Technological insight

There is a multitude of possibilities eVTOL aircraft could provide to the world, where operation demands significantly higher energy density than current battery technology can provide. In these cases an electric-hybrid propulsion systems (EHPS) seem an obvious solution.

However turbine engines have the suitable power-to-weight ratio, under 500 kW output power their efficiency is poor, therefore the fuel consumption is very wasteful.

Lupfe designs and develops a high power density and more environmentally friendly series ICE-electric hybrid propulsion system, specifically for eVTOL cargo drones up to the 750 kg of MTOW. As a part of this development, taking both environmental and economic factors into considerations next to the technical requirements, Lupfe started to develop their own innovative aero piston engine for this purpose.


Lupfe's innovation aims to increase the EHPS engine's power-to-weight ratio and significantly reduce fuel consumption at the same time. The concept is a four-stroke, turbocharged design, providing conceptually higher performance, better emission and lifespan for the engine. Technically in terms of four-stroke aero piston engines, this invention has an extreme high power-to-weight ratio that is required to keep the entire EHPS lightweight. 

The weight optimized structure combined with compact modeling, allows for the engine's arrangement to be assembled with a three-way catalytic converter and a suitable noise reduction.

The engine's advanced thermal and gas-exchange processes can provide a lower fuel consumption than the conventional four-stroke aero engines. The converter with lower fuel consumption boils down to a significantly more environmentally friendly operation. 

The other constituent parts of the EHPS such as batteries and capacitators enable the system to work in optimal operation, therefore a further optimization of fuel economy comes from the hybrid-electric co-working process.

The engine can operate with various fuels.

Without modification: 

  • Unleaded or leaded gasoline RON95 or higher (UL95, AVGAS LL100)
  • E85, ethanol, methanol
  • Synthetic fuels (e-gasoline)

With additional development: H2 (hydrogen)

Design and Technical data of the EHPS

The 3D model of the core powerplant unit of the EHPS 

To support calculations based on this technology, estimated data of the final high power density electric-hybrid propulsion system (HPD EHPS) are added below assuming different output performances, using RON95 fuel:

Power (peak)

Power (cont.)


Fuel consumption


57 kW

51 kW

55 kg

233 g/kWh


86 kW

81 kW

71 kg

230 g/kWh


115 kW

110 kW

83 kg

227 g/kWh

*Ready to use curb weight (including: power electronics, control unit, 1-2 kWh battery, system mounting, fuel system, fuel tank, cooling system, lubricating oil, coolant, 3-way catalytic converter)

Technical data of the engine design

  • liquid-cooled, 2-cylinder boxer
  • 4 valves per cylinder, DOHC
  • turbocharged with intercooler
  • electronic ignition and fuel injection
  • fuel: gasoline (unleaded, RON95)

Dimensions (WxLxH): 600x400x450 mm

For further information, please get in touch with us!