Page 27 of the file 3600TW (link by JoeF on a previous post):what do you think of such a farm pattern?

Loop trajectories seem to be identical for each kite unity which space separation is 1 km.So the ratio swept area/volume and surface aerial occupied space seems not to be  maximized.

With Kitegen Stem farm or OKB schemas,trajectories are superimposed to allow a maximization of the occupied space.But Makani's technology could allow other pathes than loop,for example eight path with little vertical variation to filling the space and allowing superimposition of swept areas,and also allowing a limited variation of winds for each kite.

DaveS' remarks about problems of Makani's prototype are pertinent but problems exist for all AWECS schemes.

15 K$ is not so much:team pay for years,working prototype with automation (greatest challenge of AWECS ) ,high level of communication with possible returns,excellent last video,etc.Such a prototype can also produce returns of technology,for example for Ampyx's rigid wing.So congratulations for Makani.

AWECS is a mix between low and high technologies,so low and high costs.A system with only one crash per month or per year will not be accepted,and it with soft or rigid wing.

Miles L Loyd patent describes gears beetween propeller and ground station with generator via turning tethers into the main (profiled) tether.But now brushless generators are lighter:Makani's choice of high ratio CL/CD (according to rough calculations 8 without propeller,and 5,33 with propellers) is a good choice to allow fast spinning generators.

However the problem of electrical cable stays.Morever with a coefficient of 5,33 for the kite,but also for tip speed of propeller,used winds can not exceed 8 m/s (= 227 m/s at propeller!):this point has been described on a precedent Douglas Selsam's post.So such a configuration seems not to be adequate for high scales.

Loyd's patent also describes a catapult for launching:the catapult is used by Makani as interesting system for specific rigid wings.

Pierre B

OKB 

 

 

I thought this post was lost.It is the same that the precedent.

PierreB

dave santos wrote:

We are really talking about two things: a field of identical units near to each
other, which may want to sync as others have written, and a wide-area grid of
fields which may be roughly adacent or entirely remote from each other. For the
near field I agree that some form of energy storage during a single power cycle
might be beneficial. It boils down to an economic optimisation problem.

Forced syncing of closely spaced kites allows better land usage but does produce
these power surges and is prone to catastrophic failure if a single kite goes
out of control.

Forced non-syncing or shifted-phase-syncing will remove the power surge problem
but require more land and may look so chaotic that observers resent it.

For the wide area, the more fields there are, the more even the total power
result will be.

There is a similar problem already with wind farms which produce lots of power
during high wind conditions, power which nobody wants as there is then too much
available already. Current practise in Germany is I believe to feed the power
into the grid anyway even though the power companies then *charge* for absorbing
the power. Perhaps it is cheaper to keep the turbines running rather than
shutting them down.

Power companies are very sensitive to load balance as unbalance costs. Here in
Switzerland all houses are wired three-phase. The heavy use of a single phase,
e.g. with simple through-flow electric showers (about 7 kW), as common in
Britain, is not allowed, even though the efficiency is better. I think the power
companies prefer to waste lots of energy in storage losses because they can sell
unwanted "dirty" atomic or fossil-fuel generated power during the night at a
large profit. The majority of politicians refuse to end this nonsense because
they want to build large atomic power plants and hydro energy storage plants
rather than invest in renewables.

Theo Schmidt

A couple of thousand years ago, right after they noticed that boats could sail across the wind faster than downwind, they worked out how to keep the kites from tangling, and on a common, reliable, consistent path. The magic was to choose a circular path, to extend the inside spars to a central hub, where the energy could be extracted. The kites thus maintained proper mutual spacing, the proper angle of attack, and a consistent circular path. The energy was extracted without downwind travel.
2 thousand years later, we can mount many of such hubs on a common driveshaft to multiply the power. Such a driveshaft could be miles long, with limited danger of the kites (now called blades) colliding with each other. Thus Superturbine provides many many levels of noncolliding blades all working together to provide consistent and powerful rotation, that can directly drive a generator, or use a gearbox.
Doug Selsam
http://www.Selsam.com

