Aluminum Blades

[ghurd]

I have a set of Cy-Clone blades.  They look to exhibit PVC blade characteristics.
Everyone who has a set of AL blades shaped like PVC blades (or even worse- flat bent to an " _/ " shape), who also has tried carved wood blades, will tell you they are slow.
They can be suited to some simple motor conversions with a steep power curve and low cut in because they do have some pretty good torque, but they are not fast enough to be efficient (monetarily speaking) for an efficient air core dual rotor, because slow means big magnets and lots of heavy wire.
G-

[ChrisOlson]

They can be suited to some simple motor conversions with a steep power curve and low cut in because they do have some pretty good torque, but they are not fast enough to be efficient (monetarily speaking) for an efficient air core dual rotor, because slow means big magnets and lots of heavy wire.

Apparently people who buy those Cy-Clone blades don't care if they make any power.  As long as they go around, that's good enough.  If you look on WindBlue's website and read the product reviews, one reviewer says:

I have tried the black plastic blades,& fiberglass blades. I wish I found the cyclone blades first. They really spin nice.
even in very low wind.Even if your not in the power band they spin. Its nice just watching on a low wind day. blades that only spin on a VERY windy day are no fun.

So I gather they're about as useful as those lawn ornament tractors that people buy and put in their front yards with little wind-turbine wheels that go around.
--
Chris

[ghurd]

They can be suited to some simple motor conversions with a steep power curve and low cut in because they do have some pretty good torque, but they are not fast enough to be efficient (monetarily speaking) for an efficient air core dual rotor, because slow means big magnets and lots of heavy wire.

Apparently people who buy those Cy-Clone blades don't care if they make any power.  As long as they go around, that's good enough.  If you look on WindBlew's...

I got my cyclone blades through some horse trading.
The previous owner (who I expect will eventually chime in) decided to connect the PMA they were specifically made for to a gas mower engine so the PMA could actually make some power.
He tried all kinds and types of blades on the PMA, but the PMA just wouldn't go fast enough in the wind to do diddley.

The typical PVC style blade ratios, from AL or PVC, can make power quite nicely, if the PMA is suited to the TSR and swept area.
American Windmill style blade set is not good for a typical dual rotor,
but a typical 3-blade dual rotor style blade set is not suited to pumping water from the same pump either.
G-

[ChrisOlson]

I got my cyclone blades through some horse trading.

I did the PVC blade thing a long time ago.  Every newbie has to try it to make sure it doesn't work very good.  Cupped pipe-section blades do go around, and they do make some power, but they only run at 4 TSR loaded no matter what dimensions you try to use.  I can imagine that if you can match the generator to them they'll work - somewhat.  But claiming they're better than anything else out there, per TLG's website, is a little far-fetched and what I'd call "optimistic advertising".
--
Chris

[neilho]

Some random thoughts on AL blades for wind turbines....

Milling a blade profile from solid 6061T6 AL is certainly possible, but it would be very heavy and stiff. Heavy makes for much higher centrifugal forces than light and stiff blades require stronger hub, mainshaft and structural support systems to withstand the higher transient loads a floppier blade system would shed.

So far as AL P51 props go, material cost of blades is a more important factor for wind turbines than military hardware. And those props are most likely xray inspected, often, and replaced when reaching a certain # of hrs.

Reynolds was, at one time, extruding a constant chord AL profile for wind turbines. Terry Mehrkam used them on his machines. They broke. Flowind used them on their eggbeaters. They broke. It may be possible to make turbine blades from AL that don't break, but so far, other materials are cheaper and more reliable, no matter what method of fabrication is used.

6061T6 clean scrap is bringing about .30/lb here in Vermont.

Neil

[ChrisOlson]

So far as AL P51 props go, material cost of blades is a more important factor for wind turbines than military hardware. And those props are most likely xray inspected, often, and replaced when reaching a certain # of hrs.

On my Seneca III, when I had it, it had McCauley constant-speed three-blade props on it with a TBO of 2,000 hours.  I had them rebuilt at Maxwell Propeller at Flying Cloud, MN and it cost around $2,000 apiece to have them done (that was 10 years ago).  They put new seals in the prop governor (gear driven on the engine), hub and blade roots, and x-rayed the blades.  They told me that they've never replaced one unless it had a ground or bird strike, had excessive damage to the leading edge from takeoffs on dirt strips (mine had hot boots on it anyway but they didn't cover the full length of the blade), and that they've even straightened blades that were bent in wheels-up landings and they were still serviceable.

