Twin prop windmill

[byndhlpng]

Please keep in mind that I am not a builder, but I sure would like to see this if it works. I have some different thoughts on this but I want to wait and see what you pros have to say first. ("waitress? bring me a couple of beers here please!!")

I have been accused of having way to much time on my hands and told that I probably need to cut down on the beer consumption.  Please reserve your opinion until AFTER you read this. (Maybe I do hab drain bamage)

I live in central Indiana and believe me there aint no hills, mountains, high spots or many bumps in the road around here.  I have been chasing information on low RPM windmill systems. Any help here would be appreciated. Wind here is far less than what is truly needed so I turned my brainc ells on with a Miller Highlife.

 Well I got ta thinkin one night while I was having me a beer for dessert.  What if I took two generators and connected them with a common drive shaft.  Turn the props on one around so the props both spin the same direction. They would now be paralell to each other and about 24 inches apart.  The blades on one generator might be fixed at 12 oclock (assuming a 4 blade set) 3 ,6, and 9 oclock. the blades on the other could be at 2,4,7,10 oclock. Both sets of blades will be fastened to the drive shaft and permanently in this offset position. I thought that offsetting the blades would help eliminate interference or turbulance from the other set of blades.  Now I am assuming that the blades are 10 foot diameter.  mount the connected generators to a round plate that is attached to a round cylindrical sleeve that can be bolted or welded to a metal pole or tower.I first pictured something along the lines of a lazy susan but heavier and with sealed bearings.  Now for the tail.  build a four legged tower that the lower portion of the legs will span over the top of the generators assembly and mount to the round mounting plate the generators are fastened to. Since the blade radius is 5 feet then the tower needs to be 5 ft. 6 inches or more tall. Mount the tail solidly to the top of the tower and in line with the drive shaft. The wind turns the tail and the tower wich turns the generator assemblies in to the wind.  Seems to me that this should work but im not sure how much drag will occur with two generators.  In my mind I feel that the two sets of blades will help each other to turn. (Geez it took me 4 beers to this point lol) Well I will let you chew on this one a little bit.  Please send info......... or more beer.

Here is a quick story too!!!

I was sittin in church last sunday with a little old lady.  The preacher was going on and on and on and on and finally that little old lady leaned over to me and said, "I think my butt is falling asleep."  I said, "I thought so hun, I think I heard it snore a couple of times!!!"

 (byndhlpng)

 

[TheCasualTraveler]

I hardley know what to say except we'd love to see the pictures when it's done.

[Dan 04617]

Not really a pro but...

A single set of blades, properly designed, will take as much energy from the wind as is possible.  There is still air movement, but not much power left in it.  You'd be much better off putting your second generator in clean air.  Or, rather than buying/building two generators, just make a single larger one, with a single set of properly proportioned prop blades all in the same plane.  You'll get more bang for your buck that way.

[finnsawyer]

Putting two wind turbines one behind the other is a bad idea.  The effects of the first one will persist far down stream, so the second one is robbed of power.  Or the two will somehow split the difference meaning you would only get about half the available power from each one.  Placing them close together side by side is also not a good idea as air must flow past each one and you then force them to share that flow with a loss of power.  For one take on what is going one read the following:

    http://www.fieldlines.com/story/2007/12/5/16183/1323

As you can see, there is both a flow of air and pressure drop through the rotor and a deflection of air flow around the turbine according to this view, none of which should be altered by surrounding structures or other wind turbines.

[byndhlpng]

Dan,

 I agree that a blade needs to extract as much energy from the wind as possible. In this case though, the blades can not spin seperately and cause blockage of airspace. None of the blades are directly blocking the wind from each other as they could do if both sets were spinning independently of each other.  Wouldnt the air blow between the blades of the "front" or "leading" set and then push on the second set?  A blade on the rear set would always be in an unoccupied spot in the leading set.  In theory then the twin prop is actually one propeller with 8 blades.

More beer please !!!

Byndhlpng

[byndhlpng]

Dan, and all others

I guess I need to explain my reasoning behind even wanting a twin prop system.