http://machinedesign.com/article/hydraulic-wind-turbines-0420

this should provide fuel for many arrogant comments. Enjoy.
-brooks

________________________________________
PeoplePC Online
A better way to Internet
http://www.peoplepc.com

Beauti full
 

---

To: AirborneWindEnergy@yahoogroups.com
From: brooksdesign@peoplepc.com
Date: Tue, 27 Jul 2010 15:41:54 -0500
Subject: [AWECS] more tech details to fight over

 

Tease the boom?

Did Makani consider the following and what was their analysis:

Having not the analysis on advantage or not, but this teacher thought it something to place the turbine at the wing tips in order to let the wing tip vortex region drive the blades:

Click through for full instruction:

The driving craft could be a kite.

The intent for discussion was the opportunity of using multiple turbines vertically and held in farm by various aloft spread-hold methods, i. e., in the family of fences, meshes, with kytoon lifters perhaps.   

In similar vein, see the start of such farming:   (click image for fuller teachings; this is with a fan-belt focus):

Hydraulic wind turbines - a very old idea.
Similar to "placing the generator at ground level", to save the tower having to support the gen weight (as though a tower that can withstand the thrust loading of the rotor would have any trouble supporting the generator's weight...).
Never panned out yet.
Professor Crackpot with his abstract concept, based on a limited perspective, is always lurking, always muddying the waters...
Hey why not have a whole hydraulic windfarm with just one generator! No wait, let's replace the power lines with hydraulic lines, and replace our entire electrical infrastructure with a hyraulic one! We can start with 3rd world countries, since it will cost more! The Amish have a good start using pneumatics, so we can piggyback on their head start.
Doug Selsam

Hey I just want to point out that wind energy installations are down 50% this year. All the talk about clean energy research etc. is in my opinion mere talk without substance. This art of flying wind turbines and advanced wind energy should be explored with utter abandon, with some heavy resources by the government, however what I see is more of the same bureaucratic miasma that serves mainly to stifle innovation and waste the time of innovators by wrestling them to the mat of grant proposals that will never be funded while the status quo is rubber-stamped relentlessly.

Their idea of research is to ignore anything new and concentrate exclusively on minor, incremental adjustments to the current 1,000-year-old design that is good, but which, after 30 years of wind energy being the fastest-growing segment of the energy industry, comprises a mere 1% of electricity generation during which time electricity use has perhaps doubled. At this rate we obviously are only getting further behind at a very fast rate. When will the right people take advanced wind energy research seriously?

I challenge anyone to provide evidence that the big labs have explored or tested ANY significantly new wind energy design or concept in the last 30 years. If not now, when? How can they expect to find something if they refuse to look?

Reminds me of the drunk who lost his keys and is only looking under a lightpost because it's too dark everywhere else. One cannot conduct advanced research, while staying safe in well-proven territory. The idea that we're about to discard and replace our fossil-fuel infrastructure is not matched by a few straggling, privately-funded, mad-money, lighthearted or semi-serious luxury playful research projects that are heavy on hype and light on results. No risk, no guts, no breakthroughs.
(Richard Nixon declared that by the end of his presidency the U.S. would be energy independent - sound familiar?)
:)
Doug Selsam
http://www.USWINDLABS

