Benesh VAWT taking shape

[Chris Bibby]

Made some progress on my VAWT, got the first of two rotors completed, disks made of exterior ply with good coating of paint, blades made of corrugated plastic.
End plan is the mount the two rotors (each 500mm diameter and 1m long) on the end wall of the house with the drag side sheltered and connect to a commercial 1.5kw generator via 4 to 1 step up belt drive.
Blades are jammed in place by second layer of material at the moment, will probably need to glue them, waiting for some wind to have a test flight.


http://www.otherpower.com/images/scimages/9158/ben1.jpg

http://www.otherpower.com/images/scimages/9158/ben2.jpg


Thoughts?

Rgds
Chris

[Mark Parsons]

Greetings Chris,

Nice work!

I really envy the green grass in your photos. All is white outside my home today...

Will a 4:1 gear up be enough RPM for your generator? What is your anticipated cut-in wind speed based on the voltage constant of your generator?

Regards,
Mark

[Chris Bibby]

Mark,

Cut in rpm (can't relate to wind speed) is 26W at 258rpm, 296w at 400rpm and 1142W at 490rpm using a 24V generator from http://www.futurenergy.co.uk/products.html
My expectation (from playing with prototypes) is that 100rpm is not too difficult from a VAWT, hence the 4 to 1 gearing, until i get it up and running I will be guessing, but trying to do as little gearing as possible to avoid compromise of gearing loss.
Now had change of mind (due to my son saying he wanted rid of his mountain bike) and will be using the chain drive off a bike, so will have some ability to alter the gearing (i am guessing that chain will have less loss than a v belt but yet again guessing!).
Just need some wind now to give the first half a test flight and see if it destroys itself

[Mark Parsons]

Greetings Chris,

Your linked PMA specs for model FE1024U indicates 258RPM for 26VDC output.

You stated in a previous posting that your VAWT is 0.5 meter in diameter. Circumference of 0.5 meters is 1.57 meters. TSR of drag type VAWTs runs about 1. Therefore, wind speed increments of 1 m/s will create 38 RPM.

To produce 26VDC from your PMA requires 258 RPM. With 4:1 gearing, the VAWT will need to turn at 65 RPM. This relates to a wind speed of about 1.7 m/s = 3.8 MPH. Not enough power in 3.8 mph to expect to overcome bearing friction. A more reasonable WS expectation is closer to 5 mph. Likely a 3:1 gear ratio will be more appropriate.

A swept area of 0.25 meters x 1 meter (dimensions of the half of the machine collecting wind)= 0.25 square meters.

Power expectations:
P = .5 * AD * SA * V^3 * Eff
Where: P = power in watts
AD = air density ( typically 1.22 at sea level )
SA = Swept area ( in square meters )
V = Velocity of the wind ( in meters/sec )
Eff = Efficiency (typically 0.25 for small projects)

Power harvested from 0.25 m^2 swept area at various wind speeds -
3 m/s = 6.7 mph -> 1 Watt
6 m/s = 13.4 mph -> 8 Watts
12 m/s = 26.8 mph -> 66 Watts

Please correct any wrong assumptions or dimensions in my math.

Let us know how it flies!

Regards,
Mark

[Chris Bibby]

Mark,

Stuck in a hotel in belgium at the moment so had some time to look at your maths.
The VAWT will be 2m tall (i have only completed the first half so far at 0.5m by 1m) the second half will be attached at 90 degrees to the first end on.

Working through your maths, are you saying that the most i can expect to get is 132W in a 26.8mph wind if my VAWT is 0.25 efficient, independent of the type / style of generator it is attached to due to that being the maximum power contained in that wind speed for that surface area? Surley the quality / speed and efficiency of the generator must be a big factor in the calculation?

Will be back at the weekend for a test flight, wind and wife dependent of course so will let you know how it goes. Would appreciate some more info on your power thoughts though.

Regards
Chris

[Mark Parsons]

Hi Chris,

Sorry to rain on your parade.

The biggest factor affecting wind energy harvesting is the Betz limit. Betz was a mathematician that calculated that the maximum theoretical energy that can be harvested from a fluid stream is 59%. This maximum has been proven with experimentation. Essentially you can't slow the fluid or extract so much energy from it that it won't exit the machine. All other system efficiencies work down from the Betz maximum. Blade and aerodynamic efficiency, mechanical friction, mechanical to electrical efficiency. The mechanical to electrical is one of the most efficient conversions at about 90% for PMAs.

