It's Ground already covered. Ok, I'll dabble in another direction. It's windy today here ,Think I'll go fly my kites 8)

[[All development teams are invited to send link to their sites, videos, and documents.  editor@upperwindpower.com   ]]

Don't you have something a little better than blue tarps at the world kite museum? (affordable though...) We're not talking about lifting several tons here. I can take steps to make a lightweight generator. Often in wind energy you try to make certain components heavier, rather than lighter, on the principle of "The 3 Little Pigs" which is a scientific theory only taught at the highest levels of academia, but I think I have some room to lighten a generator significantly and it should last days, months or more.
What kite options do we have to lift something between, say 50 and 100 lbs, that will stay up when the wind gets a bit light? What about lifting say 20 or 30 lbs?
:)
Doug S.

Now, thats what I'm talking about. IMHO, a simi-rigid wing is the way to go. Carbon fiber is not needed for the ribs as they are illustrating. The loads on the ribs are relatively small. What is still missing is a stiffening spar along the leading edge to push the wing from from a pure catenary to a straighter line. That would be a good place to use carbon fiber. This change would increase the ratio of swept area vs wetted surface. This is like the spar in the flexifoil kite.

Another optimization that I don't see is that the outboard ribs should not be placed straight front to back. The airflow in that region travels at an angle approaching the overall wing angle of attack. ... Wait, I just did the math on that. A 15:1 LD ratio is only about 4 degrees. Too small to see in that drawing. So maybe they are doing it. And actually 4 degrees could be too small to mess with. 7:1 is closer to 8 degrees and would be worth messing with.

I also don't see any attempt to deal with the differing pressures from the forward to the rearward parts of the airfoil. The only good idea I have seen for that is to use EPP foam to add stiffness. I think Dave Lang was working on that. It's kinda heavy and not perfect.

Brian

Rod,

In Visventis we have considered Kickstarter and competing schemes a
couple of times. Although I think there is certainly potential with
these sorts of fund raising processes the consensus is that Visventis
can manage for the moment on our own funds.

The problem is that there is a danger of shooting ourselves in the foot.
If anyone in the AWE community raises money through a big publicity
drive and the idea fails the whole community suffers a setback from the
negative publicity.

When I first got interested in wind power I was introduced to someone in
my community who had patented a vertical axis turbine design. There was
pressure to collaborate. He had built a toy sized model that span, but
there was no generator attached. I made my own model using old CDs and
an old floppy disc drive motor. Really crude and the parts bill was
almost zero. However, it was sufficient to prove that the design was
seriously flawed.

The message about keeping early prototypes as small as possible is
absolutely critical. Some large turbines have been built using cable
supported blades which I suspect resemble the design you are proposing.
They failed because if the wind changed direction too quickly they could
not keep all the cables in even tension.

Robert.

I don't know what a LEI is. If you will pardon the criticism, this list often uses jargon level initials without explanation. That substantially lowers the readability for new users.

Yes, AoA does only weakly predict overall L/D but that was enough for the illustration. Because having airflow across bumps caused by ribs wether it's inflated or just flight pressures leads to an airfoil cross section that is less than ideal. So the ribs would ideally run with the local airflow over the wing. What I can't tell you is if that is worth the trouble. My gut tells me yes because it is mostly a one time expense.

I don't see stabilizing the sideslip as any more of a challenge than any other reel in method I have seen. The only possibly unsolvable problem is the added cost of the high speed reel in motors that still are efficient generators. You can't leave optimal generator design by much before the cost is huge in lost efficiency. Then you have to add a second reel in motor that costs money.

The kite forms that have emerged as best for their various applications is not an automatic prediction of them being best for AWE. AWE can tolerate slower turns than kite surfing. The oversized sidewalls of a C kite provide maneuverability that I don't think AWE needs at the cost of more wetted surface and other forms of drag. Inflated, thin wall spars are a maintenance point for a 24/7 machine. Part of that dreaded complexity but not a showstopper.

I think you are excessively concerned about low wind performance. When you do groundgen you can launch different kites for different conditions. Also because of the positive effects of scale up.

Carbon, used properly, does not add weight and can easily pay for it's cost. Makani and others tends to use it everywhere much like the proverbial kid with a hammer. I used to do this till I went back over some of my designs and realized it.