I think Wayne German should build one of his free-sailing double-tethered sky-ships with microwave transmission of commercial electricity to the ground.
No really - "hey I'm just trying to help"...
"OK forget it if nobody wants my help"...
Maybe just a small model using the COTS from a microwave oven would be a good start. I hope it comes in at less than 4-5 cents/kWh so it can compete with current wind turbines. And make sure the military doesn't get ahold of it, and that the aim is always perfect, cuz concentrated microwave beams aimed at people could be dangerous...
This is similar to space-based solar/microwave installations: hey if solar is too expensive now, let's try putting it in space for $2000/lb. (???)
and
Hey what could go wrong?
Hello? You say it feels like it's getting really hot all of a sudden? Oh they're still working on the aim. Or are they? Oh they have the aim perfected and they're aiming it at us clean energy people!
:)
Nocturnal jets. I'm getting a flashback to 6th grade sex education class. OK great. A new name for an old concept. Winds are now called "jets" and now we can confirm for the thousandth time that winds are stronger at higher altitudes, and that winds occur at various times of the day, so we can pretend that by naming a time of day, specifying an altitude range, and giving the somewhat lackluster winds at this time and altitude a fancy name, we're somehow changing the face of commercial wind energy. I don't think so. This is just more endless talk while the future of clean energy slips away and we build more fossil fuel & possibly even nuke plants. The new talk is to get back to nukes, since in official circles, the "search" for advanced clean energy technologies is not yielding promising fruit. In reality, "the search" has been given up without even really trying. In reality there is and has never been any such "search" for new clean energy technologies, only empty talk. No such search was even started, let alone completed.
Result: wind energy installations are down 50% this year. What a country! Have a day.
:)
Doug Selsam
http://www.selsam.com

Attachments :

James H. Yim

Patent  US  6364251
Filed: May 19, 2000

brings some stiffening schemes. Click through for many figures.

 

Sounds like a torque tube 2 me

What about color? What color should we paint them?

Doug,   Twisted rope not too similar to even uglier hacks based on long torque tubes-

Doug,   You ask what color a flying AWECS element should be for best safety (insurability). There is an existing FAA standard of visibility from a mile away of red & white signals placed every fifty feet along a kite line.   Black, Red, & White are all high visibility according to conditions a mixed pattern of these colors covers most conditions. 50cm sizing of pattern elements minimally meets FAA standard in poor visibility.   If only two colors are used, one dark & one light is good. For example, a dark red should be used along with white.   KiteLab uses Red, Black, & White as its default color scheme, as both a quasi trade-mark & for safety, but will not contest most copycats when the safety dimension trumps merchandising.   Traditional red & white markings will be a standard for industrial AWE, but there will also be room for wild color schemes as elements scale up at low altitude. Night signal lighting will tend toward red & white as a default, but multicolors might prove a popular differentiator.   daveS

Hi Joe:
Yes it can be done, from this end.
We could build a low-weight version of our generator, and put together a low-weight driveshaft and propellers.
Do you envision this as a stationary (aerostat) turbine for ambient winds of say 15-20 mph up to 30, 40, or 50 mph max during normal operation, or a moving turbine a la McConney that might see 80 mph - 160 mph relative winds all day?
I have a huge collection (semi-truck trailer full) of carbon-fiber tubes of diameters mostly over 1", and under 5", of various lengths from under 1 foot up to around 16 feet and more, that might help, and I can splice them together.
But custom fabrication of parts may also be in order, for optimal applicability and performance. Gets into budget issues.
Also depends on how much weight can be lifted by your kytoons.
The output could be up to around 2000 - 5000 Watts max continuous power (higher peaks are OK) before we could have generator overheating issues.
then we start adding more generators or building larger generators, at least with regards to what we make right now.
I've got a few other ideas that I am not talkin' about til I get a chance to build 'em.
Later
Doug S.

Ice makes a lot of resins react very slowly, but you don't have to go to the poles for an ice mold.  There are some slow-moving alpine glaciers, but it is probably easier to just scoop out a shape in deep, loose soil and glaze it in winter, or add a skim coat of soil cement for warm weather use.

BTW, shaped sails are now made by robots laying tape into a giant mold to produce fabric.

