A few months ago, VoltAero announced that phase one tests were underway for a hybrid-electric power system in order to validate it using an iron bird test rig and a flying "prototype," based on a Cessna 337 Skymaster aircraft, which has been converted by the French company into the Cassio 1.

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Using VoltAero's proof-of-concept initiative, VoltAero hopes to pave the way for a new type of fixed-wing aircraft which will be quiet, efficient, and capable of carrying four to nine passengers at a cruise speed of 200 knots for a duration of 3.5 hours. In comparison to an electric vertical takeoff and landing (eVTOL) design, it would be much easier to certificate such an aircraft.

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As of March 10, 2020, Cessna 337 flying demonstrations equipped with Safran ENGINeUS electric motors are on the way to being tested. Two of the ENGINeUS electric motors are being installed forward-facing on the wings, and later testing will be conducted on the hybrid power module, which is currently undergoing ground-based validation tests as of March 2020.

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As a result of this test, the company announced it was making a major step towards validating a new family of hybrid-electric airplanes, which it said are intended for owners and operators of private aircraft, air taxis and charter companies, as well as for use in utility-category applications.

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During their tenure at Airbus, Jean Botti, who was co-founder and CEO of E-Fan and Didier Esteyne, who was technical director, played an integral role in the development of the E-Fan electric aircraft.

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To enable “nearly silent” takeoffs and landings, the “Cassio I” is equipped with two forward-facing electric motors named Safran ENGINeUS 45 (80 hp/60 kW each). However, the “push” is supplied by three Emrax electric motors with 80 hp (60 kW) each driving a pusherprop.

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As a result of the internal combustion engine, which generates 402 horsepower (300 kW), the pusher can be driven automatically if the “puller” electric engines fail or need more power, enhancing safety, particularly during takeoff/go around, as well as for charging batteries. VoltAero and Solution F developed the engine, which is based on a Nissan V6 design.

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VoltAero will be assembled at the Nouvelle-Aquitaine region of France, which is supporting the project. In addition to Solution F, which developed the first manned electric helicopters and contributed significantly to the E-Fan, and Aéro Composites Saintonge, which contributed to the E-Fan project and has since developed the VoltAero demonstrator aircraft battery assembly and other components. Royan-Médis has developed the ground-based iron bird rig.

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The 22-pound (10-kg) battery racks from VoltAero include a battery management system (BMS) with five sub-packs for each motor and can be replaced in two hours, according to VoltAero. Including takeoff and climb, the battery range is 30 minutes, but if used only for cruise, it is 40 minutes. Each of the five electric motors on the aircraft is powered by a battery rack on each side, while 15 are located in the nose.

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It would be "too complicated to fly" if the aircraft did not have a complex power-management system, according to Botti. There will be only one power lever on the aircraft, using a “module de puissance” (power module) that will make it "simple to fly." VoltAero has already partially patented a software package developed based on phase 1 tests. Having “two sources of power” minimized the need for a parachute, according to Botti.

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A unique feature of the VoltAero craft is its electric nosewheel drive, which will prevent the blades from turning while taxiing for added safety. Although the piston engine will run at a higher rpm for recharging the batteries, it remains at idle for taxiing and the entire flight.

There will be a fully automatic flight management system in phase 2 of the production aircraft, and the aircraft will ultimately be an all-composite aircraft. 

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It had been announced by the company in June of this year that it would be using the CS-23 category (delivered with a maximum takeoff weight of under 2.5 metric tons) to obtain certification with the French industry regulator, the DGAC.

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The Cassio hybrid electric aircraft family of aircraft was revealed by VoltAero in May 2020 in a significant development. Three variants of the single pusherprop aircraft are planned to be offered, all of which feature distinctive aft main wings and tail booms as well as forward canards. In addition to the Cassio 330, which will accommodate four passengers and has a combined hybrid-electric power rating of 330 kW, the Cassio 480 (480 kW), and the Cassio 600 (600 kW), there will be a total of ten seats.

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As part of its range, the Cassio family will offer a maximum range of 920 miles and a cruise speed of 200 kt, making it ideal for a variety of business and general aviation applications, including air taxis. According to VoltAero, the aircraft will be able to reach a takeoff and landing distance of less than 1,800 feet and will be capable of operating for up to 10 hours a day, allowing multiple rotations to take place. To comply with the CS-23 requirements, the maximum takeoff weight will be below 2.5 tonnes (5,511 pounds).

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It is a proprietary propulsion system that is powered by three electric motors that operate at 60 kW each, which is at the center of the Cassio's propulsion system. In standard operation, electric motors would be used for takeoff and landing (partly to reduce noise), while the engine would extend range. It is unlikely that the production aircraft will have the two forward-facing sets of propellers and high wings as shown on the Cassio I prototype.

