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.
Like the first page, 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.
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 / 2016: link does not work anymore).
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.
8-2021: The aircraft had a belt drive train failure and went down in a corn field Friday August 6th near Fairmont Nebraska while repositioning towards Idaho. Lets hope the project can continue... Well, a couple of days later the company announced on YouTube that the original aircraft will be used as a display aircraft. Plus that they are going forward with the Raptor NG.
8-2021: This will be a stagger wing, canard aircraft driven by a hybrid propulsion system with two 24 inch ducted electric fans on the lower wing, power generation is with a generator and batteries. The wing sits lower so the landing gear is shorter and weighs less. Pressurization has been dropped, meaning less weight of the airframe, expected gross weight is ~4000 lbs, empty around 2000 lbs. Thrust is much higher than with the Audi diesel engine. This should result in better performance than the prototype.
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.
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.
2021 Nov update from Flying Magazine: The design achieved several important targets, including a 50 % increase in total power delivered, at a peak power rating of 300 kilowatts and a component weight of 30,6 kg, which is 25 % lighter than previous generations. The liquid-cooled batteries demonstrated a peak power of 75 kW each, at a weight of 60 kg each, integrated into the wings of the Panthera. The batteries allowed for an "all-electric takeoff" at 220 kW, enabling the flight tests in October. More info in the article about hybrid electric prototypes.
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.
2018: 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.
This California, Hawthorne 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 is 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 on the AmpAir website.
2015: 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%.
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.
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 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.
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.