As research is on in parts of the world, I also wanted to design a small power generator (~10kW) using a high-flying kite. This is a personally-funded nonprofit project to help poor rural communities in Africa, Asia, etc.

Know nothing about Power Kites.

Can anyone please help me select the right Power Kite, strings and give any other advice in tihs regard? Here is approx. what I am thinking:

1. Need one that depowers -- preferably where power can be reduced in steps or gradually.

2. Two or three string would be ideal - use of the 3rd string to depower or control power.

3. Need strong and LONG strings since I will change angle of attack to maximize pull force (i.e. AoA would be > 45 deg.), and will fly between 100m and 300m (i.e. length of line 150m to 450m).

4. Self-inflation kind. Pls. suggest which kind: foil, LEI or SLE?

5. Budget: ~ $1200 incl. strings (don't know if it's realistic)

6. Area: Whatever largest possible in such a budget (at least 6 sq.m. I would imagine)


Thanks a million for your time! Need to order this by Monday. 6th July.

Interesting request

I think the Peter Lynn Synergy or any of their previous model twin skins might be best for you simply because of the auto zenith feature (the kite will fly by its self ... kinda like autopilot) and its de-powerable.

As far as the lines go you will have to make your own that are that long. Q-powerline in bulk spools should do the trick for you.

These are just quick ideas for you. Your request is not in the normal range of questions. Are you sure you don't want to take your time to do as much research as possible. Especially on the kite since it is a very important part of your project?

I know there is a company here in California that is working on this technology. In fact I believe Peter Lynns son works there. I will try and find the link.

From Delft University in Holland

PAST, PRESENT AND FUTURE OF KITES AND ENERGY GENERATION
kites came with the advent of Kite-surfing. Pioneers such as Peter Lynn and Robbie Naish have created an industry around kites. But even ...
http://www.lr.tudelft.nl/live/pagina.jsp?id=fe263f84-29af-4010-8222-2f1112c8f223〈=en&binary=/doc/Past_Present_and_Future_of_Kites_and_Energ y_Generation_(final).pdf


and

http://www.extremekites.com.au/news/general/peter-lynn-50m-s...


Im not sure you will have one working on the date you require

I don't know of a kite or any wing for that matter that flies at 45 degree angle of attack. Even the most advanced flap systems on rigid wings can't extend AOA past about 18 degrees without a full stall, and most wings have their best lift-to-drag at somewhere around 5 degrees.

And 10 kW from a 6m kite flying in surface winds? I wish you luck!

krumly

Dakitez:
Thanks for the ideas. I am not focusing much on the kite since the challenge is to design the autonomous control system that will fly it properly as wind speed, directions and gust change continually. Can worry about efficiencies and kite design later.

BASIC OP:
Wind pulls on the lines that are wound on a spool coupled to a generator. When the line unwinds, power is generated. At the end of the lines, kite is put in a low power mode and power applied to the generator to make it run like a motor and pull back the kite. This yo-yo action then repeats.

Btw, there are other ways, e.g. using kites to continuously rotate a long arm in the horizontal plane which turns a gen.


_thephantom_:
Thanks for the interesting post on the 2nd link! Couldn't get the 1st one to work. Pls. repost.

I only need to start ordering by Mon. ... the project could take 6-9 months to come into a decent running stage!


krumly:
10kW is sort of the ultimate when we would be using larger kites and flying at 150-400m, and with 2 kites flying in sync - one going up while the other is being pulled down. A lot of parameters will come out as we move forward though since we are only at the beginning.

re: AoA
Correct me if I am wrong -- An airplane (the 'wing' you refer) needs to minimize drag, whereas a traction kite needs to maximize drag. Stall happens in airplanes when lift becomes near zero (i.e. weight of the plane becomes much greater than lift). In a kite, a stall condition would work similarly but the weight of the kite being so much lower, a much larger AoA can be maintained (larger AoA means less lift and greater drag).

Here is the company that Dakitez was talking about :

http://www.makanipower.com/home.html

Here is a speech given by their president, Saul Griffith, regarding kite-powered electricity generation:

http://www.ted.com/talks/view/id/492

Look at the SLARC research by Peter Lynn...

http://www.peterlynnkites.co.nz/news/0704news.htm

and...

http://www.peterlynnkites.co.nz/news/0812news.htm

Quote:

Originally posted by 4world _thephantom_: Thanks for the interesting post on the 2nd link! Couldn't get the 1st one to work. Pls. repost.

took me 3 seconds to highlight the first 2 lines of the text as quoted right click google search and there it is first entry - total time invested 10 seconds, im thinking that the kind of effort required for the next stage of the project will need a bit more time.

