Doug,

You and Rod have both recently posted video of generator-free demos.
Both were built from the ground up not to include a generator. The
Visventis prototype has been built to take a generator. We just plan to
first test it without one to make double sure we have not overlooked
anything.

Two years ago I was talking about collaborating with a group who had a
VAWT design that they thought would be a winner. I know what you are
talking about when you say people don't calculate things or do real
tests. I am most definitely not one of them. I built a model of their
design but I made it changeable. I also, unlike them, connected it to a
generator. Then I designed a better generator to go on an improved
model. The generator worked as expected so I know my maths was good. The
turbine however did not do so well so the project went into a state
of ;- let's see if we can come up with a better plan. In the meantime
for Visventis I will do the sums for the generator and its control
electronics and I have a very high confidence that it will be right
first time.

Darrieus's of various types have indeed been around a while and do still
keep getting reinvented but I have never seen anyone else do what
Essertier is claiming. Again, I have some direct experience. A friend of
mine who had raised £50M on the basis of one of his inventions thought
he could improve the Darrieus with a mechanical blade angle control
mechanism. Similar to what Essertier is doing but mechanical. I told him
at the time that electronic control would be better. We probably had the
idea at about the same time, but I had other ideas that looked more
promising to pursue.

If Essertier has done his sums right there is no reason the Afresh could
not operate in storm winds. An aerodynamic blade turned to within a few
degrees of the wind will not experience damaging forces. In fact by
getting the blade angles exactly right at all times there is no reason
why the Afresh should not be able to generate 10kW from a range of wind
speeds from maybe 20m/s to 70 m/s. HAWT blades have a twist on them so
they cannot be turned completely out of the wind. The Afresh blades are
straight so they can be turned to experience very little force. That
allows serious economies to be taken with both the tower and the
foundations. The whole thing can be built to take the forces required to
generate the maximum power and no more. Every other turbine I have seen
needs to have extra strength built in to resist storm winds. Once one
part needs to be beefed up other parts also need beefing up and costs
escalate. Essertier knows what he is doing and the Afresh is a clever
design worth keeping an eye on.

Robert.

There is a vague possibility that the laws of physics dictate that there
is an optimum L/D for AWE kites. If that is the case maybe it is time to
start searching for what that value is. Miles Loyd derived an equation
that said that the power output for a given kite area increases in
proportion to the square of L/D. That means that if doubling L/D doubles
the cost then it is worth doing because the power increases 4 fold.

In reel in-out designs a high L/D means less energy is wasted on the
reel in stroke. These and other reasons can easily tempt us to put a lot
of effort into building kites with L/D of 30 or more. The problem is
that the advantages of high L/D come about because of the greater kite
speeds but greater speed means more noise. Noise increases in proportion
to the 5th or 6th power of the speed so it is a serious issue. For
applications far out to sea (where I foresee AWE making the biggest
impact) this might not matter so much but initially we are limited to on
shore applications.

For noise and safety issues I therefore suggest that initial
recommendations for maximum kite speed be something like 70 to 100 m/s.

Wind with a speed of less than 4 m/s does not have enough power to be
worth bothering with. That means an L/D problems under most circumstances and normally we would want it to be
much less.

Obviously we could build a kite whose main structure has L/D = 100 but
the tethers will knock it way down again. Another thing we can do to
keep the L/D of the whole airborne structure within check is to generate
some of the power with a flygen. As I have said before, mass issues mean
most of the power needs to come from a groundgen but turbines (or
equivalent) mounted on the kite could serve a useful noise reduction and
safety increase function.

The reason I went on so long in other posts about Essertier's Afresh
turbine is that the sort of control it enables us to have can be used to
optimise an AWE system. In low wind speeds the kite mounted turbine is
set to create little resistance so the flight speeds are as high as
possible. As wind speed increases and flight speeds approach the maximum
setting the turbine is adjusted to create more resistance and generate
more power. It allows us to increase the capacity factor of our system.

Robert.

Thank you, Dan, that is very welcome news. This follows one of my pet interests.   Thanks!

Sometimes I am left wondering if you're human Dave, you know a lot.

Maybe you found a way to have google computers analyse the value and effect of every question type, on every noun, verb and dust mite on the planet.

Reassured when I checked your reference to Fort Felker, yeah ok, you're human after all Dave... He's a robot for sure tho.

