Collins Completes Integration Testing On Electric Powertrain For Hybrid GTF

Electrical subsystems required to hybridize Pratt & Whitney’s Geared Turbofan (GTF) have completed initial integration testing in the U.S. and been shipped to Airbus in Germany for aircraft-level integration testing.

The hybrid-electric GTF is being developed under the Switch project within Europe’s Clean Aviation public-private research program. The goal is to demonstrate that electric machines can be integrated into a turbine engine to enable power extraction, insertion and transfer between the high- and low-pressure shafts to improve efficiency.

Called microhybridization, the technology is a key candidate for inclusion in Airbus’ next-generation single aisle, the eAction. The level of hybridization is mild—about 1 megawatt of electrical power in a 20-megawatt turbine engine—but could be used for taxiing, to boost power for takeoff, and to assist the turbine engine in transient operating conditions. This could result in a smaller, more fuel-efficient engine.

By allowing surplus power to be shifted from one shaft to the other, and between propulsive and non-propulsive systems, hybridization promises to improve energy efficiency. “One of the advantages of hybrid-electric propulsion is not to have this power takeoff wasted, but to use it,” says Pierre Durel, leader of Clean Aviation’s short- and medium-range aircraft thrust.

Led by MTU Aero Engines, Switch is a four-year, £67.6 million ($77.1 million) project launched in January 2023 and involving RTX companies Collins Aerospace and Pratt & Whitney along with GKN Aerospace and other industrial and academic partners.

Under Switch, integration testing of the hybrid-electric powertrain subsystems has been conducted in The Grid, an electric power systems laboratory at Collins in Rockford, Illinois. Equipped with 8 megawatts of power, the lab tested an 800-volt powertrain comprising megawatt-class motor generators, controllers and power distribution systems.

“Earlier this year, we started the first intermediate level of integration testing in the Grid,” says Todd Spierling, principal technical fellow for electrification at Collins. “We’ve completed that test and the hardware is now moving to Airbus Germany.”

In The Grid, powertrain subsystems were tested using simulated engine and aircraft systems. Once the equipment is installed and commissioned at Airbus in Ottobrunn, Germany, integration testing will bring in the batteries, energy management system and some real aircraft loads, he says.

“This is the largest integrated systems test conducted in The Grid since its opening in 2023,” says Kristin Smith, vice-president of electric power systems at Collins. The setup included two radial-flux, permanent-magnet motor-generators and their controllers, developed by Collins’ Solihull, England, facility.

Testing under the Switch project is planned to be completed by early 2027. A follow-on project expected to be awarded this year under Clean Aviation’s Call 4 funding round would then take the powertrain subsystems and integrate them into a GTF Advantage engine for ground testing to achieve technology readiness level (TRL) 5 by the end of 2029.

Under Clean Aviation’s Call 5 round, scheduled for award in 2028, a further project is planned to take the hybridized GTF into flight testing on a modified Airbus A380. Airbus has acquired an ex-Malaysian Airlines A380 for modification into an engine testbed under Clean Aviation’s Companion project, says Durel.

With completion of the Switch powertrain subsystem testing, The Grid is being reconfigured for another Clean Aviation project. Leia is a two-year, €49.4 million program led by Airbus to integrate and demonstrate non-propulsive electric systems for a hybrid-electric single-aisle aircraft.

“When it comes to integration, there are two sides to the coin,” says Spiering. “One side is the propulsion system, the batteries, motors and engine. Then there is the non-propulsive side, the traditional aircraft secondary systems.

“Leia focuses on how these elements of hybrid—the high-power machines, the high-voltage systems—integrate and interface with the non-propulsive stuff on the aircraft, the environmental controls and other kinds of loads,” he says.

Under Leia, Collins is to deliver four electric motor-generators, electronic controllers and power distribution equipment. Collins’ Nordlingen, Germany, site is providing solid-state power controllers and distribution panels and Nord Micro, a Collins company in Germany, is supplying environmental controls.

“Leia is more focused on development of the individual techno-bricks,” says Durel. “The idea is the electrification of all the major aircraft systems within a hybrid-electric architecture, where you have different sources of power involved.”

With Airbus heading toward decisions by the end of the decade on which technologies will make it into the eAction, the Leia team got a jump start on the project in December 2025. “It is only a two-year project. They are in a rush to get to the outcome of the project,” says Durel.

The project is planned to culminate in 2027 with ground tests at Airbus in Toulouse using the modified former A400M iron bird test rig. A Clean Aviation Call 5 project is planned to take the technologies to TRL 6 by 2030.

“Switch and Leia are essential building blocks to make the hybrid-electric short- and medium-range aircraft become a reality—they show the power of collaboration within Europe and beyond,” Durel says.