RED And Helix Challenge Turbine APU Market With Hybrid-Electric Generator

German aeroengine maker RED Aircraft has partnered with UK motor developer Helix to develop a hybrid-electric generator as a range extender for electric aircraft and auxiliary power units for regional, single-aisle and widebody airliners.

Combining RED’s A03 diesel-cycle piston engine with Helix’s SPX177 radial-flux electric motor, the series hybrid generator offers half the fuel burn and CO2 emissions of a turbine auxiliary power unit (APU) with lower maintenance costs, the companies say.

The generator system is capable of outputting up to 380 kW of peak electric power and 327 kW continuous power at up to 800 volts, with a dry weight of 350 kg (770 lb.). Based on RED’s certified compression-ignition aeroengine, the generator runs on jet fuel.

While heavier than a turbine APU, RED’s hybrid generator has a significantly lower fuel burn of 77 kg/hr. The APU in an Airbus A320 weighs 136 kg but burns 126 kg/hr. of fuel to produce 90 kVA of electrical power, according to International Air Transport Association figures.

The series hybrid generator produces less than half the noise of a turbine APU, 75 dBA and 50 m (160 ft.), RED says. “Many airports in Europe, such as Zurich, do not allow the APU to be turned on while on the ground,” says Christian Mundigler, RED Aircraft’s director for sales and commercial development.

There is no unsafe containment concern as a result of a turbine blade failure, Mundigler says, and no bleed air ducting between the APU and main engines. With a high-power density, the hybrid generator can in the future generate more electricity for aircraft systems, reducing the load on the main engines and further improving fuel efficiency, he says.

The RED A03 series is a V12 engine producing 550 hp and targeted at general aviation, small commercial aircraft and helicopters. A 600-hp version of the engine would produce 440 kW of electric power. The company plans smaller variants of the engine from a V6 down to in-line six- and four-cylinder versions producing from 280 kW down to 140 kW.

Helix’s SP117-137D motor/generator is coupled to the RED A03 engine via a 1:5.4 planetary transmission. With its roots in the motorsport industry, the UK company specializes in motors with small size and high-power density. The SP177-137D has a peak power density of 19.4 kW/kg but is just 192 mm dia. and 258 mm long (7.7 x 10.2 in.).

“For electrified aircraft, drones and air taxis, size is absolutely critical,” says James Edwards, chief engineer at Helix. “RED’s engines have an extremely higher power density in their own right, and there is a niche here where they can offer much better fuel economy than a gas turbine would—218 grams per kW is very good fuel efficiency.”