Large (2+MW) commercial horizontal machines using best practices achieve a power coefficient (Cp) of about 40%. Smaller (6+kW) commercially available machines offer Cp in the low 30% range. Most DIY machines fall with Cp's under 30%.

http://www.awea.org/faq/windpower.html

The swept area of the Savonius VAWT being only 1/2 of its cross section is certainly a disadvantage compared to a HAWT. This disadvantage also creates the added mass of the VAWT machine causing added inertia losing some of the wind gust peaks that could be harvested with a light weight HAWT. Other than that, my experience building and observing both VAWT and HAWT of similar swept areas indicated the VAWT is about as efficient as a HAWT.

Regards,
Mark

[Chris Bibby]

Mark, parade wet but not despondent.

Understand the calcs now and all makes sense.
Playing with the formula (with efficiency of 0.3 - between savonius and benesh) as a starter, I can expect 201W at 13m/s (29mph) - I originaly started this journey looking for 200W as a replacement for my hot water solar when it is not sunny.
So taking everything into account: 6m's gives 20W available.

So just taking the 200w condition, I would need wind speeds of over 13m's for that to be achievable.

The bit I am struggling with now is how to relate that back to gearing. You say tip speed ratio is 1 for savonius (will see if i can find this for benesh) so 1m's gives 38rpm for 0.5 dia, at a wind speed of 13m/s that would be 494rpm, so gear down if anything and not up.
Similar at lowest charge speed of26W at 258rpm, would need 7m/s wind to get that sort of power so 266rpm, almost exactly the speed needed for the generator.
Where am i getting this bit wrong, help much appreciated Mark,
regards Chris

[Mark Parsons]

Hi Chris,

With all wind turbines, the goal is to harvest as much energy from the wind in your location, with your machine, as possible.

I assume you are planning on battery charging by selecting the 24V PMG?

Sizing the gear box for a twice per year wind gust of 30 mph is not very practical. Have you investigated an average wind speed map for your location?
http://www.bwea.com/noabl/index.html

I would stick with the 5 - 6 mph cut-in speed plan. That is about where there is normally enough power in the wind to overcome friction losses and spin up to cut-in speed. I would start with a 3:1 gear up ratio and see how close that works for your machine. If you find it spends a lot of time spinning just under cut-in then change ratio to 4:1. If it is having a hard time starting to spin then ratio down to 2:1. My Savonius machine uses a 6:1 gear up. My diameter is 0.9 meters, so spins slower than your machine. My PMG has a 13V cut-in of 330RPM.

The TSR changes considerably with load. A TSR of about 1 is a loaded value used by most Savonius builders. Unloaded your machine may run with a TSR closer to 1.5 or higher. As you load up the machine by drawing energy from it and putting into batteries the speed will be reduced from its unloaded possibility. One of the advantages with a drag type machine is the amount of torque available when heavily loaded and spinning much slower than the wind. Most horizontal machines just fall into stall and can't produce this torque range. Your machine will spin as fast as the available wind power will provide enough equivalent power from the PMG into the load.

Power = Torque * speed / constant = volts * amps
Energy = power * time

Does this help?

Regards,
Mark

[Chris Bibby]

Mark,

Yes will be charging batteries, but still struggling with the gearing, the way my mind is working is:

1. In a wind speed of 7m/s I will have a power of 31W available from my Benesh if I have an efficiency of 0.3.
2. In a wind speed of 7m/s with a TSR of 1 my savonius should produce 266rpm.
3. My generator produces 26W at 258 rpm so it is balance? (this is where i go wrong)....

If i use a gearing of 3 to 1, my benesh would need to be assumed to turn at 88rpm in a 7m/s wind. What will cause the TSR to drop so much in the calculations, surley if I only have a maximum of 31W available in a 7m/s wind then I won't be able to charge before that?

Is it possible to produce the 26W at 88rpm even though the calculation would show that only abot 2W of power is available, thats the only way I can get my head around what you are saying?

Hope I am getting my problem accross?

[Mark Parsons]

Hi Chris,

Do I understand your concern as: PMG power output response vs. wind turbine power response?

