20km High Kite Flying

20km High Kite Flying


[MUSIC PLAYING] So normally, when you fly a
kite, you care about the kite and not so much the string. But in my research, I’m
interested in the dynamics of what the line is doing, whether
it be a kite or a tethered balloon, offshore oil
and gas platform underwater. There’s cable dynamics in lots
of different engineering systems, anything with cable
moving around in the sky. You have changing tension
along the line. You can get things like
travelling waves. And that’s what I’m
trying to model. Even in a simple system like
this – this is just a bathroom chain and a shower ring – you
can get really complicated things going on. So if I just put the ring on the
chain, so it’s just free to fall off the end like that
– I’m just going to put it back on – you can get
complicated things going on. Because if I just drop
this ring… No! Failure is a part of life. …it gets stuck. So you see that and
you wonder, well how does that work? And its to do with the
tether dynamics. So if I have this chain and
this ring falls, I get a travelling wave going down
the chain like that. So when this ring is falling,
it goes down the chain. And there’s a wave following
it down the chain. And when the wave gets to the
end, there’s a whiplash and this ring is going to fall into
that hole and get stuck. So you can see that you can get
complicated things even just on a short length
like that. But when you have something
that’s longer – a balloon tether out in the environment,
you have this long tether – you can still have these
travelling waves going down the length of your cable. There you can see that
wave travelling down. You’re going to have
changing tension. So the tension at the top,
because of the self weight, is a lot higher than the tension
at the bottom. And not only that, if this
is outside, you’re going to have wind. So you’re going to have
drag on this tether. And you can imagine that
normally you have tethers that are circular in cross section,
so something like this. And in terms of drag, it’s
really surprising that the drag on this circular cross
section is actually equal to the drag on this air foil. So you can get a huge benefit
if you can streamline the section in terms of drag,
which will decrease the tension on your overall
system. So my research has to do with
if you do change the cross section of the tether,
will it be stable? Can you even design something
that would work? So I have an aerodynamic tether
here, and I’m trying to model whether this would work. So I have this tether, and I’m
going to discortise it into a bunch of tiny sections. So I’m going to break it
up into small chunks. And that way I can model the
elasticity, and damping, the bending, torsion, all
of those things. And I can also model the
changing parameters up the length – say this
is 20 kilometres long – into the sky. So I’m going to have changing
air density, changing wind speed. So I have a computer model
to model that behaviour. But not only is that important,
the actual cross section of the tether is also important in terms of stability. So if I draw this cross section
out, I have a bunch of different centers. So on this air foil I’m going
to have a centre of mass, a centre of tension, a shear
centre, which has to do with bending, and the aerodynamic
centre, which is where the lift acts. And depending on where these
centres are with respect to each other, is going
to dictate whether this cable is stable. So I have this 10 metre long
length of the cable – of aerodynamic tether. And manufacturing this is
a project on its own. And you can see that this one
this is the very first tether that’s been manufactured
and it has some imperfections in it. You can see there hasn’t
quite filled in. So it’s just it’s just a first
attempt, but I think would be quite good fun to string this up
on a kite and have a go at flying it and see
what it does. [MUSIC PLAYING] Now pull it tight. You want to hold it? You want to hold it from here? Oh, no! GoPro rig has descended. So now we have the aerodynamic
tether section attached to the kite line flying up there. And you can see that it alters
the dynamics of the entire kite system quite a bit. This particular section isn’t
really manufactured in any way that it should be stable. It’s just an extruded
piece of something aerodynamically shaped. So it does flutter around
in the wind. It flips. And those are all of the
problems that you could encounter if you’d had something
that wasn’t stable. But when it goes under tension,
you can see that it sort of straightens out. And ideally, what you want to
manufacture is something that you’ve played around with the
cross sectional properties so that it does the align
itself with the wind. So going out and flying kites
for a Ph.D. might seem like a bit of a laugh, but this
is the part that makes a good film. What doesn’t make a good film
is me sitting in front of a computer doing a bunch of code,
or me writing out a bunch of equations. But that stuff’s really
interesting for me, and it’s those equations that dictate
whether something like this, or an aerodynamic tether
would be stable. And by the end of my Ph.D.
hopefully I’ll have a better idea of whether you can make an
aerodynamic, stable tether. I think I might need
some help first. Still recording!

