The Ce-Liner: potentially emission-free operation in commercial air travel
In 2011, Bauhaus Luftfahrt for the first time merged comprehensive contributions of all research teams into the development of an interdisciplinary group design project, then internally designated as “Concept 002”. Over the course of 2012, this project consequently evolved in a detailed concept study towards a possible zero-emission aircraft solution. It was given the name “Ce-Liner” when it was publicly presented for the first time during ILA Berlin Air Show in September 2012.
In the Ce-Liner concept, Bauhaus Luftfahrt implemented both the requirements and the technologies identified in Concept 002 for the year 2035 into a wide-body aircraft propelled by two electric engines mounted on the rear fuselage. Another eye-catching feature of the Ce-Liner is its prominent C-wing design that ensures high aerodynamic efficiency, one of the key requirements to partly compensate for the significantly higher weight of an all battery-powered electric aircraft.
The Ce-Liner in flight.The proposed configuration allows the Ce-Liner to meet the performance requirements defined in Concept 002: a range of 900 nautical miles (1,667 kilometres), a cruising altitude of 33,000 feet (ten kilometres) and a cruise speed of Mach 0.75 (808 kilometres per hour). The required onboard personnel would consist of two pilots and five cabin crew for the standard version seating 189 passengers in an all-economy class layout. Moreover, a stretched version for up to 233 passengers and a shortened version for 140 passengers have also been considered by Bauhaus Luftfahrt.
The most significant novelty of the Ce-Liner lies in its all-electric propulsion system, which enables the concept to potentially exceed even the ambitious emission targets of Flightpath 2050 considered to be the main requirements behind Concept 002. Its two ducted fans are driven by high-temperature superconducting electric motors fed through a universally electric systems architecture (UESA) with energy from advanced lithium-ion batteries.
The required energy density for the latter was estimated with 2,000 Watt-hours per kilogram, roughly eight to ten times as much as state-of-the-art batteries achieve today. A number of battery modules would be installed in specially adapted LD3 cargo containers, the so-called Charge Carrying Containers (3C). Flight control of the Ce-Liner would consist of an advanced fly-by-wire system with full flight envelope protection. Another important aspect is its novel, self-trimming wing that unlike today’s aircraft generation constantly adapts its shape to varying flight conditions utilising so-called morphing techniques. To ensure the 30-minute turnaround time defined in Concept 002 and to provide enough storage for the large battery packs, the Ce-Liner was designed to have a comparably large fuselage cross-section. This allows for a cabin with seven-abreast seating in a twin-aisle configuration. The cargo deck below would offer enough room for two 3C or LD3 containers positioned side by side.
The Ce-Liner’s cabin configuration was also strongly influenced by the passenger requirements determined in Concept 002. Thus, it is not only designed to account for the increased body dimensions and weight of travellers in 2035 and their baggage, but it also features technical innovations. These can, on the one hand, be found in the flexible seat concept potentially speeding up the boarding process by temporarily providing additional aisle space.
On the other hand, the idea of sideward folding seats provides opportunity to increase passenger comfort in case the load factor is less than 100 percent. In combination with the spectacular view through the Ce-Liner’s panoramic window belts, this feature could offer passengers an entirely new flying experience. However, in its potential future market, the Ce-Liner would not only have to win over passengers’ appeal, but it would also have to convince regulatory authorities and cost-sensitive decision-makers in the airline business. With the Ce-Liner, too, the largest share on operating cost is represented by energy expenses, in this case electrical energy. Based on a comparison of future electricity prices to those of fossil oil-based fuels, researchers at Bauhaus Luftfahrt have estimated a cost-neutral operation of an electric airliner in comparison with an evolutionary development of today’s aircraft technology. Moreover, the Ce-Liner might benefit from an exclusion from environmental surcharges, which for example could be levied at airports or by the European Emissions Trading Scheme.
With the dissemination of the group design project’s results in industry, academia, media, and general public, Bauhaus Luftfahrt aims to actively drive the discussion of a possible future for electromobility in aviation and to open up new possibilities for cooperation. The overwhelmingly positive feedback received during the public exhibition of the Ce-Liner at ILA Berlin Air Show 2012 has strongly encouraged the researchers to proceed with the further development and presentation of novel interdisciplinary concepts for future air travel.