
A Fuel-Efficient Big Rig From Walmart - scotch_drinker
http://www.wired.com/2014/03/walmart-big-rig/
======
chiph
Here's another truck that is more conventional in design, yet doubles fuel-
efficiency.

[http://www.airflowtruck.com](http://www.airflowtruck.com)

It has full skirts, aero nose, and a trailer tail. The only place left to
optimize is the tractor to trailer gap, responsible for about 25% of the aero
loss in a regular truck.

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programminggeek
If a company is going to get these vehicles to be market viable, it is
Walmart. They are ruthless in terms of cost cutting and they would be the
first to cut out "tech for tech sake" if it doesn't give them a ROI.

~~~
nashashmi
I've learned from programming that cost cutting is always the n-th step in
creating a new product. What we are talking about here is pioneering into a
new territory. Cost cutting isn't even a question right now.

~~~
JoeAltmaier
WalMart has the Glass center who's whole purpose is technology for cutting
cost. Its a thing they do.

~~~
pawn
Worked there for 9 years. Its funny. Outside of this area, it doesn't occur to
most people that Walmart would have IT, but they've got more people in that
building than some IT companies.

~~~
gregpilling
Sam Walton talks a fair bit about tech in his autobiography. He says he had to
be talked into all of it, but he thought it paid off.

~~~
pawn
One thing that impressed me all the time was that any small improvement, when
done at Walmart's scale, meant big numbers. I don't remember the specifics,
but when one guy figured out how to make the printed receipts use less paper,
that was millions of dollars saved.

If Walmart can save a little bit per truck using these trucks, it'll be big
savings.

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ChuckMcM
I've always wondered about fuel efficient trucks. A number of 'design the
future' efforts include them but they rarely make it to the road. The industry
doesn't seem to care enough to make the investment.

I really think that self driving fuel efficient trucks on their own
"truckways" would be a pretty good way to boost transport infrastructure
quickly.

~~~
mdasen
In some ways, you describe freight rail. Freight rail in the United States is
great. We use it a lot more than Europe (probably about 4x more) and the fuel
efficiency gains are huge for freight rail. It isn't self-driving, but it is
on dedicated tracks with minimal people needed given the long length that
trains can be.

I think this is the reason why the industry doesn't seem to care: they do
care, but they've already invested in freight rail which is even more
efficient. It's going to be hard to beat freight rail's efficiency and at what
cost? Trucking does have greater flexibility and is needed to do shorter
distances and last-mile stuff, but we already have fuel-efficient trucks on
their own truckways: it's freight rail.

~~~
tod222
Yes, and the trucking industry stopped fighting freight rail years ago and now
makes use of it.

Trucks are more flexible, sure, but to get that flexibility they trade off
operating efficiency. This is why many long haul trucking companies such as
J.B. Hunt [1] and even UPS [2] now make use of intermodal shipping. [3]

It's not commonly known that packages sent via UPS Ground frequently travel on
trains. As a general rule, UPS Ground packages traveling long distances across
the U.S. are shipped by train. [4]

[1]
[http://en.wikipedia.org/wiki/J._B._Hunt](http://en.wikipedia.org/wiki/J._B._Hunt)

[2] [http://www.ups-scs.com/transportation/rail.html](http://www.ups-
scs.com/transportation/rail.html)

[3]
[http://en.wikipedia.org/wiki/Intermodal_freight_transport](http://en.wikipedia.org/wiki/Intermodal_freight_transport)

[4] [http://compass.ups.com/processes-of-package-in-
transit/](http://compass.ups.com/processes-of-package-in-transit/)

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veb
From the comments, a better YouTube video explaining more:
[https://www.youtube.com/watch?v=NER9X4_gtYk](https://www.youtube.com/watch?v=NER9X4_gtYk)

~~~
darklajid
OT: Native english speakers, got some questions. I'm constantly trying to
improve my english online, so ..

3:42 "The emissions is extremely low" -> Is low? Are low? Why is?

3:46 "Diesel emissions fuel" -> Is that the canonical way of spelling
'Diesel'? I mean, that's more or less exactly the way I'd spell it, but .. I'm
surprised. Usually english doesn't quite like 'i' as in 'ee'. I know that this
is a German name after all, but .. I have a number of peers and friends that
wouldn't be able to map 'Morpheus' (Matrix), 'Zeus', 'Euler' etc. to the
German pronounciation, i.e. you'd get a 'Err.. WHAT?'. Diesel made it 1:1? Or
is that debatable and there are people that pronounce it differently?

~~~
nagrom
1) That should be 'are'. It's just a mistake.

2) Diesel is named after the inventor of that type of engine, Rudi Diesel. We
still call Euler 'oy-ler' where the expected pronunciation may be 'you-ler'. I
don't see any inconsistencies there :-) Morpheus and Zeus aren't German names,
so you wouldn't expect English speakers to pronounce them in a German style,
right?

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saosebastiao
At 200000 miles a year and 6mpg average fuel efficiency, a 1 mpg improvement
is $25k in savings. I'm surprised this hasn't happened sooner.

