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Building and Testing the Blades
9, 10, 11, 12
Title – Basic PVC Wind Turbine – Blades
By – Chad Johnson
Primary Subject – Science
Secondary Subjects – Math
Grade Level – 9-12
|Constructing Basic PVC Wind Turbine Unit|
Testing Blades on Basic PVC Turbines:
- Building and Attaching Blades:
Never make blades out of metal or any sharp edged material because they could cause injury during testing. Blades tend to spin very fast (300-600 RPM) and can easily cut people if they have sharp edges.
Always wear safety goggles when testing.
- To make blades, carve or cut different shapes and sizes out of a variety of materials (wood, cardboard, felt, fabric). Tape or hot glue them to the dowels. Students have made blades out of Styrofoam bowls, pie pans, and paper and plastic cups. Anything you find around the house or classroom can be made into blades!
As the crimping hub can be separated into two parts, you can try different creative ways to attach “blades” to the hub. One of the best blades we ever saw was made from a pizza pie box!!
- Before testing, check that the blades are securely attached to the dowel. If not secured properly, they may detach or deform as you test your turbine in high winds. We recommend using a combination of tape and hot or regular glue.
- Insert the dowels into holes on the crimping hub. It is important to tighten the hub when inserting the blades so that they do not come out at high speed.
- When attaching the blades to the hub consider a few important questions:
- How close is the root of your blade to the hub? What do you think is optimal?
- Are your blades about the same size and weight? Blades that are not balanced will cause vibrations that can reduce the efficiency of your turbine.
- Are the blades equally distributed around the hub? If not you can also have a set up that is out of balance.
- Have you secured the hub after you inserted the blades? If not they can fly out at high speed!
- Want to know how fast your blades are spinning? Get a Hangar 9 Micro Tachometer.
- Safety and Blade Testing Area
- It is important to wear safety goggles when testing blades.
- NEVER make blades out of metal or any sharp edged material as these could cause injury while spinning fast during testing.
- Setup for Testing
- It is important to clear this area of debris and materials.
- Make sure the center of the fan matches up with the center of the wind turbine. You may need to raise your fan with some books or a container.
- Some things to note about fan wind that reduces the efficiency. Fans create;
- Highly Turbulent & Rotational Wind — Blades may spin better one direction than another
- Highly Variable Wind Speed — Wind speed is about 10-13 MPH on high for a $20 circular fan. Wind speeds near the middle will be much different than the edges.
- Limited Diameter — Blades bigger than the fan will not “catch” more wind — they will just add drag and slow down your blades.
- How to Clean Up Wind?
- Want some more “professional wind”? You can try to build a simple wind tunnel. Lots of plans can be found online (search term: classroom wind tunnel or go to www.kidwind.org).
- One simple way to make more laminar — smooth, straightened — flow is to build a honeycomb in front of your fan using milk cartons, 2″ PVC pipe or some other material.
- Going Outside?
- While you can use your wind turbine outside, you must make sure that you face it into the wind. This is because this turbine is not designed to YAW (or rotate) to face the wind. If the wind shifts, and the turbine cannot rotate, wind will hit the blades from the sides causing stress and inefficiency.
- For a wind turbine that can yaw, you can check out the KidWind Yawing PVC turbine on our website (www.kidwind.org).
- Some Blade Building Tips
- Efficient blades are a key part of generating power from a wind turbine. Sloppy or poorly made blades will never make enough energy to power anything. It takes time and thought to make good blades!
- An important concept to keep in mind when making turbine blades is drag. Ask yourself, “Are my blades creating too much DRAG?“. Your blades are probably catching the wind and helping to spin the hub and motor driveshaft, but consider the ways that their shape or design might be slowing the blades down as well. If they are adding DRAG to your system it will slow down and in most cases low RPM means less power output.
- Some tips on improving blades:
- SHORTEN THE BLADES – Wind turbines with longer blades tend to generate more power. While this is also true on our small turbines, it is often difficult for students (and teachers) to make large, long blades that don’t add lots of drag and inefficiency. See what happens when you shorten them a few centimeters.
- CHANGE THE PITCH – Students commonly set the angle of the blades to around 45° the first time they try to use the turbine. Try making the blades flatter toward the fan (0° – 5°) . Pitch dramatically affects power output, so play with it a bit and see what happens. You can use a protractor to measure the pitch. Finding a way to TWIST the blades (0° near the tips and around 10° – 20° near the root) can really improve performance.
- USE FEWER BLADES – To reduce drag try using 2, 3 or 4 blades.
- USE LIGHTER MATERIAL – To reduce the weight of the blades use less material or lighter material.
- SMOOTH SURFACES – Smooth blade surfaces create less drag. Try removing excess tape or smoothing rough edges to reduce drag.
- FIND MORE WIND – Make sure you are using a decently sized box or room fan with a diameter of at least 14″-18″.
- BLADES VS. FAN – Are your blades bigger than your fan? If the tips of your blades are wider than the fan you’re using, then they’re not catching any wind — they are just adding drag!
- BLADE SHAPE – Are the tips of your blades thin and narrow or wide and heavy? The tips travel much faster than the root and can travel faster if they are light and small, which means that if you have wide or heavy tips you may be 0° 4° 0°