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Big Al 09-08-10 04:04 PM

Hawts and Vawts
One or two points from one not greatly endowed with wind power knowledge. Bob McGovern's two posts on small wind power seemed full of good sense to me. I have n't been very impressed with much else I've read (Hugh Piggott also seems pretty good) in an subject area which seems to be fashionable and therefore full of charlatans out to make a quick buck .As B Mcg says of the many small wind power systems "..what a poor lot they are.." .I would extend this description to 90% of whats written on small wind systems.

To get to my points, I have a sneaky preference for Vawts somewhat modified by B McG's comments which seemed pretty sensible to me. However Vawts definitely win on aesthetics. Bob mentions the downwind blades are in the wind shadow of the upwind blade. Presumably this point would not be true for the most aesthetic version with helical blades ?

Secondly due to 1/the possibility of at least two bearings to the Vawt rotor , with a third easily added centrally.
2/ Some balance of rotor stresses by using helical blades and extending these above and below the top and bottom bearings.
3/ Potentially stronger blades supported at at least two points for a vawt.
4/ A much lower TSR

..I feel instinctively a Vawt should be able to stand much higher operating wind speeds than a Hawt and therefore be able to extract larger amounts of power from high wind speeds at exactly the time a Hawt has to furl to avoid damage. Less maintenance should be an additional bonus.

Surely these points must be significant in narrowing the gap between Hawts and Vawts. Any comments anyone. Big Al.

Patrick 09-08-10 08:42 PM

From the research I've done, HAWTs win hands down. VAWTs have been tried many times in the past and have all either failed or not been able to compete with HAWT.

If you're dead set on a VAWT, the Lenz2 is a reasonably effective unit you can build yourself. Lenz2 turbine

Big Al 09-09-10 05:00 AM

Patrick , many thanks your response and ref to Lenz. With all due respects to Lenz this looks to be a drag turbine and a "science fair project " 63 Watts indeed !! If I ever get round to it (too many projects !!) I would build a helix bladed lift Vawt and would n't think it worth the effort unless I could get 2-5 KWhr a day.
This might sound pie in the sky but I have the metal working machines to build this and a lucky bonus in that I've just completed a tree house for the grandkids with a lookout tower extending to 10 metres above ground level. Climbing to the top of the lookout tower I noted I have nothing between the top of the tower and the Gargunnock hills 5 miles away to the south west which is where the prevailing wind comes from in Scotland.
I don't dispute your and Bob McG's point hawts win but the point is , is it better to have a reasonably quiet and attractive vawt producing say 200W @ 6 m/s wind speed or an ugly, potentially noisy and more dangerous (more RPM ) Hawt producing say 600W at 6m/s but which has to shut down as soon as the wind reaches real power producing speeds? I don't know and am attempting to find out just what the gap between Helically bladed Vawts and Hawts is ; given the points on blade strength and potential operation in higher wind speeds for Vawts (lower TSR for a given wind speed plus extra bearings and better blade support I made in my post. Rgds Big Al.

Patrick 09-09-10 07:51 AM

Hi, Al. This guy claims his carbon fiber blades will withstand up to 90 mph winds. He doesn't furl the generator because he says in higher winds you will really start to make the power. Home Page

If you do make a VAWT, please keep us posted. Sounds like an interesting project.

nibs 09-15-10 11:39 PM

Have always liked the look of savonius rotors VAWTs, problems exist with bearings, one bearing at the bottom needs to be pretty big to take the side loading, and if you have a bearing at the top it needs to be stayed, unless you are using a substantial axis. Then you will need a gear drive, where in a horizontal axis you can put the blade right on the generator shaft. Blade design is interesting, because you cannot have washout the way you do with aircraft style blades, so you wont get start up until the wind is cranking a bit higher than for horizontal blades. Efficiency will be lower, but they sure look nice.

Wood blades will withstand high wind speeds (lots of aircraft use them) if well engineered, carve your own, I will happily look over your virtual shoulder for design.

Big Al 09-24-10 06:02 PM

Done a lot of reading since my last post (H.Piggott, and the back shed website-full of useful info.These antipodeans mean bizness !!-plus a lot of other websites).
In a maze of projects have at least gone as far as purchasing a Wind Predictor which I should have mounted on my 10 metre look-out tower this week. Things will then go quiet while I measure wind speeds for a month or two-at my age I don't build anything until I have checked out the potential !!
Am struck by the similarities between wind power and metal working (another hobby of mine ) in that the Americans get things done and are very unselfish in publishing helpful info. , the Aussies and Kiwis even more so , and in the UK we now seem to rely on commercial ventures with most inputs coming from people out to make a quick buck , and with very little practical experience . Hugh Piggott , and the Home Workshop site are among the few noble exceptions.
The Backshed site I found amazing , full of good advice , and full of projects producing real power using all the technology tricks you could imagine. However they seem to love Hawts much more than Vawts. I do think however that in the UK where we have less land than the "colonials" and where neighbours and the Nimby syndrome is so strong that Vawts may be the way to go . My reasons are:-

1. Vawts have a better defined footprint , in theory should n't need such high towers, and with a lower TSR (bad )have less chance of impaling a neighbour with an absconding blade(.Mainly good)

2. From my reading so far I'm not convinced that Hawt performance is that much better for the same horizontal footprint. Admittedly Vawts need a higher vertical profile to achieve this-however we do have in the UK as much air above us as the US, OZ and NZ.

