DaveS and all,

My idea is beginning to see the difference between a mount on a stick under a kite of type parafoil (FlygenKite ) and a mount on a rigid wing (Makani),excepted the specific use of FlygenKite as a cheap model making to load batteries.

Like for precedent messages only losses of output in rapport to Betz limit of rotors aloft are taken into account.So we take a value of 76.548% Betz limit to obtain round numbers for 1 MW with wind speed = 9 m/s.It can be considered that CL/CD of Makani M1 is some value like the double of CL/CD of FlygenKite.Note the following numbers (like for precedent messages) are not the reality but only a hypothesis of working. 

Makani M1:CL/CD = 12; area is 175 m²

FlygenKite:CL/CD = 6; area is 700 m²

Makani M1:advantages could be less area,possibility of high voltage and less losses in the conductive tether because of high kite speed; disadvantages could be the reverse of the medal:problems of safety and also reliability (altitude of work is limited,so an error close to the ground can be a crash) due both to the rigidity and the weight of the wing and its great speed,and also the too high turbine tip speed.

FlygenKite:avantages and disadvantages are inverted.Other advantage:using existing soft wings (of type parafoil).

Of course a more detailed study is needed.For example what are the real aerodynamic losses of the mount of turbines on Makani M1.Indeed during loops such mounts can slow down the kite.Other examples are shown in a recent post from DaveS:losses in conductive tether,generator etc...

PierreB

http://flygenkite.com   

 

Hi Pierre,

Thank you for your reply :)

Is it easy to get this planning of flight for an experimental tethered kite? And is there a limit to the height and duration? Do you have the name of the French government agency responsible for enforcement?



... on my original post: I guess I'm looking for the aviation authority for every country, so I can ask them. Or for someone who has a general overview of international aviation regulations.

Hi,

Seeing Dave's drawing on the homepage, I am reminded about my own idea of how to hang a windmill from a kite/balloon: a loop of line wound around a spool attached to the windmill, and going down to the ground and driving a generator (you could also use this in conventional wind-turbines).

Questions:

1. What kind of line (smooth/rough) and spool (threaded/un-threaded) would you use?

2. How much tension would have to be put one the line?

3. How long could you make the line?

4. Why isn't this used in conventional windmills. The generator weighs 50 tons, after all.

In a world of ever-increasing population, employment will always be necessary and is indeed becoming a considerable deciding factor in government expenditure / policy initiative the world over. Efficient engagement of humans in profitable employment on any project (including AWE projects) for as long as possible will certainly be most beneficial.

The contact information is at the bottom of the page?

Harder is the general manager of Health and Science at U.S. News & World Report. <<<

Or you can send your inquiries to "particular staff members" at http://www.usnews.com/usnews/usinfo/infomain.htm

Hello Simon,

"Is it easy to get this planning of flight for an experimental tethered kite?".I think the user has the obligation to submit a planning of flight towards the authority.

PierreB

Aviation authority in France:Direction générale de l'aviation civile (DGAC)

 AWEify           
 Look at a tech matter and wonder if that matter could play a part in energy kite systems or airborne wind energy systems; that wondering is about integrating a subject tech into AWE or AWECS.   Verb: "AWEify" .   Ask about any tech: Can that be AWEified? 

 

Welcome David Carmein

http://energykitesystems.net/Carmein

Best of Lift to you and yours, David,

JoeF

 

Though he passed, he is returning to AWE  ...
[ ] Welcome any furthering on Hermann Oberth and his kite power station and upper windpower interests!   Here is snapshot of new folder
http://www.energykitesystems.net/Oberth/

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Thanks :)

You've cleared that up for me.

Also note:
The Betz coefficient is 59%, but few turbines attain or even approach it. To speak of achieving the Betz coefficient across a whole section of sky is to assume you have near-perfect performance across the entire flight path, with your placement and solidity perfected so that only the absolute minimum of air "leaks" through your system.

A WECS (wind energy conversion system) operating at the Betz theoretical maximum, by definition, must lower the wind speed to 1/2 at the plane of operation (assuming there IS a plane of operation), and the flow exiting the area will be an expanded wake traveling at 1/3 the ambient wind speed.

Good luck achieving anything close to that by flying a kite across a section of sky, especially when your kite itself is not even taking power directly, but with propellers mounted on the kite taking the power.

Also consider the "compound Betz coefficient" that might manifest: the system as a whole has its Betz coefficient, meaning the main wing, acting as what we call a blade, has a Betz coefficient of 59% to try and approach (30% is a high average) but then the propeller has its own Betz coefficient.

