E-Fan in the hangar. Click to enlarge.

E-Fan: electric aircraft in progress. Two years after the first electric aerobatic plane and the all-electric Cri-Cri, the smallest manned aircraft in the world (earlier post), the teams at EADS Innovation Works (IW) (the corporate research and technology network of EADS) and Royan-based ACS (Charente Maritime, France) have developed E-Fan, a fully electric general aviation training aircraft.

The two-seat E-Fan has undergone a very intensive development phase of only eight months. E-Fan propulsion is provided by two electric motors with a combined power of 60 kW, each driving a ducted, variable pitch fan. The duct increases the static thrust, it reduces the perceived noise and improves safety on the ground. With the engines located close to the centre-line of the aircraft, the E-Fan has very good controllability in single-engine flight.

Elektro 6
Also at the Paris Air Show, EADCO and PC-Aero are presenting their two-motor electric aircraft project “Elektro E6”.
The Elektro E6 is envisioned to feature a full carbon composite structure, two motors, high wing propeller, solar cells technology, 6 seats, 480 kg (1,058 lb) payload and 500-km (311-mile) range.
The partners hope to build a proof of concept in 3 years and have Certification CS23 in 10 years. The final certified version of the Elektro 6 will features all the systems of a conventional commercial aircraft including retractable landing gear, anti-ice system, cabin pressure and air conditioning.

Total static engine thrust is about 1.5 kN. The 250 V Lithium polymer batteries (40 Ah, 4V per cell) are made by KOKAM and are housed within the inboard part of the wings outside the cockpit and provided with venting and passive cooling.

Because of timing and availability constraints, off-the-shelf Lithium polymer batteries are used in the technology demonstrator, giving an endurance of between 45 min. and 1 hour, EADS said. New batteries with a higher energy density will be installed later on, which will increase the endurance to up to 1 hour 30 min.

The batteries can be recharged in one hour, or they can be rapidly replaced by means of a quick-change system (available on the fully certified version). An on- board 24 V electrical network supplies the avionics and the radios via a converter. A backup battery is provided for emergency landing purposes.

The length of the aircraft is 6.7 meters with a wingspan of 9.5 meters. Take-off speed is 110 km/h (68 mph); cruise speed is 160 km/h (99 mph); and maximum speed is 220 km/h (137 mph).

Another innovation of the E-Fan is its landing gear, which consists of two electrically-actuated retractable wheels positioned fore and aft under the fuselage, plus two small wheels under the wings. The aft main wheel is driven by a 6 kW electric motor providing power for taxiing and acceleration up to 60 km/h (37 mph) during take-off, reducing overall electrical power consumption in day-to-day operation.

An optimized electrical energy management system (e-FADEC) is integrated into the aircraft, which automatically handles all electrical features, thereby simplifying the monitoring and controlling of the systems. The e-FADEC reduces the pilots’ workloads, allowing the instructor and the student to fly the aircraft and focus on the training mission.

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.

—Jean Botti, Chief Technical Officer (CTO) at EADS

EADS IW is developing the electrical and propulsion system together with partners such as ACS, which is building the all-composite structure, the mechanical systems and conducted the aerodynamic studies.

The French innovation institutes CRITT Matériaux Poitou-Charentes (CRITT MPC) and ISAE-ENSMA, as well as the company C3 Technologies have been responsible for the construction and production of the wings. Electrical engineering experts from Astrium and Eurocopter helped out with their expertise in testing the battery packs while the livery was designed by Airbus.

The E-Fan project is co-funded by the Direction Générale de l’Aviation Civile (DGAC, the French civil aviation authority), the European Regional Development Fund (FEDER), the French Government (Fonds FRED), the Région Aquitaine and the Département Charente-Maritime of France.

Diamond Aircraft DA36 E-Star 2 series hybrid. In addition to the development of the E-Fan, EADS is also demonstrating hybrid propulsion systems. One of them is in the Diamond Aircraft DA36 E-Star 2 motor glider first introduced at the Paris Air Show 2011. 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 (220 lbs). 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.

The configuration with three fans on either side of the fuselage represents an initial starting point for future optimizations, with the optimum number of fans to be determined in trade-off studies in the DEAP project. Click to enlarge.

DEAP: distributed propulsion. Since 2012, EADS IW has been working together with Rolls-Royce within the Distributed Electrical Aerospace Propulsion (DEAP) project, which is co-funded by the UK’s Technology Strategy Board. The project researches key innovative technologies that will improve fuel economy and reduce exhaust gas and noise emissions by having a distributed propulsion system architecture.

For the E-Thrust concept, distributed propulsion means that several electrically-powered fans are distributed in clusters along the wing span, with one advanced gas power unit providing the electrical power for six fans and for the re-charging of the energy storage. The E-Thrust concept can be described as a series hybrid propulsion system.

This configuration represents an initial starting point for future optimisations, with the optimum number of fans to be determined in trade-off studies in the DEAP project. Initial study results by Airbus indicate that a single large gas power unit has advantages over two or more smaller gas power units. This will give a noise reduction and allows the filtering of particles in the long exhaust duct at the back of the engine.

