E-taxi or eTaxi (Electric Taxi) is the generic name for a fully integrated and onboard ground propulsion system for aircraft which puts an electric motor into or near an aircraft wheel to allow for backwards movement without the use of pushback tugs and to allow for forward movement ("Taxi") without using the aircraft's engines. E-taxi systems under active development drive the aircraft with power supplied by the onboard APU (Auxiliary Power Unit) rather than aircraft engine power, although one research project by DLR demonstrated a fuel cell-powered nose wheel on a A320[1] . The overall effects of implementing an E-taxi system, beyond the standard benefits of taxing with engines off and thereby saving fuel, include a wide variety of other procedural and operational changes affecting gate operations, airport operations, risk management (safety), aircraft maintenance and valuations, and scheduling. There are presently only two competing systems under development, one which is focused on the main landing gear and the other on the nosewheels in the front landing gear.
History
editA. when was it first proposed? (Other historical references?)
B. Mention the 4 companies L-3/Crane, Safran/Honeywell JV, WheelTug (alphabetical order) and give a brief ‘overview timeline’ C. Give specific timeline: WT/Boeing phantomworks, Delta ELA, S/H entry, Prague tests, L-3/Crane Entry, L-3/Crane Exit, air show milestones. (In chronological order.)
Proposed Systems
editCrane Aerospace & Electronics / L-3 Space and Propulsion Systems
editCrane Aerospace & Electronics, along with L-3 Space and Propulsion Systems, began developing a system named GreenTaxi(TM).[2]
German Aerospace Center (DLR)
editDLR conducted tests using their Advanced Technology Research Aircraft to demonstrate a fuel cell-powered electric nose wheel.[1]
Other Partners include Airbus Deutschland GmbH and Lufthansa Technik
Safran / Honeywell
editSafran and Honeywell established a partnership[2] to develop the Electric Green Taxiing System (EGTS) [3] which will use a Honeywell (APU) generator to power motors in the main wheels of Airbus A320s.
Other Partners include Messier-Bugatti-Dowty
WheelTug Plc.
editWheelTug plc is developing a system named WheelTug(TM) for both Boeing 737NGs and Airbus A320s which puts a high torque electric motor into the hub of the nose wheel and uses the existing APU. (ADD A LINK)
Other Partners include Parker Hannifin Corp, Chorus Motors plc., ICE Corporation, Endeavor Analysis, Dynetic Systems, Resource Engineering Projects, Gables Engineering, Alcoa, ETA Global
System Comparison
editA survey of recent aerospace industry sources provides the following system information.[3][4][5][6]
| Company | DLR | L-3/Crane | Safran/Honeywell | WheelTug |
|---|---|---|---|---|
| E-taxi name | GreenTaxi | EGTS | WheelTug | |
| Location | Nosewheels | Main Landing Gear | Main Landing Gear | Nosewheels |
| Motor type | Permanent Magnet Motor | 3 Phase Induction Motor | High Phase Order Chorus Motor | |
| Cooling system | Liquid | Air / Brake Cooling Fans | Air | |
| Power source | Fuel Cells | APU | Honeywell APU | APU |
| Overall System Weight | Unknown | Unknown | 800lbs | 300lbs |
| Entry Into Service | Project Canceled | 2016 | 2015 | |
| Aircraft Type | Airbus A320 | Airbus A320 | Airbus A320 | Airbus A320 & Boeing 737NG |
E-Taxi Impact on Gate Operations
editSafety
editTwo of the main risk sources for accidents and injuries at the gate are pushback errors and engine intake/blast.
Pushback errors can damage the plane and the pushback tug [4] or can injure or kill the tug operator. Collisions with the tug can take aircraft out of operation for days and have a cascading effect that adversely affects the flight and passenger schedules for the rest of the day, while smaller accidents include tow bar hookup where the tug operator risks injury to their hands or fingers.
