Back in October 2018 VoltAero reported that phase one tests had started aimed at validating a hybrid-electric power system using an iron bird test rig and a flying “prototype,” each based on a converted Cessna 337 Skymaster aircraft.
According to VoltAero, its proof-of-concept initiative could pave the way to quiet and efficient clean-sheet fixed-wing aircraft carrying between four and nine passengers with a 3.5-hour duration and a cruise speed of 200 knots that could be certificated far more easily than an electric vertical takeoff and landing (eVTOL) design.
Testing of the Cessna 337 flying demonstrator fitted with Safran ENGINeUS electric motors commenced on March 10, 2020. Two ENGINeUS electric motors were installed in forward-facing positions on the wings. Later testing will incorporate the hybrid power module, which as of March 2020 was continuing ground-based validation tests.
The company said it was a major step towards validating the hybrid-electric powertrains for a new family of aircraft, tailored for operation by private owners, air taxi/charter companies for point-to-point regional travel, and in various utility-category applications.
Co-founder and CEO Jean Botti, the former Airbus chief technology officer and technical director Didier Esteyne were the driving force behind the E-Fan electric aircraft while they were at Airbus.
The “Cassio I” uses two forward-facing Safran ENGINeUS 45 electric motors (80 hp/60 kW each) to allow “nearly silent” takeoffs and landings, while the “push” is provided by three Emrax 80 hp (60-kW) electric motors driving a pusherprop.
Installed at the rear is a 402 hp (300 kW) internal combustion engine that facilitates a unique auto-start capability to drive the pusher if the “puller” electric engines fail or need more power, providing increased safety, especially during takeoff/go around, as well as for recharging the batteries. The engine is based on a V6 Nissan design that VoltAero has developed with partner Solution F.
France's Nouvelle-Aquitaine region is helping to support VoltAero and will be the location for final assembly. Also involved are Solution F, which created the first manned electric helicopters and played a key role in the E-Fan, and Aéro Composites Saintonge, which was also part of the E-Fan team and has since focused on the battery assembly and other components for the VoltAero demonstrator aircraft. It has developed the ground-based “iron bird” rig at Royan-Médis.
According to VoltAero, the 22-pound (10-kg) battery racks include the battery management system (BMS) with five sub-packs per motor and can be changed out in two hours. The “electrical range” (meaning endurance) is 30 minutes when including takeoff and climb, but 40 minutes if used only for cruise. There are five battery racks on each side of the aircraft, with 15 in the nose, together providing power to the aircraft’s five electric motors (three in the tail and one on each wing).
Botti said the aircraft will have a complex power-management system as otherwise it would be “too complicated to fly.” It will have only one power lever, for example, using a “module de puissance” (power module) to make the aircraft “simple to fly.” This will be a software package created by VoltAero, derived from phase 1 tests and has already been partially patented. Botti noted the safety benefit of having “two sources of power,” helping to negate the need for a parachute.
Another unique feature of the VoltAero craft will be an electric nosewheel drive for taxiing, when for added ground operations safety “none of the blades will turn,” said Botti. The piston engine is at idle for taxiing and the whole flight, although it will run at a higher rpm when recharging the batteries.
Ultimately it will be an all-composite aircraft, and the phase 2 full production aircraft will have a fully automatic flight management system. The company is hoping to start a low rate production by the end of 2021, with first deliveries in 2022.
Before the Paris Air Show in June 2019, the company said it had agreed on a certification plan with the French industry regulator, the DGAC, using the CS-23 category (under 2.5 metric tons maximum takeoff weight).
In a significant development in May 2020, VoltAero revealed the production configuration for its Cassio hybrid-electric family of aircraft. It intends to offer three variants of the single pusherprop aircraft, featuring a distinctive aft main wing and tail boom plus a forward canard. These will include the four-seat Cassio 330 with a combined hybrid-electric power rating of 330 kW, the six-seat Cassio 480 (480 kW), and the 10-seat Cassio 600 (600 kW).
Intended for a variety of business and general aviation applications, including air taxi, the Cassio family will offer range of up to 920 nmi and 200-kt cruise speed. Takeoff and landing distance is projected to be less than 1,800 feet and VoltAero says the aircraft will be able to operate for up to 10 hours each day, allowing multiple rotations. Max takeoff weight will be below 2.5 tonnes (5,511 pounds) to comply with CS-23 requirements.
The hub of the Cassio’s proprietary propulsion system is an internal combustion engine that drives three 60 kW electric motors. In standard operations, the electric motors would be used for takeoff and landings (partly to reduce noise), with the engine extending range. The production aircraft will not include the Cassio I prototype’s two forward-facing sets of propellers and or the forward high wing.
The company intends to produce the all-composite aircraft in a purpose-built final assembly line in the Nouvelle Aquitaine region of southwest France. It will also seek partners for licensed production in North America and Asia.
Botti has said taking the project into production will require €70 million ($79 million) of investment. With deliveries from 2022, Botti expects VoltAero to produce 150 aircraft annually at full rate, which could be reached by 2025 or 2026.
Takeoff and landing will normally be full-electric, making for quiet operations. For a flight of less than 125 miles (200 km), Botti said all-electric power could be used; with “mild” hybrid operations for flights between 125 and 375 miles; and “heavy” hybrid” for ranges beyond that, with a maximum range of 813 miles. The fuel tanks at present hold 120 liters (31.7 U.S. gallons).
For the demonstrator, avgas is being used as the fuel but “the idea is to switch to biofuel,” said Botti. “We get a 20 percent fuel saving despite having around 400 kg extra weight for batteries,” he added.
Central to the design is the automated power management. The pilot(s) have two levers—one for thermal power and a second for electric. Pilots don’t have to be worried about how to distribute power between the puller and pusher propellers, said Botti. “So the pilot defines the hybrid strategy.”