PVC OR ALUMINUM BLADES

[Yianie123.]

Hello everyone.  I’m very grateful for this site and your help.  I would like to build wooden blades, but don’t have the time or space.  I would like to build real PVC  or aluminum blades out of tube.  I’m looking to make real quality blades.  All help is valued.
Thank you.

[makenzie71]

I really like PVC and think it's an incredible material for stuff like this.  The real problems are that it's not UV resistant, it's heavy, it's not very rigid, and it has terrible impact tolerance in cold weather.  I've been rolling the idea of making a concrete airfoil mold for shaping heated 4" SCH40 pipe into blades I could then foam fill for rigidity...just haven't gotten around to it yet.  I expect they would only be good for 36~48" blades, though, because of the weight and flex.

[bigrockcandymountain]

https://www.thebackshed.com/Windmill/articles/ChainsawBlades.asp

This is the method i use.  Select some nice spruce 2x8 lumber and hack away with a chainsaw and power planer.  They cost about $30 for the set and take about an 8 hour day to complete.  That is for a 4m set.  Smaller blades would be faster and cheaper.  Lots of ways to modify this idea for no chainsaw, just a power planer etc.  You can also do it with just one chainsaw pass instead of 2.

[ElSuperFantasma]

I would not use PVC at all.   Those things get brittle, flex too much and look ugly! 

Make some blades out of red western cedar, they come out beautiful enough that will make you feel real bad for putting them out there exposed to the elements.

TGIF -

TSG

[SparWeb]

Hi Yiannie,

I see this question from time to time, it's an easy way to get a simple prop made, as long as you don't care it won't last forever.
Retrieved the old thread where this was worked out in detail by Wooferhound.

Today I made a FAQ out of it, which I hope will thoroughly answer your questions.

https://www.fieldlines.com/index.php/topic,150094.0.html

There's even a calculator program you can download!

[ElSuperFantasma]

Ugly looking things.....

Wood is better I think.

God bless you ALL.

TSG

[Adriaan Kragten]

Already in 1978 we have tested a PVC rotor with tapered blades made out of a cylinder in the wind tunnel. These tests failed completely because a thin PVC blade is very sensible to flutter because of the low torsion stiffness. We also tried aluminium blades but they had the same problem if the sheet is that thin that the Cd/Cl ratio is low enough. Only a stainless steel blade performed well. The measurements for a stainless steel blade are given in my public report KD 616. The design procedure for a tapered blade made out of a cylinder is given in my public reports KD 617 and KD 656 (see my website: www.kdwindturbines.nl at the menu KD-reports).

[Yianie123.]

I greatly appreciate all your comments.  After playing around with AutoCAD and researching various designs, I have com to the conclusion that an 8” radius might give the correct angle for the blades.  Cutting the aluminum or steel may be easy.  Any ideas on curving the metal?

[SparWeb]

Starting with a tube was the intent of the Zub-Woofer blades.

If you're not going to do that, then you need one of these:
https://duckduckgo.com/?q=sheet+metal+roller&ia=images&iax=images

[Adriaan Kragten]

The disadvantage of using a roll bender is that you always end with two straight sides of the sheet as the blade is only bent for the part where all three rolls make contact with the sheet. I have designed and built an hydraulic blade press for the bigger constant chord stainless steel blades of my VIRYA windmills. This blade press uses two heavy hydraulic car jags. This blade press works really fast and it takes only some minutes to camber a blade. I simpler non hydraulic blade press for the aluminium blades of the VIRYA-1.04 is described in the manual of the VIRYA-1.04 given on my website at the bottom of the list with KD-reports. But I think that for steel blades, you need an hydraulic press.

An hydraulic blade press can't be used for tapered blades. So for tapered blades, I think it is better to camber two blades together using a rectangular sheet and grind the sheet in two tapered pieces after cambering.

[MattM]

It is surprising how much force it takes to press brake metal.

We had a 16 ton press for ten foot sections that was only rated for 14 gauge.  The concrete floor shook at anywhere near that material stock.  Metal can hold pretty extreme tension, so be careful.  A small flex in material can launch it across a room if you are not careful.

[SparWeb]

If it's PVC you're looking for, one way to get a large tube is to look for sewer drain pipe.  16" diameter is pretty big.  Not likely to find that in the common hardware store.

Since it usually comes in 30' lengths for the city to bury under roads, what you're looking for are the cut-off ends that are left over from a construction project.  Since it's new construction, don't worry, there hasn't been any sewage running through it yet.  Look around development projects, new houses, commercial buildings, etc.  I see this stuff lying around from time to time.  Once, I even had a 24" piece in my backyard when my kid was small to play with.

But wait...  what diameter of blades are you planning to make?
Do you really need to start with a 16" tube?

[Yianie123.]

Thank you everyone for responding.  I am looking at 36” blades.  The trailing edge will be straight, the leading edge will be tapered.  In seems that an 8” radius curve should work perfectly.

[SparWeb]

For that rotor diameter, you probably only need a 6" pipe.