My foamboard Darrius

[Norm]

  ....Darrius! Finally after about 2weeks finally managed to curve some 'foamboard' and make a blade for a Darius type VAWT. Using a very sharp utility blade I cut horizontal lines on the foamboard about 1/4 inch...cutting thru the top cardboard and the foam without touching the bottom layer of cardboard....after a few botched tries 2 or 3 ruined boards, 3 or 4 blade sharpenings, and 80 cuts later(there is about 20 horizontal partial cuts per blade.I finally managed the above...kinda resembles the top of a roll top desk. After covering the gaping cracks with white duct tape it turned out like this:     Then with a little bit of plywood I fastened it to a bicycle wheel like this... I took it outside and of course the wind is only like about 3mph so I walked against the wind and it finally started spinning and a gust? of wind and it started spinning about 60-80rpm.but about that time I could see a car coming up Thomas Drive, so I hurriedly ducked back into the shop with my 'contraption' further testing was done in front a window fan at full blast. It goes fast enough to start shaking,(everything is a little out of balance) Think I'll modify it a little, like Pico Turbine. The blades are 30 inches high x 10 inches wide...I have them about 12 inches apart but it was suggested that they could be closer than this 6 inches maybe? Was wondering if the speed could be increased if the angle were changed or the angle could be automatically changed by the use of weights and/or springs to get the optimum speed...I really don't understand how this thing works but knock me over with a feather...It really works and much better than I had ever expected...(Thanks to all you people and especially Shane who got me started on this Darrius thing. Norm.          

[windstuffnow]

  Nice Job Norm,

     You'll find that the blade angle is important.  The smaller the diameter the faster it will spin but will give you less torque.  They are fun little beast's, I've built a number of them and will most likely build more.

      Keep in mind that the Darrieus rotor works similar to the aerodynamic fashion that the horizontal's do.  Because of the rotational path they work in it appears fairly complex but it really isn't.  Airfoils generate lift perpendicular to the wind approaching the leading edge.  In the Darrieus, that relative wind changes its angle from almost straight at the airfoil to nearly perpendicular to it.  So, the amount of lift the airfoil see's constantly changes as it whips around its path.  

      I usually only build small units because of the structural needs of a large unit ( can be costly) and most of my work has been experimental in nature but definately fun!  A 3ft x 3ft unit I built would make 100 watts in a 20mph wind... not super efficient but seemed to work well for its size.

Keep up the good work and have Fun!

Ed

[Norm]

   Hi Ed, Thanks for the encouragement. Is that the one you're talking about,the one on the side of the utility pole? or is that a different one? I'm still trying to figure out how the cam works on that one...and am I ever having fun? ...you bet I am! Norm.

[RobC]

Hi Norm I think you want more of a symmetrical airfoil than a high lift type.  

I would check with Ed to be sure.

[windstuffnow]

Hi Norm,

   The one on the side of the utillity pole was very small, I believe it was about 2ft tall and 2ft in diameter.  The wings on that one were made of flat sheet with a small bend on the edges.  It worked quite well but not very efficient.

   The cam is quite simple actually.  Basically a hub with a bearing that mounts to the main shaft.  The bearing allows it to run free.  There is an offset pin in the cam that holds the rods to the wings and the tail is mounted to the top of the offset pin. The rods are attatched to the leading edge side of both wings and the offset pin.  The rods are allowed to spin free on the pin. (like a rod on a crankshaft).  Once the wind is strong enough to set the tail angle the unit will start spinning.  I should do a diagram...

   The wings should be symetrical for the best lift shown below:

 

This is an E168 air foil and works very well for this type of application.  I pour them in plastic and cover them with thin aluminum (flashing material).  The aluminum is glued in place, the picture below shows the trailing edge installed, the leading edge is then glued in place and a couple rivets are installed to make it more permanent.

Have Fun

Ed

[Norm]

   As soon as I modify the FBD...just a tube shaft with the bearing assembly from a bicycle fork...well you can imagine something like this (the blades in place of the forks and set about a foot apart?) excuse my artistry. and a little bit of testing and then on to something like you have pictured, I was thinking of making cast aluminum ribs and using like you did with the aluminum flashing for the rest of it...and yeah it would be nice to have a diagram of how the cam works. Thanks a lot for the help Ed! Lot more questions I like to ask but I'll have to call it quits for now. Havin Fun in NE Ohio (home of the 'Big Blackout' (:>) Norm.

[Norm]

  Hi RobC and according to Ed you're right about the symetrical part. Thanks for being there! Norm.

[windstuffnow]

   Norm, thats a pretty clever idea with the bike fork, all is machined and ready to go.  The ribs could be made from plywood or other light material with good results.  Alot of airplane wings use plywood ribs to for the wing some only strips of wood to form the ribs, all are quite strong.  Some of them are only glued and stapled together.  The Team aircraft used to use bulsa wood strips in a structural arrangement and glued together.  Another way that works well for small wings is a cardboard form ( like the kind they use for milk cartons-not the waxy kind- or similar) coated with fiberglass resin.  Those are quick and simple and quite strong.  Basically just a tube down the center and the form riveted on.  Also thin aluminum sheet (flashing) formed around a tube and attatched on the trailing edge to form the wing with a tube down the center and rivited make a very nice quick wing.  Lots of ways

Have Fun

Ed

[windstuffnow]

Norm,

   Here is a quickie diagram of the cam for the darrieus.

[Norm]

  Thanks for the diagram Ed. Now as soon as I get some wind around here to inspire me, 2-4 mph just don't get it! (:>) Norm.

[sean]

Good to see you have finished the vawt Norm, i know its the not the best shape but thats just how easy (with a little time even my cardboard job took a cple of nights) and the rib is just off an r/c sport glider. Although the shape Ed uses works better  i think youve made a great toy and might get some power form it....isnt it fun to watch them spin and if you get all the angles right (better ask someone else for those) and the balance then it might spin even faster and smoother. Mine was just mounted on a broom handle no bearings and LOTS AND LOTS of play but it must have hit 200+ rpm in i think 12mph wind but it needed a hand spin to get it started but what fun and it just gets you thinking more, sort of can get hooked to this stuff and i beleive the betty ford clinics dont accomadate for our type just yet!! Lets us know how it goes with that vawt im watching closely

[gumshine]

Hi Norm,

just curious, did you ever get the darrius up and running?  

Do you have it wired for juice or lighting up a light?

I have Ed's vawt kit and want to make a bigger vawt.  I'm thinking of trying his lenz turbine design.  

I like the use of the bicycle wheel.  Something I can relate to.

I really like your common sense approach to all this stuff, and read your posts regularly.

thanks

gums