I think those guys doing this are courageous to at least be trying instead of just talking, but one concern about the compound effect of a crosswind blade driving a crosswind blade, is this if the aircraft travels at say 6 times the wind speed, necessary to extract anything near the betz coefficient, then in a 40 mph wind, it's going 240 mph. Then the propeller is going mach 2.

In the real world of working turbines, this is at the edge of an overspeed situation when the blades are going this fast. I like to run my turbines this fast but most people don't. They can get a bit noisy.

Now, consider a piggyback propeller: - a whirling blade, riding on the blade. At a 6:1 Tip Speed Ratio, the propeller blade tips will travel at 240 mph x 6 = 1440 mph = Mach 2 !!!

Seems to me that any serious attempt to come anywhere near even a double-digit fraction of energy, approaching say 1/6th of the Betz Coefficient over a wide area of sky would entail high mach numbers and be noisy.

Maboomba.
Doug Selsam

Doug wrote:
I agree. The Betz limit is an important concept but I think of minor
interest for AWE. The constraints are mainly structural, handling and
safety. And we are interested in effectiveness in terms of power
produced in relationship to line force. With a stationary turbine this
would be power produced in relationship to resistance, i.e. torque on
the tower. I expect that line force costs more than tower torque.

Theo Schmidt

http://en.wikipedia.org/wiki/High_plateau

It is told on Makani website that M1 operates between 200 m and 400 m altitude.Span is 35 m;so the swept area could be 18133.5 m².So with a wind speed of 9 m/s (to obtain the theoretical 1 MW) the power at 100 % Betz limit could be 4700203.2 W. If we do not take into account the (big) other losses the obtained power is about 21 % Betz limit.

Four remarks:

1) The center of the loop is not swept.

2) Knowledge of the output in rapport to Betz limit is yet useful for the knowledge of swept area then space occupation (surface and volume).

3) It is not sure that here the swept area is optimal (perhaps too high for M1 potential,that could explain the low value of % Betz limit, or  for other considerations like a necessary high value of radius of loop because of high kite speed ).Diehl's formula does not take into account Betz limit because it does not take into account the swept area,but it would be possible to make a translation to obtain a rapport between (kite area and kite ratio CL/CD)/(swept area).I think KiteGen already made this calculation.

4) With a less performant flygen (per m² of kite area) like FlygenKite the swept area will be very different than for M1. FlygenKite flying slower the radius can be reduced:it could be a good point to reduce space occupation (this point should be clarified). 

Doug,DaveS and me are right about the necessary limits of speed because of the too high tip speed of the rotor.

PierreB,

http://flygenkite.com  

Dave Lang wrote:"...declaring such things as "double and triple Betz penalties"..."
In precedent posts"Double Betz penalties" or similar is an expression for flygen where Betz limit concerns both the rotor aloft and the whole area swept by the kite.It is true that the term "penalty" has a pejorative sense.The "penalty" is not so easy to appreciate:in the case of no regulations,no FAA,no aerial constraints,Betz limit within swept area is not so important.But now our aerial space is limited.

PierreB

Correction:"18133.5 m²"; a little less because of vertical projection
of the wing.

Note:you put a small turbine with a generator at the tip of each blade
of a conventional wind turbine.Betz limit concerns the whole
conventional wind turbine,but also concerns each small turbine in
rapport to apparent wind:Betz limit within Betz limit.

It is the same thing for AWECS of type flygen (another thing:it is
interesting that a rotor aloft with a low output produces also a low
drag (it is a point for examen)).Losses due to the rotor aloft (which
Betz limit of the rotor aloft) are the price of the conversion,a little
like losses due to reel-in phase for an AWECS of type reel-in-out.

Other example:an existing huge wind turbine sweeps about 12000 m²:%
output within Betz limit gives a main data for the global power. KiteGen
carousel sweeps about 2 km² and more: % output within Betz limit
gives a main data for the global power.

PierreB

--- In AirborneWindEnergy@yahoogroups.com, "Pierre Benhaiem"
<pierre.benhaiem@... a
%
volume).
high
account
because
of
35
=
Betz
93
m/s
http://www.energykitesystems.net/OrthoKiteBunch/OptimizationOfAManualFly\
\

Simon:
Oak Hills, California is the gateway to the high desert.
It's a plateau of sorts too.
We get very strong winds here that are funneled through the Cajon Pass.

