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34C3 preroll music
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Christoph Sieg: The idea is now to go from
space back to earth and try to use drones
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– so autonomous flying vehicles – for
power generation. So this is the second
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part. So the outline here is …
Applause
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Christoph: Thank you very much.
Applause
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Christoph: So the outline is that first I
will introduce the source here and
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motivate why it is a good idea to harvest
high altitude winds and produce energy
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from them. The technological part will
come in the second part here. This is
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about the technology which is called
airborne wind energy. And in a third part
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I want to show how you can build a wind
drone for low cost for yourself and
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experiment with this kind of technology.
So let's start with the first part. And
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here as a reminder is the conventional
energy supplier wish list, so probably
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what your global players in conventional
energy would think about it or tell you:
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They would say that is a surely clean-
enough resource and, meaning on timescales
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here, it is exploitable of the order of
one human life expectancy, it's
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controllable especially economically and
politically, it is depreciable
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economically and it leads so to a very
high profit for some players.
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Unfortunately there's also the
technological part and here sometimes it's
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driven by hope, saying it will be OK. But,
as we know, it might be mostly harmless.
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So as we see here for instance there are
catastrophes like Chernobyl. This is after
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the catastrophe where you have the
memorial for the people who died. Then you
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have scenarios during the catastrophe
here. This is Deepwater Horizon being like
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desperately tried to extinguish the fire
by the US Coast Guard and Fire Brigades.
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And of course – what I don't have to
mention here, but in times of fake news
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it's important to mention – we are before
the catastrophe. So this is here a plot of
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the carbon dioxide concentration in the
atmosphere taking from ice. And as you see
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here the ice ages give this variations
over 500,000 years, and now we are at this
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spot here that points up. And if you
resolve this into the time scale, extent
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this time scale from the last thousand to
2,000 years here – so we are here at this
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spot at 2000, year 2000 – then you see
that this rise has started at the
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industrialization. So it's a clear sign
that we have to do something. And we have
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to do it quickly.
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Applause
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Christoph: So now let's try to propose
something which can be part of the
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solution, namely sustainable energies. And
here's a wish list of what probably you
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would think it should be: It should be
sustainable, ubiquitous, continous,
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accessible and profitable at the very end.
So does such a source exist? And first I
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should define what it means. So
sustainable means it should serve present
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needs without compromising the future –
and this is clearly not what we are doing
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now – so it should be available on
timescales which are like the lifetime of
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our central star if possible. It should be
ubiquitous, meaning that it should be
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present almost on any location on earth so
that we can without a very complicated
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long-range infrastructure have access to
the energy. It should be continuous,
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meaning it should be present at almost any
day time and seasons, so that we can plan
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of what we produce. And of course it
should be accessible, meaning it can be
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tapped by the technology and lead to a
significant contribution to our energy
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mix. And profitable should of course also
be. So does it exist? And the answer is
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yes and I want to show that this airborne
wind energy can be a big part of it. So
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here I have a table of some sustainable
energy sources and the wishlist items are
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written here and I put some of the
sustainable sources. So there is fusion,
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there is solar energy – terrestrial and
also the spacial energy which was
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presented by Anja and by Stefan before –
hydro energy, geothermal energy and
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conventional wind energy; where by
conventional wind energy I mean wind
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energy up to approximately 100 meter which
is the hub height of wind turbines,
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approximately. And as you can see some of
these items here are not fulfilled by all
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these different approaches. So for example
the spacial energy is clearly not
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ubiquitous, because you have this beam as
we heard which is just like basically
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hitting a certain spot on the earth and
there are transferred into energy, so you
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have to distribute this energy. Also it is
not yet accessible. On the other hand wind
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energy – here conventional wind energy –
is not ubiquitous, because you can only
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select certain spots. And it is not
continuous, because you cannot really plan
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when the wind is blowing and when it's not
blowing. So let's add to this list what is
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called high altitude wind. And high
altitude wind is clearly sustainable,
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because it's also wind energy – so it's
like driven as all the other wind energy
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as well. And high altitude here means to
go to heights which are above 200 meters
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and try to drain energy from these winds.
