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The Hybrid Drive System

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The fully electric propulsion of aircraft would be the dream of aviation. With today's battery energy densities and the most optimistic expectations for the future, however, fully electric aviation cannot be expected for the vast majority of applications, even in the long term.

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So, we need a future-oriented technology for the next 30 years and beyond.

Many years ago Hans Schwoeller recognized that the future will require new propulsion technologies for aircraft. In 2014, the first patents for a pioneering drive technology were registered. These patents have meanwhile been granted in the EU, the USA and China. Further patents have been registered and are still being developed.
The concept has matured over many years and has been continuously optimized and adapted to new market opportunities and technology and production possibilities. However, the original concept has remained essentially the same. 

Due to the unique drive concept, the XAEROS Hybrid offers a new combination of reliability and thus safety and environmental protection for general aviation. With a host of patent-pending innovations, the benefits of electric and combustion performance have been combined in new ways. 

... not just a unique aircraft engine

The fully integrated system of the XAEROS hybrid drive is a pioneering drive technology for light aviation up to multi-seater commuter aircraft. However, it can also be used as a redundant range extender for air taxis and drones.

Especially for eVTOL air taxis for lift & cruise operation, the XAEROS hybrid drive offers a unique solution for achieving a purely electric vertical start with large ranges and high flight performance at the same time.

The XAEROS hybrid propulsion is not just an aircraft engine, but a self-contained and modular general-purpose propulsion system. It offers unique reliability with three completely independent drive units. The use extends from aircraft, light helicopters, gyrocopters to sports boats, for which the redundancy and electrical operation at night in the harbor offer great advantages.

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For aircraft propulsion, the system also includes an optional efficient wheel drive to reduce noise emissions at the airport to zero and increase efficiency.  Thanks to the unique drive concept, the triple redundant system is ideal for many other applications, such as reconnaissance drones, which, despite a very long range with fuel during take-off, landing and in the operational area, are almost noiseless can operate.

In the first step, the XAEROS system is being developed for the operation of petrol fuels, which are produced from regenerative energy, water and CO2 from the air. Of course, the XAEROS hybrid drive can also be operated with mogas or avgas (aviation fuel) and gas station fuel. A later variant for synthetic diesel/kerosene will be considered in order to create a solution for regions or users where only kerosene is available. 

Background information can be found here:

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Three Motors in One Unit


The XAEROS hybrid system integrates 3 motors in a very compact drive unit:

  • highly efficient and very light electric drive for electric take-off and landing

  • two efficient, supercharged V2 - four-stroke engines for synthetic fuel (eFuels) for CO2 neutral cruising

>  3 motors drive the common propeller shaft

  • Even if one or even two components fail, you can continue flying safely. 

Operation with an Airplane

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Operation with eVTOL Aircraft

The trend in eVTOL (Electrical Vertical Take-off and Landing) air taxis is increasingly towards lift & cruise configurations. Optimized propellers are used for electric take-off and landing, which are aligned in the direction of flight when cruising and thus cause hardly any air resistance.

Such aircraft are equipped with an optimized pusher propeller and electric motor for cruising. However, due to the low energy density of the batteries, only a very limited range can be achieved here.

Equipping eVTOL aircraft with a XAEROS hybrid drive opens up new perspectives with significant advantages:
After the electric vertical take-off, the aircraft can be accelerated purely electrically with the electric motor of the XAEROS Hybrid and the airfield can be left very quietly at cruising altitude. When cruising, away from noise-sensitive areas, the system switches to the redundant piston engine of the XAEROS drive, which is operated with eFuels. This enables a CO2-neutral cruising flight with ranges of 1500 km and more.

During the cruising flight, the electric motor of the XAEROS system serves as a generator and recharges the battery of the air taxi . These are then fully recharged for the approach and landing.

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symbolic photo

This allows the range of eVTOL aircraft to be multiplied and the batteries can be designed much smaller and lighter. The drive redundancy of the XAEROS hybrid drive brings an enormous plus in safety and with synthetic fuels, so-called eFuels, a CO2-neutral travel operation is possible over long distances.

