Video: VoltAero starts flight testing of hybrid-electric aircraft

Aircraft developer VoltAero has made the first hybrid-electric flight of its prototype aircraft in the west of France, as it aims for certification within three years and to be manufacturing 150 aircraft a year by 2025.

VoltAero plans to have started production of the final aircraft by the start of 2023 and to be producing around 150 aircraft a year by 2025.

The startup, which is headquartered in Royan, France aims to be one of the first companies to market with its 4-9 seater hybrid aircraft called Cassio, which VoltAero CEO Botti believes could radically alter the general and business aviation market.

VoltAero has been using two platforms so far in the development of its Cassio hybrid-electric aircraft – a ground-based iron bird for systems integration testing and a flight testbed.

The flight testbed is a modified Cessna 337 Skymaster, which was chosen for the airframe’s adaptability to Cassio’s “push-pull” propulsion concept.

The flight testbed was flown in electric mode using Safran Electrical and Power’s EngineUS 45 electric motors. A nacelle has been installed on each wing of the Cessna that accommodates two EngineUS 45 electric motors, along with lithium-ion batteries to provide “pull” propulsion.

Flight-Test Plan

Earlier in the year, VoltAero engineers removed the 337 Skymaster’s original front-facing internal combustion engine and replaced it with a smooth nose fairing. The original rear-mounted internal combustion motor was substituted by the hybrid power module – which incorporates three 60-kW EMRAX electric motors and a 250hp (184kW) internal combustion engine, both of which drive a common shaft for the “pusher” propeller.

VoltAero is headed up by former Airbus chief technology officer Jean Botti and technical director Didier Esteyene. Botti led the development of the E-Fan electric aircraft while at Airbus. The Airbus E-Fan, which first flew in 2014, was built by Esteyene at French company Aéro Composites Saintonge.

“I am very pleased with the testing as we accumulate time aloft and open up the aircraft’s flight envelope,” said Botti. “The current test phase is with the powertrain for our six-seat Cassio version, to be followed by validation of the final aerodynamic and powertrain configurations on both the four- and nine-seat Cassio versions.”

The testbed aircraft is expected to fly for around 20 hours before engineers modify it for its final 100 hours of flight testing by adding an optimized propeller on the rear hybrid power module.

“We picked the 337 as our testbed because we wanted distributed propulsion and nine seats. We wanted to be able to maximize power output and efficiency,” said Botti.

In the configuration to be validated during flight testing, the “pull” electric motors’ propellers will be used mainly during the Cassio’s takeoffs and landings, where it will operate in all-electric mode to reduce emissions. Batteries in the wings will provide electrical power.

For the 9-seat version an aft-mounted hybrid power module, three more electric motors, and a rear propeller will provide the “push” during cruise, with electrical power coming from the batteries installed in the nose fairing. The power module’s thermal motor will serve to recharge all of the aircraft’s batteries.

Business Market

The final version of the Cassio will weigh 2.5 tons to qualify for EASA’s CS-23 certification, will have a cruising speed of 200 knots, faster than aircraft made by direct competitors such as Cirrus and Cessna and a range of 800km. It will use 600kW of power and produce 20% fewer emissions than similar aircraft.

“The hybrid configuration means if there is a big issue with the electric side you can still land safely. We also want to stay in the kilowatt range for battery power. Certification in the MW range will take much longer,” he said

VoltAero is targeting the general and business aviation market with Cassio. The aircraft will require a maximum of 1,800ft. runway length for takeoff, opening up the possibility of using it at smaller airports. “I am convinced this is the future of general aviation. The lower cost of ownership and the business case works really well. We need to better use the small airport infrastructures. Most of them are idle,” said Botti.

There are around 30 hybrid fixed-wing aircraft in development around the world. Only a few series-hybrid electric aircraft have been successfully flight tested, including the Diamond E-Star and Ampaire’s Electric EEL.