COLORADO SPRINGS—Rolls-Royce has revealed it is developing an all-new turbogenerator for use in advanced-air-mobility (AAM) applications including primary propulsion for electric short-takeoff-and landing (eSTOL) aircraft and extending the range of electric vertical-takeoff-and-landing (eVTOL) vehicles.
Rolls says the scalable system will complement the company’s expanding electrical-propulsion portfolio, enabling extended range on sustainable aviation fuels (SAF) and later through hydrogen combustion, as it becomes available.
The new small gas-turbine core of the turbogenerator is under development at the company’s Dahlewitz facility in Germany where it is expected to begin running by year-end, says Matheu Parr, customer director of Rolls-Royce Electrical. Speaking to Aviation Week, Parr says, “When we look at the turbogenerator market at the moment, it is [made up of] repurposed auxiliary power units and helicopter gas turbines. Given what the market actually demands in terms of fuel efficiency and power density, we see a strong opportunity for a new turbogenerator.
“We’re demonstrating a core at around 800 kW. The gas turbine is about 1 m (3.2 ft.) long plus a [following] electrical machine of about 0.5 m that is turning that mechanical power into electrical power,” explains Parr. “We are demonstrating it at 800 kW because that gives us all the kind of technology challenges we need. And we are working with customers to understand what is the right value that you need for a product.”
Rolls says the turbogenerator system will be scaled to serve a 500-1,200-kW power range. The company says this will allow it to provide power systems for aircraft on “new longer routes that our electric battery-powered aircraft can also support.” The turbogenerator is targeted at entry-into-service for around 2025-26.
“We believe the turbogenerator will be market-leading when it comes through,” says Parr. “When you think about the limitations of batteries, if you have an eVTOL traveling for 100 nm and, all of a sudden you want to go 200-250 nm, then using a gas turbine as a range extender is really a valid way of doing it.
“Equally we’re seeing in the eSTOL market where there’s a pull for a gas turbine to enable those aircraft configurations as well. We see a strong role for the gas turbine as an energy source, ideally burning SAF. Then the question is how do we integrate the electrical machine to all of that in a way that’s as power-dense as possible? And then integrated onto an aircraft?” he asks.
The project is focused in Dalhewitz to leverage the company’s business-jet turbofan design and development engineering expertise. “It’s very much a clean sheet because when you have the opportunity to design a turbogenerator for the first time, how do you make that as efficiently as possible?” says Parr. Unlike conventional gas turbines which incorporate design margins for a wide range of operating points, speeds and transient conditions, the turbogenerator is engineered to operate constantly at the same speed and power. “We don’t have to design for the same margins, so all of a sudden packaging gets tighter and the machine becomes more power-dense,” he notes.
