Emission free aircraft technology

Electrically powered propulsion of aircraft is a candidate innovative technology for meaningful reduction of fuel consumption and maintenance costs. This important technology governs the competitive edge of future aircraft technology. For Japan to take and hold a dominant position in the world in this field, JAXA established a precedent for manned flight using electricity-driven aircraft. Through FY2014, we promoted the "Flight demonstration of Electric Aircraft Technology for Harmonized Ecological Revolution (FEATHER)" project to hasten electric aircraft development in Japan.
Technologies obtained through FEATHER research will be developed further to propel research on electric motor-driven, aircraft-use power management technologies and combined with fuel cells, gas turbine engines, and more to explore hybrid propulsion systems with the capabilities for even better output.

Flight Demonstration of Electric Aircraft Technology for Harmonized Ecological Revolution (FEATHER)

The developed electric propulsion system for aircraft

Although electric propulsion systems that use batteries and motors run the risk of being too heavy under long-distance flight conditions, given that the batteries currently lack the necessary energy per unit weight, they create less fuel costs and offer better serviceability than conventional engines do. These advantages help bring down overall operating costs. Environmental compatibility is another key feature of electric propulsion systems, which generate no CO₂ during flight, produce minimal noise, and cause negligible shaking.

Under the FEATHER initiative, JAXA has researched and developed an aircraft-use motor system that can be installed on small aircraft, delivers high levels of output per unit weight, boasts excellent efficiency, and even regenerates power during descent procedures to charge its battery. The developed electric propulsion system was mounted on a prototype motor glider in place of its existing reciprocated engine. Then, a series of flight tests was conducted in 2014 and 2015 at several airports in Japan, including the Otone Airport in Ibaraki Prefecture and the Japan Air Self-Defense Force's Gifu Air Base. These tests marked the first full-fledged manned electric aircraft flights to take place in Japan.

Through the FEATHER project, JAXA successfully demonstrated the following:

• Avoidance of complete thrust loss in engine failure during climb by using the fourfold electric motor
• Regeneration of electricity during descent by using the motor and propeller
• Control of descent rate by regenerating without a conventional airbrake
• Continuous "regenerative soaring" free from descent in thermal conditions

Outline of electric motor driven glider system

Original motor glider	Diamond aircraft type HK36TTC-ECO
Width	16.33 m
Max. takeoff weight	850 kgf
Power source	Lithium-ion (Li-Ion) battery (75 Ah、128 V, 32 batteries in series)
Type of electric motor	Permanent magnet type synchronous motor
Max. output of electric motor	60 kW
Inverter	IGBT
Cooling	Water cooling
Crew member	1 person

Hybrid propulsion system

By further development of technologies obtained through assessment of FEATHER, we are promoting studies of this technology, which dramatically improves environmental adaptability through the application of electric-powered propulsion systems, low-carbon fuels such as liquid hydrogen, and new alternative fuels such as biofuels. One example of this technology is a hybrid propulsion system with improved efficiency which uses liquid hydrogen, and a high-efficiency generator using a fuel cell/gas turbine combined cycle as the power source. Concepts of these promising propulsion systems will be compared. Technological verification tests will be performed after verification of their technological feasibility.