Electric aircraft taxiing system demonstrated in Paris

[RegGuheert]

Electric Taxi Puts On A Show At Paris

It seems that there is development being done at several companies to allow aircraft to taxi using electric motors in the wheels powered by electricity from the APU rather than needing a pushback and then running the main engines to get to the runway. This will apparently save fuel and help reduce wear-and-tear on the main engines as well as several other benefits.

It's kinda like a Chevy Volt driving in charge sustaining mode!

 

[lion]

I have been hearing about this (and other similar systems) for several years now, it really does make sense. I'm surprised that the motor is smaller (50kW) than what's in the LEAF, but still able to achieve breakaway torque on a 1.5% slope.

 

[ERG4ALL]

Let's see, at 150 kg times two wheels is equal to at least three passengers with their luggage. I wonder if the lost revenue has been factored in to the savings in fuel? Admittedly that only applies if the plane is entirely full, but that seems to be the case if the airline can possibly fill every seat. Flying standby now can be a tedious process anymore.

 

[RegGuheert]

Let's see, at 150 kg times two wheels is equal to at least three passengers with their luggage. I wonder if the lost revenue has been factored in to the savings in fuel? Admittedly that only applies if the plane is entirely full, but that seems to be the case if the airline can possibly fill every seat. Flying standby now can be a tedious process anymore.

Keep in mind there is supposed to be a 4% fuel savings, so perhaps the reduced fuel loaded offsets the additional weight.

 

[TonyWilliams]

When all the utopian savings are factored, it's probably with a healthy dose of "worst case scenario".

Airlines have been using single engine taxi and no APU taxi/takeoff for a LONG time. So, with an aggressive fuel savings program, how will this stack up? I don't know, but I do know that the savings will be greatest at congested airports. For all the airports that don't have congestion (most), this is dead weight and lost revenue. I absolutely guarantee that this is a great idea that few will adopt.

Here's something it could do... Regen braking on landing. Those brakes are mega expensive (like $50 to $100k) and anything to prevent overheating and wear on the brakes will equal a cost savings that might make sense to someone.

How about maintenance? How hot will this EV motor get on a rejected takeoff at V1 at gross weight? Everything, and I do mean everything, on a commercial airplane has to "pay it's way" or it won't be there.

 

[RegGuheert]

I'm surprised that the motor is smaller (50kW) than what's in the LEAF, but still able to achieve breakaway torque on a 1.5% slope.

Since these are currently being targeted at B737/A320-size aircraft, I would think that 50kW would be a sizable fraction of the APU electrical output power on those planes, so there likely isn't much opportunity to use more than that.

Everything, and I do mean everything, on a commercial airplane has to "pay it's way" or it won't be there.

Thanks, Tony! Good points! Certainly they will need to pay their way in many different areas: cost, fuel consumption, weight, performance, safety, reliability, maintenance, etc. It seems they may be able to come out ahead in most, of not all of these. So even if the product costs money, adds weight, requires maintenance and breaks down sometimes, it might be able to come out ahead by improving these factors in other systems. Ultimately I think electrical systems tend to win out. The question is whether or not the technology is sufficiently advanced today for the transition to start.

One big hurdle these companies face is how to get on an aircraft. Since such a system needs equipment in at least the landing gear, an electrical equipment bay and the cockpit plus wiring from the front to the back of the airplane, the logical place to make the install would be during aircraft final assembly. Unfortunately, the Boeing 737 MAX, Airbus A320neo, Bombardier C-series and even the Sukoi Superjet and Chinese C919 are well into their design stages and I don't think such a system is designed in on any of these programs. It may be quite a few years before another similar aircraft program comes along and I doubt that a retrofit kit for such a system could be cost-effective today. In other words, they may have a few more years to do development on these systems before they can manage to get designed in, at least as an option, so that airlines can consider purchasing these on future planes.

 

[tcherniaev]

Here are some numbers for 737:
fuel burn rate at idle is around 900 LB per engine per hour
fuel burn rate for APU is 280 LB per hour
APU output is 90 KVA

 

[foobert]

Here's something it could do... Regen braking on landing.

Hmmm...

Let's just take a 737-800 at a landing weight of 64000Kg and a landing speed of 125 knots (64.3 M/s), a bit on the slow side for that weight...

Anyway, that's a kinetic energy = 0.5*m*V^2 = 132 MJ = 132 MW seconds

So, if you wanted to absorb just 1/3 of the kinetic energy through regenerative braking, you need a battery capable of absorbing 12.2 kW Hr of energy, or, a bit more than half of our Leaf's capacity.

Now, let's say we have a modest runway of 8000 ft (2.44kM) to gather this energy over, and assume we have constant deceleration (to keep the math simple), so, we come to a complete stop in 19 seconds. That means we have a generator POWER of 2.3 MW! Yeah, that'd certainly "quick charge" a Leaf battery :lol:

Or, put another way, our 50KW taxi motor would only be capable of absorbing %0.7 of the landing energy.

Don't see that system being developed any time soon.

 

[TonyWilliams]

Or, put another way, our 50KW taxi motor would only be capable of absorbing %0.7 of the landing energy.

Don't see that system being developed any time soon.

Who said anything about a battery?

Locomotives use regen braking, and they don't have batteries.

 

[TonyWilliams]

I actually read the article this time, and I have to say that I think they're on to something. The emissions angle will be huge, but I think the automated taxi, self pushback, and tightened turn radius are all awesome. I love the joystick control idea. Further, I'd somehow integrate it into the current tiller, so that its a electronic taxi control or a tiller on jet engine taxi.

Here's a mistake:

"It will also have the power to achieve breakaway torque on a 1.5% slope at MTOW."

Actually, it needs that for Max RAMP Weight, not Max Take Off Weight.

 

[TonyWilliams]

APU output is 90 KVA

Ding, Ding, Ding!!!

Two 50kW motors and one 90KVA power source. Hmmmm... Not gunna work. But, wait, I know. I can fire up number 2, and add 90KVA so I have enough electrical power.

Or, did they plan to use... batteries?

 

[RegGuheert]

APU output is 90 KVA

Ding, Ding, Ding!!!

Two 50kW motors and one 90KVA power source. Hmmmm... Not gunna work. But, wait, I know. I can fire up number 2, and add 90KVA so I have enough electrical power.

Or, did they plan to use... batteries?

I hope they don't try to incorporate batteries into such a system. I suspect that they would not try to power both legs of the landing gear at the full 50kW simultaneously. Likely the motors are slightly oversized to enhance reliability, as well.

Going forward, I suspect the 737 MAX and the A320neo may have a bit more electrical power available from their APUs, since that is the trend for all new aircraft generations.

Unfortunately, I have not found any block diagrams of the systems being developed.