The Retractable Electric System

The Retractable Electric System (RES) is not only a sustainer but also a self-
launcher up to a maximum weight of 575 kg. 
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 Specifications

Electric MotorEMRAX 208
Propeller typeTechnoflug KS-1C-120-R-065-S
Maximum Static thrust90 daN
Maximum RPM4350
Max power for take-off40 kW
Max continuous climb power25 kW
System weight (no batteries)+/- 24kg (53 lbs)

Battery Specification

Battery TypeEMECTRIC BM 384
Battery configuration96S4P
Battery Voltage270V-400V
Usable Energy
(available energy decreases with high power settings)
3.4 – 4.2 kWh per battery
Battery weight25kg (55.1 lbs)
Maximum number of batteries2

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 with control sequencing to close the doors for both the retracted and extended positions of the pylon.
bat 1



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


Sustain performance - single batterySIIMP
Reference Mass460 kg1014 lbs
Climb rate at MP (25 kW for 4 min)2.0 m/s 394 ft/min
Climb rate at MCP (12.5 kW) 0.8 m/s 157 ft/min
Max altitude gain (approx.)+/- 900 m2953 ft
Max sustained range in 18m (approx.)+/- 81 km50 mi
Sustain performance - dual batterySIIMP
Reference Mass480 kg1058 lbs
Max continuous power25 kW33.5 hp
Rate of climb at MCP+/- 2.4 m/s472 ft/min
Altitude gain+/-2000 m6562 ft
Sustained ranged+/- 157 km98 mi
Take off performance - dual batterySIIMP
Max aircraft take-off mass575 kg 1268 lbs
Climb rate at Maximum Power (40 kW for 1 min)+/- 3.0 m/s591 ft/min
Climb rate at Max Continuous Power (25 kW)+/-1.7 m335 ft/min
Take-off distance hard surface, 15m obstacle+/- 430 m1410 ft
Peak power to clear 15m obstacle40 kW for 1min40 kW for 1min
Energy used to climb 500m (1640 ft)2.1 kWh2.1 kWh
Altitude gain+/- 1700 m5577 ft
Sustained range after self launch+/- 120 km 75 mi

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 25 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.