So let me argue why it is a ubiquitous
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source. And for this Philip who is also
here and part of the team – I'm very happy
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he has made this very nice plot here which
shows the western part of Europe and it
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shows the ratio of wind power which you
can extract at an optimal height which
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should be below 1,000 meter – so this is
just an arbitrary at the moment limit – to
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say that we can have a system which can
basically get up to thousand meter height
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and compare it to the wind energy which is
basically available at hundred meter. And
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in this plot you can see at the coastline
there is a line here and this line is the
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line where in the interior you have
already a doubling of the wind power. So
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meaning at the coast line itself if you go
to higher altitude you have the double
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wind power available then at hundred
meter. Even better, directly at the coast
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line there is another line which is a
factor of four better. So as soon as you
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put your wind turbines on land side, you
will be a factor of, you have access to a
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factor of four higher wind power. And
here, in the region slightly south of
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Leipzig, there's another line, this is a
factor of eight where you become better in
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wind power, in high altitudes wind power.
So, seeing that the coastal regions have
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already a factor of four in this ratio
better and the inland between four and
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eight. Oh, the wrong sign. Sorry, they
should be reversed of course. So, saying
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that here the site of conventional wind-
energy harvesting, which are now very
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limited, and where you put for instance
all the wind turbines in the north, they
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become much more accessible if you go to
higher heights. Because there you can
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basically use all the land sites. So this
is where you have more sites available
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when you harvest at optimal height. And
here, as an example about why it is a
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continuous source, you see a time
distribution of the wind velocity in
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January 2016 in Leipzig. The wind velocity
is here increasing from yellow to red, and
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the altitude is displayed here, and this
is the time scale of the month. And what
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you can see is, at hundred meter height
you have almost like only in the lower
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parts you have winds, whereas, if you go
to higher heights you have the reddish
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parts where you have high wind velocities.
So this shows that continuity is already
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improved if you go to higher altitude,
especially for land sites. And this is
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almost impossible for conventional wind
turbines. You would have to build a mast
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higher and much, much bigger structures.
And also, what is displayed here is the
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optimal harvesting height. So this is the
height, again below thousand meter, where
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it would be optimal to harvest wind at a
certain time, displayed over the whole
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month. And if one goes from this plot to
the histograms, so to the time
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distribution of the different wind
velocities, you get this picture here. So
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this are the spots the histograms of 100,
170, 500, 1000 meter, and of the optimal
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height, so if you adjust your height. And
one of the things that you can see is that
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the mean is clearly shifted to higher wind
velocities if you increase the height. And
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also, if you harvest at optimal altitude
you shift the whole probability
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distribution to the right. So and what
increases there is that the fraction of
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time below five meter per second, which is
like the the time where the cut in wind
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speed for a wind turbine, so you would
like starting produce energy, the
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probability to have such winds is
increased from 76% to 87%, which is quite
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a lot of increase. So adjusting to varying
optimal harvesting height is not only
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almost, but is really impossible for
conventional wind turbines. So one has to
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find another technology, which is better
and can give you access to this higher
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altitude winds. So this is the plot again
from before. So I have now a little bit
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motivated why the source is ubiquitous and
continuous. Now the question is, is it
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accessible, and how it is accessible. And
this is the technological part which is
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called airborne wind energy. So how do we
access these high altitude winds. So on
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for these, let's come back to the design
challenges, which would be necessary to go
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to higher height. So high altitude means,
that you just cannot just increase your
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tower, and have more torque on your
foundation, and just scale up the system.
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So you should avoid proliferation of mass
and proliferation of the tower and
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foundation. And also, varying altitude
means you shouldn't have passive,
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stabilizing, static structures, but find
something which can vary. So just as an
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example here this is the sky walk in the
Grand Canyon, and this is already a quite
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scary lever arm which you have. And if, in
comparison, you take your modern wind
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turbine, you rotate it by 90 degrees, and
compared it in size to this, you can see
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what kind of torque will be, like will act
on the foundation. So this is already a
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very big piece of technology you have
here. So we have to do better, and this is
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the second part, namely airborne wind
energy, so the technology itself. So the
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first slide is probably the most important
of this part because it explains the
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idea behind this technology. So you take
autonomous drones, which are the most
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flexible connected to the ground via
tethers, and extract wind energy via these
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drones. So how does it work? So look at
this conventional wind turbine here. You
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have most of the energy is produced by the
outer part of the wings. They are rotating
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with the highest velocity, and at the same
time you have the highest the largest
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lever arm. So you produce most of the
energy in the outer part. The inner part
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is more or less passive, stabilizing
structure. So you remove that structure
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and replace it by something which is
flexible, and the first which comes to
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mind probably is a tether with which you
attach it to the ground. And then you have
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just the active part here, which is now an
aircraft, moving in this circle, which
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before was circulated by the wing tips, to
extract your energy. This is the
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principle. So how do we bring down the
power when circulating this aircraft? So
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we have to, in some way, transform it to
electric power. So there are, which are
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not shown in the picture before, lighter
than air systems. So you just basically
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take a balloon, you put your wind turbine
at high altitude, and extract the power.
