The turboprop demonstrator, powered in part by batteries, aims to show improvement in fuel efficiency and explore design possibilities of the future
The intricate web of cables, hoses and wires waited in a test cell at a Pratt & Whitney Canada facility on the outskirts of Montreal.
In a control room nearby, about a dozen people – some of whom had worked on the system for years – gathered and watched. With the click of a mouse, the power began flowing to their creation.
That creation was an early version of the RTX Hybrid-Electric Flight Demonstrator’s experimental propulsion system for a regional aircraft. It will pair a thermal engine with an electric motor – and, the team hopes, tap into a new era of fuel efficiency for aviation.
The project is supported by the Canadian federal government and provincial government of Quebec along with a range of partners across industry and academia. It also reflects RTX’s company-wide approach to innovation; it combines an advanced thermal engine from Pratt & Whitney Canada, a 1-megawatt electric motor from Collins Aerospace, and a 200-kilowatt-hour battery system from the startup H55, backed in part by RTX Ventures, the company’s venture capital arm.
The goal of the project is to show a 30% improvement in fuel efficiency compared to today’s most advanced regional turboprops. The team also hopes the project will show what’s possible in designing future aircraft.
“Pratt & Whitney is the quintessential thermal engine maker, and Collins Aerospace is the quintessential aircraft system supplier on the planet,” said David Venditti, Pratt & Whitney’s program manager for the demonstrator. “There’s no other place really in the world where we have all of those experts and resources coming to bear and developing a technology like this.”
Managing high-voltage systems
Hybrid-electric propulsion for a regional aircraft requires thousands of battery cells linked together operating at high voltage levels. That creates a risk of overheating or electrical arcing, where electricity jumps from its path and forms a miniature lightning bolt between the battery and something next to it.
Having to solve for arcing is a relatively new problem in aviation, Venditti said.
“The voltage level we’re using for our system surpasses anything that’s in production right now in aviation,” he said. “Normally you don’t have batteries assisting in the prolusion of aircraft.”
The team is using several methods of protection, but one of the main solutions is the design of the battery itself.
For help on the battery system, Pratt & Whitney enlisted H55, a Swiss company with backing from RTX Ventures. The demonstrator’s battery is based on technology H55 has already put into flight on smaller aircraft, including an all-electric two-seater.
RTX’s demonstrator is much larger but will rely on a modified version of H55’s existing system, with more batteries and added protections at the aircraft level. Pratt & Whitney Canada built on H55’s safety mechanisms with features specific to the demonstrator, including an extra fireproof box that can vent gases and flames in an emergency. It is also modular, meaning batteries can be installed throughout the aircraft to distribute weight.
By using a battery system whose baseline version is already in flight and has passed relevant European Union Aviation Safety Agency tests, Pratt & Whitney can take advantage of a system that’s designed for safety and proven compliance, said Anthony D’Ambrisi, who leads design, testing and certification for H55’s electric propulsion systems.
“Our team has built and flown six airplanes with more than 2,000 hours of electric flight time without any incident,” D’Ambrisi said. “H55 has accumulated hands-on experience in certification and airplane integration, allowing us to deliver Pratt & Whitney with a safe, efficient and certifiable product.”
Advancing the unknown
H55 is a spinoff of Solar Impulse, a project that resulted in an airplane that flew around the world powered by just solar panels and batteries. That accomplishment, D’Ambrisi said, showed H55’s cofounders that electric propulsion was no longer a technology of the future.
“A lot of people from the aerospace industry were thinking it will be in the far future. We see the change arriving already today,” D’Ambrisi said. “I think the team here at H55 is proud to set the standard and show that this technology works well, it’s safe and can be certified. It’s real. It’s not just papers or presentations anymore.”
At RTX, the demonstrator has already marked many firsts. Teams at Collins Aerospace and Pratt & Whitney overcame many challenges as they modified the engine and electric motor and worked to integrate the two.
For example, it was the first time Pratt & Whitney had installed lithium-ion batteries in a test cell, which required building a special, ventilated cabinet the size of a small moving truck to house them. And it was the first time they had to charge a battery of its size – only there wasn’t a charger on the market that could do it, so they worked with the Innovative Vehicle Institute and the National Research Council of Canada to build one.
“When you think about a battery charger, you think about this little thing that charges your laptop, but for an aircraft battery, it is a big trailer where you could fit a horse,” Robache said. “Now, all the big electric trucks have technology similar to us, but at the time when we wanted to do it, it didn’t exist, and we didn’t know. It was part of the unknown unknown.”
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