The chart shown at http://www.futurenergy.co.uk/FE1024U%20(406).pdf is a wind turbine power response graph, not a PMG power response graph. I also question the accuracy of the RPM numbers recorded. Between records for 5.5 and 6.5 m/s wind speeds, the PMG RPM changes by 6 and the power output changes by 90 watts - unlikely...

Every PMG provides a linear power output relative to RPM into a fixed load, i.e. each doubling of RPM is double the power (into a battery bank the RPM base reference is at cut-in). The wind power response is a cubed function, i.e. each doubling of wind speed (WS) is 8 times the power. There is no way to match the 2 response curves across the range of wind speeds.

To run your machine on a 1:1 gear ratio means no battery charging at all until a WS of 7 m/s. You would be missing a lot of small charging energy between 3 m/s and 7 m/s which is likely where the majority of the time the wind speed is.

IMHO, I still believe setting up for 2:1 to 3:1 gear up ratio is the place to start.

If i use a gearing of 3 to 1, my benesh would need to be assumed to turn at 88rpm in a 7m/s wind. What will cause the TSR to drop so much in the calculations, surley if I only have a maximum of 31W available in a 7m/s wind then I won't be able to charge before that?
Is it possible to produce the 26W at 88rpm even though the calculation would show that only abot 2W of power is available, thats the only way I can get my head around what you are saying?
Power into batteries = power harvested from wind. No more, no less. The machine will only spin as fast as needed to produce equivalent power into the batteries. This means TSR drops very low during low battery charging wind speeds. TSR will rise as increasing wind speed (power) quickly outpaces PMG response. Observationally you will see that your machine spins up to cut-in fairly linear to wind speed and then stays around that RPM until the wind speed increases substantially.

I apologize for any confusion. I've played around with motors and generators for most of my life. I don't always remember to explain many of the fundamental things. Wind turbines are fairly new to me as well and it has only been the last year or so that I've gotten my head somewhat around them.

Regards,
Mark

[Chris Bibby]

Thanks Mark, still not fully understood but enough to move on with.
Forecast of 30mph gusts were enough to get me to strengthen the blade mounts and get ready for a test flight, ended up using metal tie strip folded round the blade profile top and bottom, pop riveted together to trap the blades and some small angle brackets to screw it to the end plates, all seems substantial.
Set it up on the gate entrance on the side of the house and it has survived a very windy night unscathed. Was quickly at blur speed. I think the addition of a cycle computer is needed to measure the rpm and tip speed, should add some more interest to watching it as well.
Some vibration at very high speed that set the gate support off, will need to have a proper look at that but I think it is the pillow bearing not being quite central in its own mount that is causing it, they are self leveling but appear not to have.
Nice to see it spinning so well, the bearings have eased off as well so spins freely now.
The gearing on the bike I will be dismantling has from 2 to 1 to 3 to 1 on it so should be ideal for what I need.
Time to get on and finish the second section of turbine as I now have the threaded bar i was short of.
Thanks for the info and support, will let you know how i get on with the next stage.
Regards
Chris

[Chris Bibby]

Well, more progress, both sets of blades have steel band added for strength:
http://www.otherpower.com/images/scimages/9158/side1.jpg

Mounted to hinged pole
http://www.otherpower.com/images/scimages/9158/end1.jpg

Pole lifted and guy ropes attached to the top:
http://www.otherpower.com/images/scimages/9158/benup2.JPG

Then the sun set and the wind stopped....

[Mark Parsons]

Greetings Chris,

Nice idea using a pipe for support of bearings.

You must have had some wind by now. How's it spinning? Much noise transfer to inside of house? Got your PMG installed yet?

Thought you were going to install against wall to see if wall aided turbine speed?

