
A Plane Just Flew Around the World Without a Single Drop of Fuel - wnm
http://www.huffingtonpost.com/entry/solar-impulse-2-around-the-world-flight_us_5796aca1e4b01180b530065b
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thinkcontext
Manned flight doesn't seem to be a good application for solar aircraft given
the weight and speed limitations. Solar drones seem a much better fit. Airbus
seems furthest along with their Zephyr [0], it has stayed aloft for 14 days
(!). They are targeting the military as a customer and are marketing it as an
alternative to a satellite, that is, an indefinite surveillance capability.

Facebook has a similar program, Aquila, which is aimed at providing internet
access. They just recently had first flight of a full scale version [1].

[0] [https://airbusdefenceandspace.com/our-portfolio/military-
air...](https://airbusdefenceandspace.com/our-portfolio/military-
aircraft/uav/zephyr/)

[1] [http://arstechnica.com/information-
technology/2016/07/facebo...](http://arstechnica.com/information-
technology/2016/07/facebook-tests-full-scale-solar-powered-internet-drone/)

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sdegutis
> Solar drones seem a much better fit

Does that mean you could have a drone permanently hovering just above the
clouds, taking constant video or photo surveillance, periodically sending data
to whomever, all of this powered entirely by the sun without ever needing to
come down or stop?

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mikeash
Yes, that's what Facebook is aiming for with their Aquila project, for
example:

[https://code.facebook.com/posts/268598690180189](https://code.facebook.com/posts/268598690180189)

(Except they want to provide wireless internet, not surveillance.)

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avn2109
* they want to provide wireless internet _for_ surveillance.

Facebook's raison d'etre is to surveil you.

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lawless123
What about the mushy on board computer powered by glucose?

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Retric
Having a person on board cost several hundred pounds where the electronics
would have been under 1. AKA, the person was closer to cargo, than necessary.

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eldude
Things get interesting when we cross the inflection point of having an
abundance of lift.

Once you can achieve X+Y lbs of indefinite lift, where X is the necessary
weight and Y is the excess, then maintaining Y*C aloft indefinitely becomes
simply a matter of scaling the number of crafts to contribute the requisite
excess lift (aerodynamics aside for the time being).

What affect will indefinitely floating object, barges, buildings (living,
restaurants, business), etc... have on society where fuel isn't a factor?
(e.g., Facebook's global internet, cheaper flying transports, cars and
eventually domiciles)

~~~
carapace
You're absolutely right, above a certain ratio of surface area to mass it
becomes downright _hard_ to keep a structure on the ground.

I'm experimenting with kites and the Magnus effect to eventually build exactly
what you describe: infrastructure in the sky. (Note the absence of "cloud"
puns, that is deliberate.) With computer control I see no reason why we
couldn't have flying buildings.

My concern is that we will need to be able to fly to pass through the current
mass extinction. I was looking at birds one day and realized that the
dinosaurs that made it could fly. One way or another we are going to need to
move lots of people and things rapidly over great distances.

I want to make swarms of cellular kite robots that can reconfigure themselves
and combine to create vast lifting bodies.

\----

Should mention Bucky Fuller's discovery: An aluminium geodesic sphere of one-
half mile or greater diameter will float.

Sunlight reflecting internally from the metal heats the air which expands.
Above the critical size the mass of the air displaced from the sphere by
thermal expansion exceeds the mass of the aluminium shell. If you sealed the
sphere (even if it leaked a bit) it would remain aloft overnight.

Bucky called them "Cloud Nine" and wanted to build cities in them.

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thinkMOAR
Next step would be building it emission free and without use of any products
that use the same fossil resources for the plastics?

~~~
melling
Why? Then you would have 1 experimental solar plane that uses 0 fossil fuels
anywhere it the supply chain.

It's not necessary to make everything use 100% renewable but rather solve some
big problems that'll make a difference in reducing green house gases. Solving
only 1% of a problem by reducing it to 0 means global disaster.

~~~
ch4s3
Yeah, you'd do far better by trying to improve the fuel efficiency for super
freighters by half a percent, or less.

