One single blade ?

[Jerry]

I have a single 5ft blade from a 10ft set. Its fairly well built. I'll never be able to duplicate 1 or 2 more blades like this. What are the positive or negitives of a single blade? What type of design obsticals are there?  How do you figure hub diameter and counterweight?

Or should I just chuck it and move on? This would be just for fun and expirimenting.

Jerry

[bj]

  Jerry: my gearhead experiences tell me that the weight balancing is no problem.  Dealing with unequal thrust from one blade on
a shaft doesn't compute very well for me.  I am pretty sure it can, and has been done however.  Gut feeling is that bearings, shafts,
and associated stuff will need to be very ROBUST.  Bragging rights however would be priceless.

[SparWeb]

You want to build one of these?



 

Sure, bragging rights aplenty.

The aerodynamic loads are balanced when you have 2 or more blades.  With one, the loads aren't balanced, so the thrust and centrifugal forces aren't just loading the shaft axis, they are bending it too, and that's what drives the complexity up and up.
You can balance the CF load with a counterweight, like in the photo, but the thrust, pitch, drag...  oof.

[ghurd]

Someone on the board tried it.  A lot.  And hard.  And repeatedly.
It didn't work.

Most were fashioned after a maple seed (helicopter).

Someone might search the board for "sycamore".  Or "sycamore G-"   or  "sycamore + G-" because I know I posted the word 'sycamore' in one of his stories.
My anti-everything software makes searches take me a LONG time.

It bothers me I can not remember his name.
G-

[Jerry]

Well I've got a 150 LB PM motor with a 1"&3/8" shaft. Only problem is how to get it up on the tower. OH I might have an idea on that one too.

This idea is so stupid it might be fun? If I get crazy (crazyer) and do it I'll  post how things are going. I think in low wind you can easily count the rpm. I'll put a drivway reflector on the counter weight. My IR tach will like that. See its getting goofy out allready.

Thanks for the picture.

Jerry

[bcalmed]

Dood,

I'll come see it.

With my wooden eye...

Go for it, man!

bcalmed in Portland

[Tritium]

I think I remember Flux mentioning this in a thread in the last week or so.

Thurmond

[frackers]

Sounds like a bit of Kiwi ingenuity is required..

http://www.powerhousewind.co.nz/story.htm

[Norm]

Ghurd,
I was the one that suggested the maple seed to 'Someone'
.....he was quite enthused at the time.
and on a small scale like maybe a 2 ft blade and if you made it like a maple seed
and didn't try to improve on nature I think it would be a real winner for TSR.Someone on the board tried it.  A lot.  And hard.  And repeatedly.
It didn't work.

Most were fashioned after a maple seed (helicopter).

Someone might search the board for "sycamore".  Or "sycamore G-"   or  "sycamore + G-" because I know I posted the word 'sycamore' in one of his stories.
My anti-everything software makes searches take me a LONG time.

It bothers me I can not remember his name.
G-

Yeah it bothers me too....but hey I think it was about 10 yrs. ago.....
Norm

[Bruce S]

G and Norm
Rotornuts?

[bj]

Very impressive Bruce.  The one I remembered anyway.

[Bruce S]

Very impressive Bruce.  The one I remembered anyway.

Thanks,
 I had a great amount of interest back then about doing something goofy like that.
Then, when even the Great Zubbly even stayed away from them, I steered towards VAWTs.
NOT allowed to put up HAWTs in city limits  .

Cheers
Bruce S

[bob golding]

Sounds like a bit of Kiwi ingenuity is required..

http://www.powerhousewind.co.nz/story.htm

looks interesting but i question the bit about 3 blade turbines being complicated. this looks a lot more complicated to me. gravity is your friend. electronics and mechanically complex systems are not. think i will be sticking to 3 blades and a swinging inclined tail. they are not comparing like with like its only 2 kw so a conventional swinging tail will do that as our hosts have shown. if it was 5 kw i would be more impressed.

[Norm]

G and Norm
Rotornuts?

Yeah...that's him!