Regards,
Mark

[Chris Bibby]

Mark,

After a test flight fixed to the garden gate frame, I lay in bed listening to woooosh brrrrrrrrrrrrrr as the wind picked up and the 'out of trueness' of the mounts became obvious, resulting in me taking it down at 4.00am in a gale and my wife saying 'that goes on the side of the house over my dead body'.
After a re-think I went for the scaffold pole mount fitted to the end of the garage so not getting the benefit of the wall i had planned.
I finished re-enforcing the welds this afternoon and got it back up just as the wind was dying down.
I fitted a cycle computer that I had in the garage, and if I got my sums right (put in a circumference of 167cm) then every 1km/h on the speedo equals 10rpm.
Watching it, it was very easy to get 80 to 100rpm, when it turned it made at least that rate, otherwise was stopped. Max I saw during a gust was 285rpm (estimate about 25mph wind).
The bearings seem to be freeing up, so I hope that the wind speed needed to get it going will reduce with time.
I have not conected the pmg yet, even though I now have it. I want to try the benesh and mount out first to make sure all is ok.
Fitting guy ropes ahs stopped a lot of the swing, but I am amazed how much twist the pole gets when it starts to spin, may need another brace.
Seems quite smooth when its turning, need more time to see if i need to work on the balancing.
In terms of noise transfer, I can not detect any from inside the garage, even though it is a single brick wall, however the woosh at slow speed each time it turns would probably have been enough to stop me fitting it in the original position.
20 to 30mph gusts due over the weekend, so will give the structure a good test.

Regards
Chris

[Negru Valea]

hi Chris,,

How is the vawt going? do you plan to up scale.
Me, i am in the planning stages of a vawt with guided vanes. Hope to build a 3.5kw (80kg) or a 5kw (171kg) vawt!!! I must say i find it daunting at the weight of the 5kw generator. The overall vawt might be around 4m to 4.5m and 1.2m or 1.5m wide. The idea behind the guided vanes is that the returning blades are shielded from the oncoming wind and increasing its efficiency

http://www.freepatentsonline.com/6740989-0-large.jpg

[Negru Valea]

Here is another promising item let hope water does not go up in price

http://www.runyourcarwithwater.com/?hop=stratcon&gclid=citjt4oxw5ecfrsfagoddjkwcw

[Chris Bibby]

Quick update, in the strong winds we have had I have been able to get about 24V in 30mph winds, enough to blow the fillament of the bulb i connected to pieces. The issue i have to look at now is the amount of loss due to drag.
I used 3 pillow bearings with high friction and a chain gear set to the pmg, all giving quite high friction force, playing with the gearing still makes it hard to get it started in anything less than about 15mph winds.
My thoughts were all based on the fact that the vawt would be a low speed machine, but with the chain and pmg taken off, so just the friction of three pillow bearings, it would easily turn at over 300rpm in about 20mph winds, so.....
Next step is to remove the middle pillow bearing and hard fix the two blade sections together (not sure why i put a bearing there anyway instead of doing this in the first place), then remove the bottom pillow bearing and hard fix direct to the pmg.
I hope the friction reduction of two pillow bearings and a chain set will reduce the start up speed whilst allowing it to turn faster at higher wind speeds.
The friction of the 3 pillow bearings was so great that it was impossible to do any type of balancing on the blade set, as you could only get about 2 revolutions of the bldes with a good push, so any out of balance was masked by the friction.
Every days a school day, time for some spannering......

Chris

[Chris Bibby]

The result of 2 hours spannering
http://www.otherpower.com/images/scimages/9158/benesh_second_try.jpg

My wind speed meter!

http://www.otherpower.com/images/scimages/9158/wind_speed.jpg

[Mark Parsons]

Hi Chris,

Any new info on your project? Get any power data yet?

I watched my wind turbine tree for a bit on the weekend. The HAWT definitely has the advantage for early start up due to increased elevation, and reduced inertia and friction. However, when the VAWT gets going it sure pumps the amps into the batteries.

Regards,
Mark

[Chris Bibby]

Well Mark, I got some learning from this one....
After the last bit of spannering the benesh was transformed from not moving to being near unstopable. Getting rid of the gearing was the way to go, I was getting over 375rpm, enough to blow a bulb that i connected up 'just to check it was working!' Not sure what power I was getting as the set up was all a bit heath at the time.

I had to go to work the next day, when the wind got up to 45mph, this unfortunatley highlighted a weakness with my design... it was out of balance enought to chatter the genny mount key way into a round hole, this let the genny drop down about 1/2 an inch, placed all the load on the threaded bar in the top bearing, which gave way throwing the 2m length of benesh free on the end of the genny. Result was a damaged main rod on the benesh.

I was a little dissapointed.

