Author Topic: Pitching the Props (Read 2927 times)

Ponderance · « **on:** October 25, 2007, 03:41:20 AM »

I've noticed that on otherpower.com, most of the turbines have been pitched for counterclockwise rotation. Is this a specific preference or a direct need for the alternator to produce AC current? Or does it have a direct bearing on how the wind turbine furls?

And, yes, I have waded through many pages and I think that I have overlooked, or missed it somewhere.

Thanks for your time,

Ponderance

dynaman · « **Reply #1 on:** October 24, 2007, 11:57:11 PM »

this is preference the alt will generate either way, clockwise just seems to be standard.

wooferhound · « **Reply #2 on:** October 25, 2007, 12:42:48 AM »

Some props are mounted to the Generator with a single Bolt or Nut. If the prop turns clockwise it will tighten up the Hardware. If the prop turns counter-clockwise, it will loosen up all the Hardware.

http://www.fieldlines.com/story/2005/12/29/1513/3449

Flux · « **Reply #3 on:** October 25, 2007, 01:01:04 AM »

Just seems natural to choose clockwise. Unless there is other factors such as nuts unscrewing you can choose either rotation, the alternator will not know the difference.

Effects on furling are small and the way most build the furling scheme it would be slightly safer with anticlockwise rotation but not an issue anyway.

Flux

paradigmdesign · « **Reply #4 on:** October 25, 2007, 08:59:23 AM »

Also, CCW just feels weird. I guess if you want to make a statement about turning back the meter it would work though.

Ponderance · « **Reply #5 on:** October 25, 2007, 09:51:01 AM »

Thanks for the straight forward answers. I don't think I've been able to find more information anywhere else on home brew gens than on here and otherpower and Huge's pages.

One last question:

When carving, I know there is little or no room for error in pitch/twist in the prop, I've perused many pages and played with a few airfoil proggy's and liked the overall info.

Should I make/carve a few test blades with single wood thicknesses before getting serious, or should I just find someone who is already skilled at wood carving? or possibly both?

Ponderance · « **Reply #6 on:** October 25, 2007, 09:52:33 AM »

Please excuse the typos! Hugh's pages *

Flux · « **Reply #7 on:** October 25, 2007, 12:16:24 PM »

Can't answer that, I don't find carving blades a problem but starting at the age of 10 may have had some effect.

If you are a bit doubtful try one with some low quality wood first. Once you understand the marking out there is nothing to it. If you get the marking out wrong it will be obvious on your trial attempt. Don't be frightened it doesn't need micrometer precision.

Flux

SparWeb · « **Reply #8 on:** October 25, 2007, 12:19:14 PM »

About carving blades:

I cut a blade from a 2x6 piece of lumber for practice before setting upon my "real" cedar blades. It was very valuable experience, especially going through all the motions of making measurements, laying out templates to get the airfoil right.

Ponderance · « **Reply #9 on:** October 25, 2007, 09:53:20 PM »

Awesome, again, thanks for all the answers. Now I just need to collect a few more tools and a few materials to test run on.

finnsawyer · « **Reply #10 on:** October 26, 2007, 08:37:25 AM »

"When carving, I know there is little or no room for error in pitch/twist in the prop, I've perused many pages and played with a few airfoil proggy's and liked the overall info."

You've got to be kidding. When carving a blade out of a 2 by 8 (really 1.5" by 7.5") there is no way you can follow the proper twist down to the root. In fact, if you just mount those 2 by 8's at an angle you'll still get power.

HomegrownPower · « **Reply #11 on:** October 26, 2007, 05:47:39 PM »

Ponderance

Avoid using maple if you can . That stuffs hard as a rock . I started 3 blades of maple lol . Before I got one blade done I determined it was a plug not a blade and I was only making one . Then take the plug and make a mold to make 3 more blades with fiberglass .

