Vertiflite May/June 2021

N umerous electric vertical takeoff and landing (eVTOL) designs rely on hybrid electric propulsion to offset the limited power density of current battery technology (see “Halfway to Paradise?” Vertiflite , Sept/Oct 2020). Hybrid-electric solutions now under development maximize design freedom by using reciprocating or turbine engines to drive generator sets to power distributed electric propellers or fans. Hybrid architectures can recharge batteries for quiet flight or battery-augmented takeoffs. VerdeGo Aero In March, VerdeGo Aero in Daytona Beach, Florida, revealed details of its third-generation hybrid-electric propulsion system for serial and parallel applications in electrified aircraft. The VH- Fuel-burning engine-generator sets offer choices of efficient power schemes and extended endurance for eVTOL vehicles. This round-up highlights some of the current plans and progress. Hard-Core Hybrids By VFS Staff

3-185 hybrid generator set integrates a modified four-cylinder, 230-hp (170-kW) Röder reciprocating engine with a customized generator/motor, control electronics and cooling systems to provide 185 kW output power. The generator set has a dry weight around 650 lb (295 kg) and can be paired to provide two completely parallel systems with 370 kW combined output. “It positions us in a nice design space where we have a much higher equivalent energy density than the best battery packs on the market,” said VerdeGo Aero CEO Eric Bartsch. The hybrid-electric propulsion package will be available in a direct- drive package or with a mechanical output shaft and clutch. “There are a lot of different operating modes,” noted Bartsch. “The simplest one is to just use it as a source of electrical power and route that power out the bus to motors elsewhere on the aircraft. That’s most common.” Bartsch added, “What we’ve found is there are some customers who have a main propulsion unit, a propeller or a rotor overhead, where a lot of power needs to go... The output shaft could split the power from the piston engine to a main propeller or rotor while the generator powers a distributed electric propulsion array.” Aircraft designers could shut down the motor and drive the generator with a battery pack alone or draw on combustion engine and battery power simultaneously to provide 370 kW burst power for takeoff and drop down to battery power for greatest cruise efficiency. The new engine-generator set is largely air-cooled but includes a small, self-contained liquid cooling system. “From the airframer’s perspective, it’s an air-cooled system,” explained Bartsch. A purpose-built control system governs the generator, power-distribution electronics and cooling system. “We’re able to deliver very consistent power output [and] maintain consistent voltage with the control architecture we’ve got.What’s important is to have a highly reliable source of energy that can interact well with the battery pack, so you’ve got a fully hybrid system.”

May / June 2021

VerdeGo’s hybrid-electric propulsion package will be available in a direct-drive package or with a mechanical output shaft and clutch to accommodate series and parallel operating modes. (VerdeGo) 64