Author Topic: Why Wood? (Read 6145 times)

ffoegw · « **on:** November 17, 2006, 01:34:41 AM »

Yes, the summer is over and I am now once again doing vawt stuff.

I am building some new blades for my vawt and will post pic's when ready.

Building them using polystyrene struts cut to a NACA 18 airfoil and strung along a pvc frame. I have covered one with a stretch poly film which serves as a wonderfully smooth skin over the very light airfoil skeleton.

It is about 1.5 x 3 ft and weighs less than 1lb.

It occured to me that hawt blades could be manufactured in a similar way using an airfoil template which slowly decreases in size to the outside.

Anyone try this yet or is carving wood still the preferred method?

Geoff

vawtman · « **Reply #1 on:** November 16, 2006, 07:45:26 PM »

Geoff any chance for a drawing of what your proposing.Thanks

DaveW · « **Reply #2 on:** November 16, 2006, 07:57:52 PM »

I don't know about other locales but the wind gusts in west Texas have me thinking about ironwood instead of pine, spruce, or cedar. Anything lighter than clear pine would probably not last longer than a week. I envy anyone with the winds steady enough to even consider such a project. I have added guy wires out to the center of the blades and they just break the tips off faster. A strong design with a controlled flex is my goal.

stephent · « **Reply #3 on:** November 16, 2006, 09:26:38 PM »

Osage Orange (hedge apple/BoDark) would be ?? harder then heck to carve, never rot and stronger then a mule.

DanB · « **Reply #4 on:** November 16, 2006, 09:50:53 PM »

strong.. but heavy, so the forces trying to tear things apart are greater.

I think the best strength/weight ratio will be conifers. Blades made from wood on HAWT 's should not be coming apart unless something is hitting them (or they are hitting something) - or... the alternator is letting them run way too fast. I think if you use spruce or pine or fir.. or something like that, you have a good safety factor and the material should not be a problem.

Osage orange is a nasty choice in my opinion. Past experience with it... you carve it a bit and it moves around - its tricky stuff to work with.. and... it's fairly poisonous if you breath the dust. It's heavy...

If your patient and dont breath it it would probably work but it would be far from my first choice.

bigdan · « **Reply #5 on:** November 16, 2006, 10:53:04 PM »

Have you thought about fiberglass cloth covering the wood? strong,light and hard.

coldspot · « **Reply #6 on:** November 17, 2006, 03:41:18 AM »

"Osage Orange"

As for wind turbine blades, ?

But as far as for

"archery self bow"

This is the wood to have and use,

Bamboo Backed, laminated is even better.

Thats something I was waiting to ask untill

I was ready to carve some myself-

Anybody here done any backing/building with bamboo or rattan or their skins?

Bow builders are using and liking these.

I have only carved 4 self bows so far, (one each for my kids), Rattan ones, lightest pulls around 30 lbs @ 28", two way above legal hunting weight, 40+ lbs @ 28", and funny as it goes, first one @ 41 lbs @ 28"

?

My $0.02

ffoegw · « **Reply #7 on:** November 17, 2006, 09:08:51 AM »

vawtman,

Need to make a correction. It wasn't stretch poly it was shrink poly which I used.

There is a big difference.

Fortunatly it is transparent shrink poly and so all i have to do is take a photo and you should see the polystyrene and pvc skeleton through the shrink poly skin. Which is good because I really suck at drawing.

These are linked images and so should not take up space on the forum.

Otherwise you can go to photobucket here to see the pic's:

http://s114.photobucket.com/albums/n278/VerticalAxis/VAWT/

<center>

Photobucket - Video and Image Hosting

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regards

Geoff

DaveW · « **Reply #8 on:** November 17, 2006, 02:04:08 PM »

The problem is the spring time gusts. It can go from 30 mph to 105 plus in a half second or so, not enough time to furl, and the blades flex. If I set for earlier furling, I don't get the power I should in the steady winds. Just kidding about the ironwood, but the frustration mounts as a set of blades slaps the pole or the tail and sheds pieces. These things are out in the middle of nowhere and run unattended most of the year, its mostly the spring breezes that tear them up. Next I'm going to try laminating some stronger stock in the midst of the pine or cedar and see if I can get less flex. After that comes mounting the blades out a foot or so from the pole and trying to figure out a tail to furl it all.

Ungrounded Lightning Rod · « **Reply #9 on:** November 17, 2006, 02:05:23 PM »

strong.. but heavy, so the forces trying to tear things apart are greater.

That's true of the forces of their own weight and motion.

But the forces of the wind don't care about the weight of the blades - just the geometry and motion.

So a heavier blade with the same strength to weight ratio can handle a heavier wind load. Thus strength to weight ratio is not the right (or at least not the only) factor to consider.

ffoegw · « **Reply #10 on:** November 17, 2006, 03:18:37 PM »

I went light because of Newtons Law.

Acceleration = Force / Mass

The lower the mass the greater the acceleration.

Therefore should be a better low wind start.

Also don't want to be so concerned about centrifugal forces riping apart the structure which extends the blades into the wind when it speeds up. Mass plays a large part in those centrifugal forces also. Or is it a lack of centripetal forces to hold the structure together?

Maybe it should be said a different way:

With a smaller mass less centripetal force is required to hold the structure together while rotating about it's vertical axis.

hhhhmmmmmmmm

Geoff

vawtman · « **Reply #11 on:** November 18, 2006, 08:42:12 AM »

Geoff that looks really cool but i think you should give the blades a little weight especially for a vawt.

Heavier blades will start just as easy and keep momentum better.My opinion

One test i did with just styrofoam for blades didnt work very well.

Give her a whirl and see.

