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

Correspondent

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