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What’s in store for electric and hybrid-electric aircraft?

18 August 2010

Electrically powered aircraft are not exactly poised to convey the holiday-making hordes to their destinations for a little while yet, but recent developments in this field offer more than a hint of what might be possible in the years to come. Few people, I think, were left unimpressed by aviator André Borschberg’s airmanship when he managed to keep his solar powered Solar Impulse HB-SIA aircraft aloft for more than 26 hours, reaching jet airliner altitudes and cruising at a rather sedate average speed of just under 21 knots.

A somewhat faster, though less durable, record breaker is the Italian SkySpark, which reached 250km/h some fourteen months ago with pilot Maurizio Cheli at the controls. This first test flight lasted for eight minutes, but it confirmed the viability of battery powered fixed wing flight. Cheli’s aircraft – a joint project between DigiSky and Turin Polytechnic University – is a two-seat Pioneer Alpi 300 with its conventional engine stripped out and replaced by a 75kW brushless motor powered by lithium-polymer batteries. SkySpark’s team says its electronic control systems are able to modulate motor speed and torque to provide dynamics that are far beyond what it is attainable from reciprocating engines.

And just a few weeks ago at the AirVenture 2010 event in Wisconsin, Sikorsky Innovations took the wraps off its Firefly electric helicopter, essentially an electrically powered S-300C that the company hopes to put through its paces before the end of the year. Sikorsky is partnered by US Hybrid, Gaia Power Technologies and Eagle Aviation Technologies in a project to replace the 300C’s 200hp piston-powered Lycoming engine with an electric machine of equivalent power from US Hybrid. The fuel tanks are replaced by two 45Ah lithium ion battery packs built by Gaia, one on each side of the cabin. Eagle Aviation carried out all the necessary modifications to the aircraft, which will initially have an endurance of 15 minutes with one pilot onboard.

The European aerospace giant, EADS is also studying alternative propulsion systems for helicopters and at this year’s ILA 2010 in Berlin it wheeled out a diesel-electric hybrid concept designed to make helicopters more environmentally friendly. High-efficiency electric motors in combination with fuel-efficient diesel engines reduce fuel consumption and emissions by up to 50 percent, says EADS Innovation Works, whose Eco2Avia research platform is expected to open up new possibilities for cleaner, safer and quieter helicopter operations. Takeoff and landing will be possible on electrical power alone, resulting in lower noise levels and improved flight safety.

The main components of this hybrid system are multiple diesel-electric motor-generator units, a pair of high-performance batteries and a power electronics unit controlling the energy flows for optimum efficiency. The OPOC (Opposed Piston, Opposed Cylinder) diesel engines offer a fuel economy improvement of up to 30 percent compared with conventional gas turbine engines. The OPOC diesel engine driven generators deliver current to the power electronics unit, which manages electrical distribution to the motors driving main and tail rotors, to and from the batteries as well as to the other user systems on the helicopter.

In the UK, Falx Air Vehicles is also pursuing the hybrid electric path and hopes soon to commercialise a concept it first unveiled just over two years ago. The Falx hybrid-electric tilt-rotor aircraft platform can be configured as either a single seat personal vehicle or a two-seater for training or personal use. Using aerospace-certified composite materials, the single seater weighs just 350kg, with the twin-seat version weighing 405kg. Falx is circumspect about the batteries it has chosen for this aircraft, but the charging arrangement comprises solar arrays and a small 100hp combustion engine that drives a lightweight, brushless generator. Falx says the aircraft will consume just ten litres per hour in flight and claims its quiet operation and manoeuvrability makes it a good candidate for deployment as a military ‘stealth’ vehicle.

In France later this year, Lisa Airplanes’ Hy-Bird two-seater recreational craft is expected to make its maiden electric flight. Hy-Bird is a hybrid aircraft that depends on two renewable sources for its propulsion system: solar energy from photovoltaic cells mounted on the wing and horizontal tail surfaces, which is stored in lithium-polymer batteries, and electricity produced by proton exchange membrane (PEM) type hydrogen fuel cells. The hydrogen, compressed and contained in onboard lightweight tanks, is derived from a water electrolysis process, powered by renewable resources. The main role of the batteries is to complement the power of the fuel cells for all phases, including takeoff, climb and cruising at peak power. The fuel cells delivers continuous power corresponding to that required for flight at cruising altitude - between 15 and 20kW.

According to Boeing researchers, PEM fuel cell technology could potentially power small manned and unmanned air vehicles. Over the longer term, solid oxide fuel cells might be applied to secondary power-generating systems, such as auxiliary power units for large commercial aircraft. However, while the company does not envisage fuel cells providing primary power for large passenger aircraft, it has pledged to continue to investigate their potential, as well as other sustainable alternative fuel and energy sources that improve environmental performance.

Quite apart from the sources of propulsion energy, removing weight is another essential element in the development of electrically propelled aircraft. Peter Harrop, chairman of the printed electronics specialist, IDTechEx says printed electronics, wireless sensors and actuators and energy harvesting systems all have their part to play. Dr Harrop’s company is staging the first ever event to cover all electric vehicle technologies in San Jose, California later this year (December 6-7 2010). The IDTechEx Future of Electric Vehicles USA 2010 will have a strong future technology theme, drawing speakers from leading companies in the field, including PC-Aero, T-Ink, CEHMS and Hawkes Ocean Technologies. An exhibition is planned, plus an awards evening and masterclasses throughout the event.

The organiser has arranged visits to local centres of excellence such as Kleenspeed, where participants will have an opportunity to view its Formula 1 200mph all-electric racing car. AFS Trinity will reveal a new advanced hybrid architecture with fast ultra-capacitor storage, while Oxis Energy and PolyPlus will enlighten their audiences with presentations on third-generation lithium-sulphur and lithium-air battery technologies, respectively.

Dr Harrop insists that the event will be of interest to all those progressing electric vehicle development for land, water and air. It will cross-fertilise new information and reveal the full potential to suppliers, he says, as well as providing the antidote to events that obsess about today's electric cars! Registration is available at where you can obtain full details of the event. And if you are interested in speaking or exhibiting, contact Teresa Henry -

Les Hunt

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