Wind Genny Blades

[knight4713]

I seem to have read somewhere that foam core fiberglass is pretty strong.

I was thinking about using the 2" rigid insulation from the local home improvement, carving the blades with the "turkey carver" then wrapping / coating with fiberglass.  Seems it will be very light and quite strong.  Any advice or ideas on this?

I'm not much of a wood carver nor do I have most of the tools I would need.  Seems like to carve the  foam, all I would need is an electric knife and some type of very coarse file / rasp... and a good shop vac.

Thanks

[tesla man]

How long are the blades? How thin?

I had a similar idea, but was going to cut "chords" (cross -sections), in the foam, of the blade, with a central opening, to pass one, (or  two), thin, metal tubes. thus taking the core sections, and place them over the central tube ( similar to placing beads, along a string)

the tube would transfer all the forces from the tip of the blade, to the hub..

by placing a pulley, on the end of the tube ( outer-tip of blade) , a thin wire passing from the base of the hub, to the pulley, and back to the hub.

by tensioning the wire, it would compress the metal tube, giving incredible strength, with very low mass, to the central 'spar" of the wing. thus all the tension would give the wing strength, and the foam can be covered with a very thin layer of fiberglass ( or preferably carbon fiber, with an outer layer of kevlar)

the idea is to make the blade as light,and as strong as possible, the more of these one can attache to the rotor hub, the lower the wind speed we can then start generating power

so we can a have quite a few of thin, lightweight, and very strong rotor blades ( the central tube/ tensioned wire..back to the hub)

just some crazy thoughts on this.. buy stacking a lot of these cores, we can then glue them together ( before fiber glassing) and then give the blade a slight twist over its  length, for added low wind speed..

I belive that very long, very light-weight,  rotor blades (foam core with a central, metal tube/ tensioned wire,  central passage,  fiber-glass outer layer), will get one toward a very light-weight, strong rotor blade..

I think that to make these foam cores, one would need to use an  electric wire cutter, or a cnc mill to create a series of templates, of the core cross sections..

just some thoughts on the subject.. just crazy thoughts..

[rotornuts]

If you get the pink high density concrete slad underlay foam you can carve it with a knife or a power plane or for best results a belt sander! It is very strong stuff as it is designed to withstand high compression applications. If you keyed into the base of the foam blade with a wooden spar or a metal rod then encompassed a portion of the spar with the fiberglass skin I believe this would provide suficient strength but tests would be in order. I'm still thinking about a good way to cast foam cores for the sake of repeatability. Anyhow good luck.

 Oh, also I don't think a full spar of wood or metal would be needed as the skin will become the effective structural component provided it is thick enough. The foam will act as a core to prevent collapse of the skin.

That my take on it.

[newguy]

i tried this but one thing to make shure is that

the fiberglass resin you use doesnt melt eat the

foam thats what happened to me so well i gave up

but i used a hot knife to cut the blades out of foam

i used the white foundation setup foam or whatever not

shure what it was if you look in my files at the posts ive

done there were a few comments to this subject

later

A egan

[electrondady1]

you would need to use the kink of foam they us for surf boards

[cdg378]

You need "closed cell" foam, type used in marine and aircraft applications which is very expensive stuff. Styrofoam insulation made by dow "blue" is closed cell and works nicely along with resin and can be purchased at any home center.

The blue styrofoam can be used with polyester resins (cheap) or the more expensive resins like the west system.

I built a cabin extension on my yacht with the blue type, I hear the pink brand works as it is closed cell also but I have no experience with it.

Also pourable foam used for flotation is the same closed cell structure and could be used in a mould, not that expensive either as a 2 part expanding product.

Use in ventilated areas...

[JeroenH]

Fiberglass on foam is used extensively by model airplane builders. The process produces light, strong wings. They put the fuberglass on the foam core, put the wing in a plastig bag and evacuate the air for a few hours (usually with a vacuum cleaner). That way they get a smooth finish and a good bond between the foam and the fiberglass.

