Applying the agile product development method Scrum, Bauhaus Luftfahrt conducted an interdisciplinary group design project in 2011. This project consequently evolved into a detailed concept study for a potential zero-emission aircraft solution. It was named “Ce-Liner” and publicly presented for the first time during ILA Berlin Air Show in September 2012. The project identified requirements and technologies that led to the design of a wide-body aircraft propelled by two electric engines mounted on the rear fuselage. The target entry-into-service-year for Ce-Liner was considered 2035.
One notable feature of Ce-Liner is its innovative C-wing design that ensures high aerodynamic efficiency to compensate for the higher wing span requirement, due to the significantly increased weight, and thus wing area, of an all battery-powered electric aircraft. The proposed configuration allows Ce-Liner to meet defined performance requirements, including a range of 900 nautical miles, a cruising altitude of 33,000 feet, and a cruise speed of Mach 0.75. The standard version of Ce-Liner accommodates 189 passengers in an all-economy class layout, with two pilots and five cabin crew members. Additionally, the group has considered a stretched version for up to 233 passengers and a shortened version for 140 passengers.
The most significant novelty of Ce-Liner lies in its universally-electric energy and propulsion system, which has the potential to exceed even the ambitious emission targets of Flightpath 2050 and which was considered to be the main driver behind the activity at that time. The aircraft is equipped with two ducted fans driven by high-temperature superconducting electric motors, supplied by advanced lithium-ion batteries. The considered energy density for the batteries was 2,000 Watt-hours per kilogram, roughly eight to ten times higher than today's state-of-the-art. Up to 16 battery modules would be installed in specially adapted LD3 cargo containers known as Charge Carrying Containers (3C).
Another important feature of Ce-Liner is its novel self-trimming wing that unlike today's aircraft generation constantly adapts its shape using morphing techniques to optimise flight conditions. To meet the 30-minute turnaround time defined for the Ce-Liner and to provide enough storage for large battery packs, the aircraft has a comparatively large fuselage cross-section. This allows for a cabin with seven-abreast seating in a twin-aisle configuration. The cargo deck below can accommodate two 3C or LD3 containers positioned side by side. The design takes into account the expected body dimensions and weight of travellers in 2035, along with their baggage, and incorporates technical innovations. Key technological pre-requisites or enablers for the Ce-Liner concept could been identified. The most important pre-requisite is the energy density of batteries with a target value of 2,000Wh/kg, roughly eight to ten times as much as the state-of-the-art batteries in 2012. The power plant utilizes ducted fans run by High-Temperature Super-conducting (HTS) electric motors and the aircraft system architecture was sized on an universally-electric (UESA) system architecture.
However, for Ce-Liner to succeed in the future market, it needs to win over passengers, to convince regulatory authorities and gain support from cost-sensitive decision-makers in the airline industry. Energy expenses, particularly electrical energy, represent the largest share of operating costs. Researchers at Bauhaus Luftfahrt estimate that with future electricity prices compared to fossil-oil based fuels, operating an electric airliner can be cost-neutral when compared to the evolutionary development of current aircraft technology. Moreover, Ce-Liner may benefit from exemptions from environmental surcharges, such as those imposed at airports or through the European emissions trading scheme.
Bauhaus Luftfahrt aims to actively drive discussions about the future of electro-mobility in aviation and foster new possibilities for cooperation by disseminating the results of the group design project to industry, academia, media, and the general public. The overwhelmingly positive feedback received during the public exhibition of the Ce-Liner at ILA Berlin Air Show has strongly encouraged researchers to continue further development and presentation of novel interdisciplinary concepts for future air travel.