Dave S.:
I'm looking at the latest issue of "Windpower Engineering and Development Magazine" - I'm sure they also sent you a free copy, right? I mean everyone who is actually involved in wind energy gets a free copy - don't they?...

The cover story:
"A Fresh Look at 2-Bladed Turbines"
2 blades or 3 has been the only choice for decades...
And
You are not having a debate with me. That's another fantasy. You are spewing nonsense, and every so often I correct something I happen to know is ridiculous that you write, to try and save others from becoming more ignorant instead of learning, that's all.

I don't need to watch a 20-minute video that has a guy saying stuff I already know is not quite right. Anyone can put a video on Youtube, and some actually play for more than 3 seconds! Wind energy has a lot of people who are not quite up to speed, or falter toward professor crackpot tendencies - wind is invisible so it is open season for idiots to spew false theories. Like I said before, spend the rest of your life visiting windfarms and let me know when you find one with more than 3 blades, K?

The rubber hits the road when you are being paid for how much electricity you can produce. Suddenly then, actually producing electricity instead of spewing bullshit becomes the important task and when the task is actually producing electricity, you choose between 2 blades or 3, or you are wasting money, and losing power.

Sorry Dave, but again, you are not debating me.
Everything I said about power being proportional to RPM squared holds true for lightweight motors too. I mentioned off-the-shelf motors since it is verifiable. Unlike you, I want people to be able to look up things I say to verify their veracity if they so choose. Truly, almost nothing I write here is my opinion, or even anyone's opinion. It's just industrial-level, simple facts. People in wind energy don't sit around debating the facts very often. I think there's even a saying:
"You are entitled to your own opinion, but you're not entitled to your own facts"

Has anybody tried a torque-limiting clutch to save the gearboxes from inertia loads?  A cheaper, trickier solution might be to control the generator to limit it's combined torque requirement for inertia and power.

DaveS posted: " I can't remember anyone on this Forum just advocating gearing as a slam-dunk solution."

Hi Joe,

 

Indeed because of large scale the angular motion of arms of OrthoKiteBunch  is very slow,so a gearbox should be required.But a hydraulic installation which a hydraulic accumulator replaces both a flywheel (flywheel is often studied for oscillating systems like JoeF' or KiteLab') as smoothing device and a gearbox since the conversion goes from pression towards generator.See another example of hydraulic installation on www.youtube.com/watch?v=mcTNkoyvLFs .

 

PierreB

http://flygenkite.com  

Safety notes: 

Looking only at the generator - the one optimised for half the speed
will weigh twice as much as the one optimised for full speed.

However, that is far from the full story when looking at the whole
flygen. There are very many things that can be changed. Maybe the Makani
M5 uses a propeller with many blades and a high solidity so that its tip
speed is not much greater than the wing speed.

Modern power electronics has come down in price so these days few new
generator designs synchronise their speed with the grid. Generator power
is conditioned so that the turbine can always turn at the optimum speed.
That is what MPPT controllers do. The generator can then have any number
of poles. Most of the electronics can be on the ground.

Robert.

Roddy
Yes, not only do I appreciate catenary suspension, I explain it in my next US patent which is still pending. You be preachin' to the choir, bro.
I'm as amazed to hear a name of anyone with actual knowledge of wind energy mentioned here, as I was when you bozo's first stumbled over the Betz coefficient, and I saw that first actual wind energy vocabulary word being (mis)used here.
My friend Hugh Piggott in Scoraig, Scotland has helped me greatly over the years. You are in error to think his axial generators have anything to do with more volts at less RPM. My generators use a tiny fraction of the Supermagnets Hugh's ironless generators use, and I can send you a 2000 Watt generator that makes 240 Volts at 300 RPM, like the one I shipped to Canada yesterday. Put me and Hugh in a race to build a generator and I'll be done by noon while Hugh will be getting started with a project that will take days and cost many times as much.
There are many people building these "homebuilt" style of axial flux generators, because they are easy to understand and "seem" easy to build. (That is if you don't know how to build a regular one).
Once I grasped the actual layout from reading literature from people like Hugh, I realized you just fold the same configuration in on itself and you have a regular radial flux generator. That was one step in my ongoing education.
The first electric generators and alternators were all like Hugh's - over 100 years ago. A lot has been learned since then, Even the advantage of lower cogging can be attained in other ways that use far less magnets and far less steel. In the real world, there are very few axial flux generators or motors in use, since the amount of material and hence cost and weight are far far higher for the same result.
:)
Doug Selsam
http://www.totalwhore.com

Theo
I don't think you really understand anything I said by your replies.
Talking about Mercury being colder than other planets is silly - it's had all its volatiles burned away and vaporized into space long ago, leaving it without an atmosphere, as you point out. As such, it makes little sense to talk about a "surface temperature" of a planet that close to the sun and then cite the temperature of the land that is on the shielded side, which might as well be hundreds of millions of miles away from the sun, since it never sees any sunlight. You know what you said is silly.

