# Optimal Blade Design and Reduction System To Lift 5lbs

1. Jan 9, 2014

### Mastermime

Hello, I'm working on a project for my college class where we need to build a windmill that will be able to lift a 5lb mass 3ft above the ground. The energy of the wind is produced by two 20 inch box fans. We are allowed to use several materials- pine wood, ice cream pails, floss, nuts, bolts, washers, screws, plywood, needles (not sure what these would be used for). The goal is to lift the 5 lbs the fastest 3 ft above the ground.

So I have the base modeled in CAD, which you can see below. My first question is about blade design? The blades will bolted to the circular hub in the image. Based on a bit of research, I figured I would use three. Is this a wise choice?
What shape would you recommend for the blade? Once again, I modeled a blade based on my findings, which you can see below. I'm a bit skeptical about this because I feel this type of blade is too skinny for the blades to 'catch' the wind' and produce rotational motion. Perhaps I could utilize the ice cream pails for this? I just need a bit of advice for this part as we haven't learned about areodynamics up to this point.

For the reduction system, I figured I'd use a system of single movable pulleys. Does this sound like a practical approach?

Thanks

John

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2. Jan 9, 2014

### Simon Bridge

You have some good questions ... but this is a project for your class. Part of the scientific process, that the project is supposed to be teaching you, is investigating the design decisions. This is the important part of the lesson. You should discover the relations yourself the best you can.

Perhaps you can model different blade designs in miniature to see what, if any, effect the different possibilities have?

You can also look at established windmill designs that are similar to the ideas you come up with and see how they are used in real life. i.e. power windmills tend to have three blades but may have two. Aircraft tend to have two blades, but may have more. Desk fans have lots of wide blades. A kids carnival windmill has 4 or 6. Farm windmills designed to pump water have a score of blades.

The scale of your design will affect the design too - the exact shape of the blades, for eg, may not be so important for small scale, low speed, windmills.

I suspect that the blade number and shape is not going to impact as much as you think - if you start with how the lifting is going to be done: do you have a choice in that? Can you use pulleys and levers? Counterweights even? If so, then quite a weak windmill can still fit the bill.

3. Jan 9, 2014

### Mastermime

Thanks for the response. You made a lot of great points. I will experiment with a few different configurations to see which one yields the best results.

In regards to lifting, we recently studied simple machines so I think that is the main focus of the project. The instructions are to build a windmill that can lift 5lb 3 ft in the shortest time possible using only the energy of wind produced by the fans which are six feet away.

Correct if I'm wrong, but, based on those instructions, I would not be able to use a counterweight because that would be utilizing gravitational potential energy and Im only allowed to use the energy of the wind produced by the fans.

4. Jan 10, 2014

### Simon Bridge

This would be the likely objection - yes.
Inclined planes and pulleys and levers could be investigated - anything that offers a mechanical advantage would slow things down though and you need fastest time.

This is also a fairly common project - so googling for "20 inch box fan windmill lift load" should help :)
You won't get actual instructions, well you might, but you will get useful resources.

And then there's the "related discussions" section below.
Have fun.

5. Jan 10, 2014