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How do you use blasa? I mean do you buy a 3/32 sheet of balsa? For our fan that got 5th at states, we used cereal box cardboard..

We do buy sheets, but usually much thinner ones. It's a bit like wright stuff or gliders but without the film. We just cut out pieces with an xacto. And some other stuff too, but that's the basic idea.

Cardboard is really easy to cut and shape into a blade similar to balsa, except cardboard is much heavier and flimsier. If I were you, I would stick with the blade shape you've already optimized, but switch to a better building material that's lighter and more rigid. I doesn't have to be balsa though. I was told that one of the really good ones at nationals for C division was black and shiny...

Right, I am very familiar with Wright Stuff, but 1/16 is the thinnest balsa sheets I'm able to find locally... Will that be suitable? I might go out this week and get some. And I must say, that I've also heard that some of the teams build their blades with precision machining tools lent from companies.

Sorry, for making another comment, but isn't anything less than 3/32 a little to flimsy? Doesn't it bend backward in the wind?

I've experimented with 1/16, 1/32, and 1/64. In terms of rigidity, I haven't had any big problems with 1/16 or 1/32, but 1/64 is definitely too flimsy. Since mass (or moment of inertia) isn't much of a problem when you're already dealing with balsa, either 1/16 or 1/32 can work fine for blades, in my opinion. If you want to steam your blades to make a curved shape, you'd have to go with 1/32. 1/16 is too thick for that (in my experience). But 1/16 is better if you want to shape your blades with a sanding tool or something similar. It all comes down to your design. If you have some 1/ 16 sheets available locally, I think it would be a good idea to experiment with those. Figure out a good way to mount them on the CD, and a good system of carving them into the shape you want. But I think that since the goal is different this year, we should all be experimenting with different blade shapes and sizes anyway.

Does anyone have any tips on what to study most for the test portion, like within the alternative energy stuff?

Celeste wrote:Does anyone have any tips on what to study most for the test portion, like within the alternative energy stuff?

Last year, we basically printed everything we could find off of Wikipedia. But If I were you, I would start by making myself familiar with all the modern methods of harvesting energy from the environment, and how they all work.

Has anyone here done any testing with the new maximum diameter? Is bigger better this year? So far my testing says yes, but I can't come to a conclusion yet.

Can I test my blades without a load resistor, and measure the volts(like Physics Lab last year) instead? Will the fastest blade produce the most amperes? What are some significant design changes that will have to done since a resistor is used this year?
Thanks, Illusionist

illusionist wrote:Can I test my blades without a load resistor, and measure the volts(like Physics Lab last year) instead? Will the fastest blade produce the most amperes? What are some significant design changes that will have to done since a resistor is used this year?
Thanks, Illusionist

There are many turbine designs that will perform extremely well with no load (resistor), and will perform terribly with a load. If you are testing without a load resistor, you will not be able to optimize your turbine for the real competition.

Having said that, yes, you do want your blades to go as fast as possible, since there is no way (as far as I'm concerned) to add a gear ratio. But your blades need to be able to generate a certain amount of torque this year. As the speed of your blades increases, the amount of torque acting against the turbine increases, primarily due to air resistance. Basically, with all other variables controlled for, every turbine will have a certain angular velocity at which the torque it is capable of generating is equal to the torque acting against it. That point should be at the highest angular velocity possible, for maximum score.

To summarize, faster is better, but the faster you go the harder your blades have to push.

There should be some significant design changes this year, since the amount of torque your blades have to overcome is higher, due to the load. Even when the blades are moving slowly or not at all, so there is little air resistance, it still needs to generate that minimum torque to get started. I would expect to see some bigger blades this year, built to the maximum diameter. If I were you, I'd start by taking the design you used last year and scaling it up to 28 cm if you can, with wider blades, and see how it does.

Ok, i've begun scaling my design up, can't wait to get a resistor and try it out. Thanks, a lot!