1. I live in Indiana and it is known here that the higher the windmill is in the air the better velocity of wind that it will be in.
   
2. A 60 or 70 foot tower (or maybe more) will be needed.
   
3. Some locations might restrict the efficiency if two seperate towers are used.
   
4.  As generators become phisically bigger , they are far more expensive to purchase.
   
5. Difficulties with larger blades I'm not sure about, but could be an issue.
   
   

So, One tower, one installation.  Two smaller generators with smaller blades. (yes I see it coming, the cost of two generators VS one larger and so on) I am only presenting a concept and theory that might be useful in certain situations.  I just want to find out if it will work or not.  Please persue this with me.

OK, THE BEERS ON ME!!!

Byndhlpng

[finnsawyer]

I think you are assuming that if the first rotor captures 30% of the power then the second rotor could capture 30% of the remaining 70% for another 21% or a total of 51% of the power.  The problem is that there is no law that says that remaining 70% of the power will ever be seen by the second rotor.  It may simply flow around the first rotor and the second and be gone.  In reality, I suppose some of the waste power may actually impact the second rotor, but definitely not all of it.  You would be better off using the same amount of materials to build a larger wind turbine.

[thirteen]

as a question what could you get if you had the front set of blades 8 ft the back set 10 or 12 ft. it looks like you could gain power on paper but in reality it is differnt I'm sure.

[byndhlpng]

GeoM,

I see where a dead space is occuring behind the first rotor and would rob air from a second that is directly behind it trying to spin independently.  However In this twin prop situation, there is two blade systems operating as a single unit attached to a single drive shaft.  If a dead space is occuring then wouldnt it transfer to behind the second set of blades?  A single shaft would not allow the second to operate at a different speed.  Now I agree that the two working in unison might tend to work slower but one is certainly not going to stop the other from spinning.  

(Waitress I need a wind tunnel and another beer!!! make that a six pack......

Byndhlpng

[byndhlpng]

13<

Thank you for bringing this up.  I thought this too.  I will wait for some reactions.

BTW do you have a wind tinnel I can borrow?? lol

Bynd

[scorman]

Altho there are many nay-sayers here, and I don't necessarily disagree with the notion that two independent rotors in the manner you describe, will get in the way of each other, there is an interesting concept you could employ.

Here is an article on "counter-rotating" rotors, and the idea isn't new ..the only diff from your idea is that the blades on one rotor are built mirror image of the other, so it turns in opposite direction:

"CONTRA-ROTATING propellers have been studied for over 60 years as a more fuel efficient method of aircraft propulsion. A CRP consists of 2 sets of propeller blades, one directly behind the other in the axial direction, spinning in opposite directions. Counter-rotating propellers spin in opposite directions, but are located on opposite sides of the fuselage. "

http://pdf.aiaa.org/preview/CDReadyMASM07_1064/PV2007_1371.pdf

I have the full pdf if anyone wants it.

BTW, if you are building 6 blades, you might as well put them on a single rotor for low WS application at higher efficiency at lower rpm (and less noise) AND this DOESN'T contradict Hugh Piggot's equations found in his notes:

http://users.aber.ac.uk/iri/WIND/TECH/WPcourse/page9.html

http://books.google.com/books?id=4UYm893y-34C&pg=PA173&lpg=PA173&dq=%22wind+turbine%22+%
22rotor+thrust%22&source=web&ots=2Maz5M06hz&sig=YRimxd4hN_IoZ1Vq47ZO9GQTibg#PPA170,M1

Stew Corman from sunny Endicott

[scorman]

sorry, that last link should have opened up to page 175 " effects of changing solidity"

[byndhlpng]