I have no idea if the forces on model airplanes and wind turbines are comparable, but when I see those big 3kg gliders pull up out of a steep dive there should be some pretty big forces, especially near the wing root. But of course, those forces only act for a short time and not very often, while a wind turbine blade sees continually varying forces as it rotates.

[MISTER FIXIT]

HELLO:

         IS ANYONE REALLY INTERESTED IN FOAM CORE BLADES?  I HAVE ACCESS TO FIBERGLASS AND RESIN . JUST INTERESTED TO SEE IF THERE IS ANY REAL INTEREST AND IF IT IS WORTH THE TROUBLE OF DESIGNING OR EXPERIMENTING WITH THE PROCESS. ANY RESPONSE WILL BE APPRECIATED.

MISTER FIXIT

[TomW]

fixit;

A friendly heads up:

Please, please do not type in all capital letters. It is considered to be shouting.

I am fairly sure there is a good bit of interest in any kind of good blade construction method for the average Joe.

Cheers.

TomW

[Seedler]

Make sure you strengthen the blades.  I made a set of fibreglass blades with an expandable foam core.  Each blade was 2.5m long.  They worked well untill we got huge christmas storms.  They just snapped off, you had to be there to see it, it went out in style.  One entire blade landed in trees 200m away.  I think there was also a weakness at the fibreglass joins.  I'm making a new set now.  They have a metal pipe running the entire length of the blade. (Better safe than sorry)

[iFred]

using tin foil ontop of the foam will protect it from the resin. experiment!

[Windworks]

Carefull using blue foam and poly resins. The blue foam will turn to liquid instantly. Epozy resins work fine though.

[wdyasq]

Composite structural design is not to be taken lightly.  Combining materials with different flexing properties will load only a part of the matrix.  Fatigue resistance of 'fiberglass' is lower than that of wood but high than that of metals.

Ron

[kitno455]

check out robert q riley's recumbent carbon fiber bike. http://www.rqriley.com/xr2.htm

i built a frame using his ideas, and it turned out to be super easy, and not all that much more expensive than fiberglass. and it is quite strong. you will have to laminate in some aluminum plate at your hard points, and watch out for stress risers at the edges of those plates.

also, someone suggested loading metal tubes in compression, using an internal tension wire. do not do this, two reasons:

1. you encourage kinking cause the tubes are so much larger than the wire, that the tension will arc the tube till the wire touches the inside. (over time, the steel cable will abrade the tube) if you added spacers inside the tube, you have created localized bending at each one, actually increasing the likelyhood of collapse
   
2. metals in general are noticably stronger in tension than compression, so you are not making good use of the material, especially given your extreme slenderness ratio (length of tube/diameter of tube)
   
   

in fact, i would go so far as to say not to put any tubing, or wood inside the foam. um, how to explain....

ok, when you twist something, the material that resists most of the force is the material farthest from the axis of the twist (which runs down the center of the object). this is why RWD driveshafts are large, flimsy looking hollow tubes that never seem to break, and FWD half-shafts and RWD axle-shafts are skinny solid bars that break all the time (well, ok, there is also the ring and pinion ratio working on those two, i cheated) the same thing goes for torsion bars, etc. hollow ones weigh less, but are just as strong as solid thinner ones.

when you bend something, the axis is in a different place, usually off of the object. (in the case of a blade, it is somewhere many feet behind the blade, about half-way up its length, and moves down and forward as the blade bends). the material that resists most of the force is in bending is the material farthest from the axis (the front surface of the blade) which is loaded in tension, and the material closest to the axis (the back surface) which is loaded in compression.

so, the absolute best place to put your mass on a blade, is the outer surface, both for bending and torsional loads, preferably with more strength near the root, especially on the back side, since the bending moment moves down and forward, concentrating the compression of the material at the root, and the material is likely more compressible than the layers on the front of the root are 'stretchable'

first post for me,

good to meet you all.

allan

[rotornuts]

I agree with the no spar theory. As long as the spar extends into the blade stucture far enough to incorporate into that structure I would simply add additional thickness to the skin at that point to preclude it becoming a weak point. If yoiu need to spar the full length them you've nulled the advantage of a foam core blade. As long as the skin is of sufficient thickness it will work great and still be lighter than sparing the length.

