Front electric sustainer (FES) is a propulsion system for gliders that uses an electric motor powered by batteries and a foldable propeller. It is produced by LZ Design d.o.o. in Logatec, Slovenia. The system uses a 22 kW compact outrunner brushless DC electric motor located in the nose of sailplane. Power is provided by two lithium-ion battery packs. Lighter gliders are able to self-launch with FES. Heavier gliders can use it as a sustainer system, i.e. climb and cruise sufficiently high and far to avoid an out-landing. Although gliders with FES have a shorter range (70–100 km) under power than gliders with two-stroke gasoline sustainer engines (10 litres at 8.5 L/h at 100 km/h = 120 km) or jet sustaining engines (150–200 km), the electric motor can be expected to start reliably provided