Making Aluminum Blades

[Bruce S]

Matt;
I gotta ask, why would you have flexing on a turbine's blades?
Doesn't make sense, the blades are to interact with the wind, that's what makes the turbine work in the first place.
Metal flexing is a bad thing, certainly not completely stoppable, but when a blade flexes it changes the dynamics of the turbine.
So possibly explain in greater detail why you believe a flexing metal blade is good.
Same goes for plastic, otherwise the PVC blades would more pervasive.

[MattM]

A fixed blade is designed to be optimal for one speed.  Why not allow the blade to shift its pitch as wind speed and pressure against the blade increases?  It makes more sense.

Flexing will fatigue the metal blades.  The blades made from sheet metal are disposable and incredibly easy to manufacture with a pnuematic shear and Autobrake press.  If they have to be changed annually it's not a huge cost.  Wooden blades on the other hand are man hour intensive and it is a huge cost to manufacture not just one, but matching sets.  Plastic and carbon fiber blades can be made with similar flexing characteristics.  Don't fight nature, bend with it.

[Bruce S]

MattM;
I totally and completely disagree on so many levels it is not even funny.

Let's look at what you are attempting to get into people's mind set.

You say metal will fatigue and let it. I call BS!! on this. Metal will fatigue then in a high wind shear off go flying and possibly do damage to someone's else's property OR worse cause physical harm.
Your statement of man-hour intensive to make wooden blades actually tells me you have NOT taken the time to read up on the chainsaw method put up here many times and even proven to take less time than it would to setup a metal form jig.

-----GM Mode----

AS a Moderator, I have been asked by more than a few long time posters to step in and get this post back on track about "Making Aluminum Blades".
Therefore I am respectfully requesting that the making of metal blades and any further posts that other not related to "Making Aluminum Blades" be put into a separate post.

---- End GM Mode ----- 

[MattM]

People have a total misunderstanding around here how metal parts fail.  Metals are stronger when under tension.  Unless they are holding tension when they break, they will not fly off.  They will fail when the tension is released.  A metal blade that fails is more likely to fold back into itself first.  In a three blade rotor the two undamaged blades will sit in the lower position and the failed blade in the upper position above it.  Maybe in gail force winds the two blades can continue to spin, but it takes quite a bit of wind to get them to rotate in that condition.

[kitestrings]

Bruce,

The OP asked about aluminum blades, but also asked:

So, is the material of choice wood? Or something else.

This led to quite a bit of discussion about wood vs. aluminum.  To me the metal/skin discussion is not really off topic.  I may have missed some mud-slinging or some such.

A metal blade that fails is more likely to fold back into itself first.  In a three blade rotor the two undamaged blades will sit in the lower position and the failed blade in the upper position above it.  Maybe in gail force winds the two blades can continue to spin, but it takes quite a bit of wind to get them to rotate in that condition.

Any blade failure is catastrophic and to be avoided.  If one blade fails the resulting imbalance can sometimes create an even more dangerous and/or damaging condition.  In the worst case bringing a tower down.  A machine may "hang" in the position you've described, but when it fails (usually in high winds), it's far from this passive image.

I do think flexing of the blades is a normal, design intended, feature of most turbines.  This is why IMO neither aluminum or metal, long-term, are good - or let's say better - choices.  When I envision the perfect rotor its more like a glider wing(s).  If the rotor is too rigid all of the stresses are transferred immediately elsewhere.  The hub, bearings, yaw assembly, etc. all receive harsher treatment that impacts respective service-life.

~ks

[SparWeb]

Matt,
You claim to have purposefully made WT blades that failed and over and over again replaced them only to see them fail again.  I'm glad you don't live next to my house.  If you built it for somebody else, then how soon will his kids get filled full of holes?

I encourage you to start another thread, maybe with some photos of your creations.  I won't ignore it - I would just prefer to stay on topic here.  We can all learn from our successes and our failures.