[gibsonfvse]

I'm not quite sure I agree with the "no spar theory," but my structures knowledge is not quite up to par just yet.  So might I suggest an in-between step: spar-caps made of carbon fiber.  They must be used on the top and bottom surface of the blades, and when this is done, the blade should be very resistance to bending loads.  Spar caps alone won't do much for torsion loads, if I remember correctly, but that is another story

[MISTER FIXIT]

thank you for the reply guys.  i did not know how this one works.  i am new to all of this.  to reply on the type of foam i would use , it is (ready for this) polyisocyanurate foam ( yellow foam )>  dow supertuff-r foam board.  the type with foil on it.  your going to say, how am i going to cut this stuff?  the answer is a length of braided wire( model airplane control line .015 or .018) used on a bow to make a bow saw.  this foam will not hot wire, and you can use any polyester resin on it. you make your templates using whatever airfoil you want, attach then to the outside ends of the foam, then saw the foam with the bow.  for the spar, you can use telescoping aluminum tubing if the blade is tapered.  all tubing MUST be ran to the root end.  so if you have say 3 pieces of tube,you will have a 3 tube thickness at the root end.  or you could use a hardwood spar.  any comments on this?      

thank you.

mister fixit

[mvr]

All of the strength in such construction is in the skin, so you have to make sure that is strong enough.  The reason why I beams have flanges is that that is where the stresses are.  One is being compressed while the other is being stretched.  Similar forces (though more complex) will be acting on a blade, and it is because of this that this technique works.  But this also means that strenghening the core won't be doing all that much unless in doing so you are somehow strengthening the joint at the root where I suspect a lot of the stress is located.

Wood is probably actually easier to work than foam, so one option is to coat your wooden blade with a similar wrapping.

best,

Mark

[healerenergy]

I love the information on this board it covers a broad range of subjects all in  one forum to further more balance in our society. I have also found lots of information in books, tv, and magazines.  I hope this bit of info helps here. For a while I got wooden boat magazine one of the artical I think fits here it talked about putting carbon fiber bars or strips in the boats mast and spars. If  anyone is interested I can look up the manufactures and mabe a website. I also have a book on building composit planes and others that might be of interest.

[TERRYWGIPE]

They make fome for roofink and masonry aplications, which you can cut with a hand keyhole saw. I would put some sort of support inside then cover it with fiberglass. the sheets come in different thickneses from 1/8" to 2" in 4'x 4' or 4'x 8' sheets that you can get at ace or lowes, etc... The stuff is easy to work with, cheap and might work out well. if you cant find it at any of those home do-it-yourself centers find a roofing supply center.

             Terry

[dustind]

You guys should check out www.homebuiltairplanes.com I already asked the owner permission to post windmill stuff there and he agreed.

I am no expert but I think I would use extruded Styrofoam (blue stuff, not the normal expanded kind) covered in graphite cloth for high strength and very high stiffness. For less money you could use foam covered in fiberglass and use an airplane epoxy system. This way you just cut the foam to shape then lay up fiberglass/carbon fiber/graphite on top of it.

If you want to make lots of blades then maybe female molds would be a good idea. Information on how to make female molds can be found on the web site that I linked to.

I will ask them how they would do it then post back here.

[dustind]

This thread has some advice. http://www.homebuiltairplanes.com/forums/showthread.php?s=&threadid=1404

Feel free to searching the forum, or post questions.

[JerryD]

SO YOU WANT TO MAKE FIBERGLASS BLADES

The Word Fiberglass can be construed to have many meanings in the plastic business also known as F. R. P.   Fiber Reinforced Plastic.

1.)      Fiberglass products contain fibers and a resin (binder).

A.    glass fibers

B.    Kevlar  (expensive)

C.    Carbon fibers (very expensive)

D.    Polypropylene

E.    Nylon

F.    Others  such as burlap among others have been used (not so good)

2.)    The Resin (Binder) contain a binder which is known as resin usually polyester resin that uses a catalyst that interacts with a promoter to cause a molecular action which enables the product to cure also known as polymerization.  Cure (not to be confused with drying) Drying depends on solvent evaporation into the atmosphere order for the product (usually paint) to dry. Curing can take place in a vacuum but is fairly temperature sensitive with the best temps ranging from about 72to 77 deg.