Stew,

Thanks for your info.  Counter rotating propellers(rotors) turn in opposite directions as you explained.  This(My concept if you will) twin propeller system has two sets of blades connected to the same driveshaft and can only have both of them turning in the same direction (eg clockwise )  The propeller blades of the rear assembly must be reversed (turned rotated 180 deg ) to match the front assembly.  They therefor wouldnt be mirror images.  They would be duplicates aerodynamically and would be fastened differently to the common single driveshaft.Let me try to explain it this way:  If i am in front of the front assembly and it is turning clockwise then the rear assembly is also turning clockwise.  If the wind is blowing from front to back then both are turning clockwise.  If i take an axe and cut the blades off the front assembly, then the wind would continue to blow on the rear assembly and it would continue to turn in a clockwise direction.  The now axed up front would have a hub but it would still be turning clockwise.   If I cut the blades off the rear assembly then the front will continue to turn clockwise.  Further, If I were looking at the whole assembly with both sets of blades permanently installed on the single driveshaft, I would see 8 blades total, four in front and four offset but behind the front. (If they were in line I would only see four blades) I hope this helps understand my intentions in this concept.  There will be two seperate generators BUT, one drive shaft extends through both motors.  Both blade assemblies are fastened to the drive shaft to create one working unit. ( I could eliminate the generators altogether and the two assemblies would still be solidly connected.)  Please continue to respond on this.

You got a wind tunnel I can borrow??? lol (Maybe a beer truck for the weekend?

Byndhlpng

[scorman]

Actually I have a psuedo windtunnel. Using it for 12 inch models of a one vs two rotor turbine experiment.

http://s145.photobucket.com/albums/r203/scorman1/Experiment/?action=view&current=4283.jpg

http://s145.photobucket.com/albums/r203/scorman1/Experiment/?action=view&current=4321.jpg

still a work in progress

But yours has been done!

Aside from two generators, why is your concept any different than Selsam's design?

http://www.dualrotor.com/

Stew

[byndhlpng]

Scorman,

It was never my intentions for anyone to believe this "twin Prop" concept was my personal project or idea.  Through many months of searching the internet I never knew anything like this existed.  Now I know. Selsams final product is slightly different than what I had envisioned, but his is a working unit.  

I apparently asked the right questions and finally someone came up with some answers.

 Selmans is only delivering 2KW at 30 MPH.  I was hoping to find a low RPM unit. that was the reason for the two generators and dual props.  Could Selmans be modified to use two 2KW motors or maybe one larger generator?  I also noticed the greater distance between the props too.  The blades were short as I had suspected they might need to be.  I am not cutting his design or product down by no means.  A job well done in fact.  Now that the concept has become reality, I need to find something that fits my needs. Maybe there are other similar units out there.  If not then why cant there be another one built to fill a need?

I am still curious about having my props so close together to see it they will work together tho.

A beer for Mr Selman and one for MR Scorman........ and two for me lol.

Byndhlpng

[scorman]

To help in your dilema and to play around with numbers, I just uploaded a section of my Excel turbine windpower calculator:

http://www.otherpower.com/images/scimages/7526/windpower.xls

any place you see a "?" ..you can fill in a customised number

Stew Corman

[byndhlpng]

Stew,

Wish I was smart enough to use it.  Send me an example please and I'll put ya on the double beer club list.

Hey, now that the concept is reality, should I still try to do my own design?

maybe with some help I can accomplish it.  If i made a home made wind tunnel from a box fan or hair dryer will it help prove or disprove some of the things mentioned in this discussion?  Assuming I made scale models.  Im talkin about the blade assemblies put together as I described, and not worrying about the generators right now.

I hope for continued discussion of the twin prop design from those still interested.  I would like to make a working unit.

Come one come all......... Drink two for me.

Byndhlpng

[ghurd]

Have you seen the Betz limit?

Are you aware of the implications of... frequency... magnet disk diameter... swept area related to power... swept area related to the tower... swept area related to the power... TSR...

And how they all interact.

The best example I ever saw was waves while suba diving on a coral reef.  No way I could explain it, but you could watch it all working together.

There is some nut that has been taking investors in his project for years.

Nobody mentioned him, or his reputation.