I wonder how mr sun will react to that film.I could see it getting pretty hot inside.

Have Fun :>)

rotornuts · « **Reply #12 on:** November 19, 2006, 01:20:03 PM »

Geoff, That's fantastic

When I was playing with Vawt's a year ago I was intentally trying to get the effect you've created here.

The effect is a sinusodal leading and trailing edge. Proven to have a significant increase in lift and reduction in drag. Look up tubercles or humback whale fins. It's all from the world of biomimicry. I've been too busy to do anything in the last year but that process you've used there is brilliant and simple.

Could you please tell me more about the shrink fit poly.

Here's what I was trying to do.

ffoegw · « **Reply #13 on:** November 20, 2006, 10:47:09 AM »

Hey bigdan,

While building my vawt I often think in terms of what a sail boat does to sail upwind.

It uses sails very effectively which are strong, soft and flexible.

Soon find out when I put it up.

regards

Geoff

ffoegw · « **Reply #14 on:** November 20, 2006, 10:55:40 AM »

Hello rotornuts,

I'm just using the shrink poly sold to temporarily insulate windows during the winter. If you live in a northern clime you should be familiar with the stuff.

A more viable shrink poly would be the stuff used to shrink wrap boats in marina's while they are stored for the winter.

A google search for either should give more info.

Didn't know that the sinusodal leading and trailing edge airfoil may be more advantageous.

Need to do some more research of my own I guess.

The technique I used is similar to the method used to make WWI type bi-planes where the wing skeleton was covered with a cloth material and then brushed with a "dope" which made it shrink and harden.

regards

Geoff

ffoegw · « **Reply #15 on:** November 20, 2006, 11:15:56 AM »

Yep, found this rotornuts:

"The humpback whale (Megaptera novaeangliae) is exceptional among the baleen whales in its ability to undertake acrobatic underwater maneuvers to catch prey. In order to execute these banking and turning maneuvers, humpback whales utilize extremely mobile flippers. The humpback whale flipper is unique because of the presence of large protuberances or tubercles located on the leading edge which gives this surface a scalloped appearance. We show, through wind tunnel measurements, that the addition of leading-edge tubercles to a scale model of an idealized humpback whale flipper delays the stall angle by approximately 40%, while increasing lift and decreasing drag."

It's on this web page:

http://cat.inist.fr/?aModele=afficheN&cpsidt=15697700

Thanks for the info.

Gonna go see if I can find some pics of a whale fin with tubercles now.

Geoff

ffoegw · « **Reply #16 on:** November 20, 2006, 11:27:52 AM »

rotornuts,

cool article here with a pic of a whale fin with tubercles.

http://www.aero-news.net/Community/DiscussTopic.cfm?TopicID=1077&Refresh=1#

Geoff

rotornuts · « **Reply #17 on:** November 20, 2006, 05:54:12 PM »

Now you can see what you have inadvertently done. Very nice.

I live in Edmonton AB so I'm familiar with the "Winter window". Good idea.

Here's a PDF that I saved about a year ago. just right click and save it to your computer and add the .pdf extention as it will not open from here.

badmoonryzn · « **Reply #18 on:** November 22, 2006, 01:37:24 PM »

I am interested in the VAUT type of wind mill and I also like your blade design. I have built many RC airplanes and gliders and I am familiar with this kind of building. The hobby shops not only have great super glues, but they have a plastic covering for the wings of model airplanes. It is a sticky backed shrink wrap. It comes in tons of colours, sizes and thickness. At the moment I am having a damn brain fart and I can't remember the name of the first stuff from back in the seventies. Oh yea, monocoat I think. I have used it for just about everything, and I used it to cover my helicopter blades and it added water and fuel proofing plus the added strength was quite remarkable. Amazing stuff! I would like to see some more information on the type of rotor you are working on. I was thinking it would be able to control the overspeed via a mechanical type link. Good luck and have fun!

Badmoon

ffoegw · « **Reply #19 on:** November 25, 2006, 08:24:17 AM »

Badmoon,

Thanks for the great info.

I did a google and some stuff called "coverite".

I learned the technique from my father who joined the British Fleet Airarm at age 15 as an Aircraft Articifer and told me lots of stories.

Here is the coverite link:

http://www.businessvision.net/Edge/Main.asp?D=%7BE7093310%2D47F6%2D4476%2D851C%2D97469D289A15%7D&
;PageType=Product&CategoryID=686570&SKU=COVQ0303&DisplayMode=Category&PageNumber=1

Geoff

ffoegw · « **Reply #20 on:** November 25, 2006, 08:31:51 AM »

Badmoon,

I am thinking that if overspeed is a problem I can used centrifugal forces to make a weight pull the blades into a stall.

Once it slows down the weight would return and the blade recover.

I am going to fully suspend the blades on a vertically rotating platform similar to the partially suspended (hinged) blades on the videos in the following link:

http://s114.photobucket.com/albums/n278/VerticalAxis/VAWT/

Geoff

badmoonryzn · « **Reply #21 on:** November 26, 2006, 05:12:49 AM »

hey geoff,

I like your blade designs I forgot all about building somthing that way. Why not, they were plenty strong, I just wonder how long mono coat will last outside all the time. I guess I will see, as I got a 1/2 hp 28 volt dc motor today to use on my vaut. I still am having problems with my woodcarving. I screwed up another blade. Oh well, wood heat. lol I'll get it down. Do you have an email? Anyway I hope you see this as I have some questions about your photos and video clips

Badmoon

ffoegw · « **Reply #22 on:** November 26, 2006, 08:43:38 AM »

Hi badmoon,

You can email me at "ffoegw at hotmail dot com"

Regards

Geoff

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Author Topic: Why Wood? (Read 6145 times)