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And here the tether can clearly serve as
the power line. But what we can also do is
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crosswind flight, which was shown in the
picture before. So here you have a moving
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aircraft, which can move in something
which is called the drag mode, meaning
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that you have onboard generators on the
aircraft. So essentially it's a propeller
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aircraft, but the propellers are reversed
in repeller mode, so that the repellers
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produce energy for you. And then the
tether serves as power line. So this
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principle is shown here. So here you can
see the generators and then the power is
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brought down by the tether. In the second
part, second strategy, is using the so
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called lift mode So here you have ground
based generators and the tether itself
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transmits the power, there are no power
lines in the tether. So here you use that
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the power is given by the pulling force
times the reel out velocity of the tether.
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So you circulate in some patterns with
your aircraft and you use the lift force
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acting on the aircraft to unreal this
tether from a drum, and at the drum, on
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the base station, there's a generator
attached which helps you to get the
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energy, to transform the energy into
electrical energy. And of course, at some
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point the tether is maximally reeled out
and then you have to have to go to a reel
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in phase, where with minimal energy you
reel in the tether again, and start
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periodically this phase again. So these
are the concepts, and there's a whole zoo
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of airborne wind energy devices and
proposals, which show that this technology
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is still in a very early stage of being
developed. So you have people here flying
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figure-of-eight patterns with the
aircraft. So some things are lighter than
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air turbines, which look very exotic like
this one, probably this one you have seen
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in media already. Proposals like this
here. There are quad copters, which
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produce the energy by rotating of their,
of the propellers here. And all kind of
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exotic lever arm and aircrafts which you
can use. So let's bring a little bit of
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more order into the technology, into the
proposals. And one of the things I want to
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discuss, which is very promising, is what
is called crosswind flight. So here as a
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example is a comparison of a conventional,
lighter-than-air system with the big wheel
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in London. So this is one of the biggest
wind turbines. And the harvesting area is,
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so the effective area of such a wind
turbine is the swept area of your
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propellers, essentially. So now let's look
what happens if you move an aircraft
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instead through the wind. Then the picture
of before is like of that size. And if you
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take an aircraft, which has the same wing
area as the wing areas of the propeller
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here, you're harvesting area is of that
size. It's much bigger. And the reason for
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this is, that the effective area is now
given by the wing area times a
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coefficient, which is the square fraction
of the lift to drag coefficient of the
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aircraft times the lift coefficient
itself. And this factors of the order of
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200. So it increases the efficiency of
your of your wings dramatically. This was
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already found by Loyd in 1980. And you can
now ask "Why does it take 30 years from
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this idea to first systems?". And the
answers is, in this community for is
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probably a very interesting is "Why are
these prototypes are appearing only 30
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years later?". It's because sufficient
computer power. So for the control
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algorithms, which allow you to control
such flight modes, was not available. So,
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as an example, here's an illustration of
one of the current leaders in the field
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called AMPYX POWER, showing a crosswind
airborne wind energy system versus a
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conventional system. So here's the
conventional wind turbine for two
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megawatts. And the conventional this is a
conventional system. And the airborne wind
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system is, this is the ground station, and
this is the aircraft. So one of the things
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which are, I mean, visible in this picture
is that it has much less like even sight
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impact in the environment. So having
something like this is much less
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disturbing from the even from the
aesthetic point of view, than this huge
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wind turbine. So now the next step would
be to look closer to the technology and
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see what are the AWE system components
that you need, that you need to build such
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a device. So first of all, there is the
drone or the fixed-wing aircraft. We have
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seen that it's very good to have large
lift and small drag coefficients, so you
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need something which is like a rigid
glider, more or less. On board you need
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sensors, like accelerometer, gyroscope,
GPS, receiver, barometer, and a pitot tube
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to measure the air the air speed. And this
is to determine the system state, that
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then is like reacted on by the control
surfaces, in the case of an aircraft by
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ailerons flaps and the rudder. Moreover,
you need of course a microcontroller and
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algorithms which do the state estimation.