G-

[spinningmagnets]

I always enjoyed reading about airplanes, and I was a fan of the "push-pull" Cessna 337

http://membres.lycos.fr/wings2/3vues/cessna337_3v.jpg

I wondered why its configuration wasn't more common. I read that a twin-engined plane with the props in the normal tractor position are biting into clean air, and the 337's rear prop is working in turbulent air, so a conventional plane with the SAME engines as the 337 will have better acceleration and top speed.

I think your idea will work, but I also think two side-by-side props or one larger prop will work better. (I'm NOT experienced with wind-gens)

"Yes, madam, I am drunk. But in the morning I will be sober, and you will still be quite ugly indeed". -Winston Churchill

[Fiddlehead44]

Byndhlpng,

    A well known factor that causes poor wind mill performance, is turbulance.

one mill will create turbulance that will spread out for several feet. This in

turn will cause poor performance for the other mill. Number two mill will also

create turbulance for the first, so on and on. To help (you) understand this better,

think of a beer in each hand (prop) and your liver as the battery. You can destroy

your battery as quickly with one set of props as you can with two. BTW. Some people

think that beer drinking will not lead to acholicism. LOL.

   Fiddlehead.

P.S. I am not preaching as I also enjoy a beer or two once in awhile.

[byndhlpng]

I actually remembered seeing this plane on some "learning" discovery show a few years back.  Thank you for bringing a name and a piture of it.

A little duck walked in to the bar and asked the bartender if he could have a beer.  The bartender looked at the duck and said sorry but we dont serve ducks in here and you will have to leave. The next day the little duck came back to the bar and again asked the bartender if he could have a beer.  The bartender looked at the duck and said i told you yesterday that we dont serve ducks in here now scram, And if you come back in here and ask me for another beer I'm gonna nail your beak to the bar.  The next day that little duck walked BACK into the bar and looked straigt at the bartender.  The bartender just glared. Then the little duck said, "DO YOU HAVE ANY NAILS???"

byndhlpng

[byndhlpng]

Selmans design has the props at some distance apart.  I can only believe that the reasoning for this came as the result of testing.  Many tests probably go undocumented and I would say probably rarely will there be visual archives of the event.  I would like to see my twin prop configuration in wind testing.  I may have to rob some of the grandkids toys for a few days and erect a scale prototype.

UH OH!!! Grandma says if I drag that "stuff" out I have to put it back up!!!

I recycle beer cans and this project is causing me to need a can crusher.....

All your help and any others who want involved is greatly appreciated.

If a man drank a six-pack everyday(on the average)for twenty years he would have consumed 43,800 beers. (OMG)

Byndhlpng

[TAH]

I tried something like this last summer. I did it to play with some other ideas I had. The second prop didn't add as much as it increased the drag unless I adjusted the position to where the second prop was basically drafting the first. At this point it did better than a six blade with even spacing. The problem was that with the extra weight and drag it was still not as good as just 3 blades alone. Some of the lower output probably had to do with the DC motor I was using getting to cutin speed. The low wind touque shorting the ouptut was better but pretty useless with a 6ft prop there was not enough power to bother with at 8 or 9 MPH wind.

[finnsawyer]

There isn't actually a "dead space" behind a wind turbine, as according to my analysis there will be a considerable flow through the rotor.  The problem is that the power available to the rotor also depends on the pressure drop through the rotor.  Placing a second rotor behind the first will cause that pressure differential to now extend from the front of the first rotor to the back of the second rotor meaning that the two may act as one less efficient rotor.

Do not try to generalize the properties of a propeller to the blades of a wind turbine.  A propeller can be 83% efficient, while a wind turbine must always be less efficient than that.

[byndhlpng]

you are the first to mention of any actual attempts at this twin prop configuration.  Am I reading you right in that you say low MPH wind speed wont turn both assemblies well enough to get the generator to begin generating??

