Hybrid and electric power units are commonplace in cars these days but they are only just starting to be experimented with in aviation. Mainly that’s because aviation is so heavily regulated but it’s also because weight is a big issue.

So the latest prototype seen here, from Austrian company, Diamond Aircraft Industries GmbH, working with German engineers at Siemens AG, is a big step forwards.

It’s a hybrid electric aircraft and it made its first flight on 31 October 2018 at Diamond Aircraft’s headquarters at Wiener Neustadt airfield, Austria.

Siemens has been working on all-electric aircraft for a while but acknowledges that the weight of the batteries required for decent performance and range is too much given current technology. Therefore, some form of in-flight recharging mechanism is needed – hence this hybrid.

Diamond hybriad electric multi engine aircraft
First flight for Diamond’s multi-engine electric hybrid DA40 aircraft.

Siemens and Diamond Aircraft say the main objective of this project is to develop an aircraft that has a lower fuel consumption as well as a lower noise footprint. The hybrid powertrain will allow for full electric take-off capabilities without the added noise and pollution of a combustion engine.

They’ve taken Diamond’s regular single-engine piston aircraft, the DA40,  and modified it with a new powertrain. There’s a 110kW diesel engine in the nose of the aircraft which powers two independent electric drive systems consisting of one motor, battery and inverter each.

The multi (ie, more than one) engine hybrid from Diamond Aircraft. The two props are powered by electric motors mounted on a canard wing at the front. A diesel engine in the nose is a generator to provide the electricity required. The aircraft made its first flight in October 2018.

Two electric engines have been added on a forward canard (wing), which combined can generate 150kW of take-off power. Two batteries of 12kWh each are mounted in the rear passenger compartment, and act as an energy storage buffer.

With a dedicated power lever, the pilot can control the energy flow between the generator, batteries and motor. The pilot can select either pure electric mode (generator off), cruise mode (generator provides all power to the motor), and charge mode (generator charges the batteries).

Pure electric, the aircraft has an endurance of approximately 30 minutes. The hybrid system extends this to 5 hours. “This is the first serial-hybrid electric plane in the world with two electrically-powered free-stream propellers and one combustion engine,” said Dr Frank Anton, Executive Vice President eAircraft at Siemens AG. 

Diamond hybrid electric aircraft
Ingmar Mayerbuch, the test pilot who flew the multi-engine hybrid aircraft, said, “The first flight exceeded all our expectations. The combination of the hybrid powertrain and the configuration of the aircraft is just perfect. We reached 130 knots at medium power output and climbed to an altitude of 3,000 feet.”

During the 20-minute first flight, the aircraft demonstrated all modes of operation. This included pure hybrid, charging flight and full electric flight. In this last configuration, the aircraft was able to fly pure electric and produces zero emissions. A full electric takeoff was demonstrated which lead to a significantly lower noise footprint.

The objective of future flight tests will be to determine the exact efficiency increase achieved in comparison to similar non-electric aircraft. Also the noise footprint will be determined. Further tests will gather knowledge on the practical operation of hybrid aircraft. Different hybrid modes of operation will be tested and their effect on efficiency, range, and energy consumption will be determined.

“Serial-hybrid electric propulsion systems and distributed propulsion architectures for us are the key to a more sustainable flight future also in higher power classes,” said Dr Anton, who is world-leading engineer in electric/hybrid aircraft.

“The Diamond flying testbed will help us to understand the requirements for these new propulsion technologies and to be prepared for the challenges of larger-scale applications.”

By that he means hybrid airliners, something that he is already working on with Airbus and engine makers Rolls-Royce.

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