The US Federal Aviation Administration has awarded US$25m to five aerospace companies under its Continuous Lower Energy, Emissions, and Noise research program to develop and test technologies that reduce aircraft emissions and increase fuel efficiency.
The two-year Continuous Lower Energy, Emissions, and Noise (CLEEN) projects are the latest in a series of research programs into sustainable aviation technologies that began in 2010.
Previous CLEEN rounds were larger, between US$100m and US$125m, and covered five-year work periods.
CLEEN contracts have been given to aircraft manufacturer Boeing, propulsion and systems suppliers GE Aerospace and Honeywell, as well as hybrid-electric aircraft developers JetZero and Heart Aerospace.
The funding is matched by the participating companies and will be used to develop technologies that improve fuel efficiency and reduce noise, nitrogen oxide (NOx) and particulate matter emissions.
CLEEN funding to fund Heart’s HYPER project
Heart Aerospace is to use its funding for a US$5.8m R&D project called Hybrid Propulsion Environmental Readiness (HYPER). The project will develop and test the turbogenerator for the hybrid-electric propulsion system Heart will use to power its ES-36 regional aircraft.
Heart, which was founded in Sweden but largely moved its operations to the US in 2025, is targeting entry into service in 2031 with Part 25 certification.
The ES-36 is a series hybrid that will use two megawatt-class turbogenerators, powered by commercially available jet turbines, to produce electricity in flight. According to Heart, the approach will extend the aircraft’s range from a 125-mile (200km) battery-only range to 745 miles (1,200km).
HYPER will begin with ground testing to evaluate how the turbogenerator, batteries and electric motors work together in different operating modes, before progressing to demonstration flights aboard the pre-production ES-36, which is scheduled to make its first flight in 2028. The project will generate data on energy use, fuel burn, emissions and noise to support ES-36 certification and inform the FAA’s approach to evaluating and certifying hybrid-electric aircraft more broadly.
The CLEEN award follows a US$4.1m grant Heart won in September 2024 from the US government to develop the avionics and software that will control its hybrid-electric propulsion system.
Ben Stabler, chief technology officer of Heart Aerospace, said, “The FAA’s continued partnership with Heart Aerospace will accelerate development of this key element of the ES-36’s disruptive hybrid-electric powertrain.
“Together, we are advancing technologies that will help bring to market a new generation of commercial aircraft that use less fuel, produce fewer emissions and make less noise, benefiting passengers, operators and the communities they serve.”
According to Heart, it has so far secured one order, for up to 100 ES-36s, from US-based charter operator JSX.