So from the sensor data they compute the
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state of the system, meaning it's
position, altitude, velocity. And you have
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to navigate. So and of course you might
need something like a propeller for
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takeoff, landing, and energy generation in
case of drag mode. The second thing is of
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course the ground station. So here you
need the drum for tether wind-up. You need
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a motor which eventually has to be
transformed into generator mode if you
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have the lift mode. You need power
converters, also microcontrollers and
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algorithms which synchronize your ground-
station operation with the drone; and you
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need a runway, catapult or something alike
for takeoff and landing. So far it looks
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quite simple, but the devil is in the
detail. And here I found a nice quote a
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colleague of mine – (uninteligble name) –
has done in one of his talks,
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and I liked it very much because it
displays very well what challenges have to
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be still overcome. So it starts with
"Theory is when nothing works but everyone
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knows why." and to demonstrate this let's
have a look at this video here which is
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one of the flight attempts of one of the
companies: So the aircraft lifts off,
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there's no sound … yet. Now there is
sound.
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Background music of shown video
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Speaker in shown video:
Abort! Abort! Abort!
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Soft laughter
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Christoph: Yeah. And the desperation of
the founder was clearly hearable at the
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end. And you could see that the tether
ruptured. And then there was no way to
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recover that most of the aircraft was
lost. Second: "Sometimes practice is when
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everything works but no one knows why." So
there are also positive surprises. And
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here is a launch, a catapult launch, for
an aircraft which now uses weight.
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Background noise of shown video
Laughter
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Christoph: So a positive surprise for a
test. And finally, sometimes if you
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combine theory and practice then "nothing
works but no one knows why". This is where
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the complication really is: The devil is
in the detail. And here you can see a
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video from a flight which is crosswind
flight: Everything seems normal …
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Dramatic background music of shown video
Christoph: … and then the prototype is
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again lost. So this is complicated. So but
there is a lot of progress and so I want
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to come closely, very quickly introduce
the current industrial status. So I focus
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on three companies which work on that: So
one of them is Enerkite in Berlin, and
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they have now a system which is basically
stationed on such a truck and this is a
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crosswind system of a passive wing. So it
steered via three tethers and it produces
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up to 30 kilowatts of energy. Then you
have Ampyx Power. They have here the
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launching site in the Netherlands and they
are currently producing this aircraft
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here. This type which is a crosswind
system in lift mode. And at the end will
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produce up to 250 kilowatts of power. This
is under construction. And, finally, there
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is Google X Makani in California. And they
have built a drag-mode aircraft – here –
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which is flying. And I can show you a
video that they have on their home page –
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very nicely. Where they show a flight so
that you can see that the 600 kilowatt
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system is working. Here you see the
onboard propellers. You can see the
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tether. Down here this is from the tether
attachment point. So the things are
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working. There are prototypes. But one of
the things which are important is: one has
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to "test, test, test" and get experience
from tests. So "experience is what you get
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when you were expecting something else".
You really. So what does it mean? So we
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have to test, analyze, adapt the systems.
So because many – as you could see from
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this design variations in the zoo which
I've shown – many of the concepts are
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still open. So for example the design of
the airframe. If you use a biplane, a
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flying wing or anything alike – or
something totally different – is still
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open. The tether construction – what kind
of materials to use – is still open. The
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materials in itself is still open for the
aircraft etc. etc.. The mode of operation
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– that means takeoff, landing and direct
versus lift mode – is still an open
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question. What is the best thing to
realize for industrial products? And then
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control hardware and software algorithms
have to be tested thoroughly. Of course
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it'd have to be certified by the aerospace
agencies, of course. You want to have a
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failsafe. So what you have to do is you
want to even, I mean, have total losses in
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experiment. You want to do the experiments
wich would lead to a total loss of your
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system. So here comes the idea that
instead you should build a cheap and
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disposable test platform instead of a
largely scaled-up system first, before you
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build the expensive prototype and do tests
on them. And this brought us to the idea
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to provide a low-cost open-source test
platform where everybody at home can build
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his own wind drone. And this is the third
part of the talk. So the do-it-yourself
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wind drone. What are the ingredients here?
