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Hefhoover
New Member
United Kingdom
69 Posts |
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bs85
Starting Member
United Kingdom
41 Posts |
Posted - 28/01/2008 : 06:23:10
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| Don't like the plastic bit that connects it to the mast, Used them for irrigation and after a while exposed to the sun the go brittle. |
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ghurd
Junior Member
USA
314 Posts |
Posted - 28/01/2008 : 13:33:19
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I don't think it's a good idea.
The Ametek is good because of the power curve and volts/RPM. The bearings are OK. Together, they make a nice little simple windmill.
The gear box changes everything that is good.
It requires larger slower blades to keep out of stall.
That makes the bearings not good enough. The power curves of the Ametek and blades are more out of balance.
Better idea to put a gear box on something that needs one to work, instead of one that shouldn't have one.
But it gives me a couple ideas!
G-
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Hefhoover
New Member
United Kingdom
69 Posts |
 Posted - 28/01/2008 : 17:03:44
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Good points,especially the plastic swivel bit, but what a neat idea overall though. One for the "ideas" box I think. Hef  |
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MattM
New Member
USA
92 Posts |
Posted - 02/02/2008 : 03:51:42
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quote:
Originally posted by ghurd
The gear box changes everything that is good.
It requires larger slower blades to keep out of stall.
That makes the bearings not good enough. The power curves of the Ametek and blades are more out of balance.
You will spend more time spinning the blades with more thin blades crammed into a tighter radius than longer and wider blades. Few people seem to realize the real potential of their blade radius because they either go too fat or too long.
You do increase the torque by increasing surface area of the wings. But a larger blade (longer and/or wider) will do that at the cost of rotational speed, which is a major drawback. The real trick to keep rotational velocity up is to keep the blades shorter AND thinner. The drawback of course is that the thinner blade decreases your ability to pick up wind because the surface area is disproportionately decreased. To offset the loss in surface area you have to increase the blade count.
If you want tangential velocity, that is high speed at the blade tips, then by all means go with longer blades. If you want blades to move under light wind then by all means use wider blades. But you get the best combination by going thinner and in a higher quantity.
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Go Huskers! |
Edited by - MattM on 02/02/2008 05:19:48 |
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gotwind
Forum Admin
United Kingdom
949 Posts |
Posted - 02/02/2008 : 11:00:22
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Hi Matt and welcome.
Nice looking blades, have you got a video online of those blades spinning? - youtube maybe.
What sort of power would you expect from them?
Ben.
The Futures Green - Getwind of it. |
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MattM
New Member
USA
92 Posts |
Posted - 03/02/2008 : 03:19:12
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Those are actually 24' diameter industrial ceiling fan blades. I was just looking for an extreme example. The long thin blades of a helicopter are a prime example of the efficient wing. Many of the helicopters today have one or two blades more than the helicopter designs they replace simply because materials have made it permissible weight-wise to squeeze them in without compromising the hub integrity.
We've made a 15' three blade design with blades made from 26 guage steel sheet metal and a simple 4" wide chord bent to approximately 35 degrees of pitch that were consistently outperforming 10' blades that were 6" wide. Basically the 6" wide blades were bent with fairly optimal angles according to the blade calculator, only we ignored the recommended chord at each segment because the material (16 ga. steel) was so difficult to cut. The same 16 ga. steel worked very well for a 7' diameter twin-blade test rig using tapered wings.
When we took the lesson learnt from the 15' set of blades and applied it on a smaller scale, approximately 5' diameter using ten blades on 45 degrees of pitch made out of 26 ga. steel, the results were exceptional. The ten blades have featherlight sensitivity to wind, plus the smaller diameter allows much higher turning speeds. We've only had the 10 blade up for a few days, and the wind hasn't been very cooperative, but even in the slightest surge of air the thing spins over 100 rpm. (Our weather the past weekend hasn't exceeded an 8mph wind.) The simple thin and hardly tapered wing on the ten blade design seems to be the best performer by far. I have a feeling if we used tapered wings and used heavier sheet metal for improved rigidity then we could get fairly close to the same performance out of something more in the 7' to 10' diameter range. We intend to work something up with a stator by spring.
Sheet metal is a fine material for wings, especially the heavier aluminum thicknesses. I don't see why more people don't use it.
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Go Huskers! |
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ghurd
Junior Member
USA
314 Posts |
Posted - 03/02/2008 : 19:28:28
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There is a huge difference between spinning and making power, as the Ametek guys will tell anyone.
Getting power out of a 5'D 100 RPM machine won't be very cost effective, or efficient with those blades, as I understand them.
Sheet metal is not a fine material for blades, especially aluminum. |
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MattM
New Member
USA
92 Posts |
Posted - 03/02/2008 : 22:45:48
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It has yet to be proven good or bad on a metric, but the superficial results are exceptionally encouraging.
You're simply wrong on the latter point.
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Go Huskers! |
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fungus
Moderator
299 Posts |
Posted - 04/02/2008 : 00:17:31
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| Have you ever heard of a thing called 'fatigue'? |
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MattM
New Member
USA
92 Posts |
Posted - 04/02/2008 : 14:11:15
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Yep. Wood is just as prone to fatigue in the weather and no amount of shellac or varnish is going to make it survive the elements indefinitely. Aluminum is more resistant to weather save high winds, easy to manufacture, resists breakage because it is flexible, plentiful in supply, extremely uniform in consistency, and its very lightweight. A good furling solution should help it survive most winds. If aluminum was such a terrible solution they wouldn't of replaced wood with it in airplane manufacturing; even in today's age of carbon fibers the subframes are still nearly all aluminum.
And I have a good understanding of cost, be it in time and material. For my costs the metal material is next to nothing because what I am using is mainly drops off larger projects. By the time I made up the same material in pvc or wood it is costing me much more of both.
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Go Huskers! |
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ghurd
Junior Member
USA
314 Posts |
Posted - 04/02/2008 : 15:14:44
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I meant alternator cost to get reasonably efficient power from a 5'dia 100RPM at 8MPH blade set.
'fatigue'. Comet. 737. 747. 767... |
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fungus
Moderator
299 Posts |
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ghurd
Junior Member
USA
314 Posts |
Posted - 05/02/2008 : 01:01:26
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I read it as the 1st set lasted 4 weeks and the 2nd set lasted 6 weeks.
Makes me afraid to get in a plane!
G-
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MattM
New Member
USA
92 Posts |
Posted - 05/02/2008 : 01:26:49
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Go research the properties of extracted aluminum and it explains his experience. Extruded aluminum is not sheet aluminum. And drilling imperfect holes in aluminum is going to promote cracking, which is exactly the problem he had. A lousy grade of aluminum cannot be straightened out once bent. Look what he did, he took lousy aluminum, twisted it, over drilled, and literally hung it with hooks because that dead space in the blade allowed the blade to pivot freely.
If the guy knew what he was doing the blades would have worked fine.
I like how people blindly label imported blades from China as "Chinese blades" when it obviously came from some specific outfit. Calling them 'Chinese blades' is almost racist. I've met some real geniuses in my lifetime that swore they knew what they were doing then literally did everything completely opposite of conventional wisdom.
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Go Huskers! |
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ghurd
Junior Member
USA
314 Posts |
Posted - 05/02/2008 : 03:11:34
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| You should notice the bent blades and the failed blades are not the same blades. Or owners. |
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What an excellent idea!
Posted - 28/01/2008 : 02:12:30