While looking at some aircraft videos on Youtube I came across a new technology which will soon be available in both new aircraft and for retrofit applications on existing airliners. The technology in question is electric wheel motors for taxiing.
While it might not seem like a big fuel user, aircraft burn significant fuel while taxing around airports after landing and before takeoff. This is because jet engines happen to be especially inefficient when idled and operating at low power settings. Therefore, once the aircraft starts up its engines and uses them to slowly move down the taxiway, it is burning significant quantities of fuel. For short-run flights, with frequent landings and takeoffs, up to 5-10% of fuel can be burned on the ground.
Airbus, Honeywell and others have been developing a system which replaces this with an electric-driven system. It uses light weight electric motors connected directly to the wheels of the aircraft. Power is provided by the aircraft’s APU. The APU uses significantly less fuel than the main engines of the aircraft.
The system has some other major benefits. Control is far more nimble and precise than is achieved using jet thrust, and less time running the jet engines on the ground means less chance for FOD to be sucked into the intakes and damage the engines. The systems also allow the aircraft to reverse on their own. Normally this would require the assistance of a pushback tractor. As a result, the aircraft can leave the gate without needing to wait for a tractor could simplify and expedite the procedures for entering and departing gates.
This technology has not been deployed earlier for a number of reasons. First, aviation tends to be very conservative about adopting new and unproven systems, especially when existing ones get the job done. Secondly, weight is always an issue, so it has required manufacturers to develop a full system of electric taxiing that is light enough that its additional weight is more than offset by the savings provided.
There have also been efforts to save additional fuel by keeping the APU off for longer periods of time or using a smaller APU through the use of more on board battery capacity. Unfortunately this has been problematic both because of the weight of batteries and because of the problems experienced with high capacity and lightweight lithium ion batteries on aircraft such as the 787.
Posted in Good Science, Misc