More to the point, how about asking WHY venus has so much CO2 in its atmosphere? Or why its atmosphere is so thick in the first place regardless of composition? In that case you see that the sun evaporated a good portion of the volatiles, but could not heat the planet enough to actually blow them all into space, so you have a really thick atmosphere. That holds all the planetary heat in, making it hot - its atmosphere is a hundred times as thick as ours, as a result of being closer to the sun. If you really want to debate whether planets closer to the sun are hotter, you should find someone without logic like Dave S. who always lovesa a seeming debate without meaning or sense. As far as the rest of all you say, "you are wrong" and all that, I don't find any of your arguments compelling. Please get back to me in 30 years and tell me I was right after all, when you are still very comfortable and not cooked to death at all, with shorelines in the same place, and the Earth going on as it has for so long.
:)
There's lots of stuff to worry about but good ole' Mother Earth will take care of you and handle any amount of CO2 you can dish out since as I pointed out the poles are our air conditioner with a negative feedback from melting ice. Don;t listen to the "politically-correct" propaganda, listen to me - what I say is just "correct".
:)

Where do you get all this? Sound in error to me and I make generators and run them and measure them all day every day.
How could you profess to have such a comprehensive knowledge of motors, and yet you say you wonder why pancake motors are not universal?
Isn't that like Dave S., the world's latest leading authority in wind energy, asking why turbines don't use kites? Like motors used to be pancake-style, turbines used to use kites as blades. Then progress happened.
Pancake motors were universal when the concept of a motor first came about, then it took a few weeks til they figured out how to do it better using less materials.
Oh, and another thing,
Magnetic saturation in your laminations can cause heat and help burn out your coils. Take it from the king of burned out generators!
Umm, listen, I'm really sorry to tell you this but, again, everyone is entitled to their own opinion but not our own facts.
Motors and generators produce power in proportion to the square of their RPM and that is just a simple well-known rule of thumb. Are you catching some disease of delusion from Dave S. or something here?
I hate to be so redundant but:
"ANYONE CAN LOOK THIS STUFF UP. IT IS NOT A MATTER OF OPINION."
:)
"Thank You"...
signed, Sister Mary Elephant

No it will weigh 4 times as much.

Kixels:
Kites used to form flying hairnet, displaying a real-time moving image of Dave S. in the sky with party noisemaker sound-effects.
:)

Hi all,

 

I have an official invitation to represent France for the next Dieppe Kite Festival www.dieppe-cerf-volant.org/  where I shall present manual lighting demonstrator POC FlygenKite (the programme is not yet available).This Festival is enormous, hundreds of thousand visitors. If the organizers of the Festival agree I would be happy that demonstrations of other players can be made.

 

PierreB

http://flygenkite.com

 

 

Great Job Pierre,

But only for crosswing aspect,unfortunately not (yet) for automatic control.

 

PierreB

Hi Stéphane,

 

For the Festival I will use small ground ram (like paragliding) kites about 1-2 m².I have also bigger kites but for your use a wing of type kitesurf (for sea) with inflatable beam would be better to go again after water contact.See also www.skysails.info/  as example of automatic control for crosswind motion [évolutions vent de travers augmentant la vitesse du vent apparent sur le cerf-volant et décuplant la puissance] according to the size (about 160 m² for a vessel of 6000 tons).But for your use with the boat of 6.5 tons a (in rapport to the size of the boat) greater static kite should be better and a system for automatic control would not be required.

 

Good sea for your boat!

 

PierreB 

http://ir.lib.ntust.edu.tw/bitstream/987654321/14207/1/Large%2BDirect-Drive%2BWind.pdf

From IEEE
Looks brilliant.

As does his other work

Structural mass minimization of large direct-drive wind generators using a buoyant rotor structure

Put a decent video camera on the list too.

