Bits and Pieces
The Green Taxi System
By Ian Brown, Editor - Bits and Pieces, EAA 657159
It was sometime in 2008 that my friend Ian Hatcher mentioned that he had been involved in a marketing team project to consider ways to reduce fuel costs when taxiing. He works for Honeywell, and the "more electric" concept was being fleshed out. Significant fuel savings can be obtained by reducing the weight of hydraulic systems and driving electric motors with the auxiliary power unit (APU) instead of the main engines.
This particular project involved mounting electric motors on the main wheels and driving them during taxiing with electricity generated by the APU.
Five years later we see the fruits of that project at the recent announcement at the Paris Air Show. Watch an interesting video about this.
Honeywell and partner Safran demonstrated their electric green taxiing system on a proof-of-concept Airbus A320 in Paris. A competitor, WheelTug, drives one motor on the nose wheel. Several years of analysis and testing led Honeywell-Safran to put electric motors on each of the two main wheel assemblies, which provide better traction on sloping or soft tarmac, snow, or ice. This also allows for turning the aircraft 360 degrees on a dime (by powering one motor in reverse and one motor in forward) - as well as avoiding additional stress and wheels-up time concerns around the nose wheel structure.
Electric motor mounted on A320 main gear
By reducing fuel burn during taxiing, the designers estimate a fuel savings of up to $200,000 per year. Airbus has announced plans to double the life expectancy of the A320 to 120,000 flight hours. At an estimated 12 hours of actual flight time, 365 days a year, that would amount to a life span of around 30 years. That's a cool $6 million in lifetime savings per aircraft. Additional benefits are reduced pollution, reduced wait time for tugs, and on-time gate departures.
The electric green taxiing system offers the most economic solution for airlines with high-frequency, short-flight schedules where a lot of daily taxiing is experienced. Expect Honeywell-Safran to market the system to original equipment manufacturers and anyone who wishes to buy it - it is obvious that the system can be retrofitted to almost any jetliner, with enough engineering effort.
Now how about us little guys? Wouldn't it be nice to taxi around quietly in our homebuilt aircraft under electric power? Our only problem is the lack of an APU. Any suggestions out there? Wouldn't it be neat to arrive at EAA AirVenture Oshkosh with a homebuilt that can actually back up and taxi around in silence and without the risk of a prop strike? Well...
You might find a Towbot useful at your local airport. It's another way to move an aircraft around without the motor running. It might remind you of the Roomba floor-cleaning robot.
It has a remote control and allows the pilot to move an aircraft without people checking the wingtip clearances. At $8,900 it might seem a bit rich for the average GA pilot, but perhaps folks who share a larger hangar might pitch in and buy one together. Watch some interesting videos of how it works.
It doesn't exactly fill the role of the electric green taxi system but it's an interesting application of new technology. The first patents on hub-mounted electric motors were dated around 1890 so electric taxiing is a technology that has patiently been biding its time.
You probably feel that a wheel hub mounted electric taxiing motor is a bit farfetched for a piston engine, but those designers of electric aircraft for the GA market could certainly take advantage of this approach for very little cost. In fact I think I can hear the gears turning already.