Learning from it all:
1. Wood and plastic form for the benesh is easy to make and strong.
2. 4 threaded bars on outside of the disks are good to level everything and keep it in shape.
3. Threaded bar for a main axel is not strong enough, needs to be larger diameter tube.
4. Pillow block bearings can take a lot of energy out, minimise to one on the end.
5. For a small diameter benesh you do not need gearing, mounting on the genny saves one pillow block and saves gearing loss.
6. A Benesh vawt is not always a slow speed machine, 350 to 450 rpm for a 0.5m diameter is easily reached.
7. If you use scaffold pole, mounting the benesh off the side will induce massive twist in the pole as it runs.
8. A benesh needs to be well balanced.

So, taking all that on board, where next:

Main thoughts / issues were due to items 3, 4, 7 and 8 above.

I want a vawt where i can mount the genny on the end of the scaffold pole and drop the vawt down from it. I want to use the scaffold pole as a main axel. I want a VAWT that can be easily lowered when 60mph winds are forecast. I want a tall and thin VAWT, I want a VAWT that i can balance.

Did lots of surfing and kind of ended up heading towards the Lenz2, BUT it just didn't fit my mindset as it seemed to be a rough approximation of an aerofoil, so why won't it be better with a full aerofoil.....

So, after some searching I came across this:
http://club.cycom.co.uk/vertAxis.html

If you read down to the bottom it describes exactly the size of VAWT i was after, plus the benefit of the profile and blade setting, yes i know it is a darrieus, but ticks all the boxes for me.

So progress so far:

Scaffold pole already in place from the benesh, bars will be cut off to give me a straight tube that can be hinged down with the existing set up.
2m length of 50mm plastic down pipe purchased.
The genny will sit on the end of the pole, the downpipe will be over the pole.
600mm of 54mm steel tube obtained, this will form two collars that the blade mounts (steel square tube) are welded to. The collars will fit over the downpipe.

Idea is that I will use just one bearing, the one in the genny, the down pipe will only come into contact with the scaffold in strong wind, to avoid too much force on the genny bearings, and by lubricating the pole it shouldn't damp the speed down too much.

I have made a 2.2m hot wire cutter using nichrome wire and this will be use to cut the blade sections from 2m lengths of polystyrene board (the heavy stuff used for floor insulation), idea is that these will be coated in some as yet unknown substance to make them stronger.

I intend to cut some rectangular sections from the polystyrene with the blade profile cut out of them at the correct setting, these will be split in two and encapsulate the balde, the steel arms will have rectangular flat steel welded to them that will bolt around the ploystyrene blade blocks.....hey presto, a VAWT

Hope the above isn't too much unintelligble drivel, but trying to get across my learning and thoughts for comment. As for the Benesh, well a 1m length is currently fitted to a washing machine tub and bearing, spins as well as i would expect but need a genny to match it, but thats another story.

Regards
Chris

[Mark Parsons]

Hi Chris,

Very nice post.

I experimented with an H rotor but wasn't overly impressed with the efficiency. I used a high cambered airfoil cut from ABS pipe. That may have been the downfall.

Your design idea of pipe within pipe lubed up should work out well for vertical support and radial thrust containment. It has worked very well as yaw axis on my little HAWT for about a year now. I used a bronze washer bushing as a thrust bearing where the 2 pipes interface. The yaw axis spins very freely still and the bronze washer is hardly wore.

I am looking forward to more photos and news of your progress. How are you planning on attaching the foam airfoils to the 'H' spars?

Regards,
Mark

[Chris Bibby]

Mark, to attach the aerofoil current intention is to use a rectangle of polystyrene with the profile cut out of it at the correct angle, will the make a clamp from steel to hold tis in place (welded to the spars). That is my current intention but all depends how well the cutter works!

Any knowledge of a magical material to strengthen the polystyrene, not sure about fiberglass, thinking there must be a resin of some sort.

Regards
Chris

[Chris Bibby]

Well had some blade cutting fun, I guess all the web sites that talk about using a battery charger aren't trying to cut 2m long blades, stone cold. In desperation opted for 240v mains and a dimmer switch....ooooooh, don't reccomend that, the singing wire cut one brilliant cut, went orange and snapped, yee haaah.
So with sensible head on, borrowed a comercial DC transformer from work, took some practice, and got better every go, but results below, look ok to me.
Any suggestions from anyone on how easiest to coat them for strength, fiberglass mat would be messy, must be some sort of paint on stuff?