[scoraigwind]

The aerodynamic loads are balanced when you have 2 or more blades.  With one, the loads aren't balanced, so the thrust and centrifugal forces aren't just loading the shaft axis, they are bending it too, and that's what drives the complexity up and up.
You can balance the CF load with a counterweight, like in the photo, but the thrust, pitch, drag...  oof.

My cousin built one of these in the 1970s.  He had me carve the blade.  It's very important to have a teetering hinge that allows the blade to 'cone' backward until the centrifugal and thrust forces balance.  This eliminated thrust as an out of balance force.  However you can't eliminate the tangential, 'cranking' force even though its a lot smaller.  In successful products this is dealt with using a soft suspension like a spin drier.

The reason my cousin did it was that it can have pitch control without the need for a thrust bearing that handles the centrifugal force.  The whole blade pitches, weight and all.   It chugged along like a lister engine.  The pitch control was a nightmare though.

Another reason given is that it runs fast (high tsr) and it's light and hence cheap, but in the end the noise levels work against that, and of course the wobble is a hard thing to live with long term.

Similar arguments are given for a 2-blader but it tends to have out-of-balance forces too (in wind-shear or during yaw movements).  I never built a VAWT (except just one) but I spent about ten years building 2-bladers when I needed the rpm.  Since I learned to make permanent magnet alternators I can stick with 3-bladers and that's nice.

[ghurd]

I remembered his name at work today.
Funny I forgot, because I mentioned him in a post 17 Feb 2011!

Here are a couple links,

http://fieldlines.com/board/index.php/topic,137623.0.html

http://fieldlines.com/board/index.php/topic,139293.0.html

Norm, it was only 6 years ago.
G-

[Thinair]

I have been very interested to read this thread, and would like to add a couple of thoughts as to what can make a single blade turbine work very well at small scale.

As others have said, a teeter bearing unencumbered by anything (springs, dampers etc) that can pass the aero moment into the shaft is essential.

Our machine has been optimized for a tip speed ratio of 7 and we limit our maximum tip speed to 65 m/s (145 mph). This means we have a wide blade chord compared to an equivalent 3 blade machine, and consequently a much higher Reynolds number. Our Re's vary from about 500,000 to 600,000 across the span, which means we get very good lift to drag ratios from our airfoils. It also means we are generating power comparable to a 3 blade machine of the same size, but with only one tip and trailing edge traveling at the same speed, which is good for noise performance.

Attached are a couple of photos, one showing a field test prototype running, and the second showing the same machine in shutdown mode with the blade furled.

[Madscientist267]

I would bet this is an engineering nightmare, but apparently doable.

Practical, well... 

Like Ghurd said, they're apparently typically modeled after the Maple seed. But that whole dynamic center of gravity thing screws the pooch when you go to hold them down.

Way I understand it, they're overly vulnerable to shredding themselves - Not something to have out in the open where the kiddies are playing if you catch my drift.

But if you got somewhere that nobody goes and all it would make is an awesome splinter show when or if it flies apart, then the only other thing you'll need is a 25/8 camera rolling to catch the event! 

On the other hand, there's some (rather expensive) inverted uses for this same concept, that have carved their own niche into the market - Ceiling fans...

So I guess if you know what you're doing, it could indeed be a very interesting project to not only build, but see in operation.

Steve

[Thinair]

Not a nightmare,Steve; rather, an interesting challenge. A properly constructed single blade machine is no more likely to fly apart than any other turbine, I would argue that ours is far less likely than most. The first cause of 'shredding' as you put it, is overspeed and we have put a lot of effort into the design to ensure it never exceeds 350 rpm. The second most likely cause is blade damage caused by bending fatigue, which a single blade with a teeter bearing is better able to stand having the compliance of being able to move with the gusts.

Over 2 years of testing to date, we have found our single teetering blade rotor to run stably in wide variety of conditions. Sometimes designing and building things is the only way to prove a promising idea...

[ginger48]

I remember reading in Alternative Sources of Energy Magazine, 25 to 30 years ago, about a turbine the West Germans were building that only had one blade. Never heard how successful or unsuccessful it was though.

[Madscientist267]

How do you get around the dynamic center of rotation thing?