Bob Stuart

Bob,   Ice would thermoset hot-blown polymers nicely. Yes, catalytic resins would slow cure, a possible quality-enhancer or process time-buyer. Average global tropopausal AWECS operational temperatures are comparable to Antarctic, a good thermo-polymer match.   The beauty of giant Antarctic ice-pack molds is that it seems a potentially benign land-use, if one wants many molds by the square or cubic mile, with less displacement of more productive ecosystems & far less embodied waste or pollution than cement, sand, plywood, etc. molds. The architect, Soleri, uses silt-molds to make large concrete domes, washing out the silt afterwards.   The forming of high end membrane laminate sails on large molds, with automated laying of fibers, is a direct inspiration for these ideas, but Wayne wants to go even farther, to make structurally efficient inflated 3D foils in one go. Getting a giant wing out its ice-cave mold by simply deflating it some is a scaling solution.   Most glaciers are pretty active these days & not so consistent or structurally stable as the deepest most-ancient ice-caps. They do generate katabatic wind & slowing this would conserve ice, but most such local wind can't touch Antarctic katabatic super wind for enabling power. Still, small glaciers could pioneer such ideas, & conserving tropical glaciers is especially urgent.   daveS

Ahh, a full female   mold, and the thermoplastics make a lot of sense,  too.  It is  basically a tension structure, so solar heating won't overcome the air cooling etc.  Very nice!  Presumably, a  section of glacier   could be stabilized with pycrete (water with a bit of wood pulp) reinforcing to avoid  cracks from surrounding motion  or existing strains.
 Still, seaming together two halves might be cheaper than freight to and from Antarctica  or Greenland for most of us.  Cheap earth and concrete molds are popular for on-site molding of architectural facades. 

Bob Stuart

Yeah, one could go on.... making no sense.
Have you tried this? Any idea how it actually works? If the wind slows, will it result in an unanticipated reverse rotation of the rotors or haven't you thought it through that far yet? Maybe we should add a ratchet. This general idea has been proposed for many years. Twisted rope down the tower. Always looks great on paper. Never seen it implemented though it is exceedingly simple.
Yes rubber-band-powered turbines - sounds great, but so many things sound great until you DO them. I guess rubber bands could be used in so many things - how about the drivetrains of cars? I think we're witnessing the birth of a new industry: Rubber-band power!
Yes if you wanted to maximize the torque-carrying capacity of the rope, and minimize floppiness, you'd have a hollow core and add resin to bind it all together and you are back to a composite torque tube.
Maboomba!
http://www.maboomba.com

Could we please see an example of any working AWE system coming from Wayne German? Any working wind energy system of any type?

Doug,   The water bucket hung form a twisted rope made great sense to Newton, as a thought study, for foundational physics was his forte.   Note that the preferred practical implementation of these buffered-drive ideas is the helical spring on a shaft. A "rubber-band motor" driven from one end & tapped at the other is a cool working illustration. Yes i have been driving small generators all these ways to get the feel. Reverse rotation is naturally damped in the experiments. Is there a simpler way transform a wildly surging rotary input into a smooth output?   These ideas seem far less speculative than your scaling claims for rotating towers.   daveS

Doug,   Stop attacking visionaries unfairly for lacking demos. Tsiolkovsky is considered the founder of rocket science well before space rockets were possible. Etzler proposed kite energy two centuries ago. Wayne German deserves time for his cool ideas to bloom.   After all, you constantly propose giant "rotating towers" as the one best answer to tapping upper winds, without providing any such demo. Wayne will prove more prescient.     daveS

Pill schedule off again, more on or less on.

Oops, forgot that KiteLab validated key Wayne German ideas in tethered foils-   http://www.energykitesystems.net/DaveSantos/hotwing3.jpg http://www.energykitesystems.net/DaveSantos/wsikfwing.mpg Doug is forgiven for asking.

There have been several commercial air mishaps caused by malfunctions of the pitot tubes. I've had wasps enter the exhaust and muffler of a parked car . . . parked for several days at an airport . . . . then the owner started up the vehicles. Fortunately few people around.
 
