RTX has validated “sustained operation” of its hybrid-electric STEP-Tech (Scalable Turboelectric Powertrain – Technology) demonstrator, even as it eyes potential future developments of the system.
Comprising an undisclosed Pratt & Whitney Canada thermal engine, electrical generator, batteries, and motors and motor controllers from Collins Aerospace, the series-hybrid STEP-Tech system is intended for prototyping future distributed propulsion concepts.
Currently configured for 250kW, the system is suitable for applications in the 100-500kW class, with capability to scale to 1MW and beyond.
Potential uses could include advanced air mobility vehicles or future high-speed vertical take-off and landing aircraft.
During the recent milestone activity, energy was transferred between the various system components through the high-voltage electrical network.
Tests included validating the capability of STEP-Tech’s battery system to start the thermal engine and use electrical power produced by the turbogenerator to charge the batteries used to drive the electric propulsor motors.
“This was the first time we were able to exercise the battery system and also work through our 800v DC distribution system as well,” says Zubair Baig, senior technical fellow, electrical systems at Pratt & Whitney, briefing journalists in early July.
“It is breaking new ground for us so we are really excited – we are on our way to a full system demonstrator as we go from the turbo-generator to our propulsors, which is the ultimate goal of the programme.”
Evaluations have been conducted at the RTX Technology Research Center in East Hartford, Connecticut.
As the target for STEP-Tech is to mature the electrical elements of the system, rather than the thermal engine, a standard P&WC powerplant has been selected for the demonstration phase.
However, Baig says an all-new thermal engine is also being contemplated as a future step.
“We are looking into options for a bespoke unit as well,” he says, potentially deriving the engine from that used a project in Canada to add a hybrid-electric powertrain to a De Havilland Canada Dash 8-100. “It is still one of those areas where we are looking into options.”
Meanwhile, a Collins Aerospace-led project part funded by the EU’s Clean Aviation initiative to develop a 500kW hybrid-electric architecture has achieved several preliminary design review milestones.
Running since January 2023 and costing a total of €45 million ($48.7 million) – including €34 million from Clean Aviation – project HECATE’s goal is to mature the technologies needed for “power distribution networks that can safely handle high power and high voltage levels, ultimately up to several megawatts,” according to EU funding documents.
Key challenges to address are system weight and power density, plus “high-voltage challenges with lightning, arcing and electromagnetic interference as well as optimised thermal management.”
The HECATE project will demonstrate an architecture of around 500kW in a ‘copper bird’ at technology readiness level (TRL) 5 by 2025, potentially leading to flight tests of a system in Clean Aviation’s second phase.
Collins Aerospace Ireland is coordinating the HECATE effort, and has passed the PDR for the project’s power conversion and secondary distribution systems. Consortium partner Safran, meanwhile, has achieved the milestone for the primary distribution, power management systems and cabling.
Collins says the project is on track to achieve TRL4 and a critical design review by year-end.
In all, there are 33 direct participants in the consortium, including airframers Airbus Defence & Space and Leonardo, alongside numerous research bodies and universities. Three UK entities are also partners, funded by the UK Research & Innovation body.
