FES (Front Electric Sustainer)The creators of Front Electric Sustainer (FES) are Luka Znidarsic and Matija Znidarsic, both experienced sailplane pilots and mechanical engineers in Slovenia. Front refers to the motor’s location, right in the nose of the sailplane. A 0.9 meter carbon fibre propeller automatically extends when the outrunner is operating. When not in use, the propeller blades fold against the nose of the sailplane thus reducing drag. Each blade weighs just 230 g and is 1.0 m in diameter. The Znidarsic's developed their own brushless DC synchronous permanent magnet electric motor and controller for the application which is light, small and mounted on top of main whell box. The motor is 5 kg (11 pounds), and puts out 15 kW (20.1 horsepower) at 85 Volts. Total weight for the power package is 35 kg (77 pounds), with Kokam lithium-ion batteries in two packs ( each behind the rear spar, balancing the weight of the motor and propeller in the nose ). If batteries are discharged during flight using the motor, they are easily accessible from the top of the fuselage so that you can take them out for charging. Unlike lead acid batteries, Li-Po batteries can be stored for 3 or 5 months without significantly losing charge. Charging time of batteries is about 4 hours using the cell balancers.
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