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A unique four-engine aircraft has literally turned the future of aviation propulsion upside down. Developed with the support of EADS Innovation Works, this low-cost testbed is a French Cri-Cri ultra-light aircraft that has been modified for all-electric propulsion – with its original pair of nine-horsepower piston engines replaced by four brushless electrical motors, each powered by a high energy-density lithium polymer battery.

The electric Cri-Cri is helping to validate technologies that could be used in next-generation applications of systems for electric helicopters, drones and other platforms including power management controllers, sensors and batteries. Its development is the result of a collaboration involving EADS Innovation Works with Aero Composites Saintonge and the Green Cri-Cri Association of France.

Following its maiden flight in August 2010 and the build-up of airborne time based on its flight endurance of approximately 20-30 minutes, the all-electric Cri-Cri began aerobatic manoeuvres before – a world’s first for an electrically powered aircraft.

As one of the world’s smallest piloted airplanes, the Cri-Cri has a wingspan of 4.9 metres and a fuselage length of just 3.9 metres. In its conversion to the role of an electrical systems testbed, EADS’ aerostructures expertise was used in the introduction of lightweight composite structures to reduce the Cri-Cri’s weight in compensation for the additional mass of its four lithium polymer batteries. These batteries provide a combined power total of 22 kW, which is sufficient for take-off, climb and a short flight.

Blades for the future

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EADS Innovation Works has advanced its concept studies on a diesel-electric hybrid helicopter as part of research towards eco-efficient propulsion system solutions for smaller rotary-wing aircraft. Using highly efficient OPOC (Opposed Piston, Opposed Cylinder) diesel engines along with electrical motors to drive the main and the tail rotors, the system eliminates the main rotor gearbox and tail rotor driveshaft of conventional systems.

The hybrid helicopter’s diesel engines will operate on algae-based biofuel and their power output shafts are to be fitted with a generator that delivers power to electrical motors driving the main and tail rotors. Two batteries provide buffer storage for the energy, enabling the helicopter to operate on electrical power alone in short periods, including for quieter take-offs and landings.

Did you know...?

Compared to a twin-turbine-powered helicopter of today, the diesel-electric hybrid helicopter could lower fuel consumption and emissions by up to 50%.

Designed to stretch engineering

In this hybrid system, the combustion diesel engines run at their most efficient operating point, known as the “sweet spot,” while the electronics take care of managing the power demands for the main and tail rotors – along with the helicopter’s other electrical components. The electrical rotor drives allow for more flexible and power-optimised rotor rpm settings compared to conventional turbine or piston engine and gearbox designs.

: Zoom

The main rotor of the hybrid helicopter and its electrical drive can be tilted for cruise flight, enabling the fuselage to remain at its optimum alignment with the airflow, thereby minimising aerodynamic drag for a reduction in both power demand and fuel consumption.