Wind Mill Blades

As having worked in fiberglas, the dimensions you gave as compared to the wood, I do not think there is would be enough strength. Someone that has more material science background can help more.

Wood has some good charicteristics.

But to answer your question about layup and not addressing the design aspect.

Try googling one off molds design. This should get you some results at least off of boat hull lay-ups and should help.

But the design will have to be addressed

p911

P911,

Thanks for the help, I'll begin nosing around some more on the tooling.

The design is the challenge (as usual).

Thanks.

Roy

A boat builder would have all the info and expertise required to build in fiberglass, wood or carbon fiber. I'm thinking specifically of the builders of the America's Cup racing yachts.

Ron,

Thanks for your direction. We have carbon and fiberglass materials in house and experience with both, however; we don't have a (fiberglass) blade design, nor access to FEA software to do a real engineering study. I'm hoping to find a current proven design concept that we can apply to our wind mill mounting configuration (thats asking allot) to get us started.

Thanks,

Roy

I believe directing a (PM) comment to this member may prove helpful in your endeavor.

elnav

and to this previous thread http://cr4.globalspec.com/thread/41736#newcomments

Thanks for the direction, i'm off to read this thread.

Sincerely,

Roy

you have wooden blades that work good for you ?

make a clay/ plaster mold of it and the lay some plastice sheeting in the mold layin the fiberglass materail. Have the mounting bolts made into the mold so you can form metal (searching for the name of it) shim into the fiberglass.

Pull it out and clean it up with a sander. then finish it

Thanks for the input, we are happy with the wood but hate to invest in tooling if there is a stronger or more efficient fiberglass blade design out there.

Thanks again for your help.

Roy

Geeze, more to think about.

I appreciate your point of view and your thoughts. I'm glad you took a few moments to help.

Roy

Hi,

I strongly support the approach of Yosemit3, (GA included), stay with wood, optimise your production methods, think about thin and elongated glass-fiber or carbon-fibers to reinforce the planes where the wooden parts are glued. (only if you are near the limit of strength).

Wood: easy to glue,

easy to repair,

easy to impregnate and re-impregnate for weather protection and sun-exposure.

Much cheaper than anything else.

Only to be changed to fiber reinforced material if stress is too high.

If one of the blades is failing - irrespective of material - there is a high probability that the whole structure including the tower will come down and has to be scrapped.

There is today no solution to this problem. I would think about some emergency pyrotechnics as in the separation of rocket stages.

Including early failure detection this would give some fantastic results.

Any insurance would be more cost effective (for the moment).

Have success.
RHABE

Maybe having a look here will help: lots of links to aerofoil design software.

Thanks for the help, I'm off to read this information

Roy

Wow. Cool.

Depending on your lay up sequence and method of manufacture in your fiberglass you could have a wide range of properties - if you're alternating layers of 1 1/2 chopped strand mat "E" glass with glass woven roving in a vinyl ester or polyester resin by the hand lay up method like most fiberglass is made for tub and spa market, storage tank market, and much of the boat market, you're looking at rough ballpark 1,200,000 psi young's modulus and 17,000 psi ultimate tensile strength if you're doing a decent job of rolling out air bubbles and you get it fully cured. With the same laminate using VARTM (vacuum assisted resin transfer molding) you can achieve much higher properties - 2 million psi + modulus and 25,000+ psi strength - and I suspect you won't need as high a safety factor, because you won't have voids and such that will be creep/micro crack sources which I'd be concerned about with this application. Carbon fiber would certainly take it up another notch.

I suspect that the most efficient design would incorporate a sculpted balsa or foam core with a VARTM skin. Where did you come up with your current design? If you like that contour and you have know-how to calculate the strength and stiffness of the current design, you could probably estimate the thickness of laminate needed on the skins to almost match the current design (remember, you have centripetal acceleration here creating a tensile load, and a bending load superimposed; there's even some twist thrown in for good measure) - the centripetal force should be a lot less, because you're talking about a lighter design. The bending and twist loads should be similar to current design IF the design is similar stiffness; I'm almost tempted to say that stiffness is the over riding concern here. I'm sure there's more to it than that when you factor in vibration, etc. Wow, what a cool project.

Good luck!

Thank you for your time.

There is allot of information here. I can now move forward with a bit more confidence, we have the 1 1/2 c/s mat and polyester resins, and a vacuum pump.

I will review the strength and stiffness information next.

Thanks again!

Roy

Roy,

i dont have any information on the design of these. i am with Continental Diamond Tool and we are dealing with several customers that manufacture the fiberglass blades. If you ever need and help on tooling, feel free to get ahold of me and i would be more than happy to help you out in that area.