All sounds great except it falls into that classification of statements that almost never turn out to be true. Starting with the "we're gonna attach a generator someday", next with "we'll get that control system worked out someday" and next it makes what's usually a typical mistake of rating the machine for damaging wind speeds rather than typical wind speeds.

Try calculating what centrifugal force will do to those straight blades in winds that strong (as long as we're in rendering-land anyway). Then think about the resonances from the blades' different bending responses at various angles to the radius. How heavy will the blades have to be to stand up to that centrifugal force? I could cut a 14-foot long 2 x 6 into a complete rotor that would give you the same power, with slightly less (apparent) complexity.
Conveniently the blades would:
a) be aligned with centrifugal force rather than perpendicular to it;
b) travel perpendicular to the wind direction at all times at all points;
c) non-pulsating power;
d) highest efficiency sweeping a given area with regard to material use.
My take: it's inadvisable to add an extra wheel to also re-invent, when already trying to reinvent a wheel.

In other words to do AWE, just use what is known to work. Like I said, anyone serious about AWE with 2 hands and a slight budget could order parts this week and have a machine in the air next week.

It MAY be possible to get a Darrieus to perform better by adjusting pitch on the fly. Lots of people have said they'd do it. The category is called a Giromill. Good luck. I'm finding that even once all the bugs are worked out of a model, you still have the challenges of making it into a successful business.
I posted a generator-free video? I guess maybe - can't think of one at this moment.
:)
Doug S.

---

When we look at the fundamentals of AWE it offers potentially massive
benefits. eg. much lower mass and access to far more wind. Why then do
we not yet have an AWE product on the market that is making an impact on
the opinion of the world-wide renewable energy community? This group is
great for collecting together a mass of diverse ideas. It is not good on
focusing on getting a product out there to prove to the skeptics that
AWE is the future. Just one product will do it. All promising AWE
designs can then get refined later because the funding will come in and
the arguments with ARPA-E will totally change. If AWE really has such
huge advantages that first product should not be so difficult to make.
Are we all suffering from fear of success?

An example is all the attention on lighter than air (LTA) devices. H2
and He are both expensive and both leak badly. To get a useful amount of
lift a huge perfectly sealed low mass container is needed. That has to
cost a huge amount. Pulling the balloon down when storms or lightning
threaten is always going to be difficult. LTA may have niche
applications (toys?) but commercial AWE is not one of them. Talk of LTA
in AWE circles is therefore a diversion. I wonder if the big money is
attracted to LTA projects to try to prove that AWE is a failure so that
they have an excuse to concentrate on business as usual.

If you dig through the German RC forums you can learn exactly how to
make a super efficient wing. The questions is; is it worth it? For now
Visventis is sticking with off-the-shelf soft kites which apparently
have L/D in the range of 2 to 5. To make a difference to world pollution
someone eventually needs to look at the economics of L/D and find the
sweep spot. Maybe it is variable. Maybe it is 7.

Robert.

I agree:AWE progression exists but is slow.It is not only because of technical challenges but also the needed share of space with aviation.

If you look the technical data of  V164/7000 you can see a high progression of ratio power/mass (only 390 tons for swept area = 21000 m² and rotor diameter : 164 m) in wind towers.A 500 m² kite with L/D = 4 could generate something like 300 kW according to an optimized reel or flygen scheme and a crosswind motion,wind speed being 11 m/s (the same for the nominal power of the example).If we are optimist with the capacity factor X 2 at altitude = 500 m, 12 kites can replace the single tower.So economically it is not yet obvious.The main advantage for such AWE configuration seems to be an easier implementation offshore.
 
AWE for massive can be irreplaceable in jet-stream which no tower can approach,and also for some commercial niche like unities for relief operations,or for regions off-grid.

PierreB,
http://flygenkite (a single scheme from toy to jet-stream)

AFAIR, Joe's idea was to encapsulate a light gas, not a vacuum.  Aerogel, etc. is interesting, but I don't think there is much need for it in any useful wind.  Even ultralight aircraft use medium density foams for structure.  

Fifteen video set in support of the WPI project: 

Welcome new member of the AWE community: 

Ken is absolutely right but to be more complete he should stress more
that that something should be small. The video mentions Makani's goal of
producing a 1MW commercial device first. Why so big? If they developed
something in the range 1 to 10kW flying at lower altitudes they would
slash their costs. Doug has been talking of their spend rate. That is
why it so high. They are trying to enter the market with something way
too big.

Robert.