I watched them overhaul one of my blades and they clamped it in a vice with a rag to cushion it, took a mill file to it and reshaped the leading edge where it was worn.  Then, where the shafts go into the hub, they polished the scores out it with emery cloth.  I shook my head - I could've done that for $2,000 but I don't have a A&P or AI and those guys do, so they can sign it off in the maintenance logs.

It's possible that wind turbine duty is more rigorous than aircraft duty because the average turbine can run 7,500 hours a year.  But I think the tradeoff there is that the wind turbine doesn't impose the loads on the blades that an aircraft engine does.  I'm convinced it's doable but the cost is prohibitive.

As far as companies who have tried aluminum blades and had them break, there's plenty of old Jakes with broken spruce blades too.  And there's also plenty of utility-scale machines that have had fiberglass blades fail.  So just because somebody had AL blades break doesn't mean it was done right, or that it can't be done.
--
Chris

[DanB]

It could be that Aluminum blades are a wise Idea.  I personally doubt it... (but I often find myself wrong and find myself changing my opinions down the road).
But: I'd like to see 1 example of a sizable turbine with aluminum blades that has 'reasonable' efficiency that's lasted a 'reasonable' amount of time and know how much energy it actually produces (or produced).

I think Chris is right... it 'could work' ~ but at the end of the day really we are probably worried about cost per kWh and I don't think Aluminum blades are going to win there.

[ghurd]

Yianie,
I apologize for possibly taking your post off topic, but the vast majority of currently available AL blades are aerodynamically very similar to PVC blades.

"optimistic advertising".
--
Chris

Naw.  You need to read news releases while looking at the photos.
Quite a few look like they would have PVC blade characteristics, and evidently that is a great thing.... unless the reader has a calculator and a brain.
Of course this company has several pics with very different blades from one to the next, although most images are graphical representations of the artist's conceptions of something.
 
"Available in two configurations, 300-watt and 800-watt versions"
"a breakthrough design with a small blade-span of less than 52 inches"
"has been created specifically for both low wind and obstructed areas, ideal for the average home roof."

"delivers a complete return on initial investment within two to five years. Unlike other wind and/or solar systems, the <brand name> has the potential to convert up to 70% of wind power into electricity, double the current average, and can operate in as little as 2mph to >25mph."

"For the average home a full system consists of four to five units, an inverter, wind monitor, and installation for around $11,000. Previously, companies sold individual units for over $30,000.00 which were bulky, unsightly, and sustained on-going mechanical problems."

"will be available at a suggested retail price of $4,800 for a complete system, including inverter system, high-performance rechargeable batteries and mounting brackets. In many states, the <brand name> qualifies for local, state and federal tax credits of up to 80%."

<end rant>

[neilho]

Chris Olson Quote:

As far as companies who have tried aluminum blades and had them break, there's plenty of old Jakes with broken spruce blades too.  And there's also plenty of utility-scale machines that have had fiberglass blades fail.  So just because somebody had AL blades break doesn't mean it was done right, or that it can't be done.

End quote.

Yes, of course.The broken Flowind and Mehrkam blades were all victims of fatigue. It's possible that some of the Jacobs failures were fatigue related, but not all of them. And any blade will fail in an overspeed.  Sure, it's certainly possible to develop an AL bladeset for wind turbines, but there are a lot of economic imperatives involved in deciding to produce blades and aluminum is on the expensive side, putting it at a severe economic disadvantage. It would have to have some physical property to justify the additional cost. I would adopt it in a second if there was such a property but I haven't heard of one yet. On the contrary, perusing a typical SN curve for aluminum was almost enough to rule it out.

I doubt very much that AL blade production would be economically justifiable when easier fabrication methods and proven, less expensive designs and materials are available. In an aircraft AL is worth it (evidently), in a wind turbine, so far, it isn't.

By all means develop your own set of AL blades if you like. I'd be interested in hearing about it. I just have no idea why anyone would want to, aside from the obvious fun of doing it and of course, the accompanying fame and fortune.