However most will cure at about 65 to 100 deg but with some unpredictable cure times and low or high peak exotherms which  low exotherm (low curing temps) may cause a part to not achieve full strength . High peak exotherm will some times cause  the part to get to hot (and on rare occasions spontaneously combust) to crack and split causing the part to be unusable. Note when using polyester and it is very hot above say 85 deg the recommended amount of catalyst must be cut by about 40/50%. When the temp is about  100 deg then the catalyst must cut by about 70%, this is all of course based on the amount of promoter the manufacture added to the Polyester resin .  Also be knowledgeable there are summer and winter formulations of polyester; obviously the winter grade has much more promoter.

 A. Epoxy   which will bind to steel much better than polyester but more expensive

B. Vinyl Ester which when used in connection with fibers yields a higher strength.  Popular usage is in Race Boats Hulls and Round Track Parts.

FOAM CORE

WHAT TYPE OF FOAM ?

Types of Foams to Consider

1.)    Polystyrene, which is mostly styrene monomer that has been formed by a gas.

Formerly freon gas was used but has been abandoned because of being linked to damaging the ozone layer.

A.    When considering polystyrene AKA Styrofoam Use Epoxy as it does not dissolve the foam.  Styrofoam dissolves when polyester is applied, because polyester one of polyesters main ingredients is polystyrene.

B.    Like chemicals (chemicals with similar makeup) will attack and most frequently dissolve the other.

C.    When Using Polyisocyanurate foam AKA urethane foam you may use Polyester, Vinylester or Epoxy, as it will not dissolve, because of it chemical composition is totally different from Styrofoam.

D.    Both types of foam are manufactured in different densities the higher the density the heaver the weight per cubic foot.

Lower density foams are lighter, contain more air/gas and have less strength.

E. Regardless of what type foam is used the mounting base of the blade has to be strong enough not to collapse when they are attached together.  No lightweight foam will meet this requirement.

Surfboards are usually made of Styrofoam, fiberglass cloth (not stranded mat) and epoxy resin. Each board the foam is formed and then made in reverse of the typical female mold process used in Manufacturing FRP, boats, bath tubs, swimming pools, etc.

Would it really be cost effective to make a female mold to make Blades?

Disadvantages

It would require at least two molds, one for the front side and one for the back side, then there is the problem of bonding the two pieces together and getting a perfect alignment, and then there is the balance to consider.  Another factor is the Mock up or prototype that you must have to make the female mold from.  In theory your mold can be only as good as the part you are pulling it from.  

Then with the two-piece mold you can only make one blade at a time and from that molds life you can only pull that exact shape, pitch and size from that mold.

To make fiberglass molds is a field of it own even requiring more skill than laying up the fiberglass part?

Making the prototype and the mold is very time consuming and expensive and must be done to exact tolerances.

Advantages

Onc't you have the molds, let's assume close to perfection you can pull several hundred parts from them.  That is if a part does not stick to the mold and also considering you know how to keep from damaging the mold when your are trimming the part and demolding it .  Demolding means, removal from the mold.

Fiberglass manufacturing has several trade skill within.  

1. )    Design of the desired part and ability to draw a scale drawing.
   
2. )    Ability to produce a 3 dimensional mock up from that drawing
   
   

A.    From wood

B.     Clay

C.     Wood,Screen,and Plaster,

D.    Shaped Foam covered with Resin

E.    And numerous other possibilities.

3.)    The Skill to be able to understand the negative  and positive draft angles

Which will enable the part to be easy to remove from the mold.

4. )    The skill to lay up the part, which the poor mans way is open contact lay up, commonly known as hand lay-up.
   
5. )    The Knowledge of which resins, fibers (glass cloth or stranded mats, etc)
   
6. )    What weight of cloths or mats to use then how many layers to lay up to achieve the desired strength, weight, of the finished part.
   