Composite compression load structures are much heavier than air based compression structures or pure tension structures. Yes "tensairity" is a good thing, but it's not the only thing.

Cool to here KiteGen though of a quadcopter for launch. I personally think that would work.

Brian

I could not find a thread on flygen vs groundgen so I decided to start one.
Flygen:
Makani
Joby
Magen

Groundgen:
About everyone else.

There are also a number of concepts that are not currently represented in
Flygen pluses:
Near continuous power output.
little mechanical losses
More likely to have severed tether flyability
powered launch option

Flygen minuses:
Expensive lightweight generators that are still heavy to lift.
Need the added weight and cost of props.
Electrical losses in the tether
May require transformers on the kite
heavier tether.
Larger diameter tether
Launch is more critical with heavier kites

Groundgen pluses:
Cheaper generators with not weight restrictions
Can use Different kites for different conditions
Can use Multikite tethers
Lighter kites present less of an impact danger
Lower cut-in windspeed
Can easily use soft-wing kites

Groundgen minuses:
intermittent power production
fatigue of tether
mechanical losses in tether and tether handling
different kites for different conditions
normally requires tether for controlled flight
More difficult to launch high performance hard-wings

That is just the off the top of my head issues. Next step would be to quantify the pluses and minuses.

I will start by countering Robert.

By the time you have enough windspeed to compete with coal the efficiency cost of lifting the generator is less than the lost generation time of reel-in. Sorry I don't have time to do the math on this, but I think the math would prove the point.

The launch is less than .5% of the total time in flight. Efficiency here is not an issue. I see no reason to believe that there is more weight and cost for launching a flygen vs a groundgen. That is because you have to be able to launch during no-wind at ground conditions in order to tap the added availability at height. So you always need a launch mechanism. (At least in the cheaper than coal systems) IMHO towed launch is the baseline for this and towed launch is essentially the same for groundgen and flygen.

Brian

Robert:
Congratulations that you saw the writing on the wall and did not remain in denial of reality forever. I saw those CD spinners on YouTube and thought "here we go again for the thousandth time"...

I think the worst aspect of these crackpot designs that start with zero knowledge and go downhill from there is this:

Coming in, they strongly state overwhelming superiority over known technology in press releases. Often these announcements are completely dismissive of turbines that can power 1000 homes simultaneously, while their prototype, usually vertical-axis, usually drag-based, as you relate, has not even been connected to a generator at all! Hey let me tell you these vertical axis machines perform FANTASTIC as long as you never take that critical step of connecting it to a (gasp!) generator...

Anyway these newbie will kick and scream and call all sorts of names if anyone with any experience with wind energy tries to give them a heads-up. They create all sorts of controversy and get really angry and also get the people they are bothering angry, and the whole time they talk talk talk about how great they are and how superior their drag-based idea is. And how stupid they think working "GE turbines" are, since they don't know any other brand names to cite. They always cite GE and never any other brand. Well, we DID say they are idiots...

Then their idea fails. It fails a few times, over maybe a couple of years. And guess what?
The perpetrators, purveyors, promoters, NEVER come back and apologize. They never return with a statement like "Well I guess I was wrong and the people making turbines based on 3000 years of experience were right after all - sorry I bragged so much - I guess I didn't know what I was talking about".
Nope, that is one thing you will never hear.
Or how about
"Sorry we wasted so much money - I guess we were idiots"
or maybe
"Sorry we lied - didn't understand how bad we were lying at the time, but you told us and we didn't listen and now we can see that everything we said was in reality a complete lie".

It would be nice to see some of these (clearly in retrospect) hucksters admit that they were wrong, just once. We need a few more Robert Copcutts who can admit that they chased a false trail.

I think I must have heard a thousand, by now, of the incoming bragging statements, and not once have we had the "exit interview" of why any of these superior ideas somehow (gee ya think?) didn't pan out.

Today we have horrendous winds and rain. The hundreds of 10 kW turbines powering the homes in this area are all sideways in self-protection mode, but still bouncing off full-power as they cycle in and out of furling. Ah prolly nobody knows what I am talking about now...
Seeya!

Doug S.

