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311fan Newbie Joined: 21/05/2008 Location: United StatesPosts: 2
Posted: 01:40am 21 May 2008
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Hello...I am a new member here and also a highschool student. In two weeks I am going to the National Science Olympiad in washington DC and I am competing in a wind power event. In the event, I have a CD disk, paper, and tape. I must create a propeller by cutting/folding/etc. the paper and taping it to the CD. At the end of a 50 minute period, The CD "propeller" will be attached to a generator and a fan will be blown onto it. I must find a design to maximize the voltage output of the generator. Is there anyone that can help?
Things needed:
Links/Ideas/Info on:
-Propeler angle for max power
-Propelor design for max power
-Any other helpful hints
...thanks
Competition Description:
http://www.soinc.org/events/trial/windpower.pdfEdited by 311fan 2008-05-22-Matt
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 09:11am 21 May 2008
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G'day Matt,
Pleased to have you join the forum. The challenge you've received is certainly an interesting one.
Initially it seems reasonable to go for a typical design that produces speed and power. However with consideration of the materials you are limited in using, I think perhaps a unique design will win out. With the windmills we use a 3 bladed propeller as normal, but I think paper will not be rigid enough to make one of a suitable size. Perhaps the best design will be that of a VAWT(Vertical Axis Wind Turbine).
One of the simplest VAWT designs is the Savinious. You could research this yourself. I think one could be made within the limitations you have. It will pay to try and practise making several before you decide on your best.
I think holding a design together in strong wind will be the thing that will destroy many otherwise excellent ideas. With this in mind perhaps what we call a drag machine that is interlocking will provide the strength needed.
I'll try to draw up an idea when I am able and post it here. In the mean time what ideas have you TRIED so far? was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
311fan Newbie Joined: 21/05/2008 Location: United StatesPosts: 2
Posted: 01:24pm 21 May 2008
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...to tell the truth, I haven't tried any ideas yet. This is a trial event and the group teacher gave it to me just a couple of days ago. I was just
I looked at the Savonious design...it looks good. I will have to try it out.
It looks promising, because it would be much sturidier than a paper propeler, but I am just wondering how well it would do. I am wondering, does there need to be a space between the red surface and the blue surface (On the picture)? I am still a little confused....
Edited by 311fan 2008-05-22-Matt
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 02:58pm 21 May 2008
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Matt,
Yes, that space is most important. It allows wind to flow through the gap and generate thrust even on the side rotating into the wind. That plan is using tube or pipe sections for the blades or wings, this is not the best shape. It is often used because that's the shape easy to come by. That gap is too small with that shaft there.
Savonious are relatively inefficient as wind mills go, but it does not need spars or struts that the better types do. You are not allowed sticks to build with. The sav' is a proven design so a definate contender.
I think the thing to go for to win this is to have the most sail area yet still strong enough to hold shape in the strong wind.
See if you can come up with a way of making the sav and I'll try and get my hybrid design onto paper so you can try one against the other. was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 08:49pm 21 May 2008
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It would be nice to know how big the fan is so you could design your device to make full use of the available air flow.
Though the Savonious looks good you might also be considering a convention horizontal design? Here is a simple scheme for making an airfoil like section from sheet material, paper in your case, sheet metal also works!
These are quite stiff and if you slide the edges of the paper along their length, just slightly, you get a curve in the airfoil! It is something you would want to practice a little before the event!
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 02:20am 22 May 2008
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Hi matt,
the contest seems to be about output voltage only. A VAWT will spin much more slowly than a HAWT. I would opt for the latter. .. Gordon.become more energy aware
petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212
Posted: 02:55am 22 May 2008
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Will I pass for grumpy by suggesting that if you must do this that getting on a forum and asking others to do it for you may not be in the spirit of the contest?
All I will suggest is that whatever design you decide on you will get a lot quicker at making it with practice.
Equally if you are allowed to use patterns and other equipment it would make it easier.
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 03:52am 22 May 2008
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Ummm... grumpy? I dont see it that way it is always a good idea to look wherever one can to find useful information.
petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212
Posted: 05:40am 22 May 2008
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At the risk of sounding really grumpy if the idea of imposing some sort of time limit was to test the participant’s problem solving ability should they have the question before hand?
How much collaboration is reasonable? Perhaps this depends on many things.
Equally there are enough variables that even with the best preparation some allowances for conditions would need to be made.
How strong is a light wind?
How strong is a strong wind?
What are the characteristics of the generator that the rotor will be turning?
More torque or more revs?
Will the generator have some sort of load?
Clogging?
As another poster suggested what will be the character of the wind?
A small desk fan would be different to a wind tunnel.
How stiff is the local typing paper?
Will the paper supplied have a pronounced grain direction?
Are the RPM of the rotor likely to be high enough that balancing will be an issue?
Horizontal axis style windmills tend to be capable of greater output but they are technically more challenging.
But it is a competition to see who can produce the greatest output voltage so probably a high RPM rotor is likely to win.
Personally I have no experience with making a wind generator from old CDs and paper
dazz Regular Member Joined: 15/04/2008 Location: Posts: 78
Posted: 06:05am 22 May 2008
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I can see both points as being valid, but could I suggest that in this particular competion they purposly informed the students before the contest of the aim and resources that will be available.
If you want them to display their quick problem solving ability, you only present all this info at the time of the contest.
Perhaps then, the aim of the contest is not to problem solve in a short time, but to test the students ability to gather information, come up with a solution and develop a method that will enable completion of the task within the allotted time.
Seems to me they are seeking for the students to demonstrate "the spirit of invention" Inventors don't run on nothing. They investigate all the principles, gain a true understanding of the problem. They analyse all that has come before and then develop something new. They also are then constrained to produce the item in the alotted time(ie before they die)
My advice is, use lots of sticky tape. Can't go wrong Actually if you cover all your surfaces with nice shiny smooth stick tape then it won't tear and will be like a freshly washed jet with less drag
See, more Sticky!
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 12:51pm 22 May 2008
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G'day 311fan,
Here's the design I was thinking of. Well, not really as exotic as I was thinking but I have tried to target strength and torque. I have built a few little wind generators and I've found the biggest problem is to get them started. This is nothing fancy in wind generator design, in fact it is rather crude being just a drag machine. Still, put it up against any others and see what performs better then enter with that one.
Here's the assembly:
1. Cut circle from Manila folder.
2. Roll remainder of folder into a cylinder and tape.
3. Fold a 3 x thickness stiffening hem to the top and bottom of 8 pages and secure with tape.
4. Cut the cylinder to 2/3 the height of a page and tape on the top hat.
5. Mark the CD into 8 x slices.
6. Tape on the cylinder.
7. By overlapping, Tape the 8 x pages to the 8 x marks on the CD.
8. Turn up-side-down and tape the 8 x top hems to the top hat.
9. Cross your fingers and toes.
All done.
Hints:
To make spars or rods; tightly roll a page.
To further stiffen KiwiJohns wing; add a rod inside, 1/3 back from the leading edge.
Now, lets see what damage you can do.........
was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81
Posted: 01:52pm 22 May 2008
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I think that it is great that you guys are helping with ideas!
Grumpy: I understand where you are coming from, but do you really expect a young inexperienced person to come up with completely original ideas that are theirs alone. Creativity is using an existing knowledge base to extend and diversify! Besides it gives this forum members the chance to help others! By the responses, everyone seems pretty happy to do that!
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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