[wyobmf]

Hello,
I need to build some 10' wind turbine blades and wanted to see if I have the right idea, This is my plan.
Take my IGES blades in CAD/CAM split them in half and then boolean them out of my stock. I was then going to mill them with my 5'x10' gantry mill.
The next part is what I am really not sure how to do, But here was my plan again:
finish the molds, spray release, get a chopper gun and spray fiberglass, remove the half blade and finish the mating side, then fiberglass the two halfs together.
If anyone has any experience with this kind of stuff, please let me know if that will work or not.
Thanks

[JerryFlyGuy]

There is more to the equation than just the surface of the blade. Joining two naked edges isn't as easy as one would think, nore finish. Designing in 'joggles' for the skins to overlap and assist w/ the finish is vital.

Also your going to need some internal structure in addition to the skin. If your just starting out, I'd recommend machining a foam blank into a 'core' and lay up 7781 or similar cloth. Then add a vacuume bag on top of that and get it down tight and smooth.

Fwiw

Jfg

[building a fibreglass airplane fwiw]

[wyobmf]

Jerry,
Thanks, Would the cloth covered fiberglass be suitable for use or just a model? I would think it would need some support structure also? Although it would be easy and cheap to machine a foam blade.
Another option I am kicking around is laminating lumber and then mill the blade out of wood. Like the old airplane props, Do you think that would work.
I have the shoftware to design airfoils for wind turbines. The blade would be heavy but with three of them they would balance each other out some, the only draw back i see is the startup speed would probably be higher.
Thanks

[wendtmk]

Another thing to consider, when you're lofting the airfoil for the blade, typically pitch does not remain constant the length of the blade, in order to optimize the blade. It tends to flatten out the closer you get to the tip. Of course, this can sometimes be done be changing the airfoil at different stations along the length of the blade, to lessen the "lift" close to the tip, and increase the "lift" closer to the hub.

There's lots of things that have to be taken into consideration when designing a "propeller" blade than just picking one airfoil. Especially if you are designing a "turbine" blade which will be turning fast. If you're building 10' blades, you're talking about a 20' diameter "propeller." You're going to have to be very careful at high RPM's so that the tips don't go supersonic.

Mark

[CarbonKevin]

I would use a foam core with fiberglass sleeving to get a stronger, one-piece composite. It can be vacuum bagged or infused for greater strength to weight ratio. Carbon could be added in strategic areas for stiffness, and you could also add aluminum or plates to the foam core prior to layup for attachment points later on.

A comment on the wood idea. Yes, it is possible to perfectly balance the three blades. However, the lateral loading on the bearings would be much higher. Also, the overall efficiency of the unit would be decreased as it takes more energy to move a heavier turbine than a lighter one to the same speed.

[wyobmf]

The software is a blade calculator, It is free at: http://warlock.com.au/tools/bladecalc.php

The RPM would be about 800 with an 80 MPH wind, very very rare where I live.
Not sure what the tip speed would be. Most recomend a tip seed ratio of 7.
Thanks

[wyobmf]

I would use a foam core with fiberglass sleeving to get a stronger, one-piece composite. It can be vacuum bagged or infused for greater strength to weight ratio. Carbon could be added in strategic areas for stiffness, and you could also add aluminum or plates to the foam core prior to layup for attachment points later on.

A comment on the wood idea. Yes, it is possible to perfectly balance the three blades. However, the lateral loading on the bearings would be much higher. Also, the overall efficiency of the unit would be decreased as it takes more energy to move a heavier turbine than a lighter one to the same speed.

Kevin,
I agree lighter would be better. Can you or somone else please explain the vacum bagging process? and what equipment i would need.
Thanks

[CarbonKevin]

Very briefly,

Vacuum bagging begins with a standard wet layup of resin and reinforcement. The part is then wrapped in a gas/resin permeable nylon cloth, then a layer of fleece. The part is sealed in an airtight bag, then vacuum is applied. The air pressure difference inside the bag results in very high pressure over the entire bag surface. This squeezes excess resin from between layers of reinforcement. The vacuum draws excess resin out from the part, and into the fleece. Vacuum is maintained until the resin has cured. Bag is removed, fleece and nylon cloth are pulled away, leaving the cured part.

Vacuum bagging uses a fair amount of consumables, but very little actual equipment. You'll need your vacuum pump, a resin trap to protect the pump from sucking up resin, and a vacuum gauge. You could also use a venturii system to generate vacuum, in which case a reservoir becomes a very good idea as well.

Infusion involves laying up the reinforcement dry, wrapping in nylon cloth, and then adding flow media over the cloth. The part is sealed in a bag, vacuum is drawn. On the end of the part opposite to the vacuum fitting, there is another line that leads to a bucket of prepared resin. When that line is opened, resin is drawn into the part, where it travels towards the vacuum source, dispersing itself through the reinforcements along the way. Once the part is fully infused, the resin line is clamped off, and vacuum continues to be drawn until the resin has cured. Bag, nylon cloth, and flow media are removed, and part is ready to be trimmed/sanded/processed.

Infusion is much cleaner than regular vacuum bagging, but does use a lot of consumables. Setup of the vacuum bag, resin lines, and flow media are also somewhat more complicated than with standard bagging. With a 10' blade, you would very likely use multiple resin feed lines sequentially from farthest to closest to the vacuum fitting. Infusion is probably the best method of getting very consistent, high-quality parts, but is the most difficult to master.