3.Most of the objections to Vawts seem to be based on older technology and don't seem so applicable to helically bladed Vawts.

4. The BIG problem of effective electrical generation at lower speeds surely does nt apply to Vawts where the space under the bottom bearing can be used to make a large radius generator , albeit expensive on magnets, WITHOUT blocking the wind path , this space could also be used (altho I doubt I'm clever enuff ) for variable pitching and for centrifugally swithching in of extra, speed-limiting, coils . This again gets rid of a host of problems and is almost impossible to do with Hawts due to windpath blocking..

5.Hawts seem to have a long history of small wind DIY development , most of the new money seems to be going into more advanced Vawts.

Anyway , enuff of my prejudiced ramblings , got a Power predictor to install. Watch this space . While my PW logs data I'll keep reading and don't be surprised if my next post is a diatribe against Vawts !!!

Big Al

nibs 09-25-10 06:56 PM

A thought about starting a Vertical Axis mach popped into my pumpkin while reading your thread. If the generator you use will also motor, you could use a sail switch to start it spinning.
I will bet you 20 pushups (honor system) that a horizontal machine will be the most efficient.

skyl4rk 09-26-10 10:35 AM

My brother has been working on some VAWT designs. He is doing it as a test project, not a working design. He does not report large amounts of power available, but his VAWT is on the ground so he can test different blades, so efficiency is low. However he has been trying a lot of different designs and is improving efficiency and buildability as he goes.

Caleb Engineering, LLC - Home

The latest thing he is working on is a Kline-Fogleman airfoil. This is significant because one could use easily use the wonder material of the future to build airfoils: coroplast.

Kline Fogleman airfoil - Wikipedia, the free encyclopedia

In particular KFm-3 looks like an easy to build airfoil with coroplast. There could be some heat applied to the coroplast to bend it as well (as in KFm-5A), to try for an even more efficient foil. Bending would also add stiffness to the airfoil.

Big Al 09-26-10 05:40 PM

Skyl4rk-Thanks your input. I'm in UK where getting suitable airfoils difficult compared with US and OZ/NZ and even then most of what is available is Hawt directed rather than Vawt.Two points of which Caleb ? may be unaware
1/ There is on web what I thought a very good thesis on small wind by Claude Guillaume , Sandra Algazze and Emmanuel Duc on home wind . They favour Vawts and recommend S2027 airfoil which they measure as giving significantly increased O/P over the other airfoils tested-they are also very good on solidity and aspect ratio.
2/ The backshed website is full of really useful information and technical ingenuity to increase O/P . This is mostly Hawt directed but a lot of it particularly on the generating and control side is applicable to Vawts.

I had n't come across KFm foils or coroplast so thanks for the reference.

My initial thoughts on airfoils of the S2027 type was to build it out of 2 thick aluminium strips Rivetted or welded together ) and machine it to the required profile. Altho I have metal working facilities I'm not sure they would easily cope with modifying the profile for a helical blade or the subsequent bending.This is also an expensive approach. My second thought was to use my Hydraulic press and a die to bend thinner sheet to most of the required profile and bonding or riveting this to wood to make up the rest of the profile . Again I suspect not easy. The backshed guys don't seem to worry too much about profile and still get amazing amounts of power but to get Vawts up near Hawt performance I think I'll need to use every trick in the book ( and even Hawts can hardly turn their nose up at a 16% increase in power by using a simpler and more efficient airfoil )

I shall be measuring and logging wind speeds for the next two or three months but will try and move my thoughts along and maybe even do a few experiments over the winter. An initial thought is to make the bottom blade support , a thinnish discus shape (low drag ) with weak spring loaded vanes popping out of this at rest to give a savonius starting effect , the vanes retracting automatically(to cut drag) under wind pressure as the rotor accelerates. I also believe this bottom plate would allow the mounting of a variable pitching mechanism which could do a lot to improve efficiency altho making this simple and reliable is a challenge. However some of the the revered Jacobs turbines had variable pitching on Hawts (much more difficult ) and are reputed to have been reliable.

While I'm logging wind don't expect any great technical progress but will post anything I find of interest. Rgds. Big Al

Big Al 09-27-10 06:18 AM

Skyl4rk Have had a look at caleb's site. V. interesting as a potential problem for me is manufacture/procurement of suitable Vawt airfoils (aerofoils to me ).
coroplast looks interesting and speaking from a viewpoint of vast inexperience (i.e none) I would have thought lining mould with thin foil (baking foil ? grease proof paper ? ) or spraying with the right compound (WD40 ? ) would ease extraction problem.
His technique of using foam laminates also looks good. He seemed a bit disappointed at lack of rotational speed using these but IMHO the Savonius type (Lenz ?) foils he has incorporated are giving tremendous drag . I like the idea of a Savonius type starter but think it has to be decoupled from the rotor (tapered track ball ratchet ?) once the lift rotor has started. Even better i feel are automatically retracting vanes as per my last post as they would have less effect on wind profiles thro the turbine--unless the Savonius starter can be designed to contribute to a more effective wind profile which ourweighs the drag it contributes once lift forces give a TSR >1.
A final thought -I hate building things I have to spend hours maintaining and would need to convince myself that coroplast or plastic foam would stay the course. How ever at worst they give good ways to produce blades for testing.
My internet skills are limited and I was n't clever enuff to work out how to contact Caleb directly. I will continue to post anything of general interest on ecorenovator but if you want to pass my email to Caleb it my be easier if he contacts me directly.
Rgds. Big Al

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