Avions electriques et hybrides !

• des "petits" moteurs électriques en nombre pour entrainer des petites hélices carénées efficaces,
  
• un générateur plus puissant que les deux moteurs normaux et donc plus efficace,
  
• plus besoin d'un moteur surdimensionné pour la courte phase de décollage : on se retrouve avec un générateur tournant à un régime plus régulier donc la aussi plus efficace, comme un quadrimoteur,
  
• mais un seul générateur, donc bien moins de maintenance qu'un quadrimoteur,
  
• freinage avec génération électrique en phase de descente pour remplir les batteries pour le décollage suivant. La descente peu donc être plus rapide plus tard, sans trop perdre d'énergie.
  

• batteries puissantes (l'avion doit pouvoir décoller sur batterie si le moteur principal fait défaut au mauvais moment),
  
• batteries légères et fiables,
  
• un bon rendement de conversion mécanique - électrique - mécanique, sinon le concept ne vaut rien. D'où une partie supra-conductrice pour améliorer ce rendement,
  
• nouvelle conception aérodynamique de l'avion,
  
• attention au poids car si on gagne sur le moteur, il faut ajouter plus de batteries, les moteurs électriques, un gros générateur électrique et le système de refroidissement cryogénique et sécurisé pour la supra-conductivité.
  

Airbus is literally powering ahead with its vision of a hybrid-electric regional transport aircraft – by preparing to begin serious development of the radical propulsion system on a [url=http://www.flightglobal.com/landingpage/Munich Airport.html]Munich[/url] testbed that will be fully functioning within two years.

And, chief technology officer Jean Botti declares, he wants to have a prototype of the E-Thrust concept flying in 10 years.

The concept calls for all of the 70- to 80-seater’s propulsive thrust to come from six internally mounted electric fan engines skimming boundary layer air off the fuselage, with electric power coming from batteries and a gas turbine generator set. Further battery top-up will come from the power fans “windmilling” during a glide segment early in the descent phase.

But, Botti readily admits, a prototype could be further away, perhaps 15 years, as all of the technology is not yet in place to create an aircraft that would help meet Europe’s “Flightpath 2050” objectives of slashing fuel burn, emissions and noise.

A commercially available E-Thrust may be decades away, but show visitors could see the first of what Botti calls “stepping stones”, in the form of Airbus Innovations’ E-Fan. The 100% battery-powered, two-seat tandem twin-fan made its air show flying display debut, after its public unveiling at the 2013 Paris air show.

And, Botti stresses, E-Fan’s technology is to underpin a side-by-side two-seat trainer called E-Fan 2.0 that Airbus will manufacture through a 100%-owned subsidiary called Voltair, at a purpose-built factory adjacent to Bordeaux-Marignac airport. Maiden flight is pencilled in for 2017. A four-seat version will follow, featuring a “range extender” kerosene engine to top up the batteries – just like in the E-Thrust concept.

The critical, enabling technology that Botti’s team needs to achieve E-Thrust is superconductivity, which will be a focus of the Munich test bed.
E-Fan carries 137kg (302lb) of lithium-polymer batteries to generate 60kW for its two motors. But to get to the megawatt system – with a power density of 10kW/kg – needed for E-Thrust will require more than better batteries. Traditional copper cables would have to be massive to transmit that much power without getting dangerously hot. But by cooling the cabling to cryogenic temperatures – about -247°C – enough electric power could be carried around the aircraft with fine wires.

A superconductivity display at the Airbus exhibit illustrates the point – where 19 copper cables carrying 4.5kA at 20°C would weigh some 12kg per foot, cryogenically induced superconductivity would see the same power carried by a thin bundle of fibres weighing just 16g.