When I first heard of the concept, I played with some maple 'copters that I found, and sure enough, like everyone said, the speed of rotation changes the axis location.

It seems like this would not be mechanically feasible to compensate for in the rotor itself, but only in the counterweight. Thing is, I would think centrifugal force would interfere unless the control mechanism had a tight grip on the weight.

I'm obviously not arguing that it can or cannot be done, but more surely intrigued and can't seem to wrap my head around it...

Then of course all of the other forces at play that you all are mentioning... but those seem easier for some reason to understand...

Same thing is happening with the wife's sewing machine... Every time I glance at it juuuust right, she says "Don't even!" LOL

But I figure there's hope in the mill department

Steve

[Dave B]

Like we have seen before, it's different and gets attention. So was the spiral vertical, flower horizontal, leaf vertical and now maybe this will be the Maple sead horizontal. I enjoy seeing all the creativity and passion for a project and this is no exception. There will always be people who want something different maybe for themselves or maybe to sell. If to sell the proof needs to be in the hard numbers, cost per watt, reliability etc. I honestly hope the numbers can prove this to be better than  just different, so many other's have come and gone. In the meantime, it's cool but I wouldn't buy cool alone.   Dave B.

[ghurd]

How do you get around the dynamic center of rotation thing?

It seems like this would not be mechanically feasible to compensate for in the rotor itself, but only in the counterweight. Thing is, I would think centrifugal force would interfere unless the control mechanism had a tight grip on the weight.

The solution is simple.
From over 3 centuries ago, Newton's 3rd Law?
Or, arguably, Aristotle from around 25 centuries ago?
Add a 2nd blade.

G-

[Madscientist267]

 

[SparWeb]

You forget: commerce is involved, and the customer is always right.
When the customer's goal is to produce electricity day-in-day-out for decades with minor maintenance, then there are certain types of wind turbine to be purchased.
When the customer's goal is to reduce their gas, save the planet, raise awareness, make a statement, and look good in the backyard, there are other types to be purchased.

Why do you think the Skystreams sold so well?  ...at first...

(Sorry for the snotty attitude, but it's solving a problem that doesn't exist.  It will sell because it's a pretty gimmick, not because there is any performance to be gained AFAIK)

[RP]

How do you get around the dynamic center of rotation thing?

I'm not sure I see an issue here.  If the rotor has a free pivot at the balance point between the blade and the counterweight, that will always be the center of rotation both statically and dynamically (neglecting cases where the thing is pivoted up against a hard stop)

I'm not a big proponent of the single blade design but I don't see balance as a huge factor. 

As far as it goes, I can see a handful of possible benefits and downsides.

Higher RPM for a given swept area may be better suited for ceramic or ferrite magnets.
Only need to carve one blade!   
The pivot system kind of requires a downwind design so gravity/spring furling is out.
Would the pivot system create its own furling by "blowing" the disk into a smaller cone?
Probably harder to start-up in low winds

[Thinair]

Interesting thoughts above, its good to see the range of opinions.

Based on our results and analysis, RP has got it right with understanding the balance physics. There is some furling effect from coning when the machine is running partially stalled, but the main effect controlling power above design wind speed is still stalling.

We are certainly not putting the effort into the development and engineering of this product that we have just for novelty's sake, or to create a pretty gimmick, we are doing it in response to our discussions with both experienced small turbine users and aspiring windmill owners who tell us they want products that are quieter, more reliable, longer lived and more economical.

We won't claim to have 'cracked it' at this stage of our development, but we are seeing some very encouraging results, and getting good feedback from people who see it running.

I welcome any ideas and developments that can help make small turbines contribute positively to a better, more renewably powered world, and acknowledge that there are some very good products out there, particularly for me the Skystream. Now is the time to be developing and innovating to make sure that small turbines become appliances of the future (for suitable sites), rather than staying with a niche of enthusiasts.

[Watt]

Interesting thoughts above, its good to see the range of opinions.

Based on our results and analysis, RP has got it right with understanding the balance physics. There is some furling effect from coning when the machine is running partially stalled, but the main effect controlling power above design wind speed is still stalling.

