RTX Hybrid-Electric Demonstrator Moves Closer to Flight

In a quiet control room, a small group of engineers gathered around a bank of monitors. Many of them had spent years working toward this moment. Then, with the click of a mouse, power surged through a system that could help redefine the future of regional aviation.

The system coming to life was an early version of the RTX Hybrid-Electric Flight Demonstrator’s experimental propulsion architecture. This project aims to combine a conventional thermal engine with electric propulsion to dramatically improve fuel efficiency. If successful, the technology could open the door to a new generation of cleaner, more efficient regional aircraft.

The initiative is the result of a broad collaboration across the aerospace industry. Supported by both the Canadian federal government and the provincial government of Quebec, the demonstrator brings together the expertise of Pratt & Whitney Canada, Collins Aerospace, the Swiss electric aviation specialist H55, and several academic and research partners.

At its core, the programme reflects RTX’s strategy of integrating expertise from across its aerospace divisions. Pratt & Whitney Canada contributes the advanced thermal engine, Collins Aerospace provides a powerful one-megawatt electric motor and associated systems, while H55 supplies a sophisticated 200-kilowatt-hour battery system. The startup’s involvement is backed in part by RTX Ventures, the company’s venture capital arm.

The first two prototypes of H55’s aircraft, propelled by the company’s fully electric propulsion technology

Together, the partners hope to prove that hybrid-electric propulsion can deliver a 30% improvement in fuel efficiency compared with today’s most advanced regional turboprop aircraft.

The demonstrator will ultimately fly aboard a modified De Havilland Canada Dash 8-100, a regional turboprop aircraft widely known for its reliability and efficiency. By combining traditional and electric propulsion, the project seeks to optimise performance across different phases of flight.

The propulsion system pairs Pratt & Whitney’s fuel-burning engine with Collins Aerospace’s high-power electric motor. A specially designed gearbox links the two systems, allowing them to drive the aircraft’s propeller either individually or together, depending on operational needs.

In cruise flight, the conventional engine will provide the majority of the power. During energy-intensive phases such as take-off and climb, however, the electric motor will assist the engine, providing additional thrust and reducing fuel consumption. The motor will also play a role during taxi operations, potentially allowing aircraft to move on the ground using electrical power alone.

Power for the motor comes from the demonstrator’s large battery pack, which stores 200 kilowatt-hours of energy, roughly equivalent to the amount of electricity an average household might use in a week.

https://youtu.be/rqWjgpm-f4k

One of the motivations behind hybrid-electric aviation lies in the inherent efficiency difference between mechanical engines and electrical systems. Traditional thermal engines convert only around 30 to 40% of their fuel energy into useful propulsion, with the rest lost through heat and friction. Electric motors, by contrast, can convert more than 90% of their electrical energy into mechanical output.

Despite this advantage, applying electric propulsion to aircraft presents major engineering hurdles, particularly around weight and high-voltage management. Batteries capable of storing sufficient energy are still relatively heavy and in aviation every kilogram matters. The heavier an aircraft becomes, the fewer passengers or cargo it can transport.

Engineers, therefore, focused on reducing weight throughout the hybrid propulsion system. Collins Aerospace worked alongside the RTX Technology Research Centre to develop lighter components using advanced materials, high-efficiency magnets and wide band-gap semiconductor technologies. These innovations allow greater power output without significantly increasing mass. “We’re developing some of the highest power-density electric motors and controllers in the industry,” explained Collins Aerospace engineering director Joshua Parkin. “Every kilogram counts when you’re designing systems for flight.”

Hybrid propulsion also introduces electrical challenges rarely encountered in traditional aviation systems. Thousands of battery cells connected together operate at extremely high voltages, increasing the risk of overheating or electrical arcing, an event in which electricity jumps across gaps and creates a small but potentially dangerous arc. “The voltage levels we’re working with exceed anything currently in production aviation systems,” said David Venditti, Pratt & Whitney’s programme manager for the demonstrator. “Normally, aircraft propulsion systems don’t rely on batteries.”

To address these risks, engineers incorporated several layers of safety protection into the battery architecture. H55’s battery design, already proven in smaller electric aircraft, serves as the foundation. Pratt & Whitney Canada then enhanced the system with additional protective features tailored for the demonstrator aircraft.

Among these improvements is a specialised fire-resistant containment box capable of venting gases or flames in an emergency. The battery installation is also modular, allowing multiple battery units to be distributed throughout the aircraft to better balance weight and improve safety.

H55 brings considerable experience to the programme. The company originated as a spin-off from the Solar Impulse project, which famously circumnavigated the globe using only solar power and batteries.

“Our team has built and flown six electric aircraft with more than 2,000 hours of flight time without any incident,” said Anthony D’Ambrisi, who leads design, testing and certification for H55’s electric propulsion systems. “That experience helps ensure the system we deliver is both safe and certifiable.”

Developing the hybrid demonstrator has required solving numerous problems that previously had no clear answers. Even basic infrastructure proved challenging. When Pratt & Whitney first installed lithium-ion batteries in its test facilities, engineers had to construct a special ventilated cabinet roughly the size of a small moving truck to house them safely. Charging the battery system presented another hurdle: no suitable high-capacity aircraft charger existed at the time.

Working with the Innovative Vehicle Institute and Canada’s National Research Council, the team eventually developed a custom charging solution, essentially a trailer-sized power system capable of delivering the required electrical load.

These lessons have already begun influencing other hybrid-electric initiatives across RTX. Projects such as the Airbus PioneerLab hybrid helicopter demonstrator, the EU-backed SWITCH geared turbofan programme, and various advanced air mobility concepts are benefiting from the knowledge gained through the demonstrator programme.

For engineers like Rémi Robache of Pratt & Whitney, witnessing the first full-power ground test marked a major milestone after years of work.

Over the coming year, the hybrid-electric propulsion system will undergo further ground testing before being installed in the modified Dash 8 aircraft with support from flight-test specialist AeroTEC in Moses Lake, Washington.

When the system finally powers the aircraft into the sky for the first time, it will represent more than just a technological demonstration. It will provide valuable data on how hybrid-electric propulsion behaves in real flight conditions and how it might shape the next generation of regional aircraft. As Robache noted, running an engine in a test cell can prove a concept. Flying it, however, reveals its true potential. “This project pushes us outside our comfort zone,” he said. “But that’s exactly how aviation innovation happens.”