"DS" as in this page:
http://rcspeeds.com/dynamicsoaring.aspx

Why you thought that everyone would understand what you meant with that abbreviation is beyond me.

Brian

Yes, good rundown of on the electric motor. I think your on about the same level as me on your study of them. On the pancake issue I think it has to do with the pie-shaped slice that the magnets and windings have to take. You can't fill the whole pie and balance the number of windings with the size and strength of the opposing magnet. There is a motor construction I saw in a solar race car once where it had a cup shape. Another thing I have noticed is that the magnets have a limited field strength while the windings are only limited by the amount of amps you can push through them. So because the windings are stronger it makes more sense to put them on the outside so they can fill the added space to the same strength level. But were at the edge of what I know and into what I guess. I do know that the ideal speed in m/s varies with how strong the magnetic field is and that stronger = faster. Also because magnetic fields fall off with some exponent of distance and bigger motors have bigger distances there may be a strong scaling loss.

We could have a whole other thread on this.

Yes remote wind sensors only make sense.

Brian

I could not agree with you more. Gearbox = bad. Direct drive = good. Anyone that has spent some time in this kind of engineering should know that the gearbox is how you fix things that can't work well enough without one.

Brian

Pierre, I believe your supposition is correct that the theoretical generator would weigh twice as much keeping certain variables the same.
Doug, You are correct that if using the same actual generator it would take 4 of them on the same shaft and therefore weigh 4 times as much.
Bob, you are correct but I have read so many posts that I lost track of why. :)

However my take on this is that when you optimize the generator by all the various ways to do so without using more expensive parts, it will weigh less than twice as much. I would guess 1.6666 times and much. ;) But I am not able to articulate the exact reasons in an intelligible way.

Power MOSFETs have improved in performance over the past 20 years to the point where their weight is virtually always paid for by the better performance they provide. Variable timing, no brush drag, no need for spark suppression, lower resistance.

None of this has anything to do with "Curvature control"

Brian

I see references in here to Lloyd's paper and power generation being the CUBE of L/D. I also see that it is the SQUARE of L/D.

So which is it? There is a BIG difference. Is Lloyd right? I thought he said Cubed.

Brian

And the simple solution is that if you don't want to run into the ground, stay away from it.

I know that sounds trite, but it is a very practical solution to a number of problems. I remember as a rookie pilot my parents were far more worried about me flying too low rather than too high. The vast majority of aircraft accidents happen at take off and landing, and although there are a number of reasons for that, the fact that the ground is close is a dominating one.

I also wish I could have to level of preparation that your looking for. Sorry about that.

We will have to revisit the violent stall issue some other time. I have to go to work.

Brian

Robert, your description of active bladder spar control to manipulate dynamics is very interesting. Beyond that I struggle to imagine how the one architecture could be used to perform so many functions. As ever I am simple and need drawings to best understand the whole story.

"roderickjosephread" <rod.read@...

Toward: 

Genesis of Crosswind Kite Power : (L/D)².Yes of course M.Loyd is 1000 times right.Wind power is cubed but L/D is squared.The formula M.Diehl uses is (I give the formula with words): Power = Force x roll-out speed;Power = 2/27 (air density) (wind speed)cubed (kite area) (coefficient of L)(coefficient L/coefficient D)².

 

Note:for flygen the formula works with some adaptations.But it seems the formula works in a first "simplified analysis".M.Loyd gives also a complete analysis where the result is by far lower (something like 1/3).

 

Concerning the weight of generator when rpm is half and power is equal,I have not the answer since I ask the question.But Doug (squared) looks right and you look also right.I think Doug has studied this problem for a similar reason:what mass is saved with Superturbine where small rotors at high rpm replace a single big rotor at low rpm.I try to compare some generators on the market;I have seen a brushless 500 kW;690 V;300 rpm for 3900 kg and another brushless 500 kW;230/400V;1500/1800 rpm for 1340 kg (see on Alibaba);but I do not know all technologic elements of both generators. 

PierreB

Loyd's paper (I hope this time!):Crosswind Kite Power - Home pages of ESAT

 

PierreB

http://www.balloonboard.org/docs/Balloon_License_0v2.pdf

http://www.ohwr.org/licenses

http://www.marathonelectric.com/MMPS/atresults.jsp?hz1=60&hz2=60&hp1=ALL&hp2=ALL&rpm1=ALL&rpm2=ALL&v1=ALL&v2=ALL&frame=ALL&phase=ALL&encl=ALL&mount=ALL&type=MULTI&category=ALL

Cut and paste the link above to go to Marathon Electric, or just google it. Find any table showing 2-speed motors and it is an easy way to verify that power is proportional to RPM squared. That means if you halve your RPM your power will drop to 1/4. It's true of all motors and generators.