Several GroundGen minuses are not really minuses

-The intermittent power production can be tolerated by the electric grid. In any case you can provide the ground gen plant with an energy buffer by the use for example of the supercapacitor, http://www.youtube.com/watch?v=v1vLQ1XYdOk

- There is of course a fatigue on the tether, but it can be accountend for, by appropriate testing, as in this test rig, http://fuoripista.webs.com/Immag0006.jpg

-The mechanical losses in the cable are really minor

-You do not have to use different kites

-I do not see a minus in the use of the tether to control the kites

-The launch is really a challenge, and this should stimulate technitian to find solutions and optimise the control in such a delicate phase.

This NASA page is a good introduction to kite physics. I have not seen
it mentioned in this group before.
http://www.grc.nasa.gov/WWW/k-12/airplane/shortk.html

If you are not producing steady power - at least as steady as the wind itself, then you have not reached the point of basic adequacy for a wind energy system. Or any other system. Name another power system that is intermittent. Achieving steady-state power was accomplished 3000 years ago. Look at the laddermill for an example of a drag-based system that would give steady-state performance if anyone bothered to build it, which they have not (perhaps because laddermill itself might suggest further refinement to a SuperTurbine(R)?). Go back to the drawing board - you don't have it yet!
:)
Yes the grid can tolerate intermittent power - especially if enough intermittent systems are averaged. What cannot tolerate intermittent operation are:
1) Your budget, since you cannot afford a generator, let alone a whole multi-million dollar system, working half the time - think about it. If you have a competitor who can use the same material to generate steady-state power they will out-compete you 2:1!
2) Your machinery, since machinery loves steady-state operation for reliablity and longevity.

PS
Most Irish people have never heard of Irish Spring soap, or Lucky Charms cereal! Now that is a travesty!
:)
"Always after me Lucky Charms!"
"But I like it too!"...

OK here is a quick back of napkin math for the generator weight issue. I am leaving out dozens of details here but I think I'm in the ballpark.

If your reeling out tether at 5 mph on a 1 megawatt generator then you have about 50 tons of tension in that line. A 1 megawatt flygen generator would weigh a bit over 2 tons. lifting 2 tons on a kite takes more than 2 tons of force so guess double that. 4 tons. Or 8% of your energy goes to lifting the generator. Not insignificant, but hardly a show-stopper.

There would be no onboard transformers. The generator would produce the transmission voltage directly. The power mosfets might or might not be needed and they would only be a few hundred pounds in any case.

The number most of you will jump on is the 2 tons. Thats because wind turbine generators weigh about 4 to 5 times that now.
Here is an article that reinforces the point.
http://digital-library.theiet.org/getabs/servlet/GetabsServlet?prog=normal&id=IEPAER000152000001000017000001&idtype=cvips&gifs=yes&ref=no
I don't know if that link works so here is the google search link.
http://www.google.com/search?client=safari&rls=en&q=E.+Spooner,+P.+Gordon,+J.R.+Bumby+and+C.D.+French,+"Lightweight,+ironless-stator,+PM+generators+for+direct-drive+wind+turbines"&ie=UTF-8&oe=UTF-8

It's rare earth magnets with an ironless core. Expensive but not unknown tech.

If someone could do a similar analysis on the how tether stretch and sag saps less than 5% that would be cool. On a short stroke it could easily sap 70%.

70% of what is a whole other discussion.

Brian

"The number most of you will jump on is the 2 tons. Thats because wind turbine generators weigh about 4 to 5 times that now.
Here is an article that reinforces the point."Not only:apparent wind on the turbine by far is higher,so the weight of aloft generator (in crosswind flight configuration) is lower,and a gear is not needed.On the other hand the weight of electric wires is not insignificant (probably higher than generator weight).

For groundgen (reel) capacitors can be a solution but are very expensive because of the level of required smoothing between power phase (roughly 2/3 of time) and retrieval phase (1/3 of time).In the other hand capacitors can be avoided for kite-farm implementation which appropriate management,but it is probably not so easy.

Flygen has another (linked to continuous power) pluse:an easier automatic management since there is only one configuration of flight (excepted launching and retrieval).

And a continuous power can be an essential feature for applications like loading electric cars according to a self-service where the customer puts off his unloaded car and takes a loaded car,that without the necessity joining the grid.

For making a correct evaluation we should see the possible applications.For conventional wind turbines joining the grid probably has been an error because of wind irregularity (variations are compensated with more coal due to the inertia of warm).

