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Does it make sense towing airplanes to the head of airstrip by electric means, whether internal or external?

Taxiing from the gate to the runway on jet power seems like a waste of fuel. Is it possible and it would make sense to tow the airplane to the start of take-off run by a motorized towing unit or perhaps with electric motors in the airplane's landing gear? Was this ever tested or assessed?

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    $\begingroup$ greentaxiing.com, safranmbd.com/systems-equipment-178/…, and many others. $\endgroup$ – Simon Oct 13 '14 at 15:47
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    $\begingroup$ Possible duplicate of How does an aircraft taxi?. Not an exact duplicate but the answers to that question already cover pretty much everything that could be said here. $\endgroup$ – David Richerby Oct 13 '14 at 18:57
  • $\begingroup$ From the amount of fuel saved on the ground you must subtract the amount of fuel wasted by carrying those motors in flight. Such system should be most beneficial on short routes, while on longest ones it could possibly turn out wasting even more fuel. $\endgroup$ – Agent_L Oct 14 '14 at 6:19
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Was [towing unit or motors in landing gear] ever tested or assessed?

Yes.

2014 Main Gear

Using the Auxiliary Power Unit (APU) generator to power motors on the main wheels, the EGTS taxiing system allows aircraft to push back without a tug and then taxi without requiring the use of the main aircraft engines. One wheel on each main gear is equipped with an electric motor to drive the aircraft

From EGTS

Airbus signs MoU with Honeywell and Safran to develop electric taxiing solution for the A320 Family

From Airbus press release

Lufthansa Technik has proven with a technology demonstrator that aircraft can be driven on ground by electric motors.

From Lufthansa Technik (with video)


2015 Towing Unit

As of 2015 Taxibot, a semi-robotic towbarless tractor which meets and connects to aircraft, is the only alternative taxiing system certified and currently in use by airlines in the market.

From Wikipedia


2016 Nose Gear

Honeywell and Safran have pulled the plug on their jointly conceived electric taxiing system, while rival developer WheelTug aims to enter service with its system in 2018.

"After thorough market analysis", the US supplier says, the two partners "agreed to stop work on the Electric Green Taxiing System due to dramatically lower oil prices and the current aviation industry's economic environment".

EGTS had been scheduled to enter service this year, with Honeywell and Safran having planned to produce a system for line- and retrofit on A320-family and Boeing 737 jets.

Meanwhile, Gibraltar-headquartered WheelTug plans to enter service with its nose gear-mounted electric drive system in 2018. ... initially on 737s and, at a later stage, on A320-family ... Neither Airbus nor Boeing are supporting the programme

From FlightGlobal

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Variations on this kind of scheme and designs are currently being worked on. From what I remember, using electric motors are still pretty expensive, and also you're using them for a very short time frame, such that you're lugging around extra weight that is useful for a tiny portion of time(aka more fuel burn). Tugs of various sorts have been used at various places as well.

Also consider that various engines need time to warm up before applying full throttle, sometimes just a few seconds, others a few minutes.

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    $\begingroup$ Opinion about wether electrical motors are relevant or not highly depend on who is givin it : A pilot looking at the fuel gauge after wasting one hour taxiing in a traffic jam will tell you "this is the solution..!" Same debate as the Winglets on 767s but with a slight difference : The extra weight of the winglets is worth it if your 767 is doing long haul flights. The extra weight of the electrical taxi is worth it if your A320 spend most of its time struggling in traffic jam on the ground along the year... :/ $\endgroup$ – Karl Stephen Oct 13 '14 at 22:51
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    $\begingroup$ It's not just the weight of the electric motors, it's also the extra weight of batteries / fuel cells needed to power the motors. This makes a system like this worthwhile primarily for planes which fly very short routes and have to taxi long distances, while it's likely less efficient for other operating cases. $\endgroup$ – Lightsider Jan 20 '16 at 9:12
  • $\begingroup$ electric motors may also avoid the delays with waiting for tags etc $\endgroup$ – Ian Ringrose Jul 7 '16 at 13:25
  • $\begingroup$ @Lightsider: Airliners already have pretty hefty batteries on board, so there might not be quite as much weight penalty as you assume. $\endgroup$ – Sean Apr 11 '18 at 0:37
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This is an older question, and I have no answer, just experience:

When I flew from Frankfurt (FRA) to Geneve (GVA) in January 2015, we were towed by a tug nearly all the taxiway to the runway. We turned to the parallel taxiway "N north" to get rid of the tug, then went back on taxiway "N" to the runway.