So first you need a drone, so here I want
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to show the airframe and reinforcement
hack which is necessary to prepare your
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airframe for the additional forces by
adding the tether. Then there's a ground
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station and here I want to motivate why
the drone is essentially behaving like a
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fish – in this case a barracuda. The next
thing is navigation on curved manifold is
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very important because you have like a
constraint coming from the tether. And
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finally you need something for control
which is the autopilot. So in this case
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it's the ardupilot open-source project
which we adapted. So let's come to the
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airframe-reinforcement-hack. So what you
use: Take your favourite polystyrene
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airframe – so in this case it's an Easy
Star II – and glue the wings together.
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This is the lower side of the wings. You
put in there a carbon rod – here in this
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part – and you stabilize it with racks
which you glue into the slits we can see
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here. And then you wrap carbon in the
forward part of it where the most of the
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aerodynamic force is attached. Then you
have the carbon ???? ???? wind around your
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00:25:35,789 --> 00:25:44,320
tether. And you install additional tubes
for fixing the wings on the fuselage. So
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the fuselage is here. We cut off the
engine blocks, included additional carbon
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rods. So you can put these carbon rods on
these carbon rods here, and fix everything
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00:25:52,639 --> 00:25:59,570
with screws. So to show you how that looks
like and what are the size of this model
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00:25:59,570 --> 00:26:05,799
is: So here is the original-size aircraft
with carbon. And you can later – if you
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00:26:05,799 --> 00:26:15,330
want – pass by the assembly area and look
at it and have a look at it and touch it.
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00:26:15,330 --> 00:26:20,580
So this is how it looks decomposed into
different components: So again wings and
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so on and so on, the servos for the
control surfaces. The central unit here is
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the Pixhawk autopilot. So there's a
microcontroller which contains some of the
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00:26:33,150 --> 00:26:37,340
sensors: You have a GPS sensor, in
addition you have a telemetry antenna for
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data – for data transfer to the ground
station. And you have RC control for
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manual control when you switch out of auto
mode to have manual control in emergency
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situations – or if you want to make other
kind of flight tests. So now this is the
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drone itself. So now is the question what
to do with the ground station. And here
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00:27:02,560 --> 00:27:09,250
let's look why the drone behaves as a
fish: Because what it does is, like in
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fishing, you would need a free-moving
tether; it has to be fast and fail-safe
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00:27:13,059 --> 00:27:16,889
reeled in and reeled out; and it should
remain twist free so that it doesn't give
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any knots if it is not under tension. And
the thing which we came up with wich best
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serves for our needs at the moment is an
off-shore fishing reel.
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00:27:27,559 --> 00:27:33,769
Applause
Christoph: So and you need offshore here
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because the drum has to be perpendicular
to the rod: This guarantees you like
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reload phases twist free on the
tether. Other fishing rods have the drum
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aligned with the rod, and then you
accumulate twist on the tether which can
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00:27:47,549 --> 00:27:52,769
lead to knots, lead to knots and then …
it's not a good idea. It will destroy your
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00:27:52,769 --> 00:27:56,950
tether. So and this is the first flight
test. So we were very enthusiastic and
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started the first flight test. And here it
is.
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Indistinct voice in shown video
Voice in shown video: OK. … Hinterher?
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Laughter
Visv: Versuch mal rauszugehen. Manual?
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Achtung, Achtung! Versuch ihn zu fangen.
Na gut.
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00:28:17,789 --> 00:28:19,779
Beeping in shown video
Christoph: OK.
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Laughter
Christoph: So unfortunately it did not
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00:28:23,259 --> 00:28:27,620
work.