With AWE let us do not the same error and let us build a whole economic system.Nor electric cars can be good if energy source is clean,and wind irregularity is not a problem for loading and stocking batteries.

Pierre.B
http://flygenkite.com  

One of my favorite village idiot patent is a helicopter/flying machine showing a guy with a shotgun and his dog getting out to go hunting in the wilderness - an illustration suitable for framing on your wall. Forgot the number - sorry...

Nice to see some simple math - this implies you should take the gen into the sky since you need to lift more than that to pull a tether. Goes along with my previous point about tension-based power transmission serving quite efficiently to pull the machine out of the sky. (doh!)

Without reading the article, ironless core alternators (at least of the axial flux variety) use a lot of steel (thick steel discs) to physically keep the magnets from pulling together, since you need twice as many magnets, to have magnets on both sides of the airgap.
I make supermagnet alternators that have the iron stator because they are faster and easier to make, and use less magnets.

http://www.PM-ALT.com There's that old "They have been doing it this way for 100 years" thing... There are many possibilities once you start using supermagnets, most probably never tried!

Doug Selsam

Today I did the math for the weight of the wire.
1 megawatt via 2000 volts at 500 amps.
0000 aluminum wire 1500 ft long tether. 3000 ft total.
resistance is .2412 ohms. wireless is 60,300 watts or 6%
heat per foot is 40 watts. Gotta make sure it has airflow.
Weight is 195lbs per 1000 ft.
So 600 lbs for the wire. Not a show-stopper.

Thicker wire might be better. And the tensile strength of the wire is not high enough. So it will need some kevlar added. The diameter of the wire will be more than Kevlar. Yes, Dave, composite tether could be a pain.

Brian

--- In AirborneWindEnergy@yahoogroups.com, dave santos <santos137@... No I'm not. I don't really have time for the ones that I am addressing.
Crashing a robot kite into the ocean is hardly a big deal. Aircraft insurance is a manifestation of the bizarre tort laws in the United States. Don't let anyone get close enough to get hurt and the liability is manageable. I know our visions of the future don't match in this area. We already had that thread.

Yes the higher cost of rare earth magnets could be a show-stopper. I have not done that math yet.
The reason that "Rope Driving" reaches I don't get this statement. Higher altitudes are more losses for virtually all systems. But yes I think that flygens will have a harder time reaching 10,000 ft than groundgens.
Yes. I have not calculated that one yet. Probably not a big deal. I think it's only about 30% more diameter.
Yes, and a possible show stopper. My guess here is that the low end of the wind is not missing that much. More math.
Yes. True. But at some scale you hit the tensile strength of your material and then even the membranes scale in 3d. It's an oversimplification.
There is an ample supply of cooling air.
Probably, That is one of the reasons why I have said that I think groundgen has an advantage.

If yahoo groups had a good search and everyone posted with searchability in mind then no all new users could just look it up. I think it's as much a limitation of the format than anything.

That is the question that I am looking to answer. I have yet to see the simple critical path to failure that you speak of. No single disadvantage I have explored is a show-stopper and I have yet to put any number of them together to lead to unavoidable failure.

Small systems of almost any type escape their flaws. That is why I like scales where the concepts can't escape their flaws. It makes me a fan of people and companies that seek to build at those scales. I don't mean to belittle the other researchers It's just more exciting to see the bigger stuff.

I would like to see the grim curve you speak of. If you remember what team, please do post.

Brian

Momentum is a vector quantity. Mass moving in a direction with a given velocity is mv. It will ever cost to change the direction of mass flying. 

Corrected phrase:
Mass moving in a direction with a given velocity results in momentum of mv.

Brian

That paper was a good find. I have been working in that direction for
some time so I will need to dig out a full copy of it the next
opportunity I get.

Last year when I considered that a certain amount of flygen was a good
idea (say 10 to 20% flygen, balance groundgen) I started a spreadsheet
looking at tether strength and drag and mass etc. I will try to get it
into a presentable form asap. Since then I have discovered a source of
dyneema for a price comparable to steel. Dyneema is so much safer than
steel - no splinters, or snap-back on breakage, far better fatigue
tolerance.

