Hybrid Electric - Likner litt på Cessna Skymaster - AW&ST

 

E-Fan Experience Spawns French Hybrid-Electric Startup

Graham Warwick

Airbus unveiled the all-electric E-Fan 1.0 with much fanfare in 2014, the little battery-powered demonstrator flying across the English Channel in 2015. But in 2017, the European giant canceled plans to enter the general aviation (GA) market with a pair of electric light aircraft.

Jean Botti was Airbus chief technical officer when the E-Fan 1.0 was developed. He left the company in April 2016, before Airbus canceled the E-Fan 2.0 and 4.0 to focus on different and larger aircraft, including the E-Fan X hybrid-electric regional airliner demonstrator now under development.

Now Botti is back in aviation and back in the electric aircraft business. He is the CEO of VoltAero, a French startup formed in September 2017. Didier Esteyne, test pilot for the E-Fan demonstrator, is technical director of the company, based at Royan-Medis Aerodrome in southwest France.

• Cassio 1 flight testbed is based on Cessna 337 Skymaster
• Production aircraft to be clean-sheet composite design

VoltAero is developing the Cassio, a hybrid-electric GA aircraft designed to seat four to nine and fly for 3.5 hr. including reserves. The Cassio 1 flight testbed, based on the already certified Cessna 337 Skymaster to reduce risk, is planned to fly in late February 2019. The clean-sheet, all-composite Cassio 2 prototype is to follow in 2020, and VoltAero plans to begin production deliveries in late 2021/early 2022.

The Cassio, like the distinctive Skymaster, has a “push-pull” propulsion system, but with unique features. Where the Cessna has piston engines in the nose and aft fuselage, the Cassio has two 60-kW electric motors driving tractor propellers on the wing and a “power pack” in the aft fuselage with a 170-kW piston engine and 150-kW motor driving a pusher propeller.

A combined power output of 440 kW and the combination of fuel in the wing and batteries in the nose and wing will give the production Cassio a 1,200-km (745-mi.) range with nine people aboard, says Botti. The aircraft will taxi using electric wheel motors, propellers not turning, and take off on battery power, for low noise, with the combustion engine in idle ready to kick in if there is a problem with an electric motor.

Above about 2,000 ft., the piston engine will begin producing power, both for propulsion and to begin recharging the batteries. Above about 5,000 ft., with the batteries depleted to around 50-60% charge, the naturally aspirated piston engine will run at its optimum, most fuel-efficient condition until the batteries are back above 90% charge then return to idle.

The Cessna 337 will be modified with electric motors in wing nacelles, engine and motor in aft fuselage and batteries in the nose and existing wing bays. Credit: VoltAero

The aircraft will then cruise on electric propulsion until the batteries are again depleted, when the combustion engine will kick in again to begin recharging. This cycle will be repeated several times during a flight, the balance between propulsion and charging maintained automatically. By doing so, fuel efficiency is maximized, says Botti. Designed to compete with single-piston aircraft from Cessna and Cirrus, the primary goal of the Cassio is to increase safety by providing dual sources of energy. “It can run on one or the other or both,” he says. “If you get into trouble, you add energy versus deploying a parachute." The Cassio is intended for point-to-point travel, both private and commercial, and a second objective is to reduce noise and emissions to enable takeoffs and landings at night. The third goal is fuel economy, achieved by operating the gasoline engine at its optimum point, significantly reducing fuel burn as well as wear. Combined with the reliability of electric motors, this will improve operations, Botti says. VoltAero is drawing heavily on experience with the E-Fan. Its partners on the Cassio are Aero Composites Saintonge (ACS), which helped Airbus build the demonstrator, and Solution F, which worked with Airbus to convert the E-Fan to hybrid-electric power. France’s Nouvelle Aquitaine region, where the E-Fan 2.0 and 4.0 were to be produced by VoltAir, a partnership of Airbus and Daher, is supporting VoltAero. Botti says the Cassio production plant will be in Aquitaine, at a location to be decided. For Cassio, ACS is focusing on the battery and components for the demonstrator. ACS is also developing the iron-bird systems rig at Royan-Medis, where components will be integrated and ground-tested before being installed in the flying testbed. The aft-fuselage power pack will not be fully integrated on the Cassio 1. Instead the piston engine and electric motor will drive the propeller shaft via belts. The integrated pack, with automatically controlled engine and motor on the same shaft, will be developed for the Cassio 2 prototype. This will be a new design, but will retain the push-pull propulsion layout of the Cessna 337. VoltAero is working with French civil aviation authority DGAC on certification of the Cassio. Botti says the company is funded by private investors and the Aquitaine region to complete testing on the iron bird and Cassio 1 demonstrator. The company then plans to raise funding for the Cassio 2 prototype, certification and production via future financing rounds.