Neil

[Perry1]

Chris, Fab, dsmith,

Since y'all know the thread on the other forum, y'all probably saw me poking holes through their design, too.  You've been warned.

I made an issue of it because parts were for sale and I thought the construction was inadequate.  I also recall that while I just took shots, another member did a lot of work to offer analysis and proof of these doubts.  After he was done with them, a lot more thought was given to the construction and at this point, there's a lot more merit to what they offer.  It still deserves caution because while the blades have a more sound attachment, the hub attachments are still being made with whatever comes to hand, and mistakes are easy to make.

Ahhh, good times that was.

Perry

[ChrisOlson]

"Available in two configurations, 300-watt and 800-watt versions"
"a breakthrough design with a small blade-span of less than 52 inches"
"has been created specifically for both low wind and obstructed areas, ideal for the average home roof."

Well, if the Eskimos are stupid enough to buy ice cubes you can rest assured somebody will start up a business selling them.
--
Chris

[ChrisOlson]

In an aircraft AL is worth it (evidently), in a wind turbine, so far, it isn't.

Aluminum came to be the standard material for aircraft propellers because it's tougher and harder than wood or fiberglass and has superior abrasion resistance at a cost that the marketplace would stand.  It's also light weight compared to a wooden propeller of the same performance characteristics - the aluminum blades can be made thinner with less drag.  Unlike wind turbines, aluminum aircraft propellers are about 80% efficient.

Aluminum is also used for boat propellers because of the same reasons.

I have no doubt in my mind that you could take a Sensenitch prop off a Cessna 150, have it re-pitched at an aircraft propeller shop for wind turbine use and run it for decades and it would never fail on a wind turbine.  And you could let it free-spin in 150 mph wind and it still wouldn't fail.  The issue is cost - that fixed-pitch two blade prop is 5 Grand new and you'll pay $2,500 for a serviceable used one.  The three-blade McCauley's on my Seneca were $22,000 propellers - each.  It was ~$5,500 for a single blade.  The wind turbine market simply will not stand that kind of cost.
--
Chris

[SparWeb]

Chris,
I hate to sound like Mr. Knowitall, but...   Well, yeah I do at times...  anyway:

Aluminum came into common use in propellers because most aircraft do better with 3 blades, and it makes a much better constant speed prop.  The aluminum base is much easier to mount to the hub than would be a wooden blade.  Most wood props (I admit not all) are single laminate units with 2 blades.  Pretty hard (though entirely possible) to make a 3-bladed wood prop as a single unit, wouldn't you say?  There's also the difference between aircraft props that can fly at 2000 RPM, and others that spin at 3000 RPM.  Again, these conditions tend to dictate the material choices.

In the quest for more performance, having more HP and thrust can win out over the cost in weight of aluminum.

The airplane analogy only goes so far when making wind turbine comparisons.

Anybody wanna get into a comparison with helicopter rotor blades??  EH?   

[TomW]

Chris,
I hate to sound like Mr. Knowitall, but...   Well, yeah I do at times...  anyway:

Aluminum came into common use in propellers because most aircraft do better with 3 blades, and it makes a much better constant speed prop.  The aluminum base is much easier to mount to the hub than would be a wooden blade.  Most wood props (I admit not all) are single laminate units with 2 blades.  Pretty hard (though entirely possible) to make a 3-bladed wood prop as a single unit, wouldn't you say?  There's also the difference between aircraft props that can fly at 2000 RPM, and others that spin at 3000 RPM.  Again, these conditions tend to dictate the material choices.

In the quest for more performance, having more HP and thrust can win out over the cost in weight of aluminum.

The airplane analogy only goes so far when making wind turbine comparisons.

Anybody wanna get into a comparison with helicopter rotor blades??  EH?   

Spar;

All good points! I would love to see a comparison of turbine blades to chopper blades.

I know a couple ex 'Nam chopper drivers and only know one thing about their blades:

The JESUS NUT is aptly named! Oh, and that whole swash plate bit lookslike acomplexicated attachment to the "wing"!!

Carry on, if you will.

