What is FES?

FES is a powerfull high-tech
Front Electric propulsion System

Developed for high performance powered sailplanes.

How it is working

Main advantages

Higher efficiency and reliability

Reduced noise

Longer lifetime (no brush erosion)

Elimination of ionizing sparks from the commutation

More power

Overall reduction of electromagnetic interference

Searching for a suitable electric motor that would fulfil all our technical requirements was one of the first challenges when we were developing the FES System. After evaluating available electric motors on the market, it was quite logical and easy to decide: We need to design our own electric motor.

Bench testing of our first prototype was encouraging. After a few more prototypes, and numerous improvements, the end result become FES M100 motor as we know it today.

FES M100 Motor is an out-runner BLDC brushless synchronous permanent magnet motor with electronically controlled commutation system 3 phase. Because of the very little internal resistance of the motor, good performances are achieved in a wide range of power with excellent efficiency.

Shape of front torsional plate is adjusted according inner spinner surface of each specific FES sailplane type. Otherwise there are just minor differences between different FES motor types.

Technical characteristics:

Max. power:22 kW
Continuous power:20 kW
Diameter:180 mm
Lenght:100 mm
Weight:7,3 - 8 kg
Efficiency:up to 95 %

Main advantages

Carbon fibre composite foldable propeller

2 propeller blades – open using centrifugal force

High quality acrylic white paint – protection against moisture and erosion

Clockwise rotation

Diameters: 100cm /102cm / 120cm

Weight of each propeller blade: cca 260g

Very light carbon fibre foldable propeller is a special high-quality product developed by LZ design. It consists of two propeller blades, which are slightly bent to take the shape of front surface of the fuselage. There are different shapes of propeller blades and spinners for every type of fuselage.

The propeller blades open quickly, using centrifugal force when rotation starts. During propeller folding, when blades rotate closer to the fuselage, the pitch of blades is reduced. Drag of the folded propeller blades is minimal, especially at higher speed range. After propeller is stopped by electronic braking it is automatically positioned to horizontal position.


The glass fibre composite spinner has recesses for the middle section of propeller blades and a central hole for cockpit ventilation and for air cooling of the electric motor. The ventilation can be closed during soaring flight and must be opened when motor is running.

Construction material

Propeller blades are made of carbon fibre composite. Production moulds were manufactured using modern CNC technology, which provides very accurate propeller geometry.

FCU Info screen
FCU Battery info
FCU Messages

FCU instrument (Fes Control Unit) is designed for simple operation of FES System. It was developed in cooperation with LXNAV company – a leading manufacturer of gliding instruments.

FCU indicates all the important parameters of the FES Battery packs and counts the total engine running time. All FES parameters are logged to internal SD card every second. In case that one of the parameters is out of limit an alarm is activated together with acoustic signal.

ON / OFF switch

FCU instrument should be always switched ON during the flight.

Throttle / Brake

The knob with rotary encoder acts as a throttle and as a propeller brake. It is also used as a press button, for functions like message confirmation, message recall etc.

Battery Pack

Indication of FES Battery Pack parameters

  • Power
  • Voltage
  • Current
  • Remaining usable battery capacity
  • Remaining endurance time
  • The temperature of motor, motor controller, battery packs

Power switch

Power switch which Enable / Disable motor is located on a suitable location in the cockpit (as key switch or as toggle switch under red safety cap).

For standard FES applications, a pair of FES Battery packs are required (one marked as A and the other as B). In each battery pack, there are 14 cells wired in serial (14S) and packed into special high-temperature resistant composite boxes.

FES system operates at a voltage range of 90 – 116 V (2x 14S cell configuration).

FES Battery packs are located in the reinforced fuselage area behind the wings. The weight of FES Battery packs fully compensate the weight of the front assembly (motor, spinner, propeller…). The center of gravity of FES-equipped gliders is in most cases in the same position as at pure gliders.

Main features

  • 14 high power, low internal resistance Kokam cells in each battery pack
  • internal BMS (Battery Management System)
  • the capacity of cells: 40Ah
  • a total of 4,2kWh energy is available in a pair of standard FES GEN2 Battery packs
  • weight: 15,7kg each battery pack
  • also used to supply 12V power to instruments
  • located at reinforced fuselage area behind the wings


In the FES Battery packs, high power cells with capacity of 40Ah are used. The cells are produced by one of the global leaders of battery industry – Kokam Co. The cells can provide high power, good endurance and many charging cycles.

Internal BMS

BMS (Battery Management System) circuit board is integrated into each FES Battery pack. It is fixed above the cells and have 14+2 (for 14S) LEDs to monitor its operation.

Supplying power

FES battery packs provides 12V power supply through a DC/DC converter, for FCU and also for other instruments. With such arrangement there is always enough 12V power supply for flight computer, PDA, transponder, radio, bug wipers etc. Even if FES Battery packs are discharged during the flight (because of using the motor), they still have plenty of power for instruments.

  • Main contactor (provide power to motor controller)
  • FCC box (Fes Connection Circuit box, also include propeller alignment electronic)
  • LXUI box (to send analogue measurement of voltage and current via CAN bus)
  • Shunt (for current measurements)
  • Power fuse (for protection in case of short-circuit)
  • DC/DC converter (to provide 12V power supply)
  • 12 V battery (as backup and buffer)
  • Guarded FES “Power switch” (to enable motor controller)
  • FES bridge (for communication with LXNAV flight computers) – optional
  • MOP2 (Means of Propulsion current sensor from LXNAV) – optional
Terms Of Service
Why choose FES?