lifecycle emissions by 83% compared to its fossil equivalent. The 17% residual emissions, plus the ground transport emissions, are to be covered by an additional supply of SAF to Los Angeles International Airport. SAF certificates (SAFc), showing ownership of the book & claim credits are supplied to Gulfstream along with the physical SAF environmental document, known as ‘proof of sustainability’. Emissions are therefore eliminated using physical SAF plus the SAFc to reach net zero and so the emission reductions are fully within the aviation sector.

World Energy also supplied 100% SAF for research flights conducted by Boeing and NASA in October to examine the benefits of 100% SAF in reducing contrails during flight.

“These partnerships are in keeping with World Energy’s commitment as a first mover in the industry to advancing knowledge about the performance of SAF, which is a critical tool in decarbonising the hard-to-abate aviation sector,” said a spokesperson for World Energy.

Photo: Gulfstream G600 takes on aromatics-free 100% SAF produced by World Energy

Christopher Surgenor

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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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