
Aviation industry tries to go green - dnetesn
https://phys.org/news/2020-02-flight-aviation-industry-green.html
======
tonyedgecombe
Aviation looks like the industry least likely to go green to me. I doubt
electric planes are ever going to be viable for anything other than a short
hop which would be better done by train. Synthetic fuels sounds interesting
until you look at how much fuel they consume.

The trend is quite obviously in the wrong direction:
[https://www.statista.com/statistics/655057/fuel-
consumption-...](https://www.statista.com/statistics/655057/fuel-consumption-
of-airlines-worldwide/)

It's often quoted as 2% of global emissions, my (admittedly back of the
envelope) calculations come out 50% higher without the cost of burning it at
high altitude nor refining the fuel nor the infrastructure on the ground to
support air travel.

My guess is emissions from air travel will continue to rise as the world
develops and they will take an increasing share of the total as other sectors
decarbonise.

This all leads on to political problems, how are you going to convince the
poor to reduce their emissions when they see their rich neighbours jetting
across the world on holiday.

~~~
stingraycharles
I think it’s important to look at this from a different angle: sure their
requirements are high, and they may not be able to go completely green in a
short timeframe, but should we therefor not even attempt it?

It’s not difficult to imagine a hybrid system at some point in the near
future, and/or other ways of reducing the carbon footprint. Focus on those
positive things, rather than “this will never be completely green, so why
bother?”

~~~
tonyedgecombe
_“this will never be completely green, so why bother?”_

You are putting words in my mouth, I never said that.

The industry has been reducing emissions per mile pretty much since it was
founded. Looking at that graph I posted it is having the opposite effect to
what we want. Jevon's paradox and all that.

My personal solution was to stop flying, I haven't got on a plane for 19
years. I'm not sure that is palatable to most people here though, it certainly
isn't to the airline industry.

------
gersh
It might be better to just capture CO2 from the Ocean or the air, and then use
renewable energy to make jet fuel. While the efficiency of the process may not
be super high, it will be carbon neutral. See
[https://www.weforum.org/agenda/2018/02/bill-gates-to-
strip-c...](https://www.weforum.org/agenda/2018/02/bill-gates-to-
strip-c02-from-air-for-clean-fuel/) and
[https://www.greencarcongress.com/2014/04/20140408-navy.html](https://www.greencarcongress.com/2014/04/20140408-navy.html).

------
cgrealy
The big win would obviously be electric aircraft, but I doubt we'll see that
in my lifetime (barring a massive breakthrough in battery technology).

The problem is even the best batteries have a much lower energy density
compared with traditional fuels. Also, a battery that weighs 100kg when full
weighs pretty much 100kg when empty.

Real Engineering did a pretty good video on the topic
[https://www.youtube.com/watch?v=VNvzZfsC13o](https://www.youtube.com/watch?v=VNvzZfsC13o)

~~~
Ididntdothis
I think hydrogen would be a candidate but then you have to deal with cooling.

~~~
danaliv
The problem with hydrogen is that it has a lot of mass-specific energy but its
density sucks. Jet-A has something like 35,000 MJ/m^3 while liquid hydrogen is
a measly 8500.

~~~
Ididntdothis
Interesting! I didn't think about volume. Is that why the Saturn V first stage
also used kerosene?

~~~
danaliv
Oh, good question - not a rocket scientist but this history seems to say
that’s the case:
[https://history.nasa.gov/SP-4206/ch7.htm](https://history.nasa.gov/SP-4206/ch7.htm)

 _”Liquid hydrogen was only one half as dense as kerosene. This density ratio
indicated that, for the necessary propellant, an LH2 tank design would require
a far larger tank volume than required for RP-1. The size would create
unacceptable penalties in tank weight and aerodynamic design. So, RP-1 became
the fuel.”_

(RP-1 And Jet A are almost identical.)

In applications where cross-sectional area is an exponential factor (read:
atmospheric flight), volume is significant!

------
jamil7
Is a large part of this also a political issue? with subsidies and tax breaks
on fuel the aviation industry is not really incentivised to innovate and
cosumers are not incentivised to seek other modes of transport since flying is
often the cheapest and fastest.

~~~
belorn
Every single mode of transport is subsidized so its hard to say if air
transportation is getting more or less incentives. Using Swedish numbers and
some estimates.

Tax on car owners only pay around 1/3 of the road network.

The ticket price on train, according to a person working in that space, said
that the ticket paid about 2/3 of the costs that the train company paid for
any given trip. The train network also get infusions from time to time by the
government, and stations are supported/built using local taxes and fees.

Boats get tax breaks on fuel, and ports are usually subsidized when built.
There might also be subsidizes involved in ice breaking, cleaning and
management of the waters and channels around ports.

Planes get tax breaks on fuel, and airports are subsidized when built.

Out of those, I would guess that the train system is the least subsidized
model but I have nothing to actually support that claim beyond a gut feeling.
I would like to see a good summarize of what each sector get and where the
money comes from.

