Can Wind Turbine Blades be Made from PVC?

[SparWeb]

Yes!

Here's a link to a Fieldlines thread that describes in detail how to make simple blades for a small wind turbine (less than 200 Watts) with sections cut out of a PVC (or aluminum) pipe.

https://www.fieldlines.com/index.php/topic,146280
http://fieldlines.com/board/index.php/topic,142104

Many years ago, one of our users was trying to make some PVC blades and was having trouble on a few details. I decided to help out and came up with some plans for a 2 blade prop cut from a single piece of PVC pipe. The original idea came from Zubbly a user who is now deceased and highly missed around here. I helped perfect the props and drew up the plans to show how easy it is to make them. So Zubbly invented them and I (Wooferhound) made the plans, naturally these props became known as ZubWoofer blades.

When the Forum changed from Scoop software to SMF software, the original postings by Zubbly and me vanished. So I am reposting the plans for the PVC props known as the ZubWoofers.

For any kind of serious wind power I would use 8 or 10 inch (maybe larger) PVC pipe. Using smaller pipe will cause the blades to be very slender and thin. Using 6 inch pipe is OK for some fun projects, using 3 or 4 inch pipe is only going to create Yard Art and won't make any Real power.

Start by cutting the PVC pipe to the length of your planned prop diameter. Then mark a line down the length of the pipe to be the Centerline. To mark a good straight line down the pipe I like to push the pipe into the hinged area of an open door, or use a piece of Angle Iron against the pipe to mark the line. Then mark a point halfway down the centerline to be the bolt hole used to mount the prop.

You can control the twist of the blade, just decide what the angle will be at the hub, and what the angle will be at the tip. If you are experimenting for the first time with these blades, then use the suggested angles of 25 degrees at the hub and 7 degrees at the tips.  Put the centerpoint of a protractor against the inside centerline mark on the pipe and find where the 7 degree point is on the inside of the pipe, make your mark there. Next find where the 25 degree point is on the same side of the pipe, and mark that point on the inside of the pipe. accurately mark the outside of the pipe at these points too. Repeat this step on the otherend of the pipe.

 The center of the prop is a circle (or oval) with the bolt hole in the middle of it. The outsides of this circle will be the same distance from the centerline as the 25 degree marks that you marked on the ends of the pipe. I would cut out a thin cardboard circle and wrap it around the pipe centered on the bolt hole mark and trace around it with a marker.

 Turn a metal tape measure around backwards and lay it numbers-down onto the pipe with one end lined up to the circle and the otherend lined up to the Tip Angle mark at one end of the pipe. draw this line onto the pipe, and repeat for the otherend of the pipe.

 All the markings are done now. Since there are no cuts into the circle or through the blades you might want to erase or markout the areas in the center that don't get cut. These areas are the dotted lines in the drawing above.

 Time to start cutting. I think a Reciprocating Saw (jig saw) works great. You can just cut straight into the pipe and get Good results. As shown in the above drawing, if you can angle the cuts you will get better results from this type of prop. However cutting angled cuts into round PVC pipe is not easy to do, and you will need to offset the cut line to get some cuts to line up correctly. You will see when you try to cut it.

Another user wrote a software program to help out an making your angle calculations.

You can find his program here . . .

http://www.otherpower.com/images/scimages/3551/ZubWooferCalc.exe

Hope this helps Ya'll to make some cheap wind power.
Thanks to Zubbly for the inspiration to make the props and the ideas for the drawings !!
Also Thanks to many on IRC Chat who have helped with the details !!

[Adriaan Kragten]

Already in 1978 I have performed wind tunnel tests on a 2-bladed rotor with a diameter of 1.8 m and with tapered PVC blades made out of a PVC pipe. However, the rotor suffered from flutter already at very low wind speeds and therefore I would not advise to use PVC for rotor blades. Flutter is a combined bending and torsion vibration and the main cause for flutter is a too low torsion stiffness. The torsion stiffness is low if the thickness of the pipe is low with respect to the chord and the blade length and if a material is used which has a low modulus of elasticity like PVC. The measurements are described in the Dutch report R 343 D of the University of Technology Eindhoven but this report is no longer available. In November 2016, I have made a new report KD 616 called: "Translation of parts of report R 343 D of June 1978 from Dutch into English. R 343 D gives wind tunnel measurements for a rotor with tapered blades made out of a cylinder". This report can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports.

Three different materials have been tested, PVC, aluminium and stainless steel. PVC has been tested for a thickness of 3 mm. Aluminium has been tested for three different thicknesses 2 mm, 3 mm and 4 mm. Stainless steel has been tested for 2 mm. Only the rotor with stainless steel blades gave an acceptably high flutter speed so only these measurement are given in KD 616. But in chapter 2 of KD 616, the problem with the PVC blades is described shortly. The problem was described more in detail in the original Dutch report R 343 D. So I now will give a translation of this description.

"It was started with a model made out of 3 mm PVC made from a standard PVC pipe (with an outer diameter of 300 mm). This went totally wrong because the rotor started to vibrate above a wind speed of 3 m/s and it rotated only very slowly. If the wind speed was increased op to 14 m/s, the rotational speed wasn't increasing but the amplitude of the vibration was enormously and the blade bent backwards like an umbrella. This is probably caused by the low modulus of elasticity of PVC and the high density".

So PVC blades give flutter problems if the torsion stiffness is too low. The torsion stiffness can be increased if thicker material is used. However, the aerodynamic characteristics of a cambered airfoil are only acceptable if the thickness is small with respect to the chord. So if you increase the thickness, the airfoil will get more drag. For the 4 mm aluminium blades, we have tried to modify the cambered airfoil into about an Eppler airfoil (Gö 804) but this requires modification of the airfoil nose and sharpening of the airfoil tail which is a lot of work. For the final stainless steel model the airfoil nose and tail were only rounded.

In public reports KD 617 and KD 656 I give the methode how to design a rotor with tapered blades using a cambered airfoil with increasing camber for decreasing radius.