7. )    The number of lawyers laid up for each blade half and the weight of the resin is critical when the balance is to be held in tolerance even where the part can be balanced after assembled.
   
   

What Do I Consider to Be the Best Choice for Performance/Cost Efficiency .

With all this said if you want a blade that has some of the properties of fiberglass superior strength, foam core is not feasible.  The best choice is probably to coat a good designed tested wood blade. Then you would kind of have the best of both worlds. Strength of the wood and the weather proofing of the fiberglass.

But a word of caution here the wood  humidity level must be at about 8% or less

And you must apply enough fiberglass to overcome the expansion (strength) factor of the wood. For instance in the morning the Wood Blade temp might be 35 deg. And by noon could be 75 deg this  continued cycling of expansion and contraction over a period of time will split the fiberglass coating if enough layers are not applied to become the dominant strength factor to reasonably restrain the wood. Also all the wood must be sealed from the ambient atmosphere or it will take on moisture which will cause expansion of the wood when it heats up.  In other words for the fiberglass/wood to work synergistically the wood must be totally encapsulated!

JerryD Manufactured fiberglass products for more than 33 years, making one piece bath tubs, dune buggy's, jeep bodies, water slides, satellite dishes among numerous other parts.  He has been a consultant to numerous fiberglass and cultured marble companies for the past 25 years

 Is any one familiar with what is known as verticell honey comb ?

It is made in cardboard, plastic, and even aluminum and when a great strength to weight ration is desired it is used.  Like in some aircraft wings.

What man can conceive he can achieve.  But you must work very hard at the achieving part. Any one can conceive ideas but until there are applied, tested and proven , only then do they benefit society.

Even though I have the skill to build FRP Molds then Blades I am looking to purchase them, because making Blades that are exactly the right shape, angle etc,  which people have already proven to work on their Gens  is a total different skill

Can you imagine if each person on the discussion board used his field of experience and we all worked together how many high quality Wing Gens we could put out each week!

Make Clean Electricity and save  the world !

JerryD. Hall

[Jerry]

Here a expanding foam blade project I started a while back not havn't had the time to get back too?

I'm using expanded foam and very thin wood paneling. This blade has a cup, a twist, a thin trailing edge, a thin and rounded tip. I havn't mad the rounded leading edge yet. Hope to get back to this one this summer. This will be an 8 ft set for my F&P.

I have aluminum sheet metal support as I do on my plastic blades at the root. It has a slight curve or cup.

                    JK TAS Jerry

[rotornuts]

Thanks for the info JerryD. I do find it curious how you know FRP's but don't want to build your blades with them and I know wood but don't want to build my blades with it(repeatability issues amongst others). Hmmm???

Is this a case of the chef who eats out because he won't cook for himself?

nuts

[JerryD]

Dear rotornuts

Thank you for your response at least I know that some one read the post.

To answer you from my prospective; By my many years of previous experiences,I now know that everytime I get involved in a new project, that there are always things

involved that I am not aware of that I will encounter before I finish the project.

I quess that you could say that I now know enough to know that I don't know everything about which I am about to encounter.   Because I know FRP does not mean that I will not have to make several attemps before I achieve a workable set of blades.  To clarify this position let us assume that I can play the guitar, that does not mean I can play evertune, to get good at a new tune requires the sheet music and a lot of practice.

rotornuts I have a formula I just came up with   K = known, U = unknown  K/U=T Squared * E  = C   (Where T squared is the time) (where E= errors)  (C= Successful Competion of the project). Short cut formula:  K-U*Tsq-E=C

rotornuts when I was young I had so much positive energy and never stoped to consider  the negative problems that I would encounter in any new project. I would merly persist until I was sucessful. When I was very young I was a distance runner now I realize that you don't necessarly have to run numerous times  around the track for your team to win the mile race.  It is called a relay and by that I mean that I will do the coils/stator and the rotors, a machine shop do some of the work  and have some make the blades, and I can finish my project in record time and not drag it out for maybe months.

Hey rotornuts it is nice to communicate with you and hope you now better understand my position.

