
Paris Air Show’s Slowest Plane Could Have Biggest Impact - fosk
http://www.wired.com/autopia/2013/06/electric-taxiing-airlines/?cid=co9091394
======
kevincennis
Does anyone have enough knowledge of commercial aviation to explain why this
hasn't been done before? To an outsider, it seems like kind of an obvious
feature.

~~~
omegant
Airbus 320 pilot here. This is something I've wondered myself for a long time.
This same idea of a electric motor on the wheels powered by the APU(auxiliar
small turbine for electricity and air presure, is the loud noise you hear when
boarding the plane), is what some other pilots and myself have talked about
for a long time. Just taking in to account that it makes you autonomous when
pushing back and taxing, the long times you spend waiting for take of at the
runway, it makes a lot of sense for this kind of planes that spend a lot of
the daily time taxing on congested airports. I don't know exactly the reason
why it hasn't been done before, I don't think is a weight or technology
reason. It surely has seated on a TODO list for a long time, just take into
account that in aviation we are way behind in aplication of the latest
technology. For example we are still using single chanel radio for
comunications with control( this is terribly frustrating and ineficient, it's
pretty common to have comunication jams due to excess of traffics on the same
frequency). Airplane computers even in new models are still 90s models (very
slow but i suppose that stability is worth the boredom). There are a lot of
other vintage technologies in aviation, after all every single release to
production must be tested and approved by the FAA and EASA. It's the same for
all major changes in systems and procedures. That makes all changes and
improvements very slow and expensive.

~~~
crazytony
Yep. The air transport industry is very very change (read: risk) averse.

The current APUs (except for 787) have traditionally supplied power at 28 VDC
and 115 VAC due to the worries about high voltage arcs. They would rather have
more current over more copper than higher voltage.

I suspect they have added significant wiring and electronics to this A320 to
get this to work. I haven't been able to find out if this aircraft has even
flown with this rigging much less gone through certification.

I bet they could slightly improve this system and get rid of reversers as well
(active braking).

That being said, I'd imagine ATC to be very wary of the current 130hp system:
there is no way you could expedite a move across an active runway at almost
80,000kg MTOW.

~~~
squidi
I think it's an oversimplification to say the reason for this innovation not
happening sooner is because of risk. The Boeing 777 flies on only 2 engines
which sounds far riskier but didn't stop it being approved. Also there's a
race for building planes from carbon materials.

Robert Witwer, vice-president of advanced technology at Honey-well of
Morristown, cited some other reasons [1]:

\- Increased congestion: "Short hauls do a lot of taxiing time, especially in
a place like Newark, where you can be 20th in line"

\- Legislation: “And there are a number of airports in Europe that have tough
emission standards that would make the Green Taxiing System appealing. I
believe it’s a game-changing technology."

\- Fuel costs: "The prospect of annual savings of $200,000 per jet from lower
fuel use and less ground time has sparked interest from Airbus and airlines
such as EasyJet and Alitalia. Airlines face the highest sustained prices ever
for jet fuel. United Continental, the world’s biggest carrier, says it burns
$25,000 of fuel per minute. Jet fuel delivery in New York averaged $3.12 per
gallon in 2012, more than four times as much as a decade ago."

\- Technological advances: "What’s new in today’s technology is the
convergence of airlines’ search for more efficiency and recent advances in
miniaturizing electric motors to propel a plane at the 32 kilometres per hour
it may need for taxiing."

[1]
[http://www.wingsmagazine.com/index.php?option=com_content&ta...](http://www.wingsmagazine.com/index.php?option=com_content&task=view&id=8036&Itemid=146)

~~~
cstejerean
It sounds risky to operate with only 2 engines, and in 1953 twin engine planes
were only allowed to be within 60 minutes of a diversion airport, mostly
because of the unreliability of piston engines. It was a fairly long journey
to allow twin engine planes to fly the kinds of routes they are allowed today.
[http://en.wikipedia.org/wiki/ETOPS](http://en.wikipedia.org/wiki/ETOPS)

As jet engines turned out be much more reliable than their piston
counterparts, the restrictions were loosened over time, starting with waiving
the 60 minute rule for tri-jets in 1964. The original concept for the 777 was
actually a tri-jet design. However the 767 turned out to be very reliable as a
twin-engine plane and in 1985 it became the first twin engine plane to be
allowed to fly 120 minutes away from a diversion airport (ETOPS-120) and in
1989 it was allowed to fly 180 minutes away from a diversion airport (but
planes had to first complete 1 year with 120 minutes before they could be
certified for ETOPS-180). Since twin engine designes were suddenly much more
capable than anticipated Boeing dropped the tri-jet design of the 777, and
eventually came back with a twin-engine design. By 1995 there was enough
experience with operating twin engine planes with the 180 minute rule in place
and Boeing was able to get the 777 certified to 180 minutes from the start.