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As a result, the company intends to manufacture the all-composite aircraft in a purpose-built final assembly line in the Nouvelle Aquitaine region of southwest France. In addition, it will be seeking licensing partners in the American and Asian markets for the aircraft.

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With deliveries scheduled to begin in 2022, VoltAero expects to produce 150 aircraft annually at its full rate, which is expected to reach peak production by 2025 or 2026, according to Botti. The project will entail an initial investment of €70 million ($79 million).

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A full-electric takeoff and landing will normally be used, so the operation will be quiet. As for a flight of less than 125 miles (200 kilometers), Botti said all-electric power could be used; a “mild” hybrid operation could be used for a flight between 125 and 375 miles; and a “heavy” hybrid operation for flights above 375 miles, with a maximum range of 813 miles. It is estimated that the fuel tanks in the vehicle are currently holding 120 liters (31.7 U.S. gallons).

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One of the most important aspects of the design is the automated power management, in which there are two levers; one for electric power and one for thermal power. 

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Earlier this year, KinectAir, a US company that specializes in smartphone booking, announced a deal with VoltAero to become a launch customer - the company estimates that between 10 and 20 aircraft will be ordered. VoltAero plans to incorporate KinectAir's smartphone booking app directly into its intelligent cockpit.

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A combination of VoltAero's proprietary hybrid-electric "power module" and a pair of Safran ENGINeUS electric motors enabled VoltAero to achieve its first flight powered by the Cassio 1 technology on October 13. As of then, it indicated that type certification and service entry would take place in late 2022 or early 2023, which suggests a slight slip in the program schedule.

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It was announced on October 21 that VoltAero would partner with airport group Edeis to develop infrastructure for commercial operations of the Cassio aircraft. To promote the aircraft to potential operators and local political leaders, the partners would tour France for 10 cities the following week.

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An airframe for the hybrid-electric Cassio has been announced by the company on October 29 in partnership with the Belgium-based Sonaca Group. The Cassio will be manufactured by Sonaca in partnership with an aerostructures manufacturer, who has not yet been identified. This marks a critical point in development as the Cassio transitions from a digital rendering to being a production-ready aircraft. Deliveries of the Cassio 330, VoltAero's smallest variant, are now expected to begin in 2023.

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Among several "game-changing start-ups" named by the European Innovation Council (EIC) on November 19, 2020, VoltAero received a grant of €2.1 million and an equity portion of up to €11 million. With the EIC's support, VoltAero strengthens its position in the European UAM market as part of Europe's Green Deal Strategy and Recovery Plan.

The VoltAero team enlisted three former Airbus colleagues as well as former colleagues of VoltAero founder Jean Botti in September 2021: Pilar Albiac-Murillo, a former executive vice president and chief operating officer for Airbus Defence and Space; Charles Champion, a former executive of Airbus' United States operations; and Sean O’Keefe, a former chief executive of Airbus' US operations. With these three additions, VoltAero will be able to reach its goal of bringing the Cassio to the market by the year 2023.

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For the Cassio prototype, Electric Power Systems agreed to provide VoltAero with energy storage systems as part of an agreement signed in January 2022.

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It is expected that Jean Botti and VoltAero, the startup founded by former Airbus E-Fans program pioneers, will be able to attract a lot of customers and investors. By deciding to use a conventional fixed-wing aircraft and a proven design derived from the Cessna 337 Skymaster aircraft, they improve their chances of getting the Cassio to market more quickly.

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The question remains as to whether VoltAero is sufficiently funded to get the Cassio certified and into production, which is not entirely clear. As far as the company is concerned, it is reported that the French region of Nouvelle Aquitaine is a "key supporter" although it has not been reported to what extent this means in terms of direct financial support.

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Certainly, there are compelling arguments for choosing this aircraft with this combination of engines, but it is important to note that the aircraft doesn't have the capability of short takeoff and landing as would be needed to operate in extremely tight spaces. 

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There are significant signs that the Cassio program will take a significant turn for the better in the future when the significant design shift to production versions is announced in May 2020. In order to stay on track with its ambitious certification timeline, the company has adopted a rather traditional fixed-wing architecture, which provides the basis for this approach. 

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A new partnership between VoltAero and French airport group Edeis, announced at the end of October 2020, has further strengthened the program by solidifying VoltAero's position in the market.

Featuring hybrid-electric power ratings of 330 kW, the Cassio belongs to VoltAero's hybrid-electric STOL aircraft family.