TheBackShed.com

Forum Index : Windmills : Thinking about styrofoam for hawt blades

Page 2 of 2

Author

Message

Throgdor
Newbie

Joined: 26/01/2012
Location: United States
Posts: 22

Posted: 08:21am 08 Jul 2012

Copy link to clipboard

Print this post

MacGyver said Throgdor

Coroflute Blades are pretty easy to build and if you put a hollow T-6 aluminum (aircraft grade) pipe up the center, it'll stand up to ginormous forces.

I buy the Coroflute (called Coroplast in the States) from a sign maker in Orange, CA. I use 2 mm and get it in 4' x 8' sheets for about $12 a sheet; pretty cheap.

Hope this helps you out some.

. . . . . Mac

Thank you Mac! I have some 1/8" thick coroplast and have often wondered how I might make wind blades out of it.

Questions:
What was the angle of attack and how did you achieve it? The same angle of attack applies to the whole blade?

The wood blades I have are at 15 degrees at the hub end and 3 degrees at the tip. So getting a twist like that with the coroplast could be a bit of a challenge.

T

MacGyver

Guru

Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 06:06pm 08 Jul 2012

Copy link to clipboard

Print this post

Throgdor

I make my hubs with a standoff, which can be bent in a bench vice. You can set the pitch at anything you want. I usually pump air with my windmills, so I set my blade pitch pretty steep; I'm after torque and could care less about r.p.m.

As for whether it applies to the whole blade, yes, the whole blade is the same pitch from the root to the tip.

I've built blades from sheet aluminum that have graduated pitch. The problem comes when you want to attach the spar. If you look up the inside, the inner sides "twist" as they approach the root. You'll have to get creative to attach a spar up the middle; I used flat T-6 aluminum bar.

The way I built these blades was to decide how wide I wanted the blade, then measure half way, THEN add a half inch. This puts the center line of the entire blade half an inch off. The side that becomes a half inch wider gets its trailing edge bent up and over to form a "V" just short of it creating a fold. Then, you fold / bend the other half of the blade such that its trailing edge tucks into that "V" and then you crimp it closed. This creates a symmetrical-section blade.

Here's the trick: Once the blade is formed and BEFORE you crimp down that trailing edge, grab the root and the tip, then twist the blade slightly. Once it's twisted to your desired pitch, crimp down that trailing-edge flap and secure it with a pop-rivit or three and it's a done deal.

You'll notice that each half now sticks out a tiny bit at the ends, which will gladly cut your hands right off for no apparent reason, so trim it off and maybe make a wood plug for the ends. HOWEVER, I used to leave the tips open in case water got inside the blade. If a load of water gets stuck inside, it can imballance the genny and it'll tear itself appart in no time at all.

Have fun!

. . . . . 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

Page 2 of 2

Print this page

To reply to this topic, you need to log in.