What then is your thoughts on a size of prop diameter and number of blades recmmended.  What I am nervous about is that what data I can find so far is not encouraging.  WS of 7 to maybe 10.  I thought that the twin (8 blades) would turn better in low wind. I guess the next hurdle might be finding a generator that will produce enough KW to make it worth the investment. I'm thinking I will need 5 KW or more in 7 or 8 MPH winds.  Am I nutso facto ?  Would two 2.1KW generators turn easier and produce 4.2 combined?

Geez it's early and I already need me one dem gold can kool ade things......

Let me back up a min........ do you have a sketch or pics of your setup?  Selmans has a unit that produces 2.1KW and is very similar to my twin prop design but the blades are further apart than I had planned to start with. He also only has one generator.

9.1 kilowatts of juice on the wall 9.1 kilowatts of juice.... ......

....... OMG I cant sing either........

Im bringin the fridge in the puter room,  wearin me out runnin and gettin beerz.......

Byndhlpng

[TAH]

The sellman thing is suposed to rotate in slower wind so the props are not inline and as the wind increases they move into a straight line instead of furling to reduce the tower load. Not the same idea really and even if it does work once I doubt they last long.

To get 5 kW in 8 mph wind you will need something around 40ft diameter I think, maybe more because the gear ratio needed to get any useable RPM in a generator will eat up a lot of the power.

[wooferhound]

I could'nt find the story that I was looking for

but I found these stories about multiple Props on a single shaft

http://www.fieldlines.com/story/2007/11/21/171443/46

http://www.fieldlines.com/story/2007/3/14/215845/361

http://www.fieldlines.com/story/2004/4/5/184919/7784

http://www.fieldlines.com/story/2005/4/11/21443/2524

http://www.fieldlines.com/story/2006/2/23/171951/663

[spinningmagnets]

I imagine if somebody had high constant winds, you could throw up any old sturdy wind-gen, and your batteries would stay topped off all the time. But, as I have been reading here, most of the discussion seems to be about getting some useable Watts more often from intermittent low winds.

After spending money and lots of effort to erect a wind-gen, it would be frustrating to find it isn't quite as productive as you had hoped. When staring at a wind-gen for hours and days, you would look for any way possible to increase efficiency even a tiny amount.

The experienced guys I've been reading always have the prop facing the wind (there are a few trailing wind-gens being experimented with), and if its on a draggy lattice tower , the prop is usually on a slender pipe stub to get it up and away from the towers wind turbulence.

If you could locate a web picture of a prop in a wind tunnel with smoke, you could see how far the turbulent air pocket extends behind it.

Here's another push-pull plane. The benefit was lower drag at top speed compared to a conventional twin-tractor engines, but worse fuel consumption at lower speeds (turbulence in the rear again) It was a short-range bomber-interceptor, fuel range was not the biggest concern.

http://en.wikipedia.org/wiki/Dornier_Do_335

I think this is still a useful discussion, because some people might only be allowed to have one wind-gen tower due to small property size and having neighbors near. If there's also limit on the allowable prop diameter, getting a few extra Watts from a second prop might be better than nothing...

[byndhlpng]

Spin,

Thanks  for a vote of confidence.  Most so far have been on the negative side of the possibility.  Like an absolute maybe.  I agree that this deserves further review with fresh minds and possibly newer untested technology.

You are correct in assuming that I need small diameter blades that will turn in 8MPH winds. You are further correct in that we have a tower ordinance in our county and trouble might brew if I start erecting a wind farm.  40 ft or more blades would cause me to use a 70 or 80 ft tower.  Most of the towers in that range are guyed with wire, which I would like to avoid.

I will add you to my double beers list.

btw I did go back and read some old discussions that were listed above.  Similar reactions then a bunch of irrelavant stuff. (UH I think beer is relavant tho lol)

UMMMM JUST THE FACTS MAAM LMAO!!!

Just kidding here..... I want to hear all comments .... good bad or indifferent.

Drink beer and be happy.

ya never know, It just might work some how?

OK now on with the show.

Byndhlpng

[Norm]

Hey ! slow down I lost track was that 12 beers

and 7 blades or 7 beers and 9 1/2 blades oh wait

there goes another blade 2 beers ago ! LOL !