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Forum Index : Windmills : Coroflute Blades
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew As many of you already know, I make my blades out of a plastic sigh material called Coroflute. In the USA, it's called Cloroplast; same stuff. It's basically the same as corrugated cardboard only it's made from very tough plastic. 
This is a small piece of the stuff. I'm using the blue tape as a background so you can better see how it's made. 
Here it is stand on its end. See the little ribs? This is 4mm Coroflute. I use 2mm as do many who build and fly R/C gliders and sail planes. In fact, I'll be building a new plane for myself out of it soon. The plane will feature an 8-foot wing span with one dihedral. The wings will bolt to the welded aluminum fuselage, which will also house the electric motor (for days without thermals), speed control, radio receiver, flight as well as power-assist batteries, servos and anything else I've forgotten. It will use "wingerons" which are merely ailerons (a little flap along the trailing edge of each wing) and a "mixing" radio. With only two servos, it'll go up, down, left, right, roll, etc. Anyway, back to the Coroflute. What I'll do here is post pictures and a running tutorial telling anyone who wants to build their blades the same way I do exactly how I do it. I took pictures all the way through an entire build. For those of you who think these blades are too flimsy, let me set you straight; they're bullet-proof! Each blade consists of a folded and glued single piece of Coroflute sheet and a wood (I used pine since it was lightweight, strong, costs next to nothing and readily available) and some well-placed globs of cyanoacrylate (CA) glue. More on the gluing later. 
Layout is key here. Once you dab on the CA glue, it's history. You must be accurate in laying out, marking, cutting and gluing. 
I use a 2' by 4' piece of "MDF" as a cutting and laying-out surface. The Coroflute is held in place using a metal ruler and a vice-grip clamp. This stuff is really slippery, so you have to make sure it's down tight before you draw on, cut or glue it; really important, even crucial step. 
Accurate measurement means starting in the same place each time. I use a flat surface (carpenter's square here) on one side and I butt both the work and the ruler against the same vertical surface to make sure each is equally places. 
This shows a sheet of Coroflute cut into a square, which is 8" wide parallel to the plastic ribs and 48" long. It will make two 4" x 24" blades when it's done. The yellow-handled screwdriver is what everyone else uses to crush the coroflute. I do it another (easier!) way: 
This is what I use. It's the little tool you use to shove the rubber welt into the slot when you re-screen an aluminum window screen. Note it has two ends. We use the rounded end and not the grooved end. 
This is the end we use and all it's used for is to "crush" one side of the coroflute so it will fold easily along the line. More on that later. 
Look closely and you'll see a little valley between the two sides of the wheel. This makes two little "knife" surfaces, which will cut the coroflute. We don't want to cut it, just mash it. Use the other end! Really, really, really important: The fold is made so that the ribs of the Coroflute are running front to back. That is, leading edge to trailing edge. This makes for built-in "ribs" as well as adds to the strength of the blade (or wing). The wood spar takes up the load along the length of each blade preventing it from bending under load. So when you're cutting things out, remember which way the ribs are running and don't cut things out the wrong way! Basic Rule: If it folds really easily, you've goofed; start over! Sorry, them's the rules. 
Note here that there is a metal ruler on EACH side of the coroflute. I did this to show that there needs to be a large flat surface on the back side of the fold or you'll "crinkle" the fold and that's not part of the plan! 
Here's what I use instead. It's a plastic drywall applicator (less than $1 @ Home Depot). It spreads the bending force over more surface area than if you were to use merely your hands. The next few pictures show how to lay things out prior to making the folds. Pay strict attention that your work is always clamped to the work table. If it slips, you start over; it's that simple. No room for errors with this stuff! 
This is an end-view of a locking clamp securing the work to the table. There is a metal ruler on top of the coroflute, then the plastic sheet, then the work table and the clamp sandwiches it all and holds everyone's place. 
This shows a sheet of creased coroflute plastic just prior to its being folded. 
I've begun the fold and am using a roll of blue tape to hold up the handle on the plastic drywall knife so I can take a picture of the whole shebang. 
This shows a flat piece of wall-trim board clamping a 4-foot blade section. 
Here's where we're headed; a nearly-perfect symmetrical-section blade! 