The hybrid architecture offers the possibility of improving overall efficiency by allowing the separate optimization of the thermal efficiency of the gas power unit (producing electrical power) and the propulsive efficiency of the fans (producing thrust). The hybrid concept makes it possible to down-size the gas power unit and to optimize it for cruise. The additional power required for take-off will be provided by the electric energy storage.

A fundamental aspect of optimizing the propulsive efficiency is to increase the bypass ratio beyond values of 12 achieved by today’s most efficient podded turbofans. For the concept, the bypass ratio must be termed “effective bypass ratio”, EADAS noted, because the fan airstreams and the core airstream are physically separated.

With distributed propulsion, values of more than 20 in effective bypass ratios appear achievable, which would lead to significant reductions in fuel consumption and emissions. having a number of small, low-power fans integrated in the airframe instead of a few large wing-mounted turbofans is also expected to reduce the total propulsion system noise.

In addition to improving the propulsive efficiency, distributed propulsion offers a greater flexibility for the overall aircraft design that could result in reduced structural weight and aerodynamic drag, for example, by relaxed engine-out design constraints leading to a smaller vertical tail plane; by being able to better distribute the weight of the propulsion system components; and by re-energizing the momentum losses in the “boundary layers” that grow over the wing and fuselage causing a “wake” (Boundary Layer Ingestion, BLI).

An additional efficiency gain appears possible if this boundary layer is “ingested” and accelerated by the fans, because it can reduce the aircraft’s wake and hence its drag. However, the implementation of a boundary-layer ingesting system means that the airflow into the fans is not uniform; to realize the potential benefits, the turbo-machinery—and in particular, the fan blades—must be able to withstand the associated unsteady conditions due to the distorted intake flow.

The design of the Rolls-Royce fans is currently being developed in collaboration with its University Technology Centre in Cambridge, and is specifically optimized to deliver the best performance in the distorted flow conditions that are experienced in a BLI configuration; its design is supported by computer analysis as well as reduced-scale testing and measurements.

To achieve an integrated distributed fan propulsion system design that matches the overall airframe requirements, three key innovative components are required, EADS said:

• A wake re-energizing fan. As the aircraft flies through the air, it leaves a wake behind it resulting in drag. The embedded wake re-energizing fan is designed to capture the wake energy by re-accelerating the complex wake. By re-energizing the wake, the overall aircraft drag is reduced. The concept uses advanced lightweight composite fan blades that are designed to maximise overall propulsive efficiency whilst minimizing the weight of the propulsion system.

• Hub-mounted totally superconducting electrical machine. The innovative hub-mounted totally superconducting electrical machine drives the wake re-energizing fan.

  Rolls-Royce and EADS IW, with Magnifye Ltd and Cambridge University as partners, are engaged in a Programmable Alternating current Superconducting Machine (PSAM) project. The PSAM project researches an innovative programmable superconducting rotor and innovative AC superconducting stator. This work is supported in part by the UK Technology Strategy Board.

  The superconducting stator generates a powerful electro-magnetic field that rotates around the circumference at a speed directly related to the frequency of the electrical supply. The superconducting machine replaces the copper and iron stator structure of a conventional machine. It is a much more powerful, lighter and low-loss design incorporating round-wire high temperature superconducting coils embedded within a lightweight epoxy structure.

  Electromagnetic torque is created by effectively aligning the rotor’s magnetic field with the field generated electro-magnetically within the stator.

  The superconducting rotor magnetic field is generated through the use of bulk superconducting magnets in a puck form. A superconducting magnetic puck of this size can, when fully magnetized, generate extremely high magnetic fields with laboratory testing demonstrating 17 Tesla—a magnetic field capable of easily levitating a family car. The magnetic pucks are innovatively magnetized in-situ by the stator to create a permanent magnet field that can be programmed to deliver different field strengths thereby improving controllability.

  The superconducting machine design is bi-directional in that it is equally efficient at driving the wake re-energizing fan to provide aircraft thrust or being driven by the fan rotating in the airstream to generate electrical power, which can then be stored within the airframe.

• Structural stator vanes that pass electrical power and cryogenic coolant. By having an embedded propulsion system, the conventional turbofan mounting structure is no longer required, thereby saving weight and drag. The stator section is carefully designed to provide a row of aerodynamic and structural stator vanes behind the fan recovering thrust from the swirling air.

  The length of the distributed fan propulsion system has been designed to be much shorter than that of a conventional turbofan so that the center of gravity is located about the structural stator vanes. In addition, some of the stator vanes are designed to accommodate the internal routing of the superconducting cables to the hub-mounted superconducting electrical machine.

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 optimises the overall propulsion system integration.

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.

—Sébastien Remy, Head of EADS Innovation Works

The development of innovative propulsion system concepts for future air vehicle applications is part of EADS’ research to support the aviation industry’s environmental protection goals as spelled out in the Flightpath 2050 report by the European Commission.

This roadmap sets the target of reducing aircraft CO₂ emissions by 75%, along with reductions of NO_x by 90% and noise levels by 65%, compared to standards in the year 2000.