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More about eVTOLs

December 19, 2023  - By

Airbus is working with a team to develop a “hybrid” approach to electric aircraft, which means that their experimental aircraft is not only using electric power — with electric motors and propellors (propulsers), an 800-volt battery, and a hi-voltage distribution and control system. It also has a conventional turbine which supplies torque to a conventional propeller and generates electrical power to maintain charge for the 800-volt battery.

Airbus EchoPulse demo aircraft. (Photo: Airbus/EchoPulse)

Airbus EchoPulse demo aircraft. (Photo: Airbus/EchoPulse)

The team working with Airbus includes Daher, which has modified its TBM 900 turboprop aircraft to add the electrical system, motors and props supplied by Safran. Airbus has developed the 800-volt battery and the Flight Control System for the aircraft, through which any future autonomous capability would likely be brought about.

The decision to try this ‘hybrid’ approach may have been influenced by Volvo, which is pressing this approach for the Series 90 and 60 of its hybrid Electric Vehicles (EV). Combining recharging by an internal combustion engine with a battery and electric drive system greatly extends the range of this model, greatly reduces its gas consumption, and minimizes the hunt for rare recharging outlets.

It would seem that the principal benefit from the Airbus team development could be the 800-volt DC battery design, and the high voltage distribution/control/recharging system when they are potentially spun off and applied to other manned/unmanned eVTOL passenger aircraft. The basic problem for eVTOL aircraft is payload and range – is that something that a huge energy reservoir such as this battery system could support?

Airbus EchoPulse demo aircraft. (Photo: Airbus/EchoPulse)

Airbus EchoPulse demo aircraft. (Photo: Airbus/EchoPulse)

Developed by Airbus Defense and Space in Toulouse, France, the 800-volt DC battery system delivers up to 350 kilowatts to the electric system on the aircraft. The battery was derived from earlier versions that were flown on Airbus CityBus eVTOL demonstrator and FlightLab helicopters. The Lithium-ion battery weighs in at 350 kg (772 lbs.) and is mounted in an enclosure of the belly of the EcoPulse demonstration aircraft.

Airbus reportedly plans on taking this high energy-density battery into its commercial aircraft business. But the main market could be for hybrid eVTOL aircraft, which can carry this heavy battery and its control system and to benefit from the massive energy density.

Meanwhile, as the Russian-Ukrainian war drags on with both sides throwing at each other increasing numbers of ‘kamikaze’ UAVs carrying explosives, interest has recently been growing around a 2020 report out of St. Petersburg Electro-technical University in Russia that critiques the Russian air defense system. According to the report, these defenses are poorly adapted to detect or destroy vehicles as small and slow-moving as UAVs.

Ukrainian UAV troops were only recently pictured assembling weaponized drones for their one-way trip to Russian-owned targets.

Photo released by General Staff of the Armed Forces of Ukraine on Telegram

Photo released by General Staff of the Armed Forces of Ukraine on Telegram

The explosive carriers are frequently simple racing UAVs. In one released photo, an inexpensive quadcopter is taped together with plastic explosives and an RPG warhead using adhesive tape. Nothing has to be very durable, just durable enough to last for its short one-way trip through Russian defenses.

The Russian air defenses rely on several tracked and/or wheeled mobile systems using both guns and missiles. This includes radar-guided and heat-seeking missiles, such as the Pantsir-S1, the Tunguska, the Tor, the Strela-10, and the Igla-S man-portable missiles, all of which are designed to combat high-speed jet aircraft, helicopters, and cruise missiles. At the same time, UAVs are slow and very small in comparison.

Unfortunately, the missiles ‘ poor target detection capability and detonation control systems appear to be the culprits for the inability to strike down UAVs. Tor radar has been seen to only detect at 3-4km (1.8 -2.5 miles), while the minimum operating range is about the same. Thus, misses are reportedly more likely than taking out attacking drones. While the system may be somewhat ineffective, the cost of using missiles is huge.

A Ukrainian UAV recording within close range of a Russian Tor defense system has captured video of a missile hurtling past and failing to bring it down. Similar results have been found with both the Pantsir-S1 and Tunguska defense systems.

For the close-in gun and cannon defense systems, Russian tests demonstrated that to raise the probability of a direct hit to just 50% for an attacking drone at a distance of 1.3 miles, between four to 13 thousand shells would need to be fired.  This is significantly more ammunition than one Tor system can fire in one volley without reloading, even at 5,000 rounds/minute of which it is capable.

Ukrainian war strategists continue to acquire thousands of UAVs each month, while its troops continue to throw them against their Russian invaders with improvised explosive payloads. Meanwhile, as of December 2023, Congress is continuing negotiations over another $61.4 billion in funding to further Ukraine’s war efforts, even while President Zelenskyy visited Washington to urge the U.S. to maintain its support.

The problem with this situation is that both sides have learned that UAV warfare’ is simpler, less dangerous for the aggressor, and less costly than regular offensives. Thus, a stalemate might prolong the war for even longer.

So, on the commercial, peaceful side of drone development, the possibility of a hybrid-electric approach for eVTOL passenger-carrying autonomous vehicles is making progress. Nevertheless, as the war continues in Ukraine, could the reduced cost of UAV warfare’ possibly prolong it?

About the Author: Tony Murfin

Tony Murfin is managing consultant for GNSS Aerospace LLC, Florida. Murfin provides business development consulting services to companies involved in GNSS products and markets, and writes for GPS World as the OEM Professional contributing editor. Previously, Murfin worked for NovAtel Inc. in Calgary, Canada, as vice president of Business Development; for CMC Electronics in Montreal, Canada, as business development manager, product manager, software manger and software engineer; for CAE in Montreal as simulation software engineer; and for BAe in Warton, UK, as senior avionics engineer. Murfin has a B.Sc. from the University of Manchester Institute of Science and Technology in the UK, and is a UK Chartered Engineer (CEng MIET).