Even though you may think you were born with calibrated eye balls, always use the proper tool to mark your cuts. This shows how to mark where a blade spar will be cut. The blades are 24" long and the spar is the same length, but 4" of the spar sticks out at the "root" end of the blade. This gives us something to attach it to the windmill hub as well as makes it easier to glue-shut and trim the blade tips (more later on). 
This shows laying-out and positioning of the blade spar. It is centered and is 24" long, but sticks out the root 4" and is 4" shy of the outboard end (tip) of the blade. Glue it in place using clamps before you fold the other side over and glue it in place.  This is a close-up of the spar layout. Go slowly and make everything nice.
Here's a little trick I use to make sure the spar is parallel to the edge. I set my square to the exact measurement, then use it to check the other end. Don't glue things until you've placed them and marked them with a pencil while they are clamped in position. Doing this, all you then have to do is dribble the glue down the marked out area and use the same lines to place the spar, then clamp it down. If you're in a hurry, while the spar is clamped and glued, re-glue the edges and use "kicker" for an immediate glue set! 
This shows the glue. The one on the left is "Gap-Filling" (thick-ish) CA while the tall bottle is "Kicker". The CA achieves full strength in 2 hours, but if you spray it with the kicker, it hardens immediately. It's not always possible to spray the glued area with kicker; it's used mostly on edge and exposed seem glue joints. 
This shows a little trickle of glue before the opposing half of the blade is mashed together. Nothing fancy! 
This shows how after glue has been applied to both the spar and the trailing edge, a flat board is clamped on top and the whole thing is left for 2 hours to cure. 
The more the merrier. Remember, with CA glue, you don't get a 2nd chance. It's very unforgiving stuff. It'll bond your fingers too, so be very careful using it. If you get it in your eyes, shoot yourself! 
This shows how to close off the wing tips. Just trickle a little CA glue on the inside on one side of the coroplast, then clamp it in place and let it cure. 
Once the glue cures at the wing tip, find a suitable radius to use as a cutting template (I used my faceplate) and first trace the cut with a pencil, then clamp the form in place and use an exacto knife or razor blade to trim off the end. 
Here's that tip cut off and that's the exacto knife in the middle. 
I fashioned a tail using coroflute as well. Unfortunately, I made the tail too small and when I tested the windmill on my test stand, it tended to "precess" in the direction of spin when the wind slowed. 
To cover my mistake, I merely cut a higher tail section and overlaid it onto the existing tail, smeared it with CA and "kicked" the seems. Hey, it's a "test" windmill so a little oversight is okay this once! 
My "tail goof" is only really obvious when you look "through" the tail with the sun on the other side. 
Finished project: Here is is on the test stand spinning around in my front yard further convincing my neighbors the guy next door is a nut case! I'll try to figure out how to make a movie and post it on You Tube! Oops! Almost forgot to show you how much one blade weighs: 
That's 4.2 ounces for a 4" x 24" blade with spar. Due to different wood densities, the 3 blades weiged 4.1, 4.2 and 4.3 ounces. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Jarbar Senior Member  Joined: 03/02/2008 Location: AustraliaPosts: 224 |
McGyver, most informative and very funny.My eyeballs are constantly re calibrated each visit to the optometrist.To make an asymmetric blade could you not offset the spar similar to what has been done with PVC blades available on this site.Great step by photos and instruction.They may even lend themselves to be twisted like the neighbors think about the builder. Anthony. "Creativity is detirmined by the way you hold your tounge".My Father "Your generation will have to correct the problems made by mine".My Grandfather. |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=Jarbar]To make an asymmetric blade . . . Yes and more: The spar in the glider wings I make out of this same stuff are cut a bit differently, but glue up the same. To make an asymmetric section "Clark-Y" wing (or blade), I cut the fold-over part 1/2" wider than the bottom section. When the trailing edges are matched up, with the spar about 1/3 of the distance back from the leading edge, it makes a near-perfect air foil. The bottom chord remains flat, while the top rises to an apex over the spar, then slopes gently to the trailing edge, where it is CA-glued. I use a piece of coroflute cut parallel to the grooves between ribs with one side of one square cell cut out and use this arrangement as an aileron. The cloroflute sheet cut this way and hanging on only one side can bend back and forth indefinitely and it never breaks. When one cell is cut out for the length of the aileron, it leaves a little "U" shaped channel. I glue a portion to one side of the "U" between the wing top and bottom sheets and the other side of the U becomes the aileron. This cloroflute stuff is amazing! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Mack Looks good so far I cant wait till you get the Genny coupled up and see how it handles that with the symmetrical blades. All the best Bob Foolin Around |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Balancing Act Just so you know, Saturday was my 61st birthday and I told everyone what I wanted most of all was to be left alone so I could re-build my little backyard windmill. I got my wish. Remember I said the blades varied in weight? One was 4.1 oz, one was 4.2 oz. and one was 4.3 oz. I dug through my damfino drawer (damfino what's in there!) and found that a half-inch 8-32 screw weighs exactly 0.1 ounce. How handy is that? At the top of the spar on the two heavy blades, where the spar holds the sides of the blade surfaces apart by about 1/2 inch, I drilled a hole and threaded the screws in place to balance things out. It worked perfectly; the thing is balanced to a tee now. I shot a couple of movies of it running a bit and will try to upload them here to the forum. If that doesn't work, I'll have to see if I can figure out the You Tub gig and if it goes that way, I'll come back here with a link for everyone. How's that for a "senior moment"? Forgot to download the damn pictures: 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Techno-Dummy Strikes Again! Well, you know what they say, "Things get better with age." If that's true, I must be approaching perfection, eh? I actually figured out all by myself how to make and post a video to Youtube. Probably no big deal for the rest of the crew, but it's "over-the-top" for me! I didn't realize the thing recorded sound too, so I just stood there for the first one. Realizing my lack of understanding, I did a second video and talked it through. 
I'll add the second video on an "Edit" in a few minutes. Gotta put it up on youtube first. Okay; I'm back with that second link. Hey! The sound actually worked on the second movie!!! Enjoy: MacGyvers Backyard Toy Windmill Second Link .....Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101 |
Hi Mac You will be putting that Gennie on a 60 ft. 19m. Tower?...Right... 
It spins pretty easy in the light winds. You should try to get it higher, to see how good it will do. Ron THE Pirate. stealing wind & solar energy is fun |
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niall1 Senior Member Joined: 20/11/2008 Location: IrelandPosts: 331 |
hi MacGyver i enjoyed the videos...looks like that machine really wants to go for it , i like the big tail as well ...the model plane builder is showing itself there a bit i think .. 
nice work... erm...why is the sky a consistent shade of blue ?...  niall |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
[Quote=Niall1]erm...why is the sky a consistent shade of blue ?... This is San Diego, mate; we pay a little extra each month for it. We simply think of it as part of the price of paradise, that's all. As far as putting this thing up into the wind, it's basically a pin-wheel at present. If I were to stick it up in the flow, it's scream 24/7 and I doubt I could convince my neighbors it was merely 'kinetic art'. Every now and then it's in the right place at the right time and it spins probably in the neighborhood of 400 or 500 rpm and it gives off a singing whine that increases in pitch and intensity as it accelerates; kinda scary actually!
[Quote=VK4AYQ] . . . cant wait till you get the Genny coupled up . . . That's liable to be a while; still waiting on magnets for the ax-fx. To top it off, I've decided to use 6" x 24" blades on the thing. It will have a mechanical blade-pitching system as well as a flyweight-operated over-speed yaw escapement. It's a bunch of machining and it's not that all that scares me, it's just going to take quite a lot of time until it's a done deal. I plan on doing a step-by-step on the blade-pitching mechanism as well as the yaw escapement mechanism as the builds come together. Until such time, it's going to be one of my now-famous "hide and watch" scenarios, I guess. Hang in there, the older I get, the more time I spend on "me". I've spent the rest of my life taking care of everyone else; it's my turn now! 
Edit: You know that little greenhouse in my backyard, shown in the second video? I just turned it into a windmill-fabrication shed. I added a workbench!
Evening Update It's twilight here now and there's just the slightest hint of a breeze, so still you can barely feel it on your skin. Still in all, the Coroflute blades are so lightweight and well balanced, the windmill continues to spin at about 25 rpm. Nice way to end the day, I'd say. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Great post Mac, video's good too, now we know what you sound like
Thanks for plugging thebackshed.com Good work Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I am surprised at your comment about the quality of the section being a near perfect airfoil. I decided to cut one of my glider wings to a X-section. Here is a slightly blurry pic. . 
This is what I would call a reasonably good airfoil. It is hard to imagine the folded plastic you are using being near perfect at the trailing edge. Folded plastic I would call quick though. Gordon. become more energy aware |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Gordon "Near-perfect" = "Close enough for government work"!