Applause
315
00:28:27,620 --> 00:28:34,720
Christoph: So what happens? This was the
result: The tail was broken. And because
316
00:28:34,720 --> 00:28:38,749
the tether apparently wrapped around the
back of the aircraft and then it became
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uncontrollable. So we came up with what do
we do: If you don't know any further, any
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better, use carbon! So we put some carbon
on the lower part of the of the fuselage
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to reinforce it. And then of course you
have to think about writing your
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navigation code, to navigate if you are
under tethered flight. So here is the
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00:29:00,019 --> 00:29:05,360
receipe for how to do it: So first you
take one git clone of ardupilot – this
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autumn open-source software. You
take one curved 2-dimensional manifold –
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00:29:09,019 --> 00:29:13,700
it's essentially giving us a hypersurface
embedded in 3-dimensional Euclidean space.
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In case of constant tether length this is
just a semi-hemisphere as to which is
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centered around your ground station. Then
you take a planar curve which you want to
326
00:29:22,160 --> 00:29:28,070
fly along – or curved segments – and a
pinch of Differential Geometry to wrap it
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on the sphere, to make this curve
appearing on the sphere. You take a little
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bit of Classical Mechanics for the flight
control to transfer the curve
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accelerations into actually control-
surface motions. And then you need, of
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course, 12 dozen coffee for doing so. You
put everything together into – of course
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not the coffee – into the computer algebra
system and stir well, and let the CPU bake
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it at 100 degrees, and then you come up
with a smooth – at least C¹ – curve.
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Applause
Christoph: So the curve is shown here. So
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00:30:09,350 --> 00:30:13,820
it's … this is one part of a figure-8
pattern. So the other part would be behind
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00:30:13,820 --> 00:30:17,949
here. It's composed of two geodesic
segments and one turning segment and they
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00:30:17,949 --> 00:30:21,720
are C¹ glued together here. And these are
the equations: So you can find in the
337
00:30:21,720 --> 00:30:26,899
paper – I don't want to go into detail. So
now you have to modify the source code of
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00:30:26,899 --> 00:30:31,450
this ardupilot project. So here there are
highlighted the patterns which you
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00:30:31,450 --> 00:30:35,289
basically have to … where you have to do
modifications: You have to implement new
340
00:30:35,289 --> 00:30:42,139
flight modes and change some of the
control algorithms. And then you come up
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with the next flight test. And here is the
next attempt.
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00:30:49,499 --> 00:31:11,389
Music and propellor sounds
Voice in shown video: Beim Auswerten
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00:31:11,389 --> 00:31:28,909
müssen wir sehen, ob wir dann verschiedene
wählen.
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Music ends
Applause
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Christoph: The whistling sound you have
heard at the end is the tether being
346
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dragged through the air. So there was
really tension on the tether. And you can
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00:31:45,259 --> 00:31:50,019
also see this if you do a data analysis on
the flight data later. So yes for example
348
00:31:50,019 --> 00:31:54,539
multiple possibilities. You have a lot of
data which is possible to analyze. So the
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autopilot this was very very it's very
very nicely done in this open-source
350
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project: So they have a data file with all
primary and secondary data you can use for
351
00:32:04,210 --> 00:32:08,049
your analysis. So for instance this is the
flight curve of different flight modes
352
00:32:08,049 --> 00:32:11,919
which we used. You have the altitude of
the aircraft, you can look to deviations
353
00:32:11,919 --> 00:32:16,440
in radial and transverse directions. You
can look to tether tension – or like a
354
00:32:16,440 --> 00:32:20,621
measure for tether tension – by looking to
the length variation of the tether. And
355
00:32:20,621 --> 00:32:26,519
you can of course do time series analysis
of how your figure-8 pattern has flown
356
00:32:26,519 --> 00:32:33,620
along. And that is what you can do with
this very very nice autopilot open-source
357
00:32:33,620 --> 00:32:40,359
software which is available when … written
by many many people on the internet. So
358
00:32:40,359 --> 00:32:44,019
the question which remains is: After all
of this is, will it be a fail-safe to
359
00:32:44,019 --> 00:32:49,929
100%? And the answer is nope, it will not!
It will … there will be of course
360
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accidents happen. But the thing is:
Nothing is failsafe. And so here's a
361
00:32:56,850 --> 00:33:00,960
standard wind turbine and look for
yourself.