Eugene Islam

31 thoughts on “20km High Kite Flying

  1. There's a bit more code in the next film with Hilary, which I'm finishing up now. I'm not sure what she uses for her finite element modelling, but the image analysis (which you'll see in that film) is currently implemented in MATLAB.

    I heartily agree that coding is cool, I just haven't yet worked out how to make films about it. Emphasis on the 'yet,' I hope.

  2. You could start with broad strokes, RFP-level then cover the more interesting actual logical portions. Maybe even what modules are used; I'm not a ML user, but its interesting nonetheless (obviously).

  3. I would love to learn what you found out? I am hoping to be starting an MSc in Aerospace Engineering and this has really caught my interest.

  4. My team broke the world altitude record for a single kite in September 2014. We flew a 12 sq meter DT delta to 16,038 ft above ground level. Type 2014 kite altitude record into the search window for the video of the event. Our web site can be found via Kite Magic with a link from the home page. We have 5 other videos of our record attempts. I recognized the importance of aerodynamic line drag 12 years ago when planning for the world record attempts. We use the thinnest, strongest line available. This is braided UHMWPE (Dyneema/Spectra). I have developed a routine in excel which simulates all the forces in kite flights.
    In 2007 I proposed an aerodynamic line profile. The Cd of round line is approximately 1.2. The contribution of line drag is about 3 times that of line weight. I anticipated aero line to be about twice as heavy as round line so their is a definite potential net reduction of negative line forces. I did not progress the concept beyond drawings but these aero lines may be applied to projects such as high altitude tethered wind generators. The Dyneema line would be encased in molded nylon extruded to an aero shape. The profile would be determined by wind tunnel testing but there is already a great body of work on aero profiles so a cataloged profile could be used. I anticipate that line flutter may be a big issue to overcome. Line vibration dynamics on very long lines are interesting. I also have an affiliation with the Ion Power Group which is investigation extracting Ionic charges from the atmosphere to charge large battery capacitor banks. I am advising them about the use of high altitude kites to support the extraction of Ionic charges through tethered conductors. The reduction of aerodynamic tether drag will be very important. After I am finished with 25,000 ft for a single kite in 2020 and 40,000 ft. for a kite train in subsequent years I may focus on aerodynamic kite tethers., preliminary designs of which I have already made. I also have sponsorship from a Japanese company which makes ultra high molecular weight polyester fibre (Toyobo/IZANAS)and a New Zealand line manufacturer, Tasline.

  5. I have just 'stubbled' across this video and as a long time kite flyer (40 years !) interested in the science of why kites fly this is interesting to me.
    The flying line (never, ever call it the string !) is often the limiting factor when trying to fly at high altitudes, well high for me, approx 1000ft when i am allowed, by this altitude a smaller kite will reach its lift limit and due to its weight any additional flying line will lay across the ground, the aero drag making the line near vertical under the kite.
    For any further experiments you may need another type of kite, i have never been a fan of the flowform type ramair inflatable kite, it appears to fly with more drag than lift not gaining a good flight angle, hence any experiments with the flying line will not be presented to the wind at the the best angle acheivable by a kite.
    I had another version of 'parafoil' type kite, A Stratscoop by Greens of Burnely (ceased trading over 30 years ago sadly) compared to a flowform this kite has a much thinner aerofoil section and has an enclosed rounded leading edge, inflated by scoops on its underside (hence the name) this had a huge amount of lift and would fly nearly overhead in the ideal windspeed

  6. All the science in this is beyond me. I am certain you understand it all. great work . The only thing I would say is please please put on some string gloves when you fly the kite the flying line will burn you and slice to the bone in a jiffy. John

  7. Looking to make a kite or balloon with a fog net to get water from the clouds as part of Water Abundance XPRIZE. Looking for advice and team mates.

  8. Be a whole lot most stable if it was ridged, wouldn't it? Stop it from fluttering in the wind. And my Grandma would smack you for "Using your teeth like that!"

  9. Bravo Hilary! Very nice research and video. My research firm is involved in atmospheric research that sometimes includes the use of tethers. I'd appreciate speaking with you about your research.
    I can be reached by using the company email address found at our website IonPowerGroup.com. Again, bravo! Lisa McCowen with Ion Power Group LLC.

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