Therefore a rotor running at a TSR of, say, 4, requires a generator 4 times as heavy (expensive) as the same rotor running at a TSR of 8. Also, the rotor running at a TSR of 8 will be more efficient, having less energy lost to wake vorticity.

-Doug Selsam

Indeed one can see on Y381, 213TTFS7238, 5/1.25 Hp, 460, 213T FR., 1800/900 Rpm [Y381, 213TTFS7238, 5/1.25 Hp, 460, 213T FR., 1800/900 Rpm] .But at 900 Rpm the motor 1800/900 Rpm is not optimized.To know how much generator mass is saved when rpm is doubled perhaps making a comparison between an optimized 900 Rpm generator against an optimized 1800 Rpm generator.

 

PierreB 

I do not know if in my precedent post my remark (about optimized both motors 1800 and 900 rpm) is correct or no,but what Doug's answer sounds correct and replies to my question:"Therefore a rotor running at a TSR of, say, 4, requires a generator 4 times as heavy (expensive) as the same rotor running at a TSR of 8."

 

PierreB

 

If we compare the following two generator power curves:
http://www.Ginlong.com/wind-turbine-pmg-pma-permanent-magnet-generator-alternator-GL-PMG-687-1c.html
http://www.Ginlong.com/wind-turbine-pmg-pma-permanent-magnet-generator-alternator-GL-PMG-541-4c.html

We see the following
687-1 541-4 Ratio
Speed at 1kW 200 125 0.6
weight 42 75 1.8

We see a 1.8 increase in weight for a .6 decrease in speed at 1kw. So if you halve the speed the weight ~doubles in this case. This matches Pierre's first assumption.

I don't know if this conclusively proves the case or not because there are other generators on that site that follow Doug's assertion that it is always 4 times.

We should be able to dig up a paper on generator theory that shows it mathematically.

Brian

Two letter abbreviations are not unique enough to be useful in the long term. Dynamic Soaring for example should be spelt out at least the first time is is used in any given thread.

http://www.acronymfinder.com/DS.html Lists 219+151 meanings for DS and Dynamic Soaring is not in there.

Personally, I would spell it out the first time I used it in each post. I try to spell out all three letter abbreviations anytime I bring them into a thread for the first time. Except perhaps AWE. I think making the forum as accessible as possible to laypeople is good for the cause. I also think it is good netiquette.

Brian

Looks like I owe Dave S. an apology. My heavy bias toward hard wings has been based on cubed rather than squared. The balance point moves.

I need to get my head around all the numbers in Lloyds paper. There are a lot of them in there.

A spreadsheet working through some of the various formulas would be helpful.

Brian

Brian and all,

 

This paper Windenergienutzung mit schnell fliegenden Flugdrachen (3.35 MO)  from Leuven pages 1-20 detail some equations from Loyd's paper.It is not so easy to choose betwen rigid and fabric wings,and between groundgen and flygen,or even hydro-gen (JoeF'scheme in message 5186).Pluses for rigid wings:high L/D (so small generators for flygens _ but in what proportion when for example TSR is doubled?);larger time of life (regarding UV for example).Pluses for fabric wings:low cost,possibility of take-off by itself due to low mass/m².

 

Concerning the weight of generators according to rpm your idea to find mathematical relations is interesting and should be developed. 

PierreB

http://flygenkite.com

Doug schrieb:
Mercury has a slow rotation - apparently not discovered until 1965. This doesn't
have much bearing here, but shows that you have managed another wrong statement.
The point is that even the *hot* parts of the surface of Mercury are *colder*
than the surface of Venus, although the solar radiation hitting Mercury is
almost 4 times more than that of Venus.

The internet is full of articles on this subject, see for example
http://www.spaceacademy.net.au/library/notes/plantemp.htm

...
Mother Earth will take good care of nature, which is resilient, but it won't
take good care of *us*. Actions by people like yourself, Doug, are endangering
human civilisation and killing countless people already today.


The melting ice gives *positive*, not negative feedback. By focusing on this
point you are simply ignoring the main issues, a common climate change sceptic
tactic.

Cheers, Theo

www.omegasails.com

PierreB