~~~
jamil7
Thanks for the detailed info. I honestly don't know the details well enough
and hence framed my comment as a bit of an open question. This makes me
wonder, in Germany it is possible to get a decently priced domestic train
ticket or at least a comparable price to a domestic flight but one needs to
book far in advance whereas this isn't the case when booking a flight. If it's
not subsidies and taxes what is making train travel so uncompetitive with
flying?

~~~
Leherenn
Infrastructure costs, they are absolutely massive compared to what you need
for planes.

------
WalterBright
The motivation for the 737MAX was it burns 15% less fuel.

~~~
gpapilion
Fuel saving solutions are always attractive in the industry. Originally it was
thought jet engines would fail due to their fuel consumption, but the reduced
maintenance requirements made them more attractive.

~~~
WalterBright
Yup. Piston aircraft engines indeed need tons of maintenance. A huge number of
moving parts coupled with trying to minimize the weight and maximize the power
is the cause.

In WW2 the Germans fitted aircraft engines to their tanks, which worked great
when the engines ran, but too often they didn't due to battlefield conditions.
(Germany was also terribly short of avgas, which crippled those tanks.)

~~~
newnewpdro
> In WW2 the Germans fitted aircraft engines to their tanks, which worked
> great when the engines ran, but too often they didn't due to battlefield
> conditions. (Germany was also terribly short of avgas, which crippled those
> tanks.)

This sounded interesting so I skimmed the tanks mentioned in [0] and only
found mention of prototypes exploring use of a turboshaft engine [1] from [2].
[1] explicitly states "none of these was fitted operationally", so I don't get
the impression that these ever even encountered battlefield conditions before
Panther II was canceled.

[0]
[https://en.wikipedia.org/wiki/German_tanks_in_World_War_II](https://en.wikipedia.org/wiki/German_tanks_in_World_War_II)

[1]
[https://en.wikipedia.org/wiki/GT_101](https://en.wikipedia.org/wiki/GT_101)

[2]
[https://en.wikipedia.org/wiki/Panther_II_tank#Engine](https://en.wikipedia.org/wiki/Panther_II_tank#Engine)

~~~
zabzonk
Don't know about the Germans, but the British used modified aero engines quite
extensively in tanks - [https://www.wikiwand.com/en/Rolls-
Royce_Meteor](https://www.wikiwand.com/en/Rolls-Royce_Meteor)

~~~
snovv_crash
Indeed, my grandfather was in one in Italy late in the war. From the stories
he told, the crew one time got it up to 40MPH, then the crankshaft snapped.

------
animalnewbie
Serious question, pardon my ignorance. How much is the per capita fuel
consumption compared to a petrol car? Small steps are good too but I sincerely
hope we can spend that effort in safety and perhaps speed. Societies progress
as distances get shorter.

~~~
jcampbell1
Airlines get about 40-60 passenger miles per gallon. Not sure if that answers
your question.

~~~
animalnewbie
It does exactly. Thank you. This is 4 times that of a singly occupied car.
Probably more effort should go towards car pooling. And maybe electric
scooters.

~~~
upofadown
That's only a meaningful comparison if you drive across oceans to different
continents. People tend to fly much much longer distances than they drive.

Supposedly a single long over ocean flight costs something the same as a whole
year of driving in terms of carbon emission.

~~~
magicalhippo
To put it in perspective, I live in Norway, and I live in the city where I
work. Driving to and from work each day for a year would be roughly the same
distance[1] as a single direct flight to and from New York.

Of course an ICE car doesn't get the same milage as that aircraft, but it's
just a factor of 2-3 off. And then there's the difference in emissions and
between a jet engine with its jet fuel vs the ICE car. For someone like me,
even if I was driving to work, that single vacation would be a significant
contribution to my travel CO2 footprint.

[1]: [https://www.airmilescalculator.com/distance/osl-to-
jfk/](https://www.airmilescalculator.com/distance/osl-to-jfk/)

------
nradov
There are a number of other initiatives underway to reduce greenhouse gas
emissions from commercial aviation. Synthetic kerosene can be manufactured
using power and heat from renewable energy sources. Electric motors can be
used for taxiing so that the turbines only have to be started immediately
before takeoff. The electromagnetic catapults used on the latest Navy aircraft
carriers can be scaled up to launch redesigned airliners from runways on land
with lower accelerations.

But it will probably take many years until any of these innovations are widely
deployed.

~~~
mtreis86
Shutting turbine engines down and starting them up is when most of the routine
wear happens, it may actually be cheaper and greener to use the fuel.

~~~
nradov
The number of engine cycles would be the same. The only difference is that the
pilots would wait to start the turbines until nearly ready to take off, and
then shut down the turbines immediately after landing.

------
ncmncm
The best prospect for the future of clean aviation depends on moving to
hydrogen fuel. The appeal of hydrogen arises from its _extreme_ energy-mass
density: a kg of hydrogen offers several times the oxidized enthalpy of a kg
of kerosene, with zero carbon pollution, so much less fuel would need to be
hoisted up to 40,000 feet. Hydrogen-burning aircraft could devote the
difference to more payload, or to the same payload with a much lighter
airframe and smaller engines. Older aircraft simply could not compete. The
hydrogen could power fuel cells for electric drive, or be burned in turbines,
or some of both, e.g. turbines for takeoff, fuel cells for cruise.