Jet Blast behind the engines and the area in front of the engines (Intake Danger Zone) are eliminated in the gate area. When no physical gate exists and passengers disembark onto the open tarmac, then with certain aircraft configurations it is normally necessary to let the engines cool down before a hatch is opened to disembark passengers.
As many of the risk factors (tug collisions, jet blast, jet intake) will be eliminated, it is expected that WheelTug equipped aircraft will have reduced insurance premiums.
Start Times
editMany airports have some form of engine noise curfew.[7] If a 6:15AM noise curfew is in effect, an e-Taxi equipped aircraft will be able to back itself out of the gate and then queue up for the runway, warming up their engines for at 6:15AM for immediate takeoff.
Upon receiving clearance from the tower, pilots in WheelTug equipped aircraft can back away from the gate immediately instead of waiting for the tug to arrive. Standard tug pushback first requires the hook-up of the tow bar to the front landing gear, then the push, and then engine warm up. An e-Taxi equipped B737 can save 120-150 seconds during pushback by changing the standard pushback process and transferring engine warm up from 'after the pushback' to 'prior to' entering the runway for takeoff.
As e-Taxi equipped planes will be at the runway when the curfew is lifted, aircraft will begin taking off ealier. e-Taxi allows for airports to increase their capacity and to add take-off slots during the time planes would normally be taxiing to the runway.
Simultaneous Pushbacks
editWith e-Taxi, there are no pushback tug disconnects or engine warm-ups; jets move forward as soon as they finish taxiing back. This means ramps are not blocked by immobile aircraft. Eliminating jet blast enables simultaneous backups at adjacent gates.
Existing approved powered pushback procedures can be used for an e-Taxi pushback; these procedures require only two ground crew who can guiding the pilot visually or with communication equipment.
Impact on Tarmac and Runway Operations
editFuel Taxi Margin
edite-Taxi will lower aircraft take-off weights by reducing the amount of fuel added by the pilot in anticipation of either expected or unexpected delays. While e-Taxi eliminates the engines fuel consumption during all but the preflight warm-up and post flight cool-down period, the needed taxi fuel margin is reduced to just the fuel needed for APU operation. For a Boeing 737, this is a drop from 25lbs of fuel per minute to just the APUs 4lbs of fuel per minute.
This means that for 300 pound system[5] like WheelTug, if more than 15 minutes of 'just in case' fuel is added and not burned, then the system is at least 'weight nuetral.' For Safran/Honeywell's 880 pound system[6] if more than 40 minutes of 'just in case' jet fuel is added and not burned, then the sytem becasue 'weight negative.'
Time Savings
editIn May 2004, a Performance Review Commission report prepared by the University of Westminster[8] put the cost of 'long' delays (of over 15 minutes) weighted by aircraft types and the known distribution at 72 Euros.
The Air Transport Association (ATA) calculated and reported the "Annual and Per Minute Cost of Delays to U.S. Airlines" as $38/hour/passenger and while Dr. Andrew Cook and Graham Tanner[9] calculated 0.36 Euros (2008).
Environmental Impact
editCO2 emissions are reduced from both the aircrafts engines and the pushback tugs engines, to only the onboard APU. With only the APU being used to power the aircrafts taxi to and from the runway, engines will be not be generating noise until it the warm up period begins before takeoff or the cool down period ends after landing.
De-Icing
editDe-Icing vehicles can maneuver around the aircraft more quickly. [10]
Impact on Overall Maintenance
editF.O.D. (Foreign Object Damage)
editEngines suck in not only what is directly in front of them, but also items blown in from natural (wind) or unnatural (other aircraft) sources. WheelTug reduces the amount of FOD caused to the engines by limiting their operating times to only the 'warm up' and 'cool down' period
Studies on FOD have broken the per flight cost of into both ""direct" and "indirect" costs. The per flight direct cost of FOD is calculated at $26[11] by considering engine maintenance spending, tire replacements, and aircraft body damage. The per flight indirect cost of FOD includes a total of 31[12] individual categories, and when added, then the cost of FOD increases by a multiple of up to 10x.[13]
Brakes
editSince standard aircraft taxi is controlled by playing the engines against the brakes, WheelTug will eliminate a significant amount of brake wear as the in-wheel motor will control movement and acceleration. Replacing brakes will become less frequent.