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Fully Integral Drive Unit


Full integration of all components in one unit:

  • Dual ignition per cylinder

  • Cylinder head hybrid cooling (no water cooling)

  • Fan cooling for all components

  • two electric compressors for charging

  • two catalysts

  • two oil pumps and oil tanks

  • integrated drive battery

  • integrated electric propeller adjustment

  • integrated ventilation, heating and temperature control for the cockpit

  • FADEC - control with redundancies

  • 270 hp / 200 kW system output

  • 160 hp / 118 kW maximum continuous power MCP

  • very small dimensions: 500 x 510 x 790 mm

  • a later variant as a kerosene engine is planned

  • modular component and control concept

  • easy integration into almost any aircraft

  • simple conversion of existing aircraft without re-certifying the entire aircraft (only STC)

  • for more than 200,000 aircraft

Customer Benefits and Advantages

  • Enormous gain in safety thanks to three independently running motors in one unit

  • Easiest operation (single lever operation + start button + selector switch: pure electric / combined hybrid / pure piston operation)

  • full performance even at higher altitudes

  • double power supply for the aircraft

  • safe instrument flight with single-engine airplanes

  • Take-off even at airfield restrictions due to minimal noise emissions

  • goes into maintenance, repair or overhaul as a complete system including all components and returns to the aircraft as a tested complete system.

  • safe, efficient, quiet and environmentally friendly

  • a conversion to the XAEROS Hybrid is significantly cheaper than purchasing a new aircraft and also turns an older aircraft into a modern aircraft.


Environmental Protection

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  • noiseless at the airport due to integrated wheel drive

  • Fully electric operation from takeoff to leaving the airport area at cruising altitude as well as for approach and landing.

  • very quiet piston operation due to low propeller speed

  • environmentally friendly thanks to integrated catalytic converters

  • also for future synthetic eFuels - enables CO2-neutral cruising

  • conservation of resources  by continuing to use existing aircraft

Technical Data

Electric motor 

High-performance axial flux electric motor 74 kW / 100 hp  (optional 110 kW/150 hp), air-cooled, integrated inverter

Piston engines

Two independently running 2-cylinder V-engines 4-stroke, 2 x 63 kW / 85 hp, 2 x 742 ccm, separate systems (ECU, cooling, lubrication, oil tanks, gearbox, etc.), double ignition per cylinder head, aerobatic Dry sump lubrication, catalytic converters


System power 200 kW / 270 hp, max. continuous power 118 kW / 160 hp MCP


two electrical radial compressors + double intercooler


all components fan-cooled, cylinder heads air-oil hybrid-cooled (no water cooling!)

Power transmission      

two Carbon belt gears, maintenance-free for 5000+ hours, large torsional vibration damper, friction clutch

Propeller speed   

max. 2100 U/min , cruise 1920 rpm

Propeller adjustment    

quick electrical adjustment, for all hydraulic controllable pitch propellers, feathering


multi-generator/starter, redundant power supply for the aircraft

Engine control 

modular FADEC control system, fully integrated

Propulsion battery         

2.4 kWh (standard), scaleable depending on aircraft, ranges from hangar to leaving airfield area at cruising altitude + reserve, rechargeable during cruising for purely electric approach and landing


WxHxL   500 x 510 x 790 mm / 19,7 x 20 x 31 inches


certified all-in-system including integrated drive battery approx. 120 kg / 265 lbs

modular component combinations for ultralight / LSA from 85 kg / 187 lbs

Intended use 

  • as a certified system for aircraft and light helicopters, 

  • the modular structure of the XAEROS enables various component combinations for the non-certified world, for ultralight, experimental, amateur built planes, light sport aircraft LSA, autogyro, UL helicopter, etc.)


For the

future of

general aviation,

eVTOL air taxis,

transport-, rescue- and recon drones and more.

Hans  Schwoeller

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