The only problem with hydrogen is that, even liquified, it takes up a lot of
space. This demands a change to an architecture with more interior space, such
as a lifting body (or just a wider body), to provide room for more tankage.
More tankage for carbon fuel would be pointless because the extra weight would
displace cargo lifting capacity; anyway, present aircraft have enough range.

Liquid hydrogen tankage has become much more practical since the discovery of
aerogels. Mass production of aerogel enables practical commercial liquid-
hydrogen tankage.

Hydrogen for aviation is much more practical than for other modes of
transportation, because there is no distribution problem. Hydrogen can be
produced anywhere using solar and wind generating systems, operating whenever
the sun is out or the wind is blowing. The oxygen also produced, that would
otherwise be vented, could also be liquified and and carried on board for
cruise at very high altitudes, further improving efficiency. A few airports
used by long-haul aircraft, locally supplied, would suffice to bootstrap the
industry.

------
justlexi93
It is definitely a good idea. The environment changes and we need to do
something about it.

------
dredmorbius
Aviation more than any earlier transport mode is fundamentally based on high
power-to-output engines and fuels with _both_ high volumetric _and_ weight
energy density.

It's little surprise that within years of practicable petrol-fueled automobile
engines, powered flight became a reality. Within a quarter century, propeller-
driven craft had all but achieved their design zenith (the DC-3), and jet
propulsion was being deployed within four decades.

Aerodynamics, controls, navigation, traffic control, and business systems
around passenger, freight, and parcel delivery have accounted for most
advances since.

Notable among failures have been both supersonic and lighter-than-air craft.
Both see limited (mostly military) use. Commercial viability has been lacking.

The alternatives to the present subsonic, large-scale, heavier-than-air, fuel-
based transports are ... limited.

Electric propulsion solves the power-to-weight problem (electric motors are
remarkably poweful and efficient), but _not_ the energy-storage problem.
Batteries have at best about 1/10th the energy storage by weight of
hydrocarbon fuels.

Supersonic flight simply requires too much fuel, on top of other environmental
concerns: noise, high-altitude pollution. Unscheduled subsonic jets achieve
better flexibility than supersonic scheduled flights for those needing (and
able to affort) it.

Lighter-than-air craft seem to fragile, finicky, dangerous, and expensive to
operate. Changed air travel economics might address that last, but the fact
that ultra-lightweight, tremendously voluminous structures capable of lifting
only modest cargos and subject to extreme peril from high winds and inclement
weather ... does not seem promising.

(Though Germany _did_ operate international Zeppelin service for much of the
1930s. I may be overly pessimistic.)

There are alternatives to fossil hydrocarbon fuels. Most have extreme
shortcomings.

Hydrogen _as an energy carrier_ is possible but has remarkably low volumetric
energy density, as well as poor storage and handling capabilities. It's
unlikely to be utilised.

Biofuels can be effectively precise analogues of present avgas (petrol) and
jet (kerosene) fuels. The problem is that _even the small fraction of energy
demand represented by aviation fuel use is beyond the capabilities of
agriculture to produce. In 2014, Boeing touted "the biggest breakthrough that
there is out there" in biofuels.

At 75 gal/acre-yr (mean of reported production) and 16 billion gallons of
aviation fuel consumption in the US (2013 BTS RITA estimate), 21.3 million
acres would have to be under cultivation. That's about 330,000 mile2, or a
region 577 miles on a side.

On the map, you could start in Shreveport, LA, head west to Hobbs, NM, north
to Denver, CO, east to St. Joseph, MO, and south to Shreveport again,
traversing seven states and completely bounding two (Kansas and Oklahoma).

[https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings...](https://old.reddit.com/r/dredmorbius/comments/1wo2hl/boeings_biofuel_breakthrough_less_than/)

The one possible alternative I've seen, and one which isn't _obviously*
impractical, is fuel synthesis: creating the liquid hydrocarbon fuels powered
flight is dependent on from non-fossil sources.

The notion's not new -- it strongly resembles the coal-to-liquid-fuels process
employed in Germany during WWII, and in South Africa since the 1950s. The
notion was suggested by M. King Hubbert in 1964
([http://www.hubbertpeak.com/hubbert/EnergyResources.pdf](http://www.hubbertpeak.com/hubbert/EnergyResources.pdf)
(PDF) p. 139), and has been explored at the Brookhaven National Laboratory,
M.I.T., US Naval Research Laboratory, and a Google X Projects startup (since
folded), over the past five decades.

The chemistry is sound. Scaling to military or commercial capacities, and
economics, have been found wanting.

There's not much in the energy situation which gives me much hope. This
remains among the very few bright spots, despite 50+ years of less-than-
overwhelming progress.

(I'd looked at a fair bit of the history and research a few years ago on
Reddit, most represented in this search:
[https://old.reddit.com/r/dredmorbius/search?q=fischer+tropsc...](https://old.reddit.com/r/dredmorbius/search?q=fischer+tropsch&restrict_sr=on)
)