Thanks

Cory cory@cdtusa.net

Any fiberglass blade will have to be hollow or cored with balsa, foam, honeycomb, etc to be lighter than wood. At 1 1/2 inches thick, hollow would be a good bet (and as you get thicker, hollow becomes essential.

In an aircraft wing, even a very light foam core (2lb/cu ft) is too heavy to be considered "light" if the entire wing is filled with it. The VariEz used this construction (i/e with the entire wing filled with foam, and the surface hot wire cut and subsequently covered with oriented-ply fiberglass) for ease of construction, not light weight. You may want to study the wing design on the Lancair or Glasair. As a wing gets thinner (as your is) the core weight is less of an issue, so you might find that the simplicity of a full foam core is worth the very slight weight difference.

It would be possible to mold the skins with integral spar caps laid in (of unidirectional carbon fiber tape) , join the two halves (front and back) and then inject a foam core, I suppose. Such a foam core might have adequate shear strength to eliminate the need for a shear web molded in perpendicular to the skin... but I doubt it.

Windmills have the peculiar trait that the bending load at the root would seem to be very high assuming a long and thin blade, but centrifugal force keeps the blade relatively straight, as in a helicopter blade, many of which bend under their own weight when standing still.

The wing on my Windrocket was 20 feet long, 4' at the tip and 6' chord at the base, and 12" thick at the base. It weighed 60 lbs. The skin was 1/8 thick foam core with fiberglass cloth in epoxy on each side, vacuum bagged. The spar was only 1/2 inch thick in the plane perpendicular to its 12 inch base thickness, and the foam core for this had a couple fiberglass plies on each side oriented 45 -45 for shear resistance, and to give the spar web adequate bending resistance in the fore-aft direction.

The spar caps (tension and compression members) were carbon fiber pultrusions from Avia Sport, which are far stronger and stiffer than carefully hand laid up and vacuum-bagged unidirectional carbon fiber in epoxy. They are also far less labor intensive than hand lay up. Design for transferring loads at tapers, and at the root has to be done carefully-- it takes a very large amount of secondary bonding area to equal the strength of the pultrusion. Great stuff for a light structure.

In my wing, I used pretty traditional wood stick ribs, spaced to keep the 1/8 thick skin from flexing. In a blade like yours, the skins could be relatively thicker, and the ribs could be integrally molded into the skins -- I'd think you could mold each blade in two pieces (front and back side) and glue them together.

All sorts of possibilities. Even thin plywood for skins and aircraft spruce (perhaps from the company of that name) for spars can make a light, strong structure. The old Bellanca had wood wings like this and performed very well -- better than the typical spam can (aluminum plane). Aircraft grade spruce is very expensive.

Although you could design this "by hand" and come up with a good structure if you are careful, I'd recommend using FEA to make sure the thing doesn't come apart.

Roy,

I don't have knowledge in overall blade design. However, I do have a suggestion for you considering blade finish. Typically blades are finished smooth on both sides. I believe that the upwind side of the blade, the side that catches the wind, finished in a rough texture would improve blade efficiency. The rough finish would "catch" the wind better. Of course, the downwind side of the blade should be as smooth as possible to allow it to slice through the air easier. Good luck.

Don

For the time, effort, and money involved plus the learning curve you may well be ahead of things to just buy a set of fiberglass blades from a reputable source.

There are several online suppliers who have good quality fiberglass blades that are used by commercial manufactures world wide. Power-max is one of the better ones I have used for home made blades. Wind-max has a new line that they came out with thats supposed to rival the Power-max ones.

However Wind-max had some severe manufacturing flaws in their old line of blades due to bad craftsmanship at a low end Chinese factory. I had three sets of blades from them all fail due to voids in the fiberglass resin at the roots and leading edges. One started to open up on the leading edge seams. One fatigued at the roots and hit the tower. And one set had one blade just rip right apart at the root in an averagely windy day. Now they claim they have a new factory and a tight quality control system in place.

The Power-max ones seem to be much stiffer and have a much better finish and feel to them. Plus they have rotor sizes from 6.8 foot to 35 foot diameters!

I have the 9.2 foot blade set from them on a 3 KW direct drive PM alternator that is going to be up and flying this fall and hopefully a full 21 foot set with a 20KW gen-set behind it as well shortly after.

Its just a thought.

TCMTECH,

That is a lot of important information; I certainly appreciate you sharing your experience. I will take a look at theses manufactures. Did you order "special design" or standard configuration blades?

Thanks again,

Roy