I'm in the middle of converting my loft anyways... So I might as well go build a kite test station on each end.

-

Now talking about Aero Elasticity...
What happens if the wing tubes on the original doughnut at the start of this post feed back round onto an outward facing ring of thin plastic alpine horns connected on the inside back big end first to a small end plug / valve or even at an utterly nutter impossible suggestion a rotor gen on the rotation plate I had in mind?

time for bed

Hi Joseph and Group,

Instead of pumping electrons down from above(two,three lines, electrical)pumping air down from above leads to just one power line containing air, none conductive. Question is are there light weight compressors that would work. Air sent down would be stored in tanks/battery for on demand use.

Dan'l

I really should crunch some numbers on the weight of various schemes for power transmission.  At first blush, I notice that my shop power tools run on an extension cord that is much lighter than my air line.  Also, it takes a 5HP air compressor to replace a 1HP electric motor on the tool, but the air motor is lighter.  There may be lighter hose designs, but light and efficient hardware may be unaffordable.  There is also the problem of what to do with the heat of compression.  It could give heat-pump like efficiencies, or it could be a major waste, depending on the local market for heat and the cost of the hardware.  Also, as an energy source, compressed air is like a high explosive - all of the energy can be released instantly, so it is probably the most dangerous storage in use.  SCUBA tanks are far more rigorously inspected than aircraft parts.  

This video shows how simple AWE can be. At least someone is not totally asleep. Bravo.
:)
Doug Selsam

How to get around those huge MegaLatticeKites for living, repairing, adjusting, etc.?

Dave S.,

Let me explain more clearly what I meant by, "1 product will do it". The
fact remains that AWE research is massively underfunded compared with
its potential. No one with serious money to spend believes in it. As you
explain in your post today about Makani history, Google are looking like
they got their fingers burned. The Magenn funders are probably feeling
the same way. Other ideas that have received wide publicity have gone
nowhere fast, and have obvious technical flaws. The public in general
therefore also does not believe in AWE. To turn that situation around we
need just 1 company to start making a profit with 1 AWE product.

Certainly it is unlikely 1 product will dominate the AWE industry - I
never claimed it would. It would not be a good thing if it did develop
that way. However, we have a public relations problem and everyone in
the AWE community will be held back until we fix it. For that reason I
am saying it would be great if more people could concentrate on fewer
products.

Those who enjoy tinkering away in a messy garage without bothering to
look for a penny of outside funding have their place. Visventis is now
in that camp. However, I do not want to stay there.

We just need 1 AWE product to be perceived as an economic success to
turn the tide on our fortunes. Internet start-ups still receive support
despite the credit crunch because enough of them have done well to
reassure the investors. While the AWE industry can list a few small
successes but no big ones, with all of the biggest ones looking like a
total loss, ARPA-E and the like will have a good excuse to ignore us.
They are listening to Makani to try to save face. Why should they listen
to the small guys when they have such a big problem on their hands.

Even if you have no interest in attracting investors with their focus on
future profits, the same arguments above apply to attracting people to
contribute to the open-source effort. Pilots to fly kites cost big
money. If AWE is ever to reach its potential it will have to rely on
highly automated systems. We are in the computer age. AWE developers
cannot ignore that fact. Developing software takes a lot of work, but
once it is done distribution it trivial. Linux outperforms software that
cost many billions to develop yet it is free. AWE control systems need
not be more complicated than Linux, but we still need a large team of
programmers to work as a highly organised team with a very focussed
objective if we are to get AWE to realise its potential. Recruiting them
will require good publicity by the bucket load. AWE could be the single
biggest contributor to solving the fossil fuel crisis so generating that
publicity should be possible.

Robert.

Pierre,

The link you gave did not work, but what I wanted to say is that the
turbine example you chose is an off-shore model and would cost at least
USD7M without the installation (foundations + power feed etc.) costs.
The later would more than double the total because of the difficulties
of working off-shore. Would the capital cost of 12 kites on a floating
platform exceed 14M? I doubt it. However, if we have to add in the cost
of manual supervision then you are probably correct about the costs
becoming uncompetitive.

The mass of turbines is proportional to their power output to the power
of about 2.7. That means that as they get bigger the material costs
escalate. There is an economy of scale in making them big, but the main
reason for their huge size is to reduce the maintenance manpower per
unit energy generated. That is why I keep going on about the need to
automate our AWE systems. Until we demonstrate that human supervision
can be reduce to a level equivalent to that required by turbines we are
fighting a loosing battle.