Yes, pitot tubes need special attention and maintenance . . . perhaps not enough redundant pitot tubes on large aircraft.
 
If we're going to install pitot tubes on to AWE technology, are'nt we getting a little too complicated and increasing the potential for breakdown?
 
The KISS approach needs to prevail in regard to towerless wind power technology . . . the simpler and more straightforward the design, the greater the reliability and in-service longevity.
 
 
Harry 

 

---

To: airbornewindenergy@yahoogroups.com
From: santos137@yahoo.com
Date: Sat, 31 Jul 2010 14:35:25 -0700
Subject: [AWECS] Effect of Mud Daubers on Six-Port Pitot-Tubes (not good)

 

If Wayne German had received a fifteen million dollar VC investment and actually built some demos, I wonder if Dave would still be so supportive of Wayne's cool ideas. Hmmm '-)

Dimitri,   You were challenged, along with everyone else, to identify what Google/Makani has contributed to AWE, in terms of genius or inventive leaps, for the 15 millions. Have you nothing to cite?   Wayne out-preformed them in creative AWE thinking LONG before Makani even started. He barely subsists in poor health with his family, not in AWE, but as a janitor, last i heard. Had Wayne gratefully received his $500 as part of the 30,000 "aerospace-student" stipends Google could have funded, it would have been well earned.   The last sort of thing he would have done is start with swarming parafoil bombs, rent an actual airbase, fund Maui-based research, & buy all sorts of useless toys; but if he had, we could as easily condemn him as Google/Makani,   daveS

You're right about KISS. If you make these things as complex as an airplane costs will go out of site.

Alright seriously,
I am happy that people like Wayne are starting to see how we could have airborne yachts powered by sails at various altitudes etc. And with hydrofoils down in the water - yes great, a great visionary. The fact that I also have been imagining all these things for many years is one factor that comes to mind. The next is that there are probably many others thinking the same things. Then you have Richard Branson who showed how difficult it actually IS to fly around in balloon yachts.
As I recall Wayne's AWEA main vision is to have big airfoils tethered at different altitudes, producing electricity by the differential in windspeed from lower altitudes to the jet stream (a al McConney? using auxillary propellers? or using the Santos method of spool-in/spool-out drums?) then the power is supposed to be converted to microwave transmission, that is beamed down to ground stations that are conveniently located all around the world and as the yachts fly over, they beam down the power by microwave and it is then all converted to grid-ready electricity and we all use it. SURE! Sounds like a great project for 10,000 years in the future, when we will likely be using cold fusion or something nobody has ever though of.
If we had even a part of Wayne's vision - the ability to have a single tethered craft in the jetstream producing electricity, we would not need the rest of his vision, the microwave transmitters and receivers.
Like so many visionary scenarios, there is a little lack of connecting the dots to create anything useful or workable TODAY or IN THE FORSEEABLE FUTURE. If you just look into the microwave transmission step, for example, you will see that if it existed in an economical form, it would be being used today for so many places with no powerlines! And the yachts flying all over - what about tangled wires? sheesh! Does anyone have a stratospheric yacht we could use? A lightweight, economical multi-meghawatt microwave transmitter/receiver?
I am serious about getting something up and running. Last I saw and heard with my own eyes and ears, Wayne was veering off from technology into religion. I applaud anyone for thinking outside the box, but I am looking for serious solutions now, not so much the super-science fiction / spiritual solutions that may have a seed of truth to them but be unlikely to ever be actually implemented.
But Maboomba anyway. Let's all keep thinking outside the box.
:)
Doug Selsam

I have been puzzling over something for the last few months and would like some help figuring it out. My gut tells me drag on airborne wind turbines (flygens) may be a much bigger issue then expected. At this point it is more of a gut feeling. If someone can help with the math below and/or set me straight it would be great.