I'd recommend you sign up at http://www.compositeforum.werksberg.com/index.php? and start reading...there's a wealth of knowledge to be found there. PM me if you need any more info.

CarbonKevin

[wyobmf]

Thanks, That is very helpful and a good explanation.
I will read up on it and probably do one of the vacuum options.

[eSilviu]

Hello,
I need to build some 10' wind turbine blades and wanted to see if I have the right idea, This is my plan.
Take my IGES blades in CAD/CAM split them in half and then boolean them out of my stock. I was then going to mill them with my 5'x10' gantry mill.
The next part is what I am really not sure how to do, But here was my plan again:
finish the molds, spray release, get a chopper gun and spray fiberglass, remove the half blade and finish the mating side, then fiberglass the two halfs together.
If anyone has any experience with this kind of stuff, please let me know if that will work or not.
Thanks

search google for "helix wind". it's easier to build with a router, and work better close to the house.

[Loco112]

I would use a foam core with fiberglass sleeving to get a stronger, one-piece composite. It can be vacuum bagged or infused for greater strength to weight ratio. Carbon could be added in strategic areas for stiffness, and you could also add aluminum or plates to the foam core prior to layup for attachment points later on.

I agree completely.


Start thinking of a way to control your blades pitch in motion, just like airplanes and high end wind-turbines use. That is how you can keep your blade at a semi-constant speed in changing wind speeds, and incase of a storm you need to flatten out those blades and put on a brake to hold it or you will have a "runaway' or an exploded turbine as soon as it hits big wind speeds.

There are a couple of good books on FRP (Fiber Reinforced Plastics, AKA-composites) that Amazon sells, get one of those to start your learning FRP and you'll be on your way.

What gen/alt are you working on using, and what, if any, transmission?

[wyobmf]

Hello,
Thanks for the reply,
I am using 1/2 the axle out of a semi-truck trialer. I choose this because they have very stout bearings, and air brakes that I can use to shut the turbine down if I need to. I have thought about ways to control the pitch but it would not be easy. I was thinking something like the swash platte on a helicopter. I have also been thinking about using a large air actuator to furl the tail in high winds. There is no transmision and the generator is PMA type.
Thanks

[CarbonKevin]

You're thinking along the right lines with the airbrakes from a heavy truck.

Whether you go that way, or use variable blade pitch, the idea is should the system fail, it will revert to the safest position - with airbrakes, the system would lock up, with variable pitch, the blades would angle themselves to get the least possible amount of energy out of the wind.

We've all seen runaway wind turbines, it really baffles me that they wouldn't have this sort of mechanism in place for all of them. Yes, it costs more, but burning, exploding, or falling over wind turbines probably aren't very cheap in terms of PR, either.

ck

[lukewarm]

I am also planning a large hobby wind turbine myself. I will be going with a three phase induction motor connected to the grid through a net meter, I prefer this because it locks the generators RPM to the grid up until a certain break-away torque. We also are also using truck axles for the rotor and nacelle with a breaking system like yours. The biggest unknown at this point is the variable pitching mechanism but we're leaning toward having each blade pitch independently for a few reasons.

One consideration you might want to make with a 20' in diameter rotor is blade flex/blade strike and large forces being applied to your blades when the wind changes. We've gone with a downwind design for these reasons. Downwind designs don't use a tail to steer them into the wind and lessen stresses on the blades and your nacelle/tail. Also it eliminates blade strikes as the wind pushes the blades away from the tower.

As for wood versus fiberglass I'd so go fiberglass. Wood is a great material but it can be finicky with moisture. If you haven't already seen the website go look up the Breezey 5.5 they have some pretty neat pictures.

[lukewarm]

The software is a blade calculator, It is free at: http://warlock.com.au/tools/bladecalc.php

The RPM would be about 800 with an 80 MPH wind, very very rare where I live.
Not sure what the tip speed would be. Most recomend a tip seed ratio of 7.
Thanks

If your rotor is 20' in diameter and it rotates at 800 RPM the speed at the tip of your blades is:

( Circumference X RPM X 60 )/ 5280
(62.8 X 800 X 60)/5280 = 571 MPH

Its not exactly the sound barrier but it's getting close. It will probably be very noisy. A rotor this size spinning at 800 RPM is also going to have a huge amount of forces applied to it that need to be closely examined. Most large wind turbines spin much slower using gear boxes etc to avoid these problems. Maybe I'm wrong, food for thought.

[dimitar]

Here is some software for wind turbine blade Applied Computational Fluid Dynamics (CFD)

[unexpectedly]

You could look into compression molding for a solid plastic blade. Not sure how light of a plastic you can get in it. Rotational molding is pretty fantastic for applications where you need strength, resilience, and it can be hollow. Plus you can control the thickness by changing the shot weight. Most kayaks are made via rotational molding. Roto won't like sharp edges, however, so the parting line probably needs at least 1/4" radius and not a sharply angled V.

Blow molding might be well suited to this, except that's the most costly choice of the three and the most complicated tooling. If you're already talking about CNCing a 10' mold, you can make your own roto or compression molds.

I'd say visit some of the rotational molders in your region with your idea. Ask first if they do kayaks or something similar. Roto molds just need to have steel reinforced plates for the 1/2" x 3" bolts everyone uses. Then they weld a frame to it. Fill it, bolt it together (with air impacts), clamp the tool to the platter. An hour later your part comes out. Figure it might be $40 per part.