There are currently 3 different electric taxiing solutions for low-emissions on ground movement for aircraft, if I'm not mistaken. 1) Safran's Electric Green Taxiing System (EGTS), which is a 300kg system permanently installed on the aircraft, 2) Taxibots, which are basically tractors in airport that pull the aircraft when its on the ground, and 3)WheelTug.

Just trying to get an opinion/industry insight here, but which electric taxiing system do you think is most likely to become more widespread in the market in the future?

Thanks in advance!

In my opinion electric tugs have the best chance of succeeding because they do not require retrofitting aircraft with 3rd party systems.

Besides that, in-wheel solutions as EGTS and wheeltug are not a zero-emissions alternatives as they are powered by the APU.

If you used in-wheel solutions during landing, or the engines whenever they are at idle during descent and landing, to charge a small battery, you could achieve (nearly) zero-emissions. Additionally, the APU would be running anyway to provide hydraulics & air conditioning. They also have the benefit of very low noise, and are more independent than external tugs that have to meet the aircraft.

No point carrying the weight around. Might be advantageous on short haul aircraft doing lots of turns but cost prohibitive being carried on long haul aircraft.

I foresee the remote controlled push back tugs becoming more common and a control terminal in the cockpit for it, handed control after p/b, so when you have a long taxy the pilots control it to within a couple of minutes away from t/o and then it automatically disengages and finds its way back to the stands- possibly on a track of its own adjacent the taxiways.

Likely would require a nose gear area camera so pilots can check all is well too

I think we've seen time and time again the weight overshadows any savings.

I think designing airports with downhill taxiways to be a better option.

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Berevoff wrote:

I think we've seen time and time again the weight overshadows any savings.

I think designing airports with downhill taxiways to be a better option.

Until the wind shifts and you are going uphill.

Berevoff wrote:

I think designing airports with downhill taxiways to be a better option.

Or just have taxiways that face South!

jetmatt777 wrote:

Until the wind shifts and you are going uphill

Now you went and done it. The obvious answer is a conveyor belt.

********

mxaxai wrote:

If you used in-wheel solutions during landing, or the engines whenever they are at idle during descent and landing, to charge a small battery, you could achieve (nearly) zero-emissions.

Nothing is free. If you are going to charge a battery or use the APU you still have to produce the kilowatts of energy to put into the process plus losses in order to take kilowatts out of the process.
Flight idle or in flight is the same, it still would mean you would have to add additional fuel to the engine to produce your energy to charge battery plus fuel for the entire flight to carry the weight of battery and electric motor/drive.
APU running would also call additional fuel to produce an additional load to the alternators base load.


Okie

Okie wrote:

APU running would also call additional fuel to produce an additional load to the alternators base load.

Extra take off when the APU or engine is running anyway is rather cheap. Most turbo machinery is notoriously inefficient
below nominal power.

WIederling wrote:

Extra take off when the APU or engine is running anyway is rather cheap. Most turbo machinery is notoriously inefficient below nominal power.

Your point is completely hollow.
If you are running your APU that means you will be suppling all the output of the unit for which the APU was designed for running electrical loads and air packs for the aircraft. There would not be any appreciable excess designed in because of additional weight.
I am not going to take the time to try and calculate the amount of torque and gear ratios to move a narrow body aircraft. I would suspect somewhere in the 25 to 50 horsepower range. That would be 18.65 to 37.3 killowatts. I seriously doubt that there is an APU that is designed for normal commercial aircraft service that is carrying the excess alternator size to handle that load much less the additional excess turbine to turn it.


Okie

I can't help having the impression that, ina properly-designed airport, these electric taxi concepts area solution in search of a problem.

You're never going to be able to justify the substantial weight penalty of carrying around an aircraft-mounted solution.

The airport-based concepts all have logistical issues that would assure delay and disruption.

I'm personally a bigger fan of using the airport based concepts for inbound taxiing aircraft that are awaiting open gates. Far bigger benefit in shutting down an engine or two for twenty minutes because the flight was early as opposed to delaying the startup for 10 minutes. Crews are less likely to feel comfortable adopting a procedure where they are delayed in starting the engine than they are in one that shuts the engines down earlier than before.

Hell, even an old-fashion towbarless capture is probably more efficient than leaving that engine running; even if its not a complete net zero.

mxaxai wrote:

If you used in-wheel solutions during landing, or the engines whenever they are at idle during descent and landing, to charge a small battery, you could achieve (nearly) zero-emissions. Additionally, the APU would be running anyway to provide hydraulics & air conditioning. They also have the benefit of very low noise, and are more independent than external tugs that have to meet the aircraft.

Even a small battery means extra weight. Something that can provide the required 20-30 kW is going to weight hundreds of kg pushing the weight of the add-ons past half a ton.

On the other hand battery weight is not an issue for electric tugs as it can replace at least some of the tug ballast and enables the use of cheaper and more reliable batteries than Lithium ones.

[quote="Okie"

Now you went and done it. The obvious answer is a conveyor belt.
[/quote]

Be careful! That word makes StarlionBlue get...testy.

You don't want to make him testy, do you?