Our Goals today are tomorrow's accomplishments. (jdh)

[JerryD]

Dear Jerry:

It appears that you are using foam (in the urethane family)  from a can to laminate

your blades together.  This will work but be aware that this is very low density foam

and has very little compressive strength. You should protect the exposed foam from the elements as it will gradually deterioate.  Ultra violet  radiation is very damaging to foam (of course the lighter the density the more venrable) Ultra violet is the short wave radiation from approx 4 nanometers to 390 nanometers in wave length

It is the wave length that cracks the urethane (dash board of vehicles) and changes the color of your carpet in front of glass sliders, and causes skin cancer etc.

Suggestion to better protect your blades use polyester resin and about two layers of

nine ounce cloth and apply using a  pure bristle (throw away brush) and then finally

follow up with a good rubber squeege. The rubber squeege will really smooth out the cloth and cleanup any humps, bumps.  However you must use the proper pressure and at at angles that do not  go against the edges of the 9 oz. cloth.  If you used mat insead of cloth you will get much more variance in the consistency of the lay up.

Mat does not like to be rubbed with a squeege. It worse than rubbing a cat the wrong way. I would also suggest that after covering with Fiberglass that you carefully

sand the entire blade until it is smooth. To sand I would start sanding lightly with 50 grit, then proceed to 80 grit then wet sand with 150 grit then 220 grit. This should give you smooth enough surface to use a two part epoxy paint (as used on swimming pools) The fiberglass layers will strengthen the entire blade and protect the foam from deterioation. The paint will protect the fiberglass from the elements and give the blade better performance and cosmetically enhance the apperance. You can also use other paints such as the urethanes (the ones that require a hardner).

When using urethane, if you want a higer quality finish, I would use a  couple of even coats catalized primer then sand it with 320 grit then 400 grit then it is ready to paint with urethane. I would never reccomend spraying blades with spray cans

as the ultra violet rays will attack it much faster than paint used in a spray gun.

If you do not have a spray gun epoxy can be brushed and even sanded after it hardens. If you get some slight roughness you may wet sand it and leave a flat finish, if you sand through you may recoat and then sand lightly again, being careful not to go through the finish.

GREAT IDEA

Your project looks great in the pictures, looks and sounds very workable.

Am very interested in hearing about how it works out.

When you get it working and get it down to a science it appears that it is a

good alternative to carving blades.

Keep up the Good work

[rotornuts]

Hey Jerry D. Well I plugged my latest project into your formula and it looks like I'll be passing it on to my grandchildren. I get where your coming from. I just wonder sometimes if we get tired of working with what we know. Like I said I have a few years experience with wood and I know I could crank out 3 nearly identical blades any shape you please, stable and strong, but I don't think it's the way to go because I know what that really involves and the very thought of it scares me, if I had a cnc router that would be different. But I'm all into the rotor(that's the blade part rod) so I'll likely find a different way.

I'm as interested in the process as I am the result and I don't mind making mistakes as I find them educational. To be honest I have no need for a wind turbine right now so  I lack the practicality incentive, sky's the limit right after motivation adjustments.

Again I get where your coming from. For my first axial alternator to match up to my latest blade(should I ever get it to work) I plan on buying a stator set from Windstuff Ed as I don't see how I could do better than that and really I don't need to because Ed has already done it. My blade Ed's alternator my project flies quicker with more predictable or I should say quantifiable results.

Have fun Jerry and thank's again for the info. Now when I finish my FRP blade I'll be able to say, "I should have listened to Jerry".

[rotornuts]

Oh, and a suggested addition to the formula would be an expectation factor to offset the potentially devistating effects of the time and error variables.

nuts

[aogden]

Lets not forget enthusiasm where the probibility of sucessfull completion = C and

K = Known

U = Unknown

T = the project Time

E = Errors made

N = eNthusiasm

X = eXpectations

The Known minus the Unknown plus Expetations times time squared minus errors plus enthusiasm

Or Simply:

C=(K-U+X)*(Tsq-E+N)

Negative probability is not a good thing!

Adrian