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00:33:00,960 --> 00:33:06,070
Laughter
Christoph: You see there is no 100%
363
00:33:06,070 --> 00:33:15,480
guarantee, but we have to try very hard to
get it as failsave as possible. So yeah
364
00:33:15,480 --> 00:33:20,220
this is essentially it. That was the talk.
So what I want to say is that the current
365
00:33:20,220 --> 00:33:28,919
status of airborne wind energy can be seen
here by a nice book on the Springer page
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which you can download here. And we are
very very happy to have any kind of
367
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critical remarks, input to help in
developing the system further. So please
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00:33:38,280 --> 00:33:41,860
if you want, look to this web page,
there's a lot of information including a
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00:33:41,860 --> 00:33:48,450
paper and we will be very happy for any
kind of help. And finally I would again
370
00:33:48,450 --> 00:33:52,279
stress that we could rely on this
tremendous work of the open-source
371
00:33:52,279 --> 00:33:56,710
community working on this autopilot
project that has helped us to realize this
372
00:33:56,710 --> 00:34:02,029
project in very short time; so very happy
about this. And I want to thank of course
373
00:34:02,029 --> 00:34:07,040
Phillip Bechtle, who is here, and Thomas
Gehrmann and Maximillian Schulz-Herberg,
374
00:34:07,040 --> 00:34:11,250
the students, and Udo Zillmann, who can
not be here, for working on this project
375
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and putting so much work also into it.
Thank you very much for your attention!
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Applause
377
00:34:17,230 --> 00:34:27,670
H: We can have two more on the microphones
378
00:34:27,670 --> 00:34:32,900
here and here – one and five – so two
questions. The first one, please!
379
00:34:32,900 --> 00:34:37,380
Question: So you talk, so you talked a lot
about powered – and not powered –, but
380
00:34:37,380 --> 00:34:41,590
controlled flight. How does it compare –
energy wise – to uncontrolled flight?
381
00:34:41,590 --> 00:34:46,400
Basically putting a propellor on a kite?
Answer: So the thing is the propellor on
382
00:34:46,400 --> 00:34:53,909
the kite … with kite you mean, I guess,
non-rigid structures. So meaning that the
383
00:34:53,909 --> 00:35:00,080
first question is how do you want to put a
propeller on a kite if it's non rigid. So
384
00:35:00,080 --> 00:35:07,030
that is a question which goes back to you.
So because that is something is not clear
385
00:35:07,030 --> 00:35:12,170
to me. But in any case rigid air
frame is harder to control than a
386
00:35:12,170 --> 00:35:17,160
kite. So there are people who work with a
kite. And by kite surfing or if you do
387
00:35:17,160 --> 00:35:21,740
like steer normal kites from the ground.
You know it's like moving not that fast in
388
00:35:21,740 --> 00:35:27,130
the wind field, so it's easier to control.
This is a big benefit of kites. And also
389
00:35:27,130 --> 00:35:32,410
the weight is a big benefit. But the power
output – because of the bad or worse lift-
390
00:35:32,410 --> 00:35:37,600
to-drag coefficient – is unfortunately not
that efficient as a rigid aircraft. So you
391
00:35:37,600 --> 00:35:42,280
want to go to the rigid air craft.
H: If you leave the room now, please be
392
00:35:42,280 --> 00:35:45,810
quiet because we have questions and
answers here! Number three please, and
393
00:35:45,810 --> 00:35:50,400
that is the last question I'm afraid. But
you can ask questions after the talk.
394
00:35:50,400 --> 00:35:57,890
Q: I want to go back to the space part. I
was wondering … there are some ideas about
395
00:35:57,890 --> 00:36:03,040
bootstrapping like a solar station on the
moon and then like shipping, I don't know,
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hydrogen or like pre-charged lithium
batteries back to earth and back and
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forth. Is it like realistic or not really?
A by Anja Kohfeldt (previous talk): I
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think also this approach would be quite
expensive. And you have to install this
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infrastructure on the moon first, and you
have to establish the flight base back and
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forward. Realistic is a thing, you know.
At the end that's a question of money and
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investment. And I'm not sure whether this
would pay out, but we haven't analyzed
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this kind of approaches, yet.
H: Thank you! So thank you very very much
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Stefan, Anja and Christoph! Give them a
warm applause again please!
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Applause
Stefan: Thank you!
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Outro music
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