If you take the 15 Freeway from L.A. to Las Vegas, you'll go by Oak Hills. Oak Hill Road is the first exit at the top of the pass, at 4200 feet elevation. We're a couple miles in at 3600 feet. The desert here looks level, with lots of mountains and lakes surrounding, but a closer look reveals long, flat, gentle slopes.
Anyway, it's like living in the sky.

All you know about Southern California - the perfect weather & the smog, both held in by a wall of mountains - well, beyond that wall of mountains is where we are at.
We had snow last night. Skiing is less than 1/2 hour away and you can see the slopes from here. It's like a piece of Nebraska slapped onto the Golden State. Well except for the skiing. Freezing all winter, then sometime soon it will quickly transition to 120 degree days.

I've been watching the output readings on the inverter for the 10 kW turbine on a 120-foot tower here, making 10, 11, 12 kW and more, just last night. It's making around 6 kW now.

The wind here blows almost all the time and you are already at 3600 feet. So that saves 3600 feet of kite line and all you need are a couple hundred feet to be way way up in the sky!

The edge of the pass is like a "skyscraper" - we look over at storm clouds and fog, all day, every day - just a few miles away, yet the weather seldom makes it here, but instead dissipates before it can get quite to here.

Ya know - clouds form then dissapate without moving though in a stream of fast-moving air. I'm sure you've seen the time-lapse videos of clouds staying in the same place all day while obviously there's a 60 mph wind trying to blow them along...

We watch clouds go by at or just above ground level, like you watch cars go by on the freeway - very fast.

I've got 20 acres with a lot of other clear land around my yard too.
If anyone wants to come here and fly your rig, all are welcome and you can stay here at no charge. Also there are some nice new major hotels within 2 miles.

While I might over-dramatize and complain about the weather a bit, it's closer to home and probably much nicer than the Tibetan Plateau.

We've had a few nice days lately, til global cooling reared its ugly head once again. S'posed to be nice again next week.
Also I'll bet they don't have a Super-Target or an In-And-Out Burger nearby in Tibet.

Maboomba!
Doug Selsam
http://www.selsam.com

Thanks for the comments DaveN and DaveL.They open my eyes about CFD models and the probably great difficulties to obtain realistic simulations of AWE.

PierreB 

I've read comments elsewhere by guys who feel challenged by the Betz limit and want to beat it.  This misses the point on two counts.  One, is that there are seldom any hard physical limits on the section of air available.  The other, more fundamental misunderstanding is that this is not like the problem of increasing efficiency in heat engines, where the limits are not fixed, but subject to improvements in design and materials.  Betz simply warns us about being too greedy, and reducing the flow through our device below the optimum level.

Thanks for the invitation :)

It'll be a couple of years before I start testing. When I come to the US, I'll be sure to stop by.

I am actually quite regularly in China ;) , and I would've liked to test there (many plateaus, strong winds over the entire country, sunny, nice food), but I am assuming the government is very restrictive in its control over the airspace.

When I start to test, I will probably contact the aviation authorities of a couple of countries to ask if I can test in the (international) waters off the coast, as I think it will be very difficult to get permission to do the kind of long term (months) testing I would like to do over land.


I started this topic because I noticed no one was talking about this. I still don't know how a plateau/mountain changes the wind over it, but if it doesn't change it much (above the planetary boundary layer), you could set up a test site on the slopes of Mount Everest, for example, at an elevation of 8000 meters, and do your experiment.

If that's too extreme, there might be smaller plateaus/settlements at an elevation of 6000-8000 meters, in China or the other countries surrounding the Himalayas, or the Andes, or somewhere near you.

http://en.wikipedia.org/wiki/List_of_mountain_ranges

http://en.wikipedia.org/wiki/Category:Plateaus

Attachments :

Thanks for your explanation Dave.

Actually, the thing I'm working on does allow itself to be tested in lower altitudes, so I will do that first. I'm just thinking about the steps after that.

Unfortunately I can't say more on what precisely I'm working on. I'm not even convinced it can compete with what other players are developing now.

Success. AWE will have an official media press pass at a conventional windpower big conference!   Following three approaches including a helpful bacing letter from AWEIA president prot-tem John Oyebanji, a press-pass first denied twice has been approved:

Prior post: program rewrote a redirected link. Here is the absolute URL:

http://energykitesystems.net/UpperWindpower/index.html

 

Pierre BENHAIEM schrieb:
...
...
...

