FES Flight Manual, v1.18 May 2020
Page 29 of 35
Caution:
Always make sure that propeller blades are clean. Dirty leading
edge reduces propeller efficiency and climb rate.
5.3.4.2 Cruise flight
The maximum range of powered cruising flight, without the water ballast, is around
100km (62 miles), depending on lift-sink conditions.
The optimum cruise speed and flap position depend on the type of sailplane. Usually,
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of power with a positive
flap setting, as used in thermals.
5.3.4.3 Maximum operational altitude
There should be no problem to fly an FES equipped sailplane at high altitude, due to
low pressure. Battery cells used in the FES battery packs passed eight different tests as
required by UN transport regulations. The first test is an altitude simulation where cells
were exposed to reduced pressure of 11.6kPa, equivalent to about 15.000m.
Cold outside temperatures down to -20°C do not represent a safety issue for battery
packs (they usually stay warmer), or to other FES system components. However, if battery
packs have a very low temperature, their performance is reduced, but it is unlikely that
you will need to use FES at high altitude.
5.3.5 Noise data
Measurements of the motor noise level are lower compared to sailplanes equipped
with combustion engines. The analysis was performed according to requirements for
certification purposes of Silent 2 Electro, where the noise level was measured to be 57db.
Maximum engine noise level is not regulated sustainer type gliders.
Engine noise level (ENL) signal for flight recorders:
Flight recorder (FR) will only record the engine noise level when the FES is running if
the sound is loud enough. Therefore the flight recorder must be mounted on the
instrument panel or equally close to the FES unit. Installing the FR elsewhere in the
cockpit will require a separate MOP sensor. Please refer to the Annex B of the IGC
Sporting Code for details.
5.3.6 Electromagnetic interferences
Proper construction of the motor prevents the magnetic field leaking outside of the
housing. We did not find any issues with the instruments, including the magnetic compass,
caused by the high power cables that are routed below the instrument panel.
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