With the goal of reducing aircraft CO2 emissions, EADS is pursuing a number of paths involving electrification.
The company calls them “E-aircraft” projects, and they include an electric general-aviation training aircraft, a serial hybrid-electric motor glider, and a hybrid propulsion system for larger aircraft.
The two-seat E-Fan represents a further advance in the work EADS Innovation Works has done with ACS on an all-electric aerobatic plane and on the smallest manned aircraft in the world with four electric engines (the Cri-Cri). EADS says the all-composites E-Fan is the first electric aircraft featuring ducted fans to reduce noise and increase safety, and it's the first purpose-built electric training aircraft.
The two-seater, introduced at the Paris Air Show in June, was a development of eight months. Each of its two electric engines (combined power output of 60 kW) drives a ducted, variable-pitch fan. Total static engine thrust is about 1.5 kN, with the energy being provided by two battery packs in the wings.
Another notable feature of E-Fan is an electric landing gear system for taxiing without the main engines and for providing acceleration boost on takeoff via a 6-kW motor powering the aft landing gear wheel.
EADS IW is developing the electrical and propulsion system together with partners such as ACS, which is also building the all-composite structure and the mechanical systems. The French innovation institutes CRITT Matériaux Poitou-Charentes and ISAE-ENSMA, as well as the company C3 Technologies, were responsible for construction and production of the wings.
Electrical engineering experts from Astrium and Eurocopter assisted with testing the battery packs. Kokam of South Korea supplied the 120 lithium-polymer cells (40 A·h/cell) for the 250-V battery system, which is housed close to the fuselage in the wings. EADS says cells with higher energy density will be used in future versions of the technology demonstrator.
The E-Fan project is co-funded by the Direction Générale de l’Aviation Civile (the French civil aviation authority), the European Regional Development Fund, the federal government of France, Région Aquitaine, and the Département Charente-Maritime of France.
“We believe that the E-Fan demonstrator is an ideal platform that could be eventually matured, certified to, and marketed as an aircraft for pilot training,” said Jean Botti, Chief Technical Officer at EADS.
Another E-Aircraft project is the Diamond Aircraft DA36 E-Star 2 motor glider first introduced at the 2011 Paris Air Show. The two-seater has been updated with a lighter and more compact electric motor from Siemens, resulting in an overall weight reduction of 100 kg, according to EADS. Electricity is supplied by a small Wankel engine from Austro Engine with a generator that functions solely as a power source. EADS IW prepared the battery packs, which are installed in the wings.
A key partner on the project is Siemens, which claims reduction in fuel consumption and emissions of up to 25%. The drive system that it developed provides an output of 80 kW during takeoff and continuous output of 65 kW.
At 5 kW/kg, the electric motor’s specific continuous output is twice that of the first prototype and about five times greater than that of a typical industrial electric motor, according to Siemens. The power electronics and gearbox are integrated into the electric motor. For takeoff and climbing, additional energy is drawn from a battery that is recharged during cruise.
The glider completed a 1-h maiden flight on June 1, 2013.
“With the second-generation aircraft we have proven for the first time that this technology is suitable for commercial use,” said Frank Anton, Head of Business Segment Traction Drives and initiator of electric aircraft development at Siemens. "The technology is scalable and will soon be making its way into small aircraft and, in the future, commercial aircraft with 50 to 100 passengers."
A third E-Aircraft project highlighted by EADS at the recent Paris Air Show is one being led by Rolls-Royce called the Distributed Electrical Aerospace Propulsion (DEAP) project, which is co-funded by the U.K. Technology Strategy Board. The very long-term (year 2050) project involves a distributed propulsion system architecture.
Six electrically powered fans are distributed in clusters of three along the wings and housed with a common intake duct. This configuration “represents a starting point,” with the number of fans required to be determined in trade-off analyses as part of the DEAP project, the companies say. An advanced gas turbine provides the electrical power for the fans and for recharging a battery that would assist in propulsion.
For the megaWatt power levels that an electrical distributed propulsion network requires, a new high-power superconducting electrical system will have to be designed and validated based on cryogenic cooling at temperatures as low as -252ºC, according to a jointly produced brochure on the “E-Thrust” concept. The aim is to reduce heat generated due to alternating current losses in superconducting wires, which are enclosed in cables and surrounded by cryogenic fluid to keep them at their optimum temperature. Minimizing such losses is critical because extracting 1 W of heat using a cryo-cooler at 20ºK (-252ºC) to ambient temperature requires 60 W of electrical power.
A major benefit of the distributed propulsion system is that it can be integrated into the airframe's structure to maximize aerodynamic efficiency and optimize airflow around it. This reduces the aircraft's weight, drag, and noise. Another advantage is that it offers the possibility of improving overall aircraft efficiency by allowing for the separate optimization of the thermal efficiency of the gas power unit and the propulsive efficiency of the fans. The gas power unit can be downsized to optimize it for cruise; the additional power for takeoff and climb will be provided by the battery.
“The idea of distributed propulsion offers the possibility to better optimize individual components such as the gas power unit, which produces only electrical power, and the electrically driven fans, which produce thrust. This optimizes the overall propulsion system integration,” explained Sébastien Remy, Head of EADS Innovation Works. “The knock-on effect we expect thanks to the improved integration of such a concept is to reduce the overall weight and the overall drag of the aircraft.”