I would think that this much copper or whatever is suboptimal. Using
high-voltage DC might be better if the inverter aloft doesn't weigh too much.
Then one could use two wires and many kilovolts, saving a lot of material and
weight in the lines. Of course one also needs a sure method of shorting this out
in case of accidents. And remember that insulation weighs, too. An interesting
optimisation problem which I'm sure has been done.

Theo Schmidt

Our group has mostly a focus on conducting macro mechanical force or electricity through a KES tether set. 

What else could be conducted through KES tethers? 
(Leave development and comparisons to another thread, perhaps.)

1. Macro mechanical force of the tether (left-right or more generall radial positions of a tether in the imaginary sphere of flight; here the tether is as a lever or a tensed pusher or puller without reel-in or reel-out). Shafts or levers may be operated here. 

2. Macro mechanical force of the tether via tension for traction or pull/relax for reel-in-reel-out purposes. Here we get power kiting, SkySails, groundgens, play-arm-moving, etc.

3. High-frequency vibrations of the tether could be mined for signals, communications, state reporting, and even making electricity or heat or pumping, though some uses here won't compete well against other tether uses.

4. Tethers may be constructed to conduct electricity directly. This might be a single conductor as part of a macro circuit between sky and ground.   Also, a two-wire flygen circuit. Or three-wire. Add the insulation matter discussed.
5. Gas-conducting tethers have been around for centuries. The purpose of the gas is varied. One of the first uses of gases in a tether was to supply the LTA gas for for large balloons.  Recharging kytoons from grounded gas generators has been described.    However, making gases aloft and sending the product to ground has also been described.

6. With energy from a working kite aloft, modify chemicals to store electricity; then conduct that reformed chemical to the ground via the tether. Send up one chemical and return the modified chemical; chemical up-and-down tech. Of course, one such player is the charging of chemical-based electrical batteries.

7. Light. A tether may be dedicated to conducting light or laser.

8.  Path.  A tether may act as a raw road for climbing and falling. Climbers and returners may be people, animals, carts, cable cars, objects of most any description.  The skyhook may be doing other things even while the tether might be used as a simple roadway. Walk up a tether set. Drive your Ford or Toyota up a tether-way. Let monkeys run up a tether for fun or to fetch things from the aloft living quarters.  Sail messages and toys or supply for the aloft KES human operator (food, medicine, clean clothes, hearing-aid replacement battery, etc.)

9.  A  kite tether (KT) may conduct one's spirit or inspiration to and from the heavens, may conduct joy or redemptive messages materially or vicariously.

10. Water conduit. Transport water up or down or up and down a tether for various purposes.

11. Loop-pulley fan-belt drive transmission of force: Have the tether be a closed loop driven from above to drive a rotating shaft below. Or trade the prime mover for some operation where the ground input is the driver.

[Open for comprehensive description of what might be conducted by tether sets of  AWECS ro KES] 

12. ____________________________

...

n#. ____________________________

What could a tether conduct?

SpiralAirfoil reminded me of what has been covered in our list messages,
so we add now such to the list.

##: Rotating tethers: stiff torque cables, torque-tube as tether,
unshrouded or shrouded torque tethers, etc. We have at least three
companies working on this direction. The aloft works drive a rotation
of the tether about its longitudinal axis. This is the twist/torque
method of conducting force. Challenges aside, this mode of conducting
force belongs in the party. In our video set there is shown a working
system using a flexible cable drive a ground genertor. Another example
is featured in a photo on our Stakeholders page. Niche uses?

Other?

JoeF

For those worried about the feasibility of automating AWE systems have a
look at this video
http://www.youtube.com/watch?v=3CR5y8qZf0Y

Quoted from the explanation,
"This is not human-piloted (please see the overview vid). The
vehicles/ball are tracked by an overhead motion capture system and
controlled by a pair of computers."

overview vid = http://www.youtube.com/watch?v=pcgvWhu8Arc&NR=1

Once the software to control the flying generators is developed the cost
of deploying it to other AWE systems will plummet. This is where the
strength of open-source should come into play, just as the hugely
complex system that is modern linux has cut the cost of legal computing.

Robert.

On Sun, 2011-04-10 at 07:26 -0600, Bob Stuart wrote:
Yes, that was me. The spreadsheet showing the calculations is still
there. I promised to update it and post an excel version but have been
too busy with other things to get it done yet. Hopefully soon.