Chris
http://www.otherpower.com/images/scimages/9158/blade_small.jpg

http://www.otherpower.com/images/scimages/9158/blade_end_small.jpg

[Mario De Castris]

Hello Chris,

I suggest a search on hovercraft construction on one of the many forum on the web, I am not a hovercraft builder myself but I read many posts on both American and European forum about how wire cutting and something called vacuum begging which I think it's got something to do with reinforcing the styrofoam construction with some kind of resin and vacuum process. One address thet comes to mind is,

http://groups.yahoo.com/group/hoverlovers/messages
http://groups.yahoo.com/group/hover-gen/messages/

I hope this is of some help to you.

TTYL Mario

[Kricnit Not]

I have cut with a 60" SS wire using a laptop computer power supply. Would probably still work OK at 2m. Give it a try if you have one laying around. Vacuum on fiberglass will give you the lowest weight but you can also just paint paper grocery bags with epoxy or vinyl resin if weight is not of the utmost priority. I prefer epoxy as vinyl resin is nasty with lots of fumes. I use vacuumed fiberglass with a carbon fiber strip reinforcement and epoxy on my model airplanes as it is very strong and lightweight.

[Harry Singh]

Hi Chris,
I was wondering if you had some sort of template that you followed while making the Benesh blades. For my science far, I am making a smale scale version of a wind turbine with Benesh blades, and I needed some help with finding dimensions for the blades.
Thanks!

[Chris Bibby]

I will have them somewhere, just need to find them! Will post them asap.

Chris

[Chris Bibby]

Had a quick look at what is on this PC, you need to get Benesh's patent us patent number 4838757 from 1989, it has all the dimensions listed, I had an excel sheet with them on but that will take some more digging. You should be able to get the patent from google patents or give me a shout and i will e-mail to you.

Regards
Chris

[Rob Beckers]

Chris, did you finish your VAWT?
I'm curious how you finished the blades (that being the last thing you were discussing when you dropped off the radar), and if the turbine is working now.

-RoB-

[Chris Bibby]

Harry, I found the excel sheet with the cals on it, let me know if you want me to mail them to you.

Rob, The blades are still as you see them in the photo, but up in the loft awaiting some spare cash to buy the matting and resin, in the meantime i nocked up a downwind turbine to get some use out of the pma, working fine so at least getting something back.

http://i425.photobucket.com/albums/pp340/chris_psmith/DSC00930.jpg

No fun compared to a HAWT, far too easy.

Regards
Chris

[Tony Savage]

Hi Chris, To my untrained eye that looks like a great job of cutting out your foam templates. I'm not sure if it is common knowledge outside of the marine industry that polyester resin will "melt" styrofoam on contact. I believe that epoxy resin will work okay but you may have to use a fiber cloth designed for use with epoxy resin. I have seen regular cloth used with epoxy but it takes a while for the resin to soak in as it isn't able to dissolve the styrene binder used in regular cloth. I'm not able to vouch for the finish strength product but haven't heard of any problems. The epoxy is supposed to be stronger. They do make a shaping foam for use with polyester resin but I'm not sure if it is able to be cut using the method you use and is pretty expensive as I recall.

[Pol Van de Perre]

Hi Chris,

I read the entire chain of this post and am intrigued with your attempt to make a useable Benesh. Is the balancing challenge the main reason why you have discarded your quest and eventually went for a HAWT. If you could solve the balancing by greater precision tooling would you go back to a VAWT? Also in the beginning of your post you mentioned that you were planning on shielding the trailing blade. Does anyone have experience on whether this really improves performance? I find the Benesh design very intriguing and would want to create one myself.

Thanks

[Chris Bibby]

Pol, main reason for stopping was finding suitable bearing material and blade material. The bearings were too tight, partly solved by removing the gearing and using direct to the generator, next atempt would be a 'sleeve fit' over the pole with a bearing at the bottom and genny at the top and put it up a bit higher. The benesh was far more satisfying than the hawt i have now and given access to the materials and equipment i would have another go. The blades i used were just strong enough, but i had piccked up the sheet on my travels and couldn't get any more easily.

Chris