17 Jun 2011 04:06:25
Airliners become electric vehicles
Airliners become electric vehicles
By Dr Peter Harrop, Chairman, IDTechEx
Aircraft are becoming more electric even to the extent of having electric traction just like an electric car. Curiously this is starting at the light and heavy end, with medium sized feeder aircraft adopting electrification later. With small single and two seater aircraft, using an electric motor driven by an on-board battery is viable for short flights of up to three hours even though the battery can constitute half of the weight and cost. Such a drive train is even being trialled on the best selling Cessna plane while it is being sold in the form of motorised gliders and custom designs. ENFICA-FC has successfully flown a two seater fuel cell powered plane after Boeing demonstrated a single seater. As with fuel cell powered buses and other vehicles, a lithium-ion battery is also needed in these aircraft to manage load variations, the fuel cell giving extra range. Also at the small end, pure electric Unmanned Aerial Vehicles UAVs are used for monitoring ice flows, military surveillance and other purposes. Some are staying aloft on solar power, again using lithium-ion batteries, and sometimes they are simply charged on the ground, so there is a great deal going on with small electric aircraft.
At the other extreme, airliners are becoming electric vehicles when on the ground. Later some will become electric in the air as well, for example to achieve silent landing in built up areas. Firstly, airliner nosewheels will be driven by electric motors providing a huge cost saving in fuel and in avoiding the wait for a tug on landing. Indeed, the noise and pollution of jet engines on the ground will be hugely reduced to the delight of those living nearby. Electric nosewheels provide both both pushback and taxi operations. They enable aircraft to be electrically driven from the terminal gate to the takeoff runway and, upon landing, from runway exit to the gate. The resulting improvements in efficiency, flexibility, fuel savings, and reduced noise and engine foreign object damage yield projected savings of more than $500,000 per aircraft per year, in the view of WheelTug, as well as substantial reductions in carbon dioxide and other greenhouse gas emissions.
The technology within an aircraft when it acts as an electric vehicle echoes the technology battles between alternative motors, range extenders and other components being tried in electric cars and other electric vehicles. For example, AC motors are increasingly used – it is no longer all about DC, as the AC motors are becoming high performance, not just low cost and allegedly more reliable, though proponents of DC traction motors are fighting back.
Energy harvesting is a new key enabling technology for all electric vehicles, starting with regenerative braking that almost comes almost free with an AC motor as used in the Tesla Roadster sports car and the Nissan Leaf car and many other electric vehicles. However, regenerative braking is not available on the first generation electric nosewheels: that will come later. Aerospace giants Boeing and EADS have already noticed the huge amount of energy wasted in braking an aircraft on landing but it is not yet cost effective to carry the lithium-ion batteries needed to store that energy on landing so there is interest in donating it to airfield capturing devices. However, that may change with the newer, improved supercapacitors combines with lithium-ion batteries. One dream is to electrically accelerate the wheels of propeller aircraft for silent takeoff, partly using electricity snatched back on landing.
As hybrid electric vehicles move towards the technology of pure electric vehicles, they cease to use internal combustion engines and these are replaced by smaller, more reliable and potentially cheaper fuel cells and mini jet engines as range extenders. Examples include the speculative research at Michigan State University on wave-disk turbines otherwise known as shock wave engines, the Bladon Jets mini turbines being developed for the planned Jaguar CX75 supercar and the larger Capstone turbines already deployed in DesignLine hybrid buses. By land sea and air, fuel cells are starting to compete with mini turbines as range extenders in hybrid electric vehicles. All need the lithium-ion battery for load management but that battery is smaller than it would otherwise need to be.
The electric nosewheel for airliners being trialled by DLR German Aerospace Center echoes this evolution in vehicles on the ground because uses a fuel cell. It also uses a high performance DC motor. The alternative demonstrated in collaboration with Boeing and Delta Airlines comes from WheelTug plc, a subsidiary of Chorus Motors Inc in the USA, and it gets its power from the airliner's turbine - the Auxiliary Power Unit APU. Here, the electric motor provided by Chorus Motors is a sophisticated AC motor that combines the benefits of both AC and DC motors – affordability and performance together and echoing the contest between DC and AC motors in land and seagoing electric vehicles.
In May 2011, WheelTug signed an agreement with Gables Engineering, Inc., a leading provider of custom avionics controls, to design and manufacture the pilot cockpit panel used to control the WheelTug system on Boeing B-737NG aircraft. Gables Engineering will design, test, certify, and manufacture the cockpit control panel and will work closely with WheelTug (system design) and its partners Resource Group Limited (software development) and Newport Aeronautical (system certification) to integrate and certify the final cockpit control panel.
The WheelTug system is being developed initially for the Boeing 737NG, one of the world's most widely-flown aircraft, whereas DLR is trialling its alternative design on an Airbus A320. Systems for other commercial and military aircraft will follow. There had been some industry speculation about whether the current B737NG APU could provide adequate electrical capacity during taxi to maintain normal airplane ground speed and operations while powering WheelTug. After all, it was not designed to double as an electric vehicle range extender. However, tests completed in February 2011 demonstrated that there is more than sufficient power available from the APU to enable a fully-loaded WheelTug-equipped B737-800 to taxi at normal speeds.
"This test was instrumental in our next steps to make WheelTug a reality for the aerospace industry," says Isaiah Cox, CEO for WheelTug. "The results will also be helpful in developing WheelTug systems for other OEMs and aircraft models."
DLR German Aerospace Center is presenting on its system and hosting a visit at the IDTechEx event Electric Vehicles Land Sea Air in Stuttgart June 28–29. WheelTug presents its alternative system at the US version of this event Electric Vehicles Land Sea Air in San Jose California November 1–2. Both events have several other speakers specifically focussed on electric aircraft and many other speakers presenting relevant technology. Both events have optional masterclasses, an exhibition and an awards dinner.
For a complimentary press pass for this event, please contact Cara Harrington.