...and crack! it said

[Sponge]

Hmm, pictures warm from the camera. I learned my lesson not to use plywood for testing purposes . The wind got a lot stronger suddenly, and I was taking some pictures through the window.

Moments before.

The last 5 secs of this hub.

Never use plywood. (or layered stuff)

Luckily the blade went into the ground. And yes, that motion blur is REAL!

I'm still a bit shaky, wow that went so fast! (The PVC blades are 100% intact though)

-Sponge

[whatsnext]

I wouldn't blame the plywood as much as I would your hub design or the balance of ther thing. Laminated wood can be very very strong.

[Sponge]

Yes, but it can't take eh.. "external pulling" . Everything was balanced 100% . Definetly the wood .

[hiker]

no furl!!!!!!

[Sponge]

test setup ith my first alternator thing. If this blade is fixed, I'm going to make something new I think..

[hiker]

or should i have said--NO FURL AND IT WILL HURL !!!!!!!

  live and learn---what kind of power was it puting out when it gave out

[Sponge]

There's no magnets on it . I was just testing the blades, the coils you see are from the old alternator.

[richhagen]

Please be careful, I like reading your posts.  With no electromotive drag on the rotor, and no furling, it spun up real fast.  Like you, as I surmise from the photos, I have neighbors, and have been toying with the idea of using kevlar or carbon fiber fabric bonded to the outside of the blades with a polyester resin gel-coat and finish sanded.  The idea being that if a blade gives it may be more inclined to stay attached and flop around as the rotor slows due to the increase in aerodynamic drag.  I don't know if anyone has experience with that, but the idea is that it might add a small measure of safety.  The idea of throwing a blade in a gust and having it end up in a neighbors window or hurt somebody concerns me.  Rich

[DanB]

I like plywood fine - Id agree with the other post suggesting it's the design here.

No furling and no load didn't help either - although it's nice if a blade can withstand that sort of abuse for a bit, because it could happen sometimes, but overall - its the thickness of the plywood you used, and the design.  A much stronger hub could be made from ply.  

This may be a bit of a controversial statement here, but  - even though they survived this one... I would never make blades from PVC, Im very doubtful they can hold up for long - the stuff gets brittle and I think it suffers from fatigue.  Its a neat - quick way to make a blade that evidently works... but it would make me nervous to live near one.

[whatsnext]

It's hard to tell from the picture but that looks like the plywood that the Chinese use to make crates. I believe it's called ruan(sic). If that's the case it's not designed to take any load at all. Go buy some Baltic Birch plywood. Any seller of good hardwoods should have it. It may not be optimal for a hub but it will not explode like the stuff you had did. It's void free and dimentionaly stable. It's also quite dense. Most people don't understand the forces that dynamic assemblies see and I find it very unlikely that it was "100%" balanced.

John........

[BT Humble]

Everything was balanced 100% . Definetly the wood .

Yeah, I see the smileys and I know you're kidding, but the primary cause for this failure was the design.  Sure it looks better to have a star-shaped hub, but it's never going to be as strong as a full disk - whatever type of wood it's made from.

BTH

[Sponge]

I've done some stress testing on the PVC, Dan. Put in the freezer at -18C (never gets that cold in here), and start bending it again. No problems. Whe nhitting it with a hammer -and still takes effort-, pieces will shatter from it.

I couldn't break the first protype blade I made, which was only 2,3 mm. This one is 3,2mm thick I believe. It's like breaking a CD-ROM. You can't! (unless you go back/forth all the way to the end).

I'm carefull with it, though.

It was just one blow of wind this time, which was harder than the average that day, otherwise I wouldn't have put the mill outside. With load, the windmill will go a lot slower anyway.

And yes, I will use different wood now, probably unlayered stuff, although I've been thinking of some metal too, that could be bended so the blades are position on a nice angle, and I could attach it with more screws then. But I have no idea where to do that.

Sponge

[PaulJ]

   Don't give up on the plywood. Good quality marine ply is amazing stuff, strong yet flexible enough to cope with the vibration of a wind generator. I use 12mm (1/2") thick 5-ply. I agree with BTH that the full disk would be much stronger.

   Just my 2 cents worth, my only experience is with wooden blades.

[Ungrounded Lightning Rod]

I've done some stress testing on the PVC, Dan. Put in the freezer at -18C (never gets that cold in here), and start bending it again. No problems. Whe nhitting it with a hammer -and still takes effort-, pieces will shatter from it.

Try leaving it out in the sun for two years and then torturing it again.

The issue with PVC (and other plastics) is their strength and brittleness AFTER the damage their molecular structure takes from ultraviolet light (and other sources, though that's the biggie).  Broken bonds.  Extra bonds making it more brittle.  Etc.

[bob golding]

to save waiting 2 years  go and get some old  pvc drainpipe or preferably guttering and torture that. could try using high pressure gas main instead. that is made of polypropylene and is designed to not shatter. in the UK it tends to be yellow.

bob

[Sponge]

If it lasts a year, I'm happy enough. I can make these in a day. Sun will probably hurt after a year (how old is your rainpipe - PVC? ). I couldn't find yellow plastic, or ABS inhere, unfortunatly. But this will hold up for a pretty while I think.