Loyd estimated that the optimum reeling out speed is half the wind
speed. Therefore in your example the wind is at 10mph. You would need an
absolutely enormous kite to generate 50t tension plus the excess needed
to keep the generator airborne in such a mild wind. A flygen still needs
a stiff turbine and they get rapidly heavier as they get bigger. With
the size of generator Pierre uses it should be easy to reach the 0.5W/kg
example you use. A paper I found claimed that turbine mass increases in
proportion to the diameter to the power of 2.7 (I think). They used real
examples, not any theoretical estimates. Therefore groundgens scale much
better than flygens.

Another thing against flygen is radar interference. Not a trivial matter
apparently.


Robert.

On Sat, 2012-03-17 at 16:14 +0000, blturner3 wrote:
This is not an issue. Any wind generator needs to be hooked to either
the grid or a battery bank. Neither will be bothered by the intermittent
power.


Dyneema is incredibly good.

Not if it is designed well.

This is a potential advantage. For a flygen you could swop the
generator/turbine unit between different sized wings but it could only
be optimised for one size. With groundgen the airborne component (kite)
is low mass so it is potentially much cheaper that the flygen kite.
Groundgen can therefore afford to have a range of kites to suit a range
of wind conditions which greatly increases utilization of the expensive
generator and power electronics. Each kite would have its own tether and
reel because the low wind kite will need heavier tethers on a bigger
reel. When you have several to use tether and kite wear becomes less of
a problem.

Pull the kite away at ground level to extend the tether then use the
rewind mechanism to launch the kite.

I started working on it but have too many others things to do to finish.
Motivation also dropped when it became obvious groundgen is the clear
winner.

Robert.

Doug,

Just to be clear I have not seen anything on Youtube resembling what I
made. This inventor had patented a variation of a common Savonius
turbine. I made a Savonius by cutting a Pringles cardboard tube in half
to make the blades. I sandwiched the blades between 2 CDs. Gives you an
idea of its size and how easy it was to make. Tiny turbines are
appallingly inefficient but you can do comparisons. Building the same
sized turbine according to the patent produced worse results so that
settled the issue in my mind.

A pair of separated independent ropes made from steel is the only
sensible option for flygen. Its conductivity is good enough and anything
else costs too much. Combining steel with any polymer is asking for
trouble. The interface between the 2 will wear badly. Even though
Dyneema has a similar elasticity to steel I think it would just get in
the way.

Robert.

Watching Startram for any AWES rubs: 

Yes, I should add that to the list. Changing directions is a function of speed and mass. The energy to do that has to come from somewhere. Control inputs also consume power.

Brian

Newton's first law of motion: "The velocity of a body remains constant
unless the body is acted upon by an external force."
from
http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

and

"In physics, velocity is speed in a given direction." ie. a vector.

A single kite flying in circles or figure 8's will use energy to change
direction. That is just one reason why dancing pairs is ultimately the
way to go. The work done by one kite to change direction is transmitted
by the tether between them to move its partner in the opposite
direction.

The pair becomes like a 2 blade turbine. Obviously 3 kites could also be
used but I see little advantage. The advantage over a turbine is that
everything is in tension so mass is greatly reduced. Airborne mass is
real bad news as already discussed.

The huge importance of all airborne structures being under tension also
means the power must be transmitted to the ground by tension - not
torsion.

Robert.

On Wed, 2012-03-21 at 13:56 -0700, dave santos wrote:
Power lines all over the world transmit 32kV and more and they are
insulated only by the gap between the lines. There is no reason a flygen
should not do the same. Therefore the resistance of steel is not a
problem. Strength is the issue and in terms of ROI nothing I can find
comes close to steel. I will post the spreadsheet proving that once it
is made presentable. We are agreed UHMWPE (Dyneema) wins for groundgens.

We need a website with a concise clear tutorial.

Robert.

It makes so much more sense than the space elevator. They have a few
things wrong though; the tube should be vertical and it should be near
the equator.

A clarification for Joe. In Loyd's 1980 paper in J. Power in Fig 4 he
plots 3 curves. Fs is of no practical interest. Fc peaks at 1/3 wind
velocity and Fd peaks at 1/2. The paper needs to be read carefully to
understand what Fc and Fd mean. My understanding is that Fd requires a
controllable angle of attach. It is the best outcome so it is what I
work with for my feasibility studies.

Robert.