We are certainly not putting the effort into the development and engineering of this product that we have just for novelty's sake, or to create a pretty gimmick, we are doing it in response to our discussions with both experienced small turbine users and aspiring windmill owners who tell us they want products that are quieter, more reliable, longer lived and more economical.

We won't claim to have 'cracked it' at this stage of our development, but we are seeing some very encouraging results, and getting good feedback from people who see it running.

I welcome any ideas and developments that can help make small turbines contribute positively to a better, more renewably powered world, and acknowledge that there are some very good products out there, particularly for me the Skystream. Now is the time to be developing and innovating to make sure that small turbines become appliances of the future (for suitable sites), rather than staying with a niche of enthusiasts.

Just curious if you are basing your single blade rotor performance on that of the skystream products.  Thank you

[Thinair]

Apart from sharing the downwind, stall regulated approach our turbine is very different to the Skystream, but I think anyone who is thinking about designing a small wind turbine to be an appliance like product should look at that machine as a benchmark.

[Norm]

I'm thinking that you can only get so much power from a certain area.....so ooo
.....since a two blade is easier to make and design than one blade.....why not
just make a 2 bladed HT?

If the 2 blades will only go x speed in a y wind whereas a 1 blade will go
2x in a y wind....then hook a 2 blade to a alternator or generator with a geardrive
to turn the alternator at 2x .

  I see nothing at all to be gained by a 1 bladed contrivance other than
attention or novelty.
  I think a large majority feel the same way as I do....

   anyone wanna start a poll ?
Norm.

[Thinair]

Norm, It might be time for me to stop posting on this conversation as it is starting to go round in circles.
Our machine does not turn at twice the speed of a two blade equivalent, we have optimized for a TSR of 7, and get a benefit in a much wider blade chord and consequently high flow Reynolds numbers and good airfoil performance.
The teeter bearing does not introduce instability, but allows the blade to move with gusts and de-stress the blade root. Incidentally, many two blade machines also use a teeter bearing to lower root stress.
If we were going to change from the single blade design, we would go to three not two, as two blade free yaw machines have some terrible dynamic problems as they yaw and couple motions between the two axes.
A poll won't change the physics, and there is no cost to keeping an open mind to new possibilities.

[Dave B]

Just an observation that possibly other's have seen also who are keen on the attention one blade brings to balance questions. You might want to look at the wiggle waggle yawing on your video (most apparent at "incredibly simple") and the speed here if real time doesn't seem to be much over only 120-150 rpm. The unequal left / right thrust pushing against the blade from 0-180 degrees one side one half rotation and then 180-360 degrees against the other side the other half rotation will make this happen no matter how well all the balance issues are taken care of. Tower shadowing could accentuate this also even with the tapered top section of tower. Right thrust, no thrust, left thrust etc. etc. Crank it up to TSR-7 20+ MPH winds ? Sorry, I'm honestly trying to see the advantages too but I can't help but see your machine as a Skystream with 2 broken blades. As far as marketing goes, might be good might be bad. You can be sure their unique blades sold a lot of units. Anxiously waiting on performance specs. I really hope to be impressed.  Dave B. 

Norm, It might be time for me to stop posting on this conversation as it is starting to go round in circles.
Our machine does not turn at twice the speed of a two blade equivalent, we have optimized for a TSR of 7, and get a benefit in a much wider blade chord and consequently high flow Reynolds numbers and good airfoil performance.
The teeter bearing does not introduce instability, but allows the blade to move with gusts and de-stress the blade root. Incidentally, many two blade machines also use a teeter bearing to lower root stress.
If we were going to change from the single blade design, we would go to three not two, as two blade free yaw machines have some terrible dynamic problems as they yaw and couple motions between the two axes.
A poll won't change the physics, and there is no cost to keeping an open mind to new possibilities.

[Madscientist267]

I get what you're trying to do, and I say go for it. There is never any harm in experimenting provided you stay out of the blade

Not everything necessarily needs to result in a "practical" product... Intrinsic value is sometimes just as important (if not more occasionally). Understanding comes from the strangest places once in a while.

Steve