So it basically took from 1953 to 1995 to allow a brand new twin-engine plane
to fly most transoceanic routes (with a 180 minute rule in place), based on
increasing evidence that the jet engines themselves are fairly safe, and
learning more about additional safety mechanisms and procedures required to
safely operate twin engine planes at extended distances from diversion
airports.

~~~
squidi
Great post, thank you.

------
zaroth
I think I like the sound of the Taxibot over installing electric engines which
weight 660 lbs on the wheels. It's like a Roomba for push backs :-)

I assume the bot autonomously 'docks' with the plane, then the pilot takes
over control and pushes back. Then the bot autonomously returns back to its
docking station by the jet bridge.

I suppose a single bot could do push backs for 3 or 4 neighboring jets, if
they're just doing the push back. If it's taxing the jet all the way down the
runway, I guess it's more of a 1:1 ratio, and probably a lot more complicated
to work the returning units into ground traffic control, to the point where
you need to work it into the overall airport design?

~~~
rodgerd
Taxibots need to be installed in every airport and for every jet at peak
capacity.

These units go where the jets goes, and are available for exactly the utilised
capacity of the airport.

~~~
danmaz74
On the other hand, a taxibot would be working most of the time, while this
system would be sitting idle most of the time. Not just sitting sitting idle,
it would be weighting on the airplane while flying.

EDIT: And this system, like the other one, would be just an alternative
solution to the plane main engines, so if they were not working, not enough at
peak hours, or not available at every airport, it wouldn't be such a big
problem.

------
jerrya
Does this take away from being able to warm the engines up to prevent thermal
shock and/or ensure give them enough run time before takeoff to ensure they
are running well?

------
mehmehshoe
Wouldn't they also have to place an electric air conditioning system on the
plane as well? When they disconnect the shore power at the terminal, the air
does not come back on until the engines spin up.

 _edit_ Read the comments on the article page and a reply stated the APU
powers the ac.
[http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Auxilia...](http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Auxiliary_power_unit.html)

~~~
omegant
Air conditioning and electricity are suplied by the APU, not only by the
ground units. For engine start up you must use the air presure(the startup
motor is pneumatic not electric), that's why you don't have air conditioning
till the engines are running, but you can have it till the moment that you
begin pushing back. Also low cost companies try to save every cent so they
don't use the APU till they have to start the engines. This can be pretty
unconfortable when you have more than 28C inside, but they don't care too
much.

Edit: redaction.

------
stcredzero
I wonder if they could spin up the tires before they hit the tarmac on
landing? Think about it: the landing gear tires go from 0 rpm to spinning
rapidly enough to carry the plane going about 140 mph _in a fraction of a
second_. That puts the tire under enormous strain, which causes them to blow
out all the time. A pre-landing spin-up system might be able to save a lot of
petroleum by conserving synthetic rubber.

~~~
nether
They don't blow out "all the time," that's why you've never experienced a
landing with a blow out. Any way this is a FAQ and has been investigated
before:

> While I was in college at the University of Cincinnati, I was watching
> television and saw a shot of an aircraft landing. There was the normal boil
> of tire smoke at touchdown. I had the same thought as your reader. Thinking
> that I had a great invention on my hands, I did some research in the
> library. I found some U.S. Government (Air Force or Navy) documents that
> addressed this issue. They were complete with photographs of a very
> elaborate test sled designed to accelerate a test tire over various surfaces
> and measure the effects of load and spinup time. Tests were done also of
> pre-spinning the tires. Much to my surprise, tire spinup was not a
> significant factor in tire wear.

> Flight crews did not like having almost 1000 lb. of spinning mass ~15 ft
> below the center of gravity. The special tires made the aircraft very hard
> to turn, especially at low airspeeds associated with the approach and
> landing phase. The crews wanted gyroscopes in the cockpit, not under the
> wings. But it seemed like a good idea at the time.

[http://archives.sensorsmag.com/articles/0300/14/index.htm](http://archives.sensorsmag.com/articles/0300/14/index.htm)

------
nealabq
The Taxibot system, where a small tug vehicle positions itself under the
plane's front wheels, would be very promising if it could be self-driving and
fully automated.

And think of the cost saving when we get rid of the pilot and cockpit. And
heck, let's get rid of the landing gear too, and have the plane drop into a
cradle running along underneath the plane on a track to catch the plane. The
cradle would also provide a lot of the acceleration of liftoff, and the
cradle's liftoff track could climb a few hundred feet like a roller coaster,
so maybe the plane's engines could be smaller.