Quote:

Originally posted by _thephantom_ Quote: Originally posted by 4world _thephantom_: Thanks for the interesting post on the 2nd link! Couldn't get the 1st one to work. Pls. repost. took me 3 seconds to highlight the first 2 lines of the text as quoted right click google search and there it is first entry - total time invested 10 seconds, im thinking that the kind of effort required for the next stage of the project will need a bit more time.

Bahdah Bing, Bahdah Boom! (Clash of symbols)

4World: Basically incorrect.

You are describing what might be refered to as a reel mill. The generator/motor system is land based. Kites pull out line to generate power, while returning in a 'depowered' state which requires minimal power consumption. Net power generated is the difference between the two phases.

During the power generation phase, your most efficient point will be with the kite/wing flying at maximum lift to drag. You actively fly the kite at maximum lift-to-drag, generating the most force you can get perpendicular to the apparent wind with the least force parallel to apparent wind. Since lift is dependent on apparent windspeed squared, velocity with respect to apparent wind is of utmost importance. That means if you have a high performance kite that can operate at L/D of say, 6:1, you're gonna fly it at 90 mph in 15 mph wind to generate the most force.

Now, Betz's law which applies to wind turbine rotor efficiency also applies to your kite: the most power you can possibly extract from the wind is 59% of the available power, and that would be achieved with a 67% reduction of 'true' windspeed through the rotor or past the kite. So you will reel out at 10 mph in a 15 mph wind, meaning your 6:1 L/D kite will be flying in 10 mph 'true wind' and actually be flying with 60 mph apparent wind. For reel in, fly to zenith with the kite at a position with enough lift to keep it aloft and minimize drag, and pull it back in. But even that takes some thought - if you take too long reeling it in, thinking that keeps power requirements down, it also wastes time you could be powering up on a reel out.

Few of the problems are trivial, especially the problem of tracking kite position and trim attitude and having a responsive control system to take care of adjusting it's optimal trajectory and velocity at any point. Many smart people are working on this stuff right now, and it is a very interesting and compelling problem. TU Delft's public information is good - although they are working on proprietary schemes, they are probably the most open about disseminating information.



krumly

Instead of reeling the kite in just use 2 depower kites. one in depower position the other in power positon. the powered kite will pull the depowered kite back down then reverse the depower to the other kite. Generate power both ways.

krumly:

You are obviously more knowledgeable in aerodynamics than me so I am trying to understand what you are saying.

"...kite/wing flying at minimum lift to drag. "

That's min. L/D, or maximize D (it's in the denominator). That's what I was also saying. :puzzled:


"... fly it at 90 mph in 15 mph wind to generate the most force. "

Didn't get this. When the kite is moving nearly in the direction of wind, how can kite's speed w.r.t wind be greater than the wind's ground speed?



You mean to maximize P, right?

Btw, I was also considering the famous NASA Parawing as it is very light (albeit somewhat harder to control.)


"Few of the problems are trivial, ..."

Yes, I am aware of that. And, the heavyweight guys that are in Makhani Power is apparent from their website; other companies would have similar profiles. However, my aim is neither to compete with anyone nor to spend excessive amounts of money/time on optimizations (this is my pocket money!). The idea is to get the kite to stay afloat with a reasonable flight path to generate small amounts of power. It's a project to help the poorer communities that are hardest hit by the captialistic/exploitative tendencies of economy - the system is very unfair to them with no fault of theirs.

Your help is very much appreciated. If you know more and can help off and on, I can ping you when in difficulty. If this forum is not right, we can talk off line by email.

Thanks much!

So, with the above discussion, can anyone else recommend suitable kites for this application?

Perhaps, one that's a hybrid of the Nasa Parawing and Power Kites of today?

Will also try to attempt making one myself at some point :o
... so a source for the fabric (nylon ripstop?) would be appreciated too.


