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Rotax Hybrid Engine

Hybrid Aircraft Propulsion

A number of companies are developing electric power plants for aircraft, basically for powered gliders and small ultralight aircraft. In most of these designs the power plant is of secondary importance and the aircraft can fly, or better, glide considerable distances without an engine purely by its basic aerodynamic properties.

Hybrid propulsion means a combination of electric and internal combustion motors. The idea is that you use the best of both worlds to come to the same or even better result. In the case of aviation this means: lower fuel consumption, lower emissions and as such a cleaner flight with less impact on the environment. Keep in mind that this must mean the whole picture from fabricating of the engines, maybe batteries (chemicals) and all that is needed for the installation and final removal.

Hybrid Development

United Technologies - DASH 8-100

UTC is developing an electric assist (hybrid) drive for the Bombardier Dash 8-100 regional aircraft where the electric motor will support the gas turbine during takeoff and climb. Fuel savings up to 30% can be reached but this is partly caused by the more efficient gas turbine. Operational range is almost halved to 600 nm due to an increased empty weight (source: Flight Global, March 2019).

Pipistrel, Slovenia

Alpha Electro Engine

Pipistrel, Slovenia is also flying with an electric powered training aircraft. Their former WATTsUP project is now the two seat Alpha Electro, equipped with a 21 kWh battery (weighing 120 kg) and a 60 (50 continuous) kW engine. The Alpha Electro can fly one hour with 30 minute reserves, at reduced power settings compared to the normal Alpha Trainer. See our next page for more information.

This endurance should be enough for a flying school when they have a number of batteries fully recharged on standby. There is also a fast charger available able to recharge within an hour, but this method will kill any battery prematurely.
On AERO 2015 the company explained that they had no policy on what to do with batteries from customers that were worn out or had failed. One could argue that electric aircraft (and cars) could potentially become a large source of non-recyclable chemical waste.


Hypstair - PantheraHypstair - Panthera

Pipistrel (translation: Bat) is also experimenting with a hybrid drive where a gas engine supplies the power to an electric motor in combination with a small battery so that the aircraft can takeoff on electric power. This should reduce the noise foot print of the aircraft considerably. Move the mouse over the image.

At AERO 2016 Pipistrel introduced the Panthera Hypstair (www.hypstair.eu). This is a hybrid drive with a Rotax 914 driving a generator charging batteries in the wing. The propeller is driven by a 200 kW electric motor from Siemens, of course the combination has electronics to charge the batteries and control the three(!) engines and propeller.
We all know how complex a Rotax engine is, let alone the turbo version added with two electric engines. This hybrid drive redefines the word complexity to the third power, take a look here. One wonders about the cost (maintenance too) and if any fuel savings are worth it.

Tecnam Rotax Siemens

These three companies are joining forces to develop a Tecnam P2010 aircraft equipped with a Rotax 915iS engine connected with a Siemens electric motor forming a Hybrid P2010. The plan is to take off with the electric motor after which the Rotax engine will provide power during cruise.

Comco Ikarus

This German company has developed a hybrid C42 aircraft with an electric motor and batteries in the engine compartment and a sort of a range extender in the aft fuselage with a 15 gallon fuel tank.

Siemens Hybrid Drive

Siemens in cooperation with EADS and Diamond Aircraft developed an electric hybrid drive which consists of a 30 kW Wankel engine with generator, a battery developed by EADS and electric motor of 60 kW. This configuration is tested in a Diamond DA-36 motor glider and is expected to reduce fuel consumption by 25%.

DA-36 Electric

A Siemens converter supplies the electric motor with power from the battery and the generator. Fuel consumption is very low since the internal combustion engine always runs with an efficient constant low output of 30 kW. The battery system from EADS provides the increased power required during takeoff and climb. The accumulator is recharged during the cruising phase. (Source: September 2011, instrumentation.co.za and phys.org July 2013)

Update 2015: Siemens developed an electric motor of 260 kW (348 hp) for use with small regional aircraft. AVweb has the story: http://www.avweb.com/avwebflash/news/New-Electric-Aircraft-Motor-From-Siemens-223995-1.html.

Magnus Hybrid

Update 2018: At AERO2018 Siemens showed a full electric and a hybrid equipped Magnus Aircraft (which is build in Hungary). They were shown side by side.
The hybrid model is equipped with a three cylinder SMART diesel driving a generator, battery pack and electric motor at the propeller. See image to the right for the hybrid.

BRM Aero H55

BRM Aero has a project were they built a electric version of their successful low wing aircraft. The electric power plant has 90 kW (122 hp) for take off and a 65 kW (88 hp) cruise power setting. The battery has enough capacity for one hour flight and 20 minutes reserve.

Merlin PSA

Aeromarine LSA from Lakeland Florida is developing, designing, experimenting with an electric version of their Merlin PSA (one seat Personal Sport Aircraft). They expect a 93 mph (80 kts) cruise with a 1 hour endurance. The custom designed electric motor weighs 12 kg with 55 kW output power. The battery is a LiPo Cobalt chemistry with a capacity of 65 Ah. Recharging is done in 2,5 hours with a life expectancy of 2000 cycles.

Raptor Aircraft

Raptor Aircraft once also promoted a hybrid driven aircraft: "The Raptor Hybrid will be powered by a 250 hp modern, automotive derived, diesel engine in combination with a 62 hp electric motor and battery pack. This combination will provide the full 312 hp for takeoff and climb continuing all the way to FL 250. Once there you will throttle back to run on just the diesel engine." (source: http://www.raptor-aircraft.com/models/hybrid.html).

Update 2016: it seems that Raptor dropped development of the hybrid drive as their is no mention at all on their website and the page is gone for the time being. Maybe they will continue this on a later date.


Hybrid drive trains are commonly used in diesel electric locomotives and generator sets since the beginning of the last century and one wonders why this technology is not used more often in cars and aviation. As this seems the best solution up until now while battery technology is still light years away (and might never get there) from a good power density. And running a gas or diesel engine supplemented with a small battery and electric motor could mean more fuel savings while not generating a huge pile of wasted, worn out or failed chemical batteries in the environment.

written by EAI.


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