Technological insight

There is a multitude of possibilities EVTOL aircrafts 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 system (EHPS) seems an obvious solution. Unfortunately it is not so simple to choose an engine with a sufficiently high power-to-weight ratio and put it into an EHPS. Considering operation and maintenance costs, workload reliability and environmental effects of the engine, one has to realize that a design of a suitable innovative aero piston engine for this purpose is inevitable.

Lupfe designs and develops a lightweight and more environmentally friendly series ICE-electric hybrid propulsion system for the EVTOL industry, within that for the segment of 60 kW to 150 kW performance. This task starts at the design of a suitable internal combustion piston engine.


Lupfe's innovation aims to increase the EHPS engine's power-to-weight ratio and reduce the fuel consumption and maintenance costs 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 the terms of the four-stroke aero piston engines, this concept has an extreme high power-to-weight ratio that is required to keep the entire EHPS lightweight. 

Furthermore a very important point is that this feature is combined with compact design allow to 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 catalytic converter with lower fuel consumption boils down a significantly more environmentally friendly operation. The other constituent parts of the EHPS such as batteries and capacitators enable to the system to work in optimal operation, therefore a seconder optimizing of the fuel consumption come from the hybrid-electric co-working process.

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 dense electric-hybrid propulsion system (HPD EHPS) are added below assuming different output performances:

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): 600x400x500 mm

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