Honeywell Reveals APU-Based Hybrid-Electric Power Plan

Credit: Moses Bunting,

In response to higher power requirements for the emerging autonomous air cargo and urban air mobility markets, Honeywell is developing a 1-megawatt turbogenerator based on the company’s HGT1700 auxiliary power unit (APU).

The new unit, which will begin demonstration tests in the third quarter, is two and a half times more powerful than the company’s first HTS900 turboshaft-based turbogenerator system announced in 2019. The larger generator, which weighs 280 lb., will build on lessons learned during the design and test of the smaller design, as well as from a 1-megawatt generator that Honeywell developed for DARPA’s XV-24A LightningStrike Vertical Takeoff and Landing (VTOL) hybrid electric X-plane.

Although the Aurora-developed XV-24A project was canceled in 2018, Honeywell continued work on the generator, which formed the design basis of the integrated 200-kW units unveiled with the HTS900 the following year. Designed to achieve an efficiency of 98% compared with 92% for traditional aircraft generators, the XV-24A unit was packaged with five times the power density of existing megawatt-class generators to enable the high levels of power required for electric propulsion.

The move to the larger turbogenerator, which is based on the APU developed for the Airbus A350 XWB airliner, also reflects what Honeywell sees as a shifting market trend toward more demanding power needs for electric aviation, particularly for nearer-term cargo applications. This was underscored after a muted response to the HTS900 initiative and a strategic shift by Honeywell to boost additional efforts in all-electric, battery-powered propulsion. This culminated in mid-2019 when Honeywell announced a collaborative deal with Japan-based electric automotive specialist Denso that was focused on all-electric and hybrid-power concepts.

But since then, the hybrid-electric market has begun to surge with a variety of cargo and passenger vehicle projects for missions requiring greater payloads and longer ranges. A range of startups are working on the first hybrid-electric types, including UK-based Faradair Aerospace, with which Honeywell signed a memorandum of understanding in December to collaborate on systems and a turbogenerator unit.

Faradair’s short takeoff and landing Bio Electric Hybrid Aircraft (BEHA) is a triple box wing concept designed to take off and land in less than 985 ft. Powered by a 1,600-shp turbine engine and 500-kW electric motor driving a contra-rotating ducted fan, the BEHA will take off using primarily battery power to reduce noise and emissions. The vehicle will transition to the sustainably fueled turbine to cruise and recharge the batteries, which provides a reserve power capability in case of engine failure. Honeywell’s turbogenerator will supply power for two magni500 electric motors, while the integration of the turbine and motors will be led by research and development company Cambridge Consultants.

The initially planned first member of the family is the MH1, a 55-ft.-span aircraft capable of quick change between 18 passengers, three LD3 cargo containers or 5 metric tons of payload. Faradair aims to fly a full-scale prototype by early 2024 and to deliver 300 BEHAs into service by 2030, of which 150 will be in a firefighting configuration. 

Guy Norris

Guy is a Senior Editor for Aviation Week, covering technology and propulsion. He is based in Colorado Springs.