French company VoltAero, led by former Airbus CTO Jean Botti, has started phase 1 tests to validate its hybrid-electric aircraft systems with a new iron bird test rig and a flying “prototype,” each based on a converted Cessna 337 Skymaster. The initiative could lead to quiet and efficient aircraft carrying between four and nine passengers. The company hopes that the reduced noise levels will help placate many airport authorities where conventional aircraft are being shunned due to noise—at Toussus-le-Noble near Paris, for example.
During an open day at the company’s Aérodrome de Royan-Médis base on October 18, CEO Botti and technical director Didier Esteyne—who were the driving force behind the E-Fan electric aircraft while they were at Airbus—explained their new project to AIN.
VoltAero uses two forward-facing electric motors (60 kW each) to allow “nearly silent” takeoffs and landings, while the “push” is provided by three 60 kW electric motors (total 180 kW) driving a pusher prop. Installed at the rear is also a 170 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 recharging the batteries.
The 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.
The five REX90 60 kW electric motors have been sourced from the Czech Republic. Paul Lemoire, electrical engineer with VoltAero, said the 10-kg battery racks include the BMS (battery management system) with five sub-packs per motor and can be changed out in two hours. The “electrical range” is 30 minutes including takeoff and climb, and 40 minutes if only used for cruise. There are five battery racks on each side of the aircraft, with 15 in the nose, together driving the aircraft’s five electric motors (three in the tail and one on each wing).
The mtow is two metric tons and, according to Lemoire, the aircraft needs 300 kW for takeoff and climb.
Didier Esteyne, who was involved in the Cri-Cri in 2011 and E-Fan in 2015, said the Cessna 337’s structure is perfect because parts can be removed easily to add batteries. He said a normal single-engine airplane “would not work.”
Jean 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 partly 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 safety “none of the blades will turn,” said Botti. The piston engine is at idle for taxiing and for the whole flight although it will run at a higher rpm when recharging the batteries.
Botti told AIN that funding of the project was “well covered for all iron bird and flight testing” but “not for phase 2.” 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 for very low rate production “by the end of 2021.”