~~~
thedrbrian
We could get rid of those pesky complaining meat sacks too. I never quite
understood the fiscal arguements for pilotless passenger aircraft. It's not
like a single seat fighter jet where you can ditch the pressurisation gear,
you've got to still keep the cargo alive no matter how much noise that they
make.

~~~
shpxnvz
> It's not like a single seat fighter jet where you can ditch the
> pressurisation gear, you've got to still keep the cargo alive no matter how
> much noise that they make.

Furthermore, my understanding is that modern fighter aircraft are generally
limited in performance to operational envelope of the human driving it, i.e.
most modern fighter airframes are capable of performance that could literally
kill a human pilot. Getting rid of the pilot opens up the possibility of
gaining significant manoeuvrability.

------
X9
Been also watching WheelTug[1] as a result of Andrew Tobias' interest (and
investment) in it[2]. Sounds like they have more customers lined up, but
competition already in this market should be a good thing!

[1] [http://www.wheeltug.gi/](http://www.wheeltug.gi/)

[2] [http://andrewtobias.com/column/hot-
brakes/](http://andrewtobias.com/column/hot-brakes/)

------
olympus
I wonder how much weight this adds to the plane. A full jet is often right at
the edge of it's envelope and adding a few hundred pounds of electric motors
could mean that they lose a row of seats. I would love it if extra leg room
was an unintended consequence of electric ground propulsion.

~~~
smoyer
"And that includes the 660-pound weight penalty of installing the system on an
airplane."

~~~
fishtoaster
The context makes it sound like they included the extra weight in fuel
calculations, but it's not clear whether they included overall weight
capacity. As the parent points out, this probably isn't worth it if they have
to cut a row of paying passengers to do it.

~~~
jmharvey
An A320 burns about a half pound of fuel per second when taxiing. [1] So it
seems plausible that the amount of weight you save on fuel could go a
significant part of the way toward offsetting the weight penalty from carrying
the extra motors.

I suppose if you're pushing the envelope precisely, and push back overweight,
count on the taxi burn to get you down to max take-off weight, and plan to
land with the legal minimum fuel reserve, then yeah, you'd still pay the full
weight penalty. But I'm guessing that most airlines, as a policy, anticipate a
range of possible taxi times in calculating their weight and fuel budgets, so
significant weight savings should be realized.

[1]
[http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011....](http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011.pdf)

------
jljljl
_" The companies claim the result is a potential savings of more than 150
gallons during a multi-flight day for an airplane like the A320 or Boeing’s
737. Overall an airplane equipped with the EGTS could cut fuel consumption by
four percent over the course of a year."_

Another step to help reduce the costs of air travel. Follows the trend of
airlines and manufacturers choosing to provide more efficient air travel vs
faster air travel to consumers: [https://medium.com/lift-and-
drag/7885a299bca2](https://medium.com/lift-and-drag/7885a299bca2)

It's a pretty funny trend since, as both articles suggest, speed is the
cooler/sexier technology. Goes to show that it isn't always the cooler
inventions that have the greatest impact.

------
savrajsingh
As we've agreed, this is not a new or novel idea, but it does illustrate why
the patent system is broken. A quick, cursory search yields a patent from 1994
for the exact same thing. " Preferably, a motor (27, 44) powered by the
auxiliary power unit of the aircraft is used to drive the wheels of the
landing gear."

[https://www.google.com/patents/EP0756556B1?cl=en&dq=electric...](https://www.google.com/patents/EP0756556B1?cl=en&dq=electric+taxi+aircraft&hl=en&sa=X&ei=pPrFUYG3J6HH0wGJyoGoCQ&ved=0CEgQ6AEwAzgK)

Search Google Patents for "electric taxi airplane". Even so, there are many
subsequent patents on the same overall concept. A broken system.

~~~
bconway
Is there any evidence that patent issues are what has kept this idea on the
sidelines until now?

------
gambiting
I think the Concorde was the worst offender when it comes to taxing to the
runway, if I remember correctly, because its jet engines were hugely
inefficient at low speeds, it would burn almost 2 tonnes of fuel just to get
to the runway

~~~
ghshephard
At 2 tonnes I suspect they would have had someone tow them to the runway
rather than run their engines.

~~~
gambiting
That's what I thought - if it uses so much fuel, towing it to the runway
should always be cheaper, under any circumstances, right?

This is mentioned here:
[https://en.wikipedia.org/wiki/Concorde#Engines](https://en.wikipedia.org/wiki/Concorde#Engines)
and there is a source for that as well.

------
dorfsmay
That was the next logical steps after Boeing electrifying most of the 787
functions (I'm still wondering why Airbus didn't go with bleedless engines for
the 350).

~~~
snogglethorpe
My impression was that Airbus quite consciously decided to be a bit more
conservative with the A350 after seeing all the problems Boeing had with the
787 switching to a zillion new technologies, _all at once_...

~~~
dorfsmay
Airbus had also said that the Boeing was using too much carbon fibre on the
787, saying that it was too new a technology, but they ended up using more of
it on the A350.

I bet all the newer airplanes will switch to bleedless engines in the near
future.

------
tocomment
Could they also use he motors to spin the wheels up to speed right before
landing? I always see a puff of smoke when the wheels first touch the runway.
I imagine that wears down the tires pretty quickly?

