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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 at least the same but preferably an even better economic 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 the engines, maybe batteries (chemicals) and all that is needed for the installation and final disposal/ removal/ recycling of those items.

Hybrid Developments

After the initial electric aircraft boom, which deflated quickly after realizing that increasing battery density is more or less of a dead end, we see more companies aiming for some sort of hybrid propulsion system for aircraft. This page tries to sum all those efforts to give us an insight in this technology and where it currently stands and who is developing what.

2020: AVweb presented a podcast about the future of hybrid propulsion systems and battery driven aircraft and which are technically and commercially viable. Very interesting, see more here: Electric Hybrid Aircraft Drives.


2021: They were busy working on a 2.5 MW Power Generating System demonstrator in Trondheim Norway. It now has been moved to Bristol in the U.K. for further testing. This generator is designed to power regional airliners with hybrid-electric propulsion systems. The unit is the size of a beer keg and is ground breaking of whats physically is possible. More info in the article from AINonline: Rolls readies Propulsion Trials.

deHavilland Dash 8

2021: Pratt & Whitney Canada is working together with deHavilland Canada to test a hybrid-electric propulsion system on a Dash 8-100 aircraft as a technology demonstrator. The program is expecting ground testing in 2022 and hoping for flight testing in 2024. The electric motor and controller is from Collins Aerospace and Raytheon Technologies. This hybrid drive is expected to save 30% in fuel burn compared to a modern turboprop.


2021: This U.K.-government backed company is using a pair of Dornier 228 twin turboprops as test aircraft for the 600 kW hydrogen-electric powerplants. One aircraft will fly in the U.K. and the other in the U.S in California. The fuel tank will contain 100 kg hydrogen and has an expected 500 mile range.

This is a follow-up from the Piper Malibu that had a 250 kW hydrogen hybrid drive. That aircraft was damaged during landing on April 29th.

Sling Aircraft, South Africa

2021: Sling is also developing an electric, hybrid aircraft (e-Sling) which has three battery packs (based on 18650 cells) cooled by silicone oil. One in each wing (in place of the fuel tanks) and one in the engine compartment together with a range extender. Electric capacity is 55 kWh. The airframe used is based on the TSi low wing model.

VoltAero, France

VoltAero develops the Cassio 1 aircraft (basically a Cessna 337 Skymaster) installed with two electric motors (Safran EngineUS 45). The rear engine functions as a generator (170 kW) with a 150 kW motor for the rear propeller, the front engine should be removed for production. They plan deliveries in 2022, lets wait and see.

That early test design has been abandoned in favor of a new canard model with a twin tail. More info on the website of VoltAero.

The company also is manufacturing a hybrid power module consisting of a 300 kW V-6 engine combined with three (3) electric motors of 60 kW each. This power train has been developed in the Cassio 1 aircraft.

United Technologies - DASH 8-100

2019: 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).

Airbus & Rolls-Royce

PARIS 2019: These two players are on track to develop a hybrid Bae 146/TJ100 airliner into an E-Fan X hybrid electric demonstrator in 2020. Siemens is also involved in this project with developing the drive train for the demonstrator aircraft.

Ampaire Inc

This California based company is using a Cessna 337 SkyMaster and they have removed the rear engine, installing a battery powered electric engine to reduce emissions and noise. It's one of the largest hybrid aircraft to date (their claim in 2019). They also say the third revolution in aviation being electric. We can only hope they know something about battery physics (that we don't) making this possible. More here: https://www.ampaire.com.

Oct 2020: They completed their first cross country flight, the distance was 341 statue miles. More in the article from AVweb here: Ampaire Cross Country.

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/ MAHEPA

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 914/5 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.

MAHEPA, Modular Approach to Hybrid Electric Propulsion Architecture is the follow up of the Hypstair project which never flew. Funded by the EU and consists of eight companies to develop hybrid propulsion systems for aircraft.
Even AVWEB noticed: "a slow but discernible realization that batteries aren't going to be the golden path to electric flight for the near future and perhaps ever" within Pipistrel.

2021 update: From AVWEb the next link on the Panthera & electric flight.

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.

2021: The above specifications have been removed from the site and only a page has been left stating that electric power works for very light and low-energy aircraft. They do offer a V-twin two cylinder hybrid drive where the electric motor is mounted on the propeller shaft of the gear box. See the next video from Light Sport and Ultralight Flyer about the 60 HP V-Twin Hybrid.


Plus some other comments and specifications about the Zigolo trike e-powered ultralight. Which are: Battery Packs: 2 x 3.1 kWh 14S/20P/15 kg, 60 Ah, Motor: 20 kW continuous, 28 kW peak, low noise, low RPM; Controller: 28 kW continuous/ 40 kW peak; Advanced Drive Interface for an extensive display and recording of flight parameters and a 3-blade composite propeller. The charger is 15 A/ 980 W

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 after flight testing of their current project has completed. 2021: Their prototype has been completed and the designer is transferring the aircraft to the manufacturing location.


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 from a good power density (and might will never get there).
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, burnt or failed chemical batteries in the environment at the same time.

Written by EAI.

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