~~~
esrauch
Actually, that sort of logic is probably exactly why it hasn't happened. The
marginal increase in costs for this is almost certainly much much higher than
$25k.

~~~
eigenvalue
Yeah, but the $25k is recurring so you would have to capitalize it to compare
it to the one-time cost of the new truck.

~~~
esrauch
A cab and trailer is probably already something like $200-300k already, so I
could see this sort of truck easily being more than $100k more expensive just
in the upfront cost.

~~~
gaadd33
But trucks tend to last 10+ years. Not sure what the lifetime of trailers are
though.

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shirro
Turbine powered battery electric drive train that can burn multiple fuels. It
seems like that would be a nice combination in a car that you could drive long
distances on cheap fuel without worrying about recharge stations and still get
electric motor torque and regenerative breaking.

~~~
ajcarpy2005
And compressed air regenerative breaking.

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ma_mazmaz
Since the siding is no longer metal, does that mean that it no longer acts a a
Faraday cage, and will be susceptible to damage by lightning?

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Theodores
...so long as they remember to only turn right (UPS style) then this should be
fuel efficient.

In reality though this truck is not currently or likely to be economically
viable. In Europe Mercedes have had a problem selling their latest and
greatest 'eco' truck as it costs more and the fuel savings just don't cover
the added up-front expense.

~~~
bjz_
If carbon emissions were priced, then maybe these kinds of technologies would
be more viable.

~~~
icebraining
In many European countries, they are, as part of a fuel tax:
[https://en.wikipedia.org/wiki/Carbon_tax#Europe](https://en.wikipedia.org/wiki/Carbon_tax#Europe)

~~~
cbr
While fuel is more expensive in Europe, their trucks are actually less
aerodynamic, with big flat fronts [1]. This is because truck lengths are
strictly limited, so a shorter cab means you can run a longer trailer. Even
with their high fuel costs the gains from the longer trailer outweigh the
savings from better aerodynamics.

[1]
[http://www.emercedesbenz.com/Images/May08/15_Mercedes_Benz_C...](http://www.emercedesbenz.com/Images/May08/15_Mercedes_Benz_CharterWay_European_Championship/646054_1157374_4252_2835_08A421.jpg)

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lr
I saw this when it aired in the 80s:
[https://www.youtube.com/watch?v=9ndY8g0cuEI](https://www.youtube.com/watch?v=9ndY8g0cuEI)

Walmart could be saving lots of money now if they wanted to, and without any
special technology.

~~~
Sanddancer
Walmart's newer fleet already tends to be trucks and trailers with side skirts
and other aerodynamic features, plus tend to not be of the cabover design
which pretty much mandates a brick wall of a front end that rams into the air
around it. Most prototypes, like what this truck is, tend to be like high
fashion designs. Yes, they look ridiculous and extreme and weird, but the
aspects, the bits and pieces of the designs tend to show up in the finished
product.

A truck like this lets them see with one rig how much is saved by the aspects
they want to explore -- a new cab design, even more radical aerodynamics, a
new powertrain, new materials for the trailer -- altogether, and do tests to
see which areas are worth further exploration in a finished product. Plus,
it's flashy and eye-catching, which is useful for the departments that work on
these sorts of things. It lets them say, "hey, we make neat things, and get
people talking about walmart, keep funding us."

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markbao
I can't imagine how much those 53-foot carbon fiber panels cost.

~~~
Theodores
...or how much the energy bill is for the Airbus sized autoclave needed to
make them.

