The Retractable Electrical propulsion system

The retractable electrical propulsion (RES) system is not only a sustainer but also a self-
launcher up to a maximum weight. The team aim to achieve a maximum mass of 500kg.
The system is high voltage designed with two removable batteries stowed in the fuselage.

The system is developed in partnership with well-known aircraft engine producer, SOLO
Aircraft Engines, designed for comfort, safety, operation flexibility and impressive performance.

The fully automated system is easy to operate with the power setting adjustable with a
rotary dial on the control panel.


System specification
Electric motor
Propeller type
Two bladed 1.2m (3.94 ft)
Maximum Static thrust
90 daN
Maximum RPM
Max power for take-off
40 kW
Max continuous climb power
25 kW
System weight (no batteries)
21 kg (46.3 lbs)
Battery specification
Battery type
EMECTRIC 96-4 400V
Battery configuration
96S4P LiFePo
Battery Voltage
Capacity per battery
Battery Weight:
22kg (48.5 lbs)
Maximum number of batteries

Standard features for your comfort

  • Low noise propeller design
  • Pilot interface: single switch controls pylon extension and doors
  • Choice of dual-battery configuration or single-battery configuration
  • Automatic centring of propeller after shutdown
  • Pilot interface: One switch controls pylon extension and doors
  • Engine bay door opening/closing via electric linear actuator – with control
    sequencing to close the doors for both the retracted and extended positions
    of the pylon.



The RES provides very competitive performance with good power-to-weight

The system is design for maximum flexibility and carefully compromised to
allow contest pilots the possibility of a low minimum wing loading, and for the
leisure pilot to have self-launch options at reasonable high wing loadings.

The multiple battery configuration provides unmatched wing loading flexibility


Take off Performance Dual battery
Max Aircraft Take off- Mass
500 kg ( 1102 lbs)
Rate of Climb (for 500kg)
2.3 m/s ( 453 ft/min)
Take off distance Hard surface, 15m obstacle
500 m ( 1640 ft)
Peak power To clear 15m obstacle
40 kW for 2minutes
Max continuous power
30 kW
Energy used to 500m climb
Sustain Performance - Single battery SI IMP
Aircraft mass (including 90 kg pilot)
413 kg
911 lbs
Rate of Climb (500kg)
± 2 m/s
±393 ft/min
Max Altitude Gain
1500 m
4921 ft
Max sustained range
125 km
78 miles
Sustain Performance - Dual battery SI IMP
Aircraft mass (including 90 kg pilot)
435 kg
959 lbs
Rate of Climb (500kg)
+3.0 m/s
591 ft/min
Max Altitude Gain
2 750 m
9022 ft
Max sustained range
175 km
109 miles
Max sustained range After 500m launch
122 km
76 miles

Standard Performance Features

  • Two-blade carbon-fibre 1.2 m [3.94 ft] diameter propeller designed to optimally
    match the battery/controller/motor specifications.
  • High volt system for reduced current flow and increased efficiency

Optional Performance Features

  • Second battery pack option for increased sustaining range or self-launch capabilities



JS safety is not negotiable. Operating the RES system gives you the in-control-feeling combined with highly desirable man-machine-interface characteristics.

For safety reasons the two batteries weighing 22 kg each are located in the fuselage, and are removable for safe charging. The novelty of this design is that glider can be
flown with the batteries removed, or with one or both batteries installed.

Standard Safety Features

  • Removable batteries for our-of-sailplanes charging
  • Automatic battery power connections
  • Electrical (430 VDC) isolation monitoring
  • Battery, motor and controller temperature monitoring
  • Battery internal relay-safe handling, isolating high voltage from terminals
  • Internal Current Sensor with Internal Fuses
  • Independent fire warning (heat detection) system



Elon Musk turned the car industry on its head.  Who would think a few years back that the most luxury sedan would leave a Porsche behind in a drag race… and do this
in silence with style….

Battery driven vehicles took the world by storm, and the general aviation is slowly catching up.   No fumes of fuel, no oil leaks, no vibration, no engine noise, no breaking belts, no starter button.. This all sounds extremely attractive… but where is the catch?

Clearly the energy density is not nearly as good as their petroleum counterpart and therefore battery installations are still heavy for the performance they offer, and they are not as yet well priced.  The risk associated with battery fires is a reason for concern, and EASA is actively working on improved special conditions to ensure safe designs – don’t underestimate manufacturers headaches when it comes to certification of systems with large LiPo batteries


Well-known aircraft engine producer, SOLO Aircraft Engines, was the major inspiration behind the retractable electrical propulsion system.  SOLO used the JS3 fuselage to model their sustainer design in the “smallest possible modern fuselage”.

JS and SOLO studied the maximum performance of the system and realized self-launching may just be possible. The concept of having not only a sustainer, but also a
limited self-launcher with removable batteries is very exciting.

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