If I get this right the first pic should show it flat you can't really see the pitch . I was worried it was to thin at the end but seen some slender ones about like it since . I try to show the twist in the prop in the second pic . It's fairly straight on the leading edge and twist about 3/4 of a turn . lol I have no idea if three of these will work just have to see.

May be able to reinforce them with a couple slinder steel strips while laying up the glass . Need to make the mold on the next nice day when I should be working on my wifes car .

Ponderance · « **Reply #12 on:** October 26, 2007, 05:50:17 PM »

the actual implication was to do a few test runs to get the "general art" of carving down before I attempt to do composite blades.... where you came up with the notion of me using 2x8's to do a quality set of blades is waaay beyond me....

I appreciate the reply tho!

Ponderance · « **Reply #13 on:** October 26, 2007, 05:59:05 PM »

lol yeah, maple and mahogany both are really great for making electric guitar bodies, but I will agree, they're not good woods for making prop blades lol, my other idea was really going to copy the actual blade composition that was used on the 20' wind turbine on otherpower -- http://www.otherpower.com/20page4.html -- for even small test units. composites seem to be easier to get lots of thickness to work with and still retain a solid durable blade, much like long and recurve bows in archery. I would use a polymer composite, but most I can afford is the rotor/stator mouldings.

HomegrownPower · « **Reply #14 on:** October 26, 2007, 06:27:16 PM »

I read where maple was good . I didn't have the tools to carve with and that made maple way to hard .I had to use a wrasp like thing that was too small for the job . I'll make the mold myself and save considerable that way . I might be off a little but think I can make the mold and 3 blades with 1.5 gal of resen .

Already have it just cheap bulk stuff but should work I'll use a lot of layers of very thin weight cloth over a couple layers that will kinda melt into the gel coat . Gell coats went bad but I thinned some with acitone and made a small test mold of a coffee jar lid and the stuff worked lol . It wouldn't spray in a gun but I brushed it right on and it reacted and done perfect . It was more like bondo than gel coat but I liked it better after thinning .

Good luck from another newbe

Flux · « **Reply #15 on:** October 27, 2007, 01:31:03 AM »

I used maple once, but never again. It was the only occasion I had to resort to power tools. I hate the noise and mess of power planes.

Flux

finnsawyer · « **Reply #16 on:** October 27, 2007, 08:08:27 AM »

The point was not your using 2 by 8's, but to warn you about getting too tied up in trying to reach perfection. The 2 by 8's, by the way, reflect the sort of thing that is done here.

HomegrownPower · « **Reply #17 on:** October 27, 2007, 11:50:10 AM »

Flux

I determined one maple blade was enough for me . Shesh this stuff was hard to do anything with . Even once I desided to use it as a plug it was hard to work with . Thank goodness it's had two coats of parting wax applied and is about ready to use and be done with .

Bad thing is I could have used about any type wood I wanted . No rare woods or anything like that but all woods common to east Tenn I have some of the seasoned lumber setting here and still picked maple for some reason . I'm like you in that " Never again " lol

If the mold thing doesn't work out I think I'll try popular next time . It's a good solid hard wood thats easier to work with and is very light compared to an oak or some simular hard wood . Not sure if your familliar with this wood but sawing it many times it has some interesting qualities I think could make it an excellent choise if one started with it while it was green .

When milling this stuff it litterly seperates as the blade goes through it . riping a 2x8 down to two 2x4's and when you cut through say 4 feet of a 12 ft board the end will be spread 10 inches apart .

To use it I have to absolutly nail it in the stack and pull it straight to dry . Works great with the double headed nails . It's so hard it wants to split when you nail it inless you hammer the end of the nail to dull the point .

With all that said the reason I think it could make an excellent choise is when it's green " fresh sawed " it would be easy to twist a 4 to 5 ft 2 x 6 board 90 degrees . Nail it or bolt it down to dry like this and in a few weeks it would remain like this . Then carve the blades from the twisted board . Although a sealer or something would probably be best to prevent it from getting wet and perhaps loosing some of the twist .