Here is our way as tracked by my mobile GPS:

enter image description here

The pilot told us in advance that we will to this, and that it is some kind of experiment / project / study about if it works. (I guess more from logistics / operation side)

From my data, I also have some time information:

12:12: End of push-back
12:15: Leaving terminal
12:21: turn right on "N North"
12:22: get rid of tug, start engines 12:27: Start moving again, and back to "N"
12:29: arriving at runway
12:31: accelerating

If I remember correctly, the engines were started when we were on "N north", so 5-6 minutes before takeoff. However, we were taxiing to that place 20 without engines.

It would be interesting to know how much fuel could be saved by this procedure (It was a A320 or similar, I don't know), but at least, the aircraft didn't need any extra equipment.

(And yes, it was an ordinary tug, not this electrical stuff or similar.)

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    $\begingroup$ A few years back, the last semester of my MBA I took a class in advanced simulation and optimization, and the course professor told us about an industry-sponsored (Delta Airlines was the corporate sponsor) project the previous the class had worked on. They used simulation to explore the feasibility of using so-called "supertugs" to move aircraft between the terminal ramps and the maintenance hangar at ATL. Aggregating all the scenarios they explored, the estimated project NPV was pretty solid (don't remember exact figures), so there are savings to be had, under the right circumstances. $\endgroup$ – habu Jan 21 '16 at 16:05
  • $\begingroup$ @habu What's "NPV"? $\endgroup$ – David Richerby Feb 7 '17 at 13:23
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    $\begingroup$ @DavidRicherby Net present value, a measurement of the profitability of something (has not necessarily to do with aviation). $\endgroup$ – PerlDuck Feb 7 '17 at 13:58
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Along with fitting electric motors to allow push-back without a tug and more efficient taxiing, there is a plan to use tugs controlled by the aircraft for the taxi.

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One simpler alternative for multi-engine aircraft is to taxi out with only some (or just one) of the engines running, starting the remainder within a few minutes of take-off. It might not save as much fuel as, say, a tug, but it can be done with existing aircraft and without any extra equipment.

The major drawback of any of these approaches is that running time during taxi contributes to check-out of the fuel, fuel system and other engine systems which all have to perform properly for a safe take off. Delaying engine startup reduces/limits the opportunity for such checks.

Nevertheless, I think this practice has been done/is being done in some situations.

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    $\begingroup$ Delta Air Lines experimented with a variation of this - taxiing on only the left engine. It did indeed save fuel, but maintenance costs on the right engine went through the roof. Turns out the nice, long, low idle "warm up" of a taxi is good for the engine. They went back to dual engine taxi and right engine maintenance levelled back out to match the left. – ScottSEA $\endgroup$ – Firee Aug 31 '16 at 8:04
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    $\begingroup$ Someone edited the question and my comments under the claim of 'improving readability'. Sorry, you can't substitute electrical where the original wording was 'external', it may be good, but it's different. Of course, you can propose changes in MY wording, but the polite and practical way for doing this is a copy and paste of MY text, and then, in response box, make your proposals for 'corrections'. How did someone manage to edit something that I can only access after entering an username and a keyword? This isn't good! Thanks, regards. Salut + $\endgroup$ – Urquiola Feb 26 '18 at 9:54
  • $\begingroup$ This has a tangential connection to the issue of electric towing for Aircraft, patents: US2305237, J A Carpenter; US2312159, A Gulotta; US2333191, R E Mitton, all are about devices for having the undercarriage wheels rotating at touchdown, to avoid vibrations and tire problems. $\endgroup$ – Urquiola Feb 8 at 18:50

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