The basic problem I see is that the turbine part of a flygen system may need to be much larger then expected, thus adding much more drag. High drag will kill the high flying capabilities even sleekest flying wing or vehicle. My problem centers around the theoretical tip speed limit of about Mach .85 of a rotor/turbine. If some one with some math skills can help think this through it might be interesting. Or correct me if I am way off base.

Here is my thinking.

Consider a 3MW Vestas turbine http://www.vestas.com/en/wind-power-plants/procurement/turbine-overview/v90-3.0-mw.aspx#/vestas-univers

When it is making rated power the tip speed at the end of the 45 meter blade is roughly .25 Mach.

What would the very theoretical power of this Vestas 3MW model be if the the relative wind at the tips was increased to Mach .85? (this is of course assuming the materials and foil shape could handle it, which they can't.) I know the power would be much more then squared but I don't know quite how to approach this mathematically. Can I have some help here.

When the above theoretical power number is found, it can be divided by the area of the 3MW Vestas turbine (6,362 m2) to get the average power per m2 at mach .85 tip speed.

It would seem that the above power number per m2 would also be a theoretically close (at least well within an an order of magnitude) to the the power per m2 of a smaller fly gen turbine. I believe the power/rotor area would scale down somewhat linearly.

Next question, using this per m2 number how big would a flygen rotor need to be to make a healthy 3MW of power with the rotors at the max tip speed of Mach .85? How much drag would this amount of flygen turbine area add to the air vehicle? My gut says this might be more then expected and would require very large amounts of lift to overcome the turbine drag.

Any thoughts? I have made a number of assumptions here which need to be checked/verified.

Grant Calverley

Hi Grant,
 
 
Several of the newer 3-bladed, tower mounted turbines rotate at very low speed, eg 10RPM regardless of wind velocity . . . . you need good generating capacity to restrict RPM to that speed. Also helps to adjust blade pitch to deal with ultra-powerful winds.
 
Flying turbines driving airborne generating equipment, whether carried by kite of balloon or a hybrid of the two, are going to present some horrendous problems that will need to be resolved . . . the exercise may take years to refine.
 
The concept of kites pulling cables that drive ground-level generating equipment has considerable merit . . . high-strength lightweight fabric combined with high-strength lightweight structural members combined with lightweight
 cables of extra-ordinary tensile strength are evolving technologies. This technology would likely become ccmmercially available within the next few years . . . . I expect that flying turbine technology would follow by a few years.
 
 
I expect progress to be made in the area of cable-suspended turbines being installed over windswept ocean inlets and over mountain valleys. The competing technologies include Doug Selsam's superturbine (including large-scale versions), Broadstar-type linked transverse-axis turbines. Both designs involve multiple turbines driving very few electrical generators . . . . cheaper to have a bank of mechanically linked turbines directly driving generating equipment.Eg: 30-link turbines can drive a bank of 3 or 4 different size generators to cover a wide power range.
 
 
Groups of mechanically linked turbines capable of withstanding multiple encounters with hurricane-force winds is a potential a very competitive technology.
 
 
The power output depends on wind velocity (the cube thereof), not turbine rotational speed.
 
 
 
Harry
 

 

---

To: AirborneWindEnergy@yahoogroups.com
From: grant@sanjuantimberframes.com
Date: Sun, 1 Aug 2010 20:35:16 +0000
Subject: [AWECS] Flygen drag puzzle needs an answer

 

I could outline a plan to have many working systems of many kinds operational, now, for much much much less money. I agree with Wayne German about the $10,000 figure: With blades and generators already in production, it's not a great leap to get something airborne, from my garage even. For example the demo I brought to the conference cost perhaps than $1000, including 25 rotors, driveshaft, generators, frame, & helium. This week I am going to the Techonomy Conference in Lake Tahoe. I'll be representing advanced wind turbine design, including AWE. Eric Schmidt, CEO of Google is supposed to be there, along with Jeff Bezos, CEO of Amazon, Bill Gates, and a couple hundred other big-name visionaries. Maria Bartiromo is on the participants' list and I heard she's bringing a video crew and that it's going to be on CNBC. I'll let you know how it goes.
Maboomba!
Doug Selsam
http://www.selsam.com

