Lucked into some blades

[(unknown)]

I got lucky again and am getting 2 sets of TLG's 5 foot diameter 4 blade setups for close to free (shipping). I have 2 8 inch rotors and was pondering the possibility of using some 1 inch diameter N42 Neo's in the standard 12 per rotor/9 coil arrangement. Any suggestions on the number of coil turns? Looking for 12 volt charging to supplement my solar I use for the house lights. I am still working on the larger alternator too so this is going to be #1 or 2 depending on which I finish first. Average wind speed here is 17 mph so  am in a good wind zone :-) I know some say aluminum won't last but I had 33 foot long ham antennas survive over 10 years in my wind environment. 1 or 2 90+ mph storms a year are common as are 30+ mph steady winds for days at a time. I am close to the Buffalo Ridge wind site here in MN :-)where there are a lot of commercial wind sites.

[Flux]

If you don't expect too much then it should work. You are probably limited to 8 poles with 8" discs. That doesn't leave you a lot of flux to work with.

You don't say if you have the magnets and if so you don't give the thickness.

If you don't have the magnets then I personally would use the common 2 x 1 x 1/2 magnets. That would get you a better match. 8 magnets on one disc and a blank spinning disc to return the flux would get you a decent match.

If you have the 1" magnets and they are at least 1/2" thick and you are happy with 100W then it should be possible. I really don't know much about the blades but I suspect they are about tsr 5 or lower.

If you settle some of the variables then I will try to give you some figures.

Yes aluminium does suffer from fatigue and if you exceed a certain number of stress cycles then it WILL fail. For small and what looks to be fairly rigid blades you may never exceed the stress cycles in your lifetime. To some extent small is beautiful and many small things are inherently stronger than their larger counterparts. My prediction is that the blade mountings will fail long before the actual blades. I haven't heard any disaster stories for the TLG blades. I have seen far worse things in pictures posted here.

Flux

[Mary B]

I can get 24 1 inch diameter by 1/2 N42 magnets for $30 or so, the 2x1 is to big to use a trailer hub with on an 8 inch rotor. 100 watts or so during my average wind is fine, and there are plenty of days here with winds over 25 mph so I expect to see a bit more than that. I disagree on the aluminum blades. There are way to many antennas made from aluminum that suffer from extreme flexing, I know I had some in the air that would bow 5 feet in a heavy crosswind.

[Mary B]

I forgot to add, the TSR of the 3 blade version is 12, I am guessing the 4 blade to be around 10.

[Flux]

Yes I understand your problem with the 2 x 1 magnets, I forgot that I made the hub for the one I did. There is no room at the centre of the stator if you use a conventional hub and allthread.

I have looked at 12  magnets 1" diameter and it is perfectly possible, the spacing is not so bad.

I really have no confidence in your tsr figure for those blades. Taking something nearer tsr6 which may still be fast then you are looking at about 50 turns per coil.

Try a 50 turn test coil and see what size wire you can fit into a stator 1/2" thick. With care you might get #13 in if you squeeze the coils into more of an ellipse. If you need thinner wire it will not matter because the #13 will need added line resistance especially if that tsr is up where you say.

If you are in a high wind area then I certainly wouldn't go for too high a cut in speed

and you may manage with less than 50 turns.

Flux

[wdyasq]

MaryAlana,

You may disagree with anything you care. An aluminum antenna will flex a few times in a heavy wind. An aluminum blade will flex a minimum of twice each rotation on a furling windmill. Numbers like 300rpm/24/7 add exponential power factors rather quickly. The amount of flex is also a consideration.

The fact that aluminum WILL develop stress problems is well documented. The Smith-Putnam  mill on Grandpa's Knob Vermont, the first large scale wind turbine built, and the deHavilland Comet are the two classic examples of aluminum fatigue often noted. There are thousands of examples of aluminum aircraft parts being scrapped because of 'metal fatigue'.

NASA commissioned a test on various materials for wind turbine blades in the late 80's or early 90's. Material strength, weights and fatigue resistance were compared. The results were interesting. The report is worth securing and reading.

Ron

[Mary B]

Actually, those antennas sat up there and vibrated rather badly, could hear the elements from the ground. The rattles from it were obnoxious and annoying :-)It really depends on the aluminum alloy.

[wdyasq]

"It really depends on the aluminum alloy"

Just plain flat wrong... some alloys ARE better than others. ALL ALUMINUM ALLOYS HAVE A FATIGUE LIMIT.

I really don't care if someone has a catastrophic blade failure. I don't care if the dog and/or children are killed due to ignorance or stupidity.

I do care if by someone's stupid, ignorant and/or arrogant attitude a failure occurs and politicians decide 'homebuilt wind turbines' should be outlawed.

Ron

[Mary B]

having aluminum antennas last for 10+ years and they don't just bend in a wind, they oscillate quite badly and have them survive says that aluminum is fine in a stress application if it is designed right. ANY material will stress fatigue if it is overloaded.

[dinges]

Steel has a definite 'fatigue limit' : below a certain cyclic stress (N/mm^2) it can withstand an infinite amount of flex cycles.

Above this limit, the amount of cycles it can withstand drastically drops as stress increases.

Aluminium does NOT have this lower fatigue limit (or rather, the limit is 0 N/mm^2); at ANY stress, even small cyclic stress, aluminium WILL fatigue! It can NOT withstand an infinite amount of stress cycles, even at low stresses, as steel can.

There's no safe threshold that, if you stay below it, it won't fatigue, as in steel.

