What is FES?

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 tests and improvements, the end result become a family of a few different FES motors as we know them today.

Typical FES Motor is an out-runner BLDC brushless synchronous permanent magnet motor with electronically controlled commutation system 3 phase. Because of the low internal resistance of windings and very small gap between stator and rotor, exceptional performance are achieved in a wide range of power with excellent efficiency. Typical maximum power is in range of 22-30kW, at motor weight of only 7,3-8kg depends on specific version of FES motor.

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.

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.

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

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 instrument controls and indicates all the important parameters of the FES system and counts engine running time.

Different Green, Yellow “Caution” or Red “Warning” messages appears in case that any important parameter reach certain preset value

All FES parameters are logged to internal SD card every second.

For standard FES applications, a pair of FES Battery packs are required (one marked as A and the other as B).

In the latest FES GEN4 family of battery packs, there are 14 or 16 cell blocks wired in serial (14S or 16S). Each cell block is assembled with 20 or 30, high power 18650 cells wired in parallel. They are packed into special high-temperature resistant composite boxes, with aluminum top cover.

FES system operates at a voltage range of 90 – 116 V (2x 14S cell configuration) or 102-133V (2x 16S cell configuration).

FES Battery packs are placed into battery compartment which is in the reinforced fuselage area behind the wings. The weight of FES Battery packs compensates the weight of the front assembly (motor, spinner, propeller…) and so the center of gravity of FES – powered sailplane remains practically unaffected.

In the FES GEN4 Battery packs, number of high power cylindrical 18650 cells are connected with fusible links to bus-bars with ultrasound bonding technology. Cells are equipped with double safety vent, which efficiently prevents side rupture and resulting propagation to other cells in the worst case of single cell thermal runaway, as demonstrated during extensive EASA certification.

Selected type of cells, provide optimal ratio between energy storage capacity, power, safety and number of charging cycles.

BMS (Battery Management System) circuit board is integrated into each FES Battery pack. It is fixed above the cells and connected to e-ink display to monitor its operation.

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.