An innovative hybrid propulsion system (HPS) for light aircraft – manned or unmanned – is being unveiled here at the Paris Air Show. The HPS was developed by an international consortium headed by Israel’s Ashot Ashkelon, Italian light aircraft developer CFM Air and Italian hybrid propulsion specialist Efesto.

Designed as a retrofit kit for Rotax 912 or 914 aircooled aero engines, the HPS incorporates a new gearbox developed by Ashot, a new propeller shaft, a DC/AC power converter and controller, and light, permanent-magnet synchronous electric motor acting as motor-alternator, coupled to the new shaft. The hybrid propulsion elements provided by Efesto also include a high-capacity lithium-polymer battery with power management system for power storage.

The HPS, which adds about 30 kg. in net weight, can operate in one of six specific modes, maintaining uninterrupted piston engine propulsion or decoupling the main engine from the shaft in case of a malfunction such as engine cutoff, or in circumstances requiring “silent mode” flight, a feature particularly interesting operators of unmanned aerial vehicles (UAVs).

Operating the two engines simultaneously increases the power available, thus shortening take-off run and safely clearing obstacles at the airport. On landing, the electric motor can be activated in counter-rotation mode, providing thrust reversal for shorter landing runs. The electric engine can also be used as an alternator for battery charging and as a starter for the main engine. Electric propulsion can also be used in the air, providing active vibration damping for smoother, low-level flight.

Here at the show the HPS debuts on the hybrid version of the DARDO light aircraft developed by CFM Air, serving as an optional safety measure and replacing an emergency parachute recovery system. HPS provides the pilot with six minutes of critical flight time after engine cutoff, which should be sufficient in which to find an emergency landing site and set down safely operating on electrical power only. HPS

is currently offered for the Rotax aircraft engines produced by BRP. Rotax engines are used by some 200 light aircraft types worldwide, and many could be candidates for the new hybrid propulsion system.