Every new turbine idea starts out saying they can out-produce a G.E. turbine. Often these turbine designs are solid concrete, drag machines with rotating walls, etc. There is usually some abstract aspect fixated on such as being magnetically levitated. In that case, there is of course no discussion of exactly how much energy the GE turbine is losing to bearing friction (very little), just the notion that magnetic levitation is "good", and they leave it at that. Same thing about flying kite/glider/airplanes bearing power-producing turbines: sounds great but what about all those details and mitigating factors? I'd say get something working at 10 kW, and do it now. Or 1 kW.
Nah, far easier to talk about the boundless future.
One overarching recurrent theme in wind energy is that ideas for "improved" wind energy systems always target systems too big to build today. That way they never have to prove a viable system. The basic idea is that the superior economics will not manifest until a certain scale is reached. The thousand details that have not been worked out are thus avoided perpetually. With the excuse of requiring a large scale to work, the thrust toward raising turbines transitions to an endless thrust to raise money, with no superior turbine ever emerging.
talk talk talk - the all-talk format...
:)
C'mon everybody let's blog!
Doug Selsam
http://www.selsam.com

Doug,   You are absolutely right about how incompetent &/or fraudulent WP actors use scaling as false rationale for open-ended investment. If you can't make something work on a tabletop, its unlikely to start working at monster scale.   Magenn started by promising a backpackable unit, then a 10kw unit, & now its got to be a 100kw unit with a diesel back-up, with no deliverables year after year, just a constant PR campaign & hunt for gullible investors. The pattern goes back for decades to the Magnus Airship, with never a deliverable, but somehow 25 millions were raised & spent.   One might think Makani & Joby's well funded teams could toss out convincing small-scale working AWECS, as early deliverables, for there is a market for such systems, but the claim is the same, that only major investment in utility scale technology will allow them to field a properly working system.   The quick way to settle the conflicting claims is independent (ie. Academia) comparative evaluation, at a modest scale, of competing AWE concepts. Hype-driven VC starts would be under great pressure to adapt to proved best practice or die. At worst we can count on the market & history to eventually sort out true winners.   At some point the principals of failing tech starts acquire guilty-knowledge of their shortcomings & face disclosure requirements to investors. We can help speed that process along.   daveS

Hi Grant,
 
 
The 170m diameter blade tip is travelling at 292-ft/sec or 428-mi/hr . . . . no wonder the pro-bird environmental activists are up in arms against wind turbines. For a air temperature of 40-F (cold weather), the speed of sound for air calculates to sq.rt (air heat ratio x gravity x gas constantt x abs temp) = sq.rt (1.4 x 32.2 x 53.35 x (460 + 40)) = 1096.6-ft/sec = 747.675 mi/hr. The blade tip is moving at MACH 0.573 . . . this value will decline as air temperature rises.
 
The question that perhaps needs to be resolved is to identify the RPM at which maximum conversion efficiency occurs for the bladed turbine . . .  and conversion efficiency will change with wind speed. The big diameter covers a very large swept area (244.800-sq. ft) and perhaps the developers chose a desgn that maximizes swept area and efficiency at low RPM.
 
There are many years of massive state subsidy behind the development and operation of the tower-based 2-bladed mega-turbines (HAWT's) that now proliferate worldwide. It will certainly be a challenge for competing designs to catch up and grab market share.
 
 
Harry
 

---

To: AirborneWindEnergy@yahoogroups.com
From: grant@sanjuantimberframes.com
Date: Mon, 2 Aug 2010 11:36:57 -0700
Subject: Re: [AWECS] Flygen drag puzzle needs an answer