I'm with the airport based options. Especially as self driving vehicles improve even further. I could easily forsee a future of uncrewed tugs that come up to a plane, hook up/lift, then taxi the aircraft to a designated point for engine startup before disconnecting and heading to the next plane. And the reverse could happen when things get congested on arrival and planes find themselves taxiing for ages.

Not going to happen tomorrow but 10 years from now? Quite doable I think.

What is the actual "wasted" fuel from taxiing? I don't mean total fuel used. I mean how much additional energy is used to taxi with the engines vs an electric system? This whole issue seems to be companies solving a problem that doesn't exist and using environmental buzzwords to try and get mandates to buy their product.

Any onboard system is going to increase the weight of the aircraft with a system that is completely useless for flight. Ground based tugs or bots will also waste energy returning from the drop off. There isn't an equal flow of takeoffs and landings to allow the tug to drop off one aircraft at the runway and pick up another that just landed. During a hub bank, they'd constantly be deadheading and wasting energy.

mxaxai wrote:

If you used in-wheel solutions during landing, or the engines whenever they are at idle during descent and landing, to charge a small battery, you could achieve (nearly) zero-emissions. Additionally, the APU would be running anyway to provide hydraulics & air conditioning. They also have the benefit of very low noise, and are more independent than external tugs that have to meet the aircraft.

How "small" of a battery would you be charging? My wife's Ford Escape Hybrid has a battery pack that weighs over 100 lbs that stores enough power to move a 2700 lb small SUV about a mile at 40 MPH (when starting from already in motion). An aircraft is going to be over 60 times the weight at takeoff.

During the big fuel cost spike several airlines were looking into these systems as they would have saved money. However after the price dropped again they no longer became worth it.

As for reducing greenhouse gas emissions this would be a good way to do it. Electric tugs that can recharge from renewables is a pretty good way to reduce the amount of fuel used in congested airports. Of course it isn't a silver bullet, but every bit helps. And if you can make them fully or semi autonomous the deadheading becomes much less of an issue.

planecane wrote:

What is the actual "wasted" fuel from taxiing? I don't mean total fuel used. I mean how much additional energy is used to taxi with the engines vs an electric system? This whole issue seems to be companies solving a problem that doesn't exist and using environmental buzzwords to try and get mandates to buy their product.

Any onboard system is going to increase the weight of the aircraft with a system that is completely useless for flight. Ground based tugs or bots will also waste energy returning from the drop off. There isn't an equal flow of takeoffs and landings to allow the tug to drop off one aircraft at the runway and pick up another that just landed. During a hub bank, they'd constantly be deadheading and wasting energy.

No concrete numbers here, but I'd imagine alternately leaving the turbofans on standby and nudging them to taxi forward (the current method) to be a much more of an energy (more critically, fuel) waster compared to an electric system that can be turned on and off at will. Especially when taxi times go over 10-15 minutes (very common in many slot-restricted airports).

Critically, if implemented well, electric taxi systems are a viable way to reduce aircraft fuel consumption, even if net energy consumption is the same, it reduces operational costs to airlines (fuel) and increases aircraft performance (more range/payload instead of fuel).

Main engines are designed to produce fairly constant high levels of thrust in a cold (-50C) thin air environment. Running at idle in thick warm air, with sudden power surges for acceleration, is far from optimal. Additionally, the thrust output is continuous, but the aircraft does not need to accelerate all the time, so the brakes are used to compensate.

An dedicated taxi system would use energy only when required, and be set for optimal performance under typical taxiing conditions.
So the fuel savings do exist (even for systems powered by the APU), and on top there is a bit less engine wear, brake wear, and much less noise and pollution.

Regarding the 2 main alternatives :
>>> An on-board system provides the advantages of eTaxi, plus autonomy vs tugs, minus a slight extra fuel burn in flight due to the extra weight. It would be a good option for single-aisle aircraft running fairly short routes at high frequencies, with a big airport at either or both ends. Typically, CDG-MAD, or shuttles running CDG-TLS, for example.

>>> A tug system would have no impact on the aircraft or its flight performances, but the airport operations are more constrained. Attaching a departing aircraft at the gate for taxi-out is easy, but hooking up with a landing aircraft in the middle of an active field is much less practical. And the utilization of the (expensive) tug would be low, as each one would be attached to a single aircraft from push-back to near take-off, which by nature of the business case would have to be a relatively long time.
This solution would be more appropriate for heavy long-haul aircraft departing from big hubs, in which case there is little sensitivity to a few extra minutes on ground but much more sensitivity to fuel burn.

So the 2 solutions are for a large part complementing each other, IMO. The issue with both solutions is that the initial investment is non-negligeable, and so needs high fuel prices to compensate within the 3-5 years typically used for return on investment targets.

jgei97edb wrote:

1) Safran's Electric Green Taxiing System (EGTS)

pedantic note : EGTS was the Safran/Honeywell joint venture. Once Honeywell pulled out I think Safran just called it electric taxiing

jgei97edb wrote:

3)WheelTug.

This is actually not an electric taxiing solution. As the name suggests (but the marketing skillfully blurs), it just replaces a current tug.
Even if it works one day, WheelTug is too under-sized to actually taxi the aircraft at acceptable speeds. It is merely useful for short distance maintenance maneuvering, and push-back (but that still requires a wing-walker). I don't see the value, especially as semi-autonomous tugs for maintenance already exist (see Mototok for example).