By the way, aiming for the jet stream is a bad idea. There is more than
enough wind for our needs at lower altitudes. Going too high sends
tether costs into the stratosphere and tether mass kills power output.
It does not give you time to retract tethers when lightning approaches
and the aviation authorities would not like it either.

Robert.

This is a repeat notice: 

Joe,

Rod, 

Joe Faust,

And thanks for your future work.The originality of EnergyKiteSystems is
a constant update which is only possible with its actual
configuration,due to the huge reservoir of datas and the necessity to
keep the files.However a supplement page for presentation,or a parallel
site from Roderick is an idea to think.

PierreB



--- In AirborneWindEnergy@yahoogroups.com, Dave Lang <SeattleDL@... wrote:

Robert,

Perhaps a mistake in my precedent post on the subject if one consider the potential power extraction at altitude of 500 or 600 m is 4 times that at 100 m;so only 6 (500 m²) kites L/D = 4.
 
My idea is the necessity of making an enough great kite (with the GigaFly for example) to show the potential of AWE:if it is done some smaller systems will can be marketed before high-scale AWECS.

PierreB,
http://flygenkite.com

So if I want to launch extending crosslinked stacks of kites out from
the rim of the trampoline....

Can I check?...
I should mount a multireel winder in the middle of the trampoline to
extend the stack one by one,
wind a graduated cody ball line set to engage graduated ring sizes, one
for each stack on each winder...

Is it a sleeved multi line winder reel at a larger radius needed to feed
line out to the kite back end and tethering it to the following stack?

Got any good photo / diagramatic links....
Pictures Dave ...
Would you like a Camera from Santa?
I was pretty good as the tooth fairy last night.




--- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@... wrote:
the loads a single kite puts on a tether. The slightly greater tension
at the kite (that daveL found in his simulations)�favors�the
line parting�at the kite�in the event of break-away, so that
the kite will not drag along XC indefinitely, but glides down.
Eddy/Patton trains include tri-swivels inserted�along a main
tether, so that kites can branch off and not develop line twist as they
loop. Trains and stacks develop far greater tension at the surface; the
sum of all the kites pulling together, therefore an optimal tether is
graduated in stages, much like a multi-stage rocket tapers toward the
top. The end result is similar; a capacity to fly higher than any
single-stage. Stages can also be assembled and disassembled�on the
fly from separate winders, adapting to changing wind, and�damaged
sections hot-swapped.
kitiest method to connect links is with a larkshead loop and stopper
knot, which everyone should know how to make. For a graduated
line,�a thinner link should larkshead onto a thicker
line�stopper knot. Properly done larkshead knots�are secure,
especially�under load,�and easy to connect and disconnect.
With very fine line,�a tail is sometimes�added on the knot
loop, to grab if needed for easier disconnect.
above, but a common instance is a shackle of some sort. Rigging,
sailing, fishing, and climbing all have great versions of shackles to
use or�learn from. In the case of kites a good shackle is light,
generally aluminum in any size larger than sport fishing shackles. Snap
shackles are handy, but beware the potential of such�shackles to
snap onto a line unintended, with potentially disastrous results. Where
a risk of such fouling exists, choose a locking shackle.�Always
select the "perfect" shackle from the endless selection of products.
pulleys are designed to allow knots and low profile shackles to pass.
Graduated rings and stopper balls allow multi-link tethers to display
programmed dynamics as multi-tethers (original Cody War Kite
staged-launch method). Varied components, like NAV markers, can be
linked in between line sections. The possibilities are infinite, and
extend into 3-D lattices for mega-scale latticework.
kite buggy system. One of his proudest innovations was to put all three
of�the traction-kite lines in a silk sleeve, thereby preventing
most snagging, sawing, and looping twists. Protected so, the lines could
be specified thinner,�offsetting sleeve�weight. Its possible
that the neatness of sleeved lines even reduced aerodrag, further
offsetting�any extra weight. Pocock did not�report that the
bit of extra actuation�friction was a problem. especially compared
to the robustness of being able to�yank sleeved lines out of trees,
as happened�on occasion.
riggers, but like all else Pocock discovered, are due for a comeback. A
natural�trick is to use modern braid-over-core, or hollow-braid
with custom core added,�as a multi-line by pulling on the core
differentially from the outer braid.�Many basic control functions
could be so�enabled, like steering or kite-killing.