HF AC down a single line would be inefficient. The way to go is 2 lines
carrying single phase AC, or preferably DC. Single phase generators tend
to vibrate too much so 3 phase is better. It only needs a simple
rectifier to convert to DC and a multi-kilovolt version would weigh very
little. Inverters are for going the other way.

Using 2 wires has an important safety benefit because if one breaks the
other can still be used to pull the airborne generator back to a safe
place. There is no need to insulate these lines and in fact the
insulation would just get in the way.

Something that no one else seems to be considering is using a
combination of airborne and ground-based generators. The airborne
generators/motors only need to be powerful enough to get the wing off
the ground and into the wind. Any more powerful than that and their
mass, and the mass of the tethers, start to become a problem. The main
generator will be on the ground driven by the reeling out of the twin
tethers.

Another reason for restricting the power of the airborne electrics is
the tip speed of the blades - as recently discussed by Pierre et al.
Noise from the blade tips rapidly increases as their speed increases
(5th to 6th power) so to be a good neighbour the blade rotation rate
needs to be kept down.

Quadracopters can be controlled very precisely. Putting more than 4
generators on a wing would be extravagant. Less than 4 makes control
difficult.

Robert.

"Consider a realistic example of what one might try to build, a 100 kW

We need to be careful with the rather misleading terminology here.
"Brushless DC" refers to the whole package including the electronics.
The motor/generator itself will be 3 phase AC.

Robert.

Dave,

You got my name wrong which hints that you think I was criticising you.
That is not the case. Doug made a good point in his post about the space
tethers saying that it is a popular subject because no one can point a
finger and say, "why didn't you build it?".

Fear of failure can be a huge barrier. The rewards for getting AWE
commercial could be enormous. People are already saying, "if it so good
why can't we buy one already?".

I am not sure the level of airworthiness required for passenger carrying
aircraft will ever be required for AWE. Turbines are already being
installed offshore. That is a good place for AWE too. No problems with
fires from burning generators crashing to the ground. Fewer problems
from the sonic booms when the blade tips exceed the speed of sound and
more likelihood of getting permission to fly high.

Google have demonstrated technology that can drive a car better than a
human. Moore's law is still working and computing power per unit cost is
still doubling in less than 2 years. Given good software a modern
standard laptop PC probably already has the power to fly a set of kites
better than a well trained human.

The proposal I announced recently talks of starting with a small kite
flown manually. The plan is automate it step by step. Skysails already
have their ship hauling kites fully automated. Maybe they will licence
others to use their software.

Robert.

Someone looking for a location for experimenting might consider Mohave, California.  It is a favourite location for homebuilt aircraft experimentation, so there is tech help around, the air space has minimum restrictions, and the wind is very impressive.

As I suggested to our friend from NASA Langley that's where NASA Dryden Flight Research Center is. If you get them interested they can work the airspace problem and work with you in many other ways.

Dave,

This business of fear of failure is subtle and deep-rooted. I have been
studying the mindset of self-made millionaires and looking back on their
lives it is not easy to see what risks they took. It is easy to be wise
in retrospect, but before you know the outcome it takes considerable
courage to invest your time and money in projects your friends are
laughing at (or simply ignoring). Many are still laughing at AWE and
nearly everyone else is ignoring it. I still have a sneaking suspicion
you are using this issue of airworthiness of kites as an excuse to hold
back.

We are agreed that developing the software is likely to be the biggest
job getting AWE automated. However, I thought that was the objective of
this list - to get a team together to do some open-source development.
The hardware needs to be developed in places where the manpower, and
physical resources and money are locally available. However, the
software can be done anywhere by motivated individuals with computers.
They could submit their code for testing on real systems and then modify
it based on the results of real tests. I have discovered 2 other
enthusiasts here in Cambridge who share my interest in building real
kites. Are there any programmers on this list interested to contribute
to the software for it? Are Skysails interested to get involved in an
open-source software development?

I do have experience of writing control software and fully appreciate
how long it takes. My one colleague is a professional in the field of
computer vision and the other has connections with Kitegen.

Linux is a success because it is a world-wide effort. The software for
AWE is a project of similar magnitude and probably even greater value.
Is it going to be seeded here or elsewhere?

Robert.

Retail product from Pacific Power Sails

Neutral-news instance report:
Note: lifter and personal power station are extra.
Generators are kite lifted. Lifter pilot kite trained above the generator-holding kite is a recommendation by the company. Shown seems to be two turbines held in framework in front of the kite's sail.

=================================

Product is up for retail sale:

PacificPowerSail

100 w at 25 mph wind.

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