4world

Quote:

Originally posted by 4world krumly: You are obviously more knowledgeable in aerodynamics than me so I am trying to understand what you are saying. "...kite/wing flying at minimum lift to drag. " That's min. L/D, or maximize D (it's in the denominator). That's what I was also saying. :puzzled: "... fly it at 90 mph in 15 mph wind to generate the most force. " Didn't get this. When the kite is moving nearly in the direction of wind, how can kite's speed w.r.t wind be greater than the wind's ground speed?

I think Krumly has the kite flying perpendicular to the wind (at some point), in which case your vector diagram is closer to a right triangle. One base, the shorter, is local true wind, the longer base is the kite speed and the hypotenuse, the longest leg) is the apparent wind.

I think a Peter Lynn would suit your needs.

1. Auto-Zenith
2. Self-Inflation/no bladders to worry about.
3. 4 lines to the kite, no bridles to worry about
4. Although I've never flown mine, they are supposed to handle wind gusts well.

You might need a couple of different sizes to cover the range of wind speeds they will be flown in.

There's an instructional video on video.google.com that shows how to rig/self-launch/fly/self-land a Peter Lynn. There are also videos on youtube showing its Auto-Zenith feature.

4World: My gaff - MAXIMIZE L/D, not minimize. I fixed that in the post.


Not to be discouraging, but methinks if your goal is to generate small amounts of power economically, and with quick results, the approach you are taking - flying a depowerable kite under fully autonomous control - is not the way to go. There are plenty of other technologies already available that might be a better fit.

If what you want to do is explore a new technology from a cold start, then go for it. Your plan to help underdeveloped countries or economies may be a ways off, because the solutions won't come easy.

Do as thephantom suggested - start googling. Get a solid understanding of physics and aerodynamics; search the US Patent database and study what's out there, and filter through what is ridiculous and what is tenable; fly traction kites, fixed bridle and depowerable, to gain a kinesthetic understanding of how it might work; and then start working on your prototypes.

krumly

burritobandit:
4 strings would be difficult to manage on a reel. I was wanting 2 strings but can go with 3 (the 3rd one for depowering). Any other suggestions?

Might not need multiple sizes once we have the control algorithm properly set.

krumly:
Even for 'small' amounts of power, (once the kit-controls are developed) I feel the manufacturing cost of a kite-powered gen. would be significantly lower than a wind-turbine (if that's what you were referring to) that stands >25m tall. And winds at 25m won't be as good as those at 200m either.

Anyhow, got nothing more to lose to try except maybe $10k and maybe 6 months.

Thanks for all the suggestions; I am already checking out some sites on the maths of flying.

-4world

Here is a great link for you. Loads of info here. Looks like Peter Lynn kites are the ticket for this sort of thing.

http://www2.me.wpi.edu/wpi-kites/index.php/Main_Page

Quote:

Originally posted by 4world So, with the above discussion, can anyone else recommend suitable kites for this application? Will also try to attempt making one myself at some point :o ... so a source for the fabric (nylon ripstop?) would be appreciated too. 4world

In a link to peter lynns own personal site (in acampbell post earlier) you can read the following .....

[basically for a nominal fee he will give you free kites to engage in projects. His own view is that the SLARC - which is what all variants of ARCS derive from, can be flown by a single line which will fit in to this application quite nicely, so drop him a line - im sure he will be delighted to help]

"If enough kite fliers are interested in participating, these few hundred kites could be distributed now. Shipping costs would have to be charged, and there'd probably best be a token price on each kite to discourage looters and tire kickers (NZ$10 and NZ$50 depending on size and age?), but they're mainly perfect new unused kites with fabric value alone in the hundreds of dollars.

This project is actually up and running already in a minor way but with just four participants so far,- so everywhere above where I've said "I" it should have been "we": Andreas Fischbacher(Germany), Orlando Ongkingco (Phillipines) and Johan Hallin (Sweden)- and there are others who have expressed interest.

We will share all the Slarc bridle and rigging systems developed so far (probably 10 or more across perhaps 20 sizes and models), and I'll write up some of the theories I've developed so that not everyone needs to start by re-inventing the wheel. However, I'll be surprised and disappointed if some contributors don't ignore all this received wisdom and find better ways to make things work than I've never considered.

As soon as possible, we'll also publish a list by model, size, and condition (there are some ex-demonstrators as well) and their location (roughly equal numbers in Singapore, Holland and New Zealand as of now)."