Engines
editEngine maintenance is partially dependent upon the total numbers of hours the engine operates. For taxi times of 23 minutes on each end of the flight, with multiple flights in a single day, a Boeing 737NG equipped with a WheelTug can save hours of engine operation time and reduce the frequency of the plane being taken out of service. Another factor that affects engine maintenance is the Foreign Object Damage (FOD) to the engines which creates nicks and dings on the turbine blades. To remove nicks and dings, and to return the blades to a more aerodynamically efficient shape, the blades are 'blended;' however the blending process does not return them to their optimal shape, and therefore engine efficiency decreases. WheelTug's reduction of FOD will slow the degradation of engines efficiency over time .
Landing Gear and Aircraft Frame
editAs a standard pushback tug has its own inertia (separate from the aircraft), pushback tugs impart a shock to the landing gear as the tug and tow bar move with their own inertia before the aircraft moves. For a system where the motor is inside the wheel hub of the landing gear itself or adjacent to it, all starts are smooth and there is no shock to the landing gear or airframe.
In most commercial aircraft, the brakes are located in the main gear. Of the three e-Taxi systems, only WheelTug is focused on the nosewheel to take advantage the additional space provided and the lack of heating that a brake system generates. The Safran/Honewell and L-3/Crane systems are focused on the main landing gear where there are more wheels. L-3/Crane is using a permament magnet motor and will require a cooling system to keep heat from destroying the magnets in the motor.
References
edit- ^ "DLR Airbus A320 ATRA taxis using fuel cell-powered nose wheel for the first time". German Aerospace Center (DLR). December 2011. Retrieved Dec 22, 2013.
{{cite web}}: CS1 maint: date and year (link) - ^ "Crane and L-3 Reach Agreement to Market GreenTaxi™ Electric Taxi System". www.craneae.com. Crane Aerospace & Electronics. July 2012. Retrieved December 22, 2013.
{{cite web}}: CS1 maint: date and year (link) - ^ Addison Schonland. "Electric Taxi comes on strong". Air Insight. Retrieved December 22, 2013.
- ^ Yann NICOLAS (January 2013). "eTaxi Taxiing aircraft with engines stopped" (PDF). FAST 51 (Flight Airworthiness Support Technology). Bruno PIQUET. p. 2.
{{cite web}}: More than one of|pages=and|page=specified (help)CS1 maint: date and year (link) - ^ Aimee Turner (March 26, 2013). "Hail and Ride". Air Traffic Management. Key Publishing Limited.
- ^ Jon Ostrower (June 2013). "Jet Shows Its Maneuverability—on the Ground". The Wall Street Journal. Retrieved Dec 22, 2013.
{{cite web}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)CS1 maint: date and year (link) - ^ Raquel Girvin (2009). "Aircraft noise-abatement and mitigation strategies" (PDF). Elsevier Ltd.
- ^ University of Westminster (May 2004). "EVALUATING THE TRUE COST TO AIRLINES OF ONE MINUTE OF AIRBORNE OR GROUND DELAY" (PDF). European Organisation for the Safety of Air Navigation (EUROCONTROL).
- ^ Dr. Andrew Cook and Graham Tanner (Sept 2009). "The challenge of managing airline delay costs" (PDF). University of Westminster.
{{cite web}}: Check date values in:|date=(help) - ^ Aimee Turner (March 26, 2013). "Hail and Ride". Air Traffic Management. Key Publishing Limited.
- ^ "The economic cost of FOD to airlines" (PDF). Insight SRI Ltd. March 2008.
- ^ "The economic cost of FOD to airlines" (PDF). Insight SRI Ltd. March 2008.
- ^ "The economic cost of FOD to airlines" (PDF). Insight SRI Ltd. March 2008.