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Gordon I don't know, man; it doesn't get much sweeter than this: 
Side-view of a 6" x 16" symmetrical-section blade on a black background. That trailing edge looks pretty okay to me; it's the leading edge I'm concerned with though, so the view from the back porch doesn't matter much as far as I'm concerned. 
Same section from a different view on a black background. 
Similar view using a white background just for kicks. Bottom line here is just this: These blade sections pictured take me about 4 minutes to lay up and glue together. I'm sure that's a far cry from what it takes to make your wings and as far as I can see, it's pretty symmetrical. These are "driven" blades and what I'm after is a smooth pathway through the wind. The faster I can spill the wind, the better this thing will fly. These three I just made today will be going on a (very) small axial-flux generator. The magnet wheels are only 4 1/2 inches in diameter, using 6 pairs of 1" N52 neo magnets and a new stator design I cooked up (details when it works!). I expect this little windmill to turn around 500 rpm no load! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| dwyer Guru Joined: 19/09/2005 Location: AustraliaPosts: 574 |
Hi Mac i love your symmetrical-section blade so I am wondering if you able to attend the Mackey Queensland Eco Expo and show everyone your ideas in Australia Maybe a board jet tonight?? You are most welcome and visit us ??
Dwyer the bushman |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Dwyer The Bushman Kind words and thanks for the invite. I like the "Free Admission" part, but an airplane ride from California to Australia is a bit over the top for me right now. Another thing, I have time-share condos all over the world (4 kids!) and in fact, my oldest son and his wife are today in Fiji (my kids take advantage of all the time-share condos), yet I've never been to even one of them. I'd rather lock myself in my shop and build stuff. The EcoExpo sounds like it's right up my alley, but I'm going to have to pass. Why don't you go and share all my ideas? You have my express permission to share everything! When I was in kindergarten, the teacher taught us to share everything, even the BIG wooden building blocks (which the boys were certain had been reserved for their use only) and that idea "stuck" with me. Everything I come up with is free for the asking as far as I'm concerned. Thanks again for the invite. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Come on Mac, thats not like you. I would have expected you to whip a plane up over night in the shop from soda cans, and fly in with a set of coroflute props. 
All powered from a home built flux capacitor and a 20 watt solar panel, coupled to a F&P motor. Pete. Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
I'm working on it . . . . Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Xmaswiz Regular Member  Joined: 14/04/2011 Location: United StatesPosts: 69 |
Hi, my first post here. I am looking at using the airfoil you made but using it for a VAWT design for a very small turbine (just starting with all these neet projects). what would you suggest for closing off the trailing edge (since it would become the leading edge)? and love your post! thanks Santa Maria, CA Noel Santa Maria, CA. Noel |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Noel & Mac, Missed Mac`s posting on Coroflute when searching posts on compressed air. By bloody coincidence I fly R/c thermalling gliders(must be a plumber thing) have a level mowed strip in backyard(200acres backyard). By any chance Noel, would you be a plumber? Might be better not to inform me if you are, as would start to think all plumbers are bent the same way. Lot of my customers would`ve agreed with that. Will be chasing up a source of Coroflute (here in the land downunder) pronto. We come from the land downunder. Vic |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Noel Not sure I understand your question. The leading edge is smooth, since it is just a bend in the plastic. The trailing edge is where two flat surfaces come together and are glued in place with CA glue. The trailing edge is rather abrupt, but when you tuck in an aileron tab, it "steps down" the bump and makes it a bit closer to a thin edge. With the type of flying I do (motor assisted most times) that scruffy trailing edge doesn't matter much at all and the speeds I fly are way past soaring speed most of the time. For you to use the blade or wing in a VAWT situation, that would be fine since, to my knowledge, they turn in only one direction, so it would be no different than when used in a HAWT or on a glider wing. An "airfoil" blade on a VAWT creates lift just like when it is used on a plane or on a HAWT and as it speeds up, it's "apparent wind" starts it "flying" and you get even more lift than you would if it were merely immersed in a fluid flow. Of course, if you're using a "symmetrical-section" wing, lift is only determined by angle of attack. If you are interested in the blade creating lift by it's shape, you'll have to bend it into what is called a "Clark-Y" configuration, where the bottom is flat and the airfoil is on one side only. If I've missed the mark here, straighten me out and I'll help if I can. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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