~~~
AutoCorrect
solar oven would be great to bake these

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chrisBob
I am very surprised by the turbine engine. They are not know for being fuel
efficient.

~~~
ams6110
They are not efficient in a car which is constantly stopping and starting. If
they can run at a constant speed (e.g. driving a generator, propelling an
aircraft in cruise) they can be much more efficient.

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stcredzero
"Arise, Rodimus Prime!"

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LukeB_UK
It looks like a train and a sports car had a baby

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zackmorris
I am a little skeptical that air resistance is a huge factor for an 80,000
pound fully loaded semi. Probably most friction losses are due to rolling
resistance. As it’s a sunday and I’m daydreaming anyway, I might as well try
some back of the napkin calculations:

[http://www.engineeringtoolbox.com/drag-coefficient-
d_627.htm...](http://www.engineeringtoolbox.com/drag-coefficient-d_627.html)
[http://www.engineeringtoolbox.com/rolling-friction-
resistanc...](http://www.engineeringtoolbox.com/rolling-friction-resistance-
d_1303.html) [https://en.wikipedia.org/wiki/Semi-
trailer_truck](https://en.wikipedia.org/wiki/Semi-trailer_truck)

Before I start, I don’t know if the Engineering Toolbox answer is wrong,
because I get 217.5 N for (0.29 * 0.5 * 1.2 * ((90 * 1000)/3600)^2) * 2. At
least it’s close to the 181 N they claim. So my results could be off but I’m
hopeful they’re within the correct order of magnitude..

If we assume a drag coefficient of 1 for a flat plate representing the front
of the truck, with most losses coming from form drag, A semi with a frontal
area of 2.5x4 meters at 105 km/hr (65 mph or 29 m/s) would feel a force of:

Fd = 1.0 1/2 (1.2 kg/m3) ((105 km/h) (1000 m/km) / (3600 s/h))2 (10 m2) = 5104
N = 520 kg = 1147 lb

If we assume the high drag coefficient of 0.01 for truck tires, the rolling
resistance of a 36287 kg (80000 lb) truck (idealized as independent of
velocity) is:

Fr = 0.01 (36287 kg) (9.81 m/s2) = 3560 N = 363 kg = 800 lb

Power P = F * v so these are:

Air resistance power = 520 * 29 = 15080 W = 20.22 hp Rolling resistance power
= 363 * 29 = 10527 W = 14.12 hp

So on flat ground, amazingly it only takes about 26.1 kW (35 hp) to keep a
semi moving at 105 km/hr (65 mph)! This makes sense to me because a human can
pull a semi at about 5 mph. Power goes up roughly by the square of velocity so
a human with a power of 300 W would need 13 * 13 = 50.7 kW (68 hp) to go 65
mph. We’ve seen here that roughly half the power goes to rolling resistance
which stays roughly constant with velocity, so 35 hp is conceivable.

As a sanity check, climbing a 5% grade at 105 km/h is a climb rate of 5.25
km/h or 1.46 m/s. The power required to lift the mass of the truck is:

Power P = F * v = m * g * v = 36287 * 9.8 * 1.46 = 519194 W = 696 hp

So it takes toughly 20 times more power to go up a 5% grade, and that’s why a
typical semi truck engine with 600 hp can’t climb a 5% grade at 65 mph.

Semi trucks get 5.5 miles per gallon, so use about 12 gallons per hour. There
are 38 kWh of energy in a gallon of diesel fuel, so that’s 456 kW burned in an
hour, or a continuous power used of 456 kW (612 hp). If we compare that to the
ideal of 35 hp needed, we can see that:

Engine to road efficiency of a semi truck = 26.1 kW/456 kw (or 35 hp/612 hp) =
5.7%

That’s really quite remarkably low and doesn’t surprise me, since semi truck
technology has not changed much in 50 years. I read somewhere that cars are in
the 8-15% efficiency range. That’s why it’s so trivial for Tesla to beat an
internal combustion engine, because electric motors are 95% efficient vs.
about 25% efficient for an internal combustion engine.

So the real increase in efficiency of a hybrid gas turbine/electric semi comes
from the turbine, which has an efficiency of 40% vs about 25 or 30% for a
reciprocating diesel engine. Improved aerodynamics and decreased rolling
resistance of a carbon fiber trailer are mostly for show. Hybrid
turbine/electric propulsion has been used on trains for decades and I’m kind
of flabbergasted why it never took off in semis, or cars for that matter.

~~~
tod222
> Hybrid turbine/electric propulsion has been used on trains for decades…

I'd love to see a citation for this statement—it's far more accurate to say
that turbine/electric propulsion has been _tried_ for decades. Since 1969
there have only been a few test units built. [1]

The largest fleet of gas turbine-electric locomotives was operated by the
Union Pacific until 1969. "Fuel economy was poor" and the units were not
considered a success. [2] These units are quite well-known in railroad
circles.

If gas turbines were as good as you say they'd be in heavy use on railroads
today. Instead the dominant motive power is electric for lines already under
catenary and diesel/electric everywhere else.

[1] [http://en.wikipedia.org/wiki/Gas_turbine-
electric_locomotive](http://en.wikipedia.org/wiki/Gas_turbine-
electric_locomotive)

[2]
[http://en.wikipedia.org/wiki/Union_Pacific_GTELs](http://en.wikipedia.org/wiki/Union_Pacific_GTELs)

~~~
zackmorris
Ya true, I guess you are right. I thought trains used turbines because it
would just make sense (there's no transmission, so the engines can run at one
optimal speed). I'm thinking that maintenance costs/reliability issues make
turbines impractical in most cases except aviation and power plants.

On that note, I've never been much of a fan of turbines anyway, because they
are outrageously complex/expensive. I think a Tesla turbine would be fantastic
for applications like this though. For one thing, the disks could be cast out
of ceramic. There must be some reason why they aren't being used (especially
in hybrid electric systems like this) but I can't think of one.