Conclusion: aluminium WILL fatigue if subjected to stress cycles. Steel (and some other materials) may or may not, depending on whether the stresses stay below the fatigue limit.

Guess that in the case of your antennas you just haven't had enough stress cycles to cause catastrophic failure. Then again, have you -really carefully- checked for fatigue cracks in your antennas, with e.g. dye penetration checks or ultrasound?...

</lecture>

All this is pretty much documented, btw, as Ron has said. You do what you think is best. But I feel it's important to have the details out here in the open so everyone can make an informed decision about their course of action.

[Mary B]

10 years of constant oscillation in the winds here is pretty good stress testing. Aluminum will work harden if bent past its limits repeatedly. And seeing a pair of 33 foot long antennas move in a storm is scary, they twist, bounce, vibrate and in general take a huge beating. And there are aluminum antennas that have been up for many years longer than I had mine up. But 10 years of constant wind exposure, ice loads, birds using them as a roost is a pretty good test of aluminum. The were flexed repeatedly day in and day out, my average wind speed is 17 mph and storms a few times a year with 90mph winds. If the blade is designed within the safe working load for the alloy used it should last quite a while. And I am not building my own, these are commercial blades sold by TLG windpower.

[dinges]

Work hardening occurs as an effect of plastic deformation in the material.

Fatigue is (normally) due to stresses that remain within the elastic region of materials (the region where Hooke's law applies).

The two have nothing to do with eachother, apart from the fact that intentional work hardening (as a surface treatment) can sometimes increase the resistance to fatigue.

The fact whether blades do change hands for money (i.e. are sold) matters little to the mechanism of fatigue and crack development.

Regards,

[SamoaPower]

Re: Aluminum vs. ??

All of you are both right and wrong. It's all a matter of design and application whether ANY material will stand up to the induced stresses and for how long.

Numerous examples, positive and negative, can be found to support either argument. I'll give a few more.

Probably, the closest analogy to our wind turbine rotors are aircraft props. It's been a long time since wood has been used in this application on commercial aircraft. Aluminum props have been the mainstay for many years and considering that they have to absorb 100's to 1000's of horsepower at high RPM for 1000's of hours, their failure rate is quite low.

I can both support and deny Mary's claims about antennas. I have an aluminum  Cushcraft A3 that has been up for over 20 years with the only failure being the fiberglass insulator rod on the driven element. It survived four hurricanes. She's right, they do move around and vibrate a lot. On the other hand, I had a 6 meter antenna that shed an element tip within two years.

The 16' diameter aluminum blades for my current wind machine project have already had four years of continuous service and close examination revealed NO fatigue cracks. I'll use them again.

While it's true that material science can tell us much about material properties, the PRACTICAL application is a matter of engineering.

I should add, I know nothing about the TLG blades.

Mary:

--...  ...--   -..  .   .-  ....  ---..  .-

[Mary B]

material strength of 6061-t6 aluminum http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MA6016

[Mary B]

I had 13 M^2 Antennas, dual 5 elements spaced 15 foot vertical, twin 17 element 33 foot long 2 meter yagis on a fiberglass cross boom, 2 31 foot long 432 antenna, 4 1296 yagis in an h frame, and misc loops for mobile use. All made from aluminum. And many of the big c band sat dishes are aluminum, I had a 10 footer on 1296mhz eme. That thing really took some wind abuse, it flexed and vibrated horribly in high winds. I broke several 1/4 inch steel mounting brackets but the dish held up.

[coldspot]

GHEEEEZ-

Please, everyone! Be Nice!

"Numerous examples, positive and negative"

Here near my home town, Wolverine Creek Wind Farm lost a blade set off one of their 43 GE 1.5 Megawatt SLE's within a year of going up!

 I've lost two sets of blades in two years now, both sets where just ceiling fan blades on an ametec that was only 13' off the ground. (first set 70+ mph, 2nd set was only 50ish mph, but in a very turbulant spot). {OK maybe 3 if counting the HF Mole Chaser wooden blades that fell off my garb-O-gen a couple weeks back on a 7' tower,[My fault screw came loose], but my anometer also was blown off its tower at 30', not just the cups but the top tube in tube was some how picked up and out of lower tube about a foot! ruined the reed switch,^#@%&!}

 Anyway,

TLG's blades would be a great start for any newby.

I'd love to play with some, I'm still trying to start the carving of a set of little ones 6-7' but can't seem to get brave enough to do more than the 60` end cuts with the cut to narrow as it goes out to the tip end! From here on the removal of wood will be by eye, not with guides and fences to make all the same so I'm stalling building other things.

MaryAlana- Have some fun!

[Mary B]

I have been playing with the TLG blades, very stiff and little flex or twist. They spin up very rapidly on the 30 volt Ameteks I have (not very good ones, 2 amps is going to be max). There was an extra blade with the set so I have been seeing what it takes to twist it and bend it. I can just twist it by hand and I can't bend it at all.

[alancorey]

Look at the common CB ground plane antenna.  9 foot vertical and slightly longer ground radials, made out of 1/2" at most aluminum.  They don't even try to be rigid, they flop all over the place like spaghetti.  And do it for 30 or more years.

On the other hand I've got a pickup cap with aluminum frame and skin, and within 5 years all the frame joints had cracked.  Guess it depends on the aluminum.  I still like wooden blades though.

  Alan

[Mary B]

here is a picture of a bit of aluminum in the air http://web.wt.net/~w5un/mba2003.jpg

He has had no antenna failures!