Lonnie

DanB · « **Reply #18 on:** October 27, 2007, 03:20:57 PM »

Yes - that's right. All anybody has to do is look at blades on the following fairly well known machines....

Bergey

Jacobs

wincharger

Hardly any twist and taper on any of those (bergey has none) and the hit they take in efficiency is very small.

You can make a very nice blade out of the right 2 x 8. You can also make life as complicated as you like... ;-)

finnsawyer · « **Reply #19 on:** October 28, 2007, 08:08:11 AM »

You say the hit they take in efficiency is very small. Compared to what? How close do they come to the Betz limit?

DanB · « **Reply #20 on:** October 28, 2007, 09:25:08 AM »

In the 30% ball park which is consistant with most small wind machines. Bergey makes a very efficient machine. So does Proven - have you seen their blades? They do about exactly what they should for their swept area. Blades we make - hard to say, I do not have the resources to be terribly scientific about it but I do feel (and perhaps Im being optimistic) that - at least in low winds we do about as well as most machines - with similar swept area. (better than some)

I think blades are a lot more forgiving that some people do and some of the most successful small wind turbine manufacturers seem to agree.

finnsawyer · « **Reply #21 on:** October 28, 2007, 09:51:17 AM »

You seem to be comfortable with the 30 to 35% efficiency, but if one accepts that that is all that can be had, well, then forget the Betz Limit. It becomes irrelevant. You may be right from a practical stand point that putting the proper twist in may be counter productive. This could be because of the turbulence that arises at the root and the vortices off the tip, and unless these effects can be reduced there is no point in bothering. It would be nice to know how much power is actually robbed by those effects. Even if one could improve the efficiency incrementally it would be tough to prove it in one's back yard.

Flux · « **Reply #22 on:** October 28, 2007, 12:20:09 PM »

The Betz limit is based on simple momentum theory, there are some that actually question whether it is possible even to reach it. As nobody has exceeded it yet there seems little point in worrying about it.

Commercial big machines claim a blade efficiency of about 45% with all the effort that is put into doing the very best with that level of finance invested.

Small machines typically manage about 35% without a lot of special effort. I have never seen any genuinely proven figures for much higher than this with all the clever profiles and twists that some seem to think necessary.

With a mppt scheme where the blades can operate on the peak of the curve I suspect blade design may be just a little more critical, my findings show that the best results are with blades running slower than the theoretical speed in higher winds. There is almost a doubling in output power with mppt compared with fixed voltage loading and that is s far bigger gain than any messing with the perfect blade is going to produce ( you are not going to see higher than 45%).

I have never seen any evidence to support the crazy angles and widths that the calculators predict and my experience is that they are a hindrance rather than a help except for machines with start up problems.

If you can manage mppt there is probably a case for trying to accurately duplicate a proven aerofoil shape, but for conventional fixed voltage loading I doubt that it is worth the bother.

As you say the problem of measurement is virtually beyond the average experimenter and what seems to be an improvement due to one change may really be caused by a change in another factor. Forget Betz, if you can manage 40% you have done extremely well.

Flux

finnsawyer · « **Reply #23 on:** October 30, 2007, 08:23:34 AM »

You may be right about not being able to exceed 45%, as the big boys claim to reach, but maybe they haven't figured it out yet, either. Or maybe you could do things on a smaller scale that wouldn't be practical on a large scale such as my idea of a large central structure to speed up the air and eliminate the central turbulence. Since most people just want to get some power, I have no intention of being strident about it, but do hope someday when my ship comes in to investigate it.

As far as mppt is concerned, I'd like to see someone present a design that people could tailor to their particular circumstances. I am not aware of such and until I see such a design I consider the subject rather esoteric and probably beyond the reach of most of the users of this site.

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Author Topic: Pitching the Props (Read 2927 times)