Tom

[fabricator]

I have spent many hours rebuilding swash plates and replacing chopper blades, I spend a lot more time fixing than flying, the nice thing is my chopper is only two feet long, it's a Aling T-Rex and hard as hell to fly, I specialize in barely controlled hovering and tail boom blade strikes.

[SparWeb]

Anybody wanna get into a comparison with helicopter rotor blades??  EH?   

Spar;
All good points! I would love to see a comparison of turbine blades to chopper blades.
I know a couple ex 'Nam chopper drivers and only know one thing about their blades:
The JESUS NUT is aptly named! Oh, and that whole swash plate bit lookslike acomplexicated attachment to the "wing"!!
Carry on, if you will.
Tom

Here you go, Tom.  Hopefully this show up as "attachments". 

[SparWeb]

Good, those pix showed up.

The "Jesus Nut" is #2 in the top diagram.  It's called that by pilots because that's who they pray to that it stays on.  It's called that by mechanics, because of the wrench they need to put 520 foot-pounds of torque on it!

[97fishmt]

Here are my aluminum blades

Well they are cedar but with all the talk
about aluminum I decided to paint them
with an aluminum paint.  10 foot rotor
ready to go up on the mill.

[Ungrounded Lightning Rod]

Aircraft propellers are only in use for a limited (though reasonably large) number of hours.  So (like aircraft bodies) they can be retired before fatigue progresses though cracking to catastrophic failure.  Wind machines run essentially continuously for decades and the temptation is to make the blades thin to make them lighter and less expensive - leading to greater stress and a nasty surprise some years later.

I have no doubt in my mind that you could take a Sensenitch prop off a Cessna 150, have it re-pitched at an aircraft propeller shop for wind turbine use  ...

Actually (depending on how you look at it) props have the twist backward, or the hump of the airfoil on the wrong side, to make efficient wind turbine blades.  Propellers are about speeding up the wind, turbines about slowing it down, so they have the lift pointed in opposite directions.

The issue is cost - that fixed-pitch two blade prop is 5 Grand new and you'll pay $2,500 for a serviceable used one.  The three-blade McCauley's on my Seneca were $22,000 propellers - each.  It was ~$5,500 for a single blade.  The wind turbine market simply will not stand that kind of cost.

Total agreement.  To get the stresses down to where fatigue doesn't break 'em in a reasonable life you need a lot more aluminum, and it CO$T$.

[ChrisOlson]

Actually (depending on how you look at it) props have the twist backward, or the hump of the airfoil on the wrong side, to make efficient wind turbine blades.  Propellers are about speeding up the wind, turbines about slowing it down, so they have the lift pointed in opposite directions.

I think we're all doing it wrong.  There's a guy up by Cumberland, Wisconsin that drives a 100 amp truck alternator with an old 8' Aermotor windmill.  He claims it'll put out 80 amps without even really working it that hard.  Somehow I could believe that.  We had an old 8' Aeromotor mill on the farm when I was a kid.  The well had been abandon and it was capped but the lift rod was still banging around in those loops inside the tower.  My brother and I used to climb in there, grab on that lift rod and ride up and down on it.  It was great fun!

I don't think my 8' PowerMax turbine rotor would make enough torque to do that even geared down in a 30 mph wind.  And all that windmill has is a bunch of pieces of galvanized sheet metal bolted to angle iron at an angle to the breeze.
--
Chris

[domwild]

This site is in Australia but may be of interest to those, who are interested in extruded PVC or Alu blades. They are extruded and therefore do not exhibit tapering or change in pitch. As an American has initiated the manufacture of it in China I suspect this prop is also available in the USA, perhaps only in the PVC configuration.

The site is http://www.thebackshed.com

To strengthen the prop the suggestion is to push in 1" exhaust tubing and a 22mm mild steel rod. Because of this strengthening the prop just is not going to fail ever.

[hayfarmer]

Have had 3 sets of metal blades on a amtek micro 500 watt @ 26 feet in a windy area,1st set  Aluminum    3 foot swept area blew off in a month,down sized to 2 foot and lasted for 3 months then blew off,tried the composite fiber blades but were too narrow to catch the wind @ 26 feet.finally went with galvanized steel with 2 foot span  and not as wide as earlier blades and doing great for 2 years now powering with very little wind.