~~~
thinkMOAR
oh yeah if they would already enforce current regulations on emissions of
these big ship (freighters, cruise, all of them) in international waters. Now
they only have to be efficient, low emission near ports for example.

~~~
HelloImDumb
Ships must abide by flag country laws in international waters. There are
treaties that cover most states. Compliance is an issue now though to say the
least.

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vkou
This is less a plane, and more of a battery with wings. The amount of cargo a
solar plane could carry is minuscule.

Limits to battery energy density means that we can't improve very much on
this.

~~~
keenerd
Batteries are (in theory) optional and irrelevant for solar planes. The 747
uses about 80MW of power on takeoff, and maybe half that for cruising. The 747
has 525 m^2 of wing surface area. The sun blankets the earth with 1kW per
square meter.

Solar cell efficiency is the limiting factor, if you are willing to fly only
at day. No batteries needed. And it will never be enough with current designs,
since 500kW is well under 40MW.

Of course a solar plane can cruise much higher since it doesn't need oxygen
for the motors. And it gets more range traveling westward. At a fast enough
speed (tantalizing "easy" mach 1.4) a plane on the equator could cruise under
high noon forever. Wing size tends to go down with speed, so I doubt that
design will ever be possible.

~~~
vkou
Edit: You were originally off by three orders of magnitude.

Solar flux at 1 AU is ~1.3 KW/m^2. At sea level, due to atmospheric
absorbtion, it is between 1 KW/m^2 and 500 W/M^2.

And yeah, 500 KW of power is probably enough to get a Cessna off the ground...
Not so much a useful aircraft.

~~~
keenerd
Sorry, I think I fixed it while you were typing out your post?

Atmosphere conditions are usually a bit better at 9km up than at sea level. If
the numbers weren't quite so bad there would be a case for detachable JATO
units to get a solar plane off the ground, which then fly back to the airport
to launch the next plane.

... and I forgot the speed of sound gets slower at altitude. It would need to
do mach 1.6 to stay under the sun.

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ef4
My bet for carbon-neutral aviation is not batteries, it's synthetic
hydrocarbon fuels.

A factory that can make kerosene out of atmospheric carbon and electricity at
a reasonable cost seems like a smaller stretch than an exotic new battery with
orders of magnitude better energy density.

~~~
davidgerard
Yep. If only we can make it work economically, carbon-neutral oil will be a
complete win.

~~~
curtis
I think that hydrogen may be a practical alternative. Hydrogen seems vastly
inferior for _cars_ but I think the economics are very different for large
aircraft.

~~~
HelloImDumb
Hydrogen is low energy density and next to impossible to contain or transport
without lossage. These are major barriers to commercial adoption absent a
breakthrough, laying aside the problem of generation.

~~~
curtis
Hydrogen has low energy density by volume, but very good energy density by
weight. The overhead of the volume might be offset by the gains from the
reduced weight, which is especially important for aircraft.

Lossage is certainly a problem, but I think once your aircraft is airborne,
you can basically burn any hydrogen as it outgasses.

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jdhawk
I wonder if the plane had a small backup generator of some type in case they
had total power loss over water, or was there a chase plane?

~~~
greendesk
Was not there just a parachute for the pilot?

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sp332
You still need someone to pick up the pilot before they drown.

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trothamel
For the heck of it, I compared this to what it would have taken to ship the
SI2 via container ship. Apparently, a container ship can move a ton of cargo
500 miles on a gallon of fuel, so to ship the SI2 the entire distance of it's
trip would take about 120 gallons of fuel.

The container ship would have been significantly faster, taking 50 days to
complete the trip, versus over 500.

~~~
greendesk
SI2 was the first time a trip around the world without chemical fuel was
attempted.

Container ships move much more than that, leveraging the scale of cargo
transport.

When the same amount of cargo is moved by non-chemical means, I'd be
interested to compare the two.

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overcast
That pic over the pyramids is stunningly beautiful. Hopefully this achievement
opens more eyes.

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erwinkle
Except the fuel used to create the airplane ;)

