wind turbine fiberglass&metal spar blade construction

[Len Von Speedcult]

First off, hello everyone. I'm Len from Michigan (Detroit area) This is my first post. I've learned quite a bit as a casual observer over the last month and thank

everyone for sharing their wealth of knowledge. Here goes.  My goal is to build a wind turbine in the 5KW-10KW size Range. From what I learned , If I went

with a 3 blade system, The diameter could range from 16' dia.thru 24' dia. respectively. One blade design that really caught my eye for the larger diameter is

the method of construction as seen here ( http://warlock.com.au/10kwblades-abstract.htm ) It basically consists of a round steel tube spar and thin metal

airfoils tacked along the length at different angles (twist) filled with expanding foam ,sanded and shaped, then wrapped with fiberglass. The end result I believe is something that can be more efficiently shaped than what you could pull off with wood alone..

Now that I layed out the scenerio, Does anyone foresee any problems with using a

tubular metal spar? The common consensus here is metal is not good for blades but

I haven't found where its differentiated between 100% metal blades or perhaps its use only as a spar. Also,..I would not use aluminum ..I would use 4130(chromoly)

tubing which has amazing strength and quite a bit of elasticity. Another reason I would like to try this is I have a CNC plasma cutter in the shop here and cutting the different airfoils would be a breeze. Any help is appreciated. Also,

If anyone needs steel parts cut out, feel free to contact me. If anyone is interested I can e-mail you my capablities or check out my website http://www.speedcult.com . Thanks  Len

[wdyasq]

Len,

Blades have a rough time in an "Elliptical Furling" mill as is commonly shown here.  When furling the glades are required to go from full load to stall to negative lift and back each revolution. Flexural cysles build rather quickly with that treatment.

 Sandia labs and Gougeon Brothers did some fatigue tests years ago and concluded in order of failure Aluminum, Steel, Fiberglass and Carbon-Fiber.  This was on samples designed by aerospace engineers.

Foam, steel and GRP have different expansion co-efficients.  It will be difficult to build with these properties, My Opinion.

"The end result I believe is something that can be more efficiently shaped than what you could pull off with wood alone.." is just the skill of the craftsman. Please refraim fron general insults to a man's(or woman's, dog, whathaveyou) skills. Some are better than others. I can build as accurate in wood, or more accurate, as I can in a material that moves quite a bit with temperature changes.

Your mileage may differ.  I don't think you will find material properties changing.

Ron

[Len Von Speedcult]

It was not an insult..jeezzzz. I wasn't saying it could not be done. All I was

implying was it could be done easier.(Especially with my resources) A couple blade modeling programs I used had 11' blades with a root chord of an average of 36" tapering down to 10" with a twist

going from 38 degrees to 5 degrees. I know I could cut out all the airfoils ,slide

them on the tube ,position them ,weld them in day (3 blades). The rest is gooping

in the foam ,sanding, and glassing. If you could make that identical blade form with all wood, let me know how much and fast you can do it. I'll just pay you instead. Thanks, len

[paradigmdesign]

I have seen that design too.  It was my understanding that the aluminum sparr, and airfoil sections were only for forming the foam, and not for and kind of structural capacity.  The strength comes from the glass, not the internal spar.

[Len Von Speedcult]

Nope, he mentions specifically its steel tube and sheet metal airfoils. The fact that he welds them to the tube tells me its all steel. I agree that most of the

steel structure is nothing more than form for the fiberglass. The tubular spar though in this case appears to be the mount point as well. Reading over the Sandia Lab reports..I could not find (yet) any reference to a composite use of a steel tube

combined with a foam core and wrapped with fiberglass.   len

[paradigmdesign]

You said that you live in the detroit area?  I live in Northwest Ohio, and have been getting jacked arround my my local metal guys.  Couple questions, what is the thickest steel you can cut?  And what would you charge for like 30 airfoil sections cut out of a really thin steel(or whatever)?  

I am using the basic process you listed to create my a positive foam mold for a 11 ft. blade that I have been working on for about 2 years.  I would be willing to share my design for that blade, (airfoil sections, glass layup-schedule etc.) for some discounted steel work.  email me at paradigmpower_05@yahoo.com if you are interested.

[Len Von Speedcult]

Hey Ron, sounds good, I can cut up to 3/4" thick steel. I sent you an e-mail with some pics and stuff. len

[behoof]

Len,

Hello from Yale, MI... Interesting idea you've got there. Will watch your posts to see what you make of it... sounds like you've bitten off a pretty big challenge. I enjoyed reading about your airfoil idea.

Funny you should mention CNC and cutting and anyone needing any? Perhaps we could chat sometime as I've got a couple of projects I'm looking into that will no doubt need some cutting.

I'm planning on going to Detroit next week to meet some folks that do a lot of winding and such down by the old ball park at Michigan and Trumbull.

behoof

[behoof]

Len,  forgot to add my email  skipb@greatlakes.net

behoof

[Seedler]

I built these blades.  They aint too difficult to make if you got the rite tools, and it sounds like you do.  I played around with an angle gringer to cut the small sections.

The blade is very strong except for the root(where the glass ends).  Its amazing how much force the wind puts on this area.  When you think that you've made it as strong as you can and nothing can bend it! Make it at least 3 times stronger.

Good luck.

Dee.

[paradigmdesign]

How many layers of what kind of glass did you use? How long was your blade? Did you go with just a skin or a skin + cap spar system?  Also, what kind of foam did you use for the core?  

I am wondering all this because I am also building a blade that is similar to this, and would like to hear what other people are doing.

[dinges]

I don't know if 4130 is the best alloy. You should not only look for tensile strength, but for fatigue strength. Aluminium is, as you've said yourself, not very suited.

The method may be feasible, but to me it seems much harder/more complicated than carving a wooden blade. Admittedly, I can think of nicer ways to spend my time than carving wood. It's a dumb, tedious job, but in the end you end up with good blades. Especially for single-offs (or three-offs) as most of us build (each and everything I build is more or less a prototype ). If you would want to scale it up to industrial production, carving wooden props may not the best route.

I'd probably rather build blades in another way first (before your method), I mean by making a mould and making fiberglass/epoxy laminate blades. And even this is not my idea of 'fun'. But I guess it all depends on how good one is with wood/metal/fibreglass. Some are better with wood, others with metal.

If you do go this route, I'd be very interested in hearing updates!

Peter.

[scottsAI]

Hello  Len Von Speedcult,

I have seen similar designs for wind turbine blades.

The difference I saw is the tube was more centered on the spars.

They were balanced so there was no twisting forces on the tube.

2/3 rds of the way down the blade the tube size was reduced to reduce weight.

Don't waist time with the center few feet or the first couple feet on the blade.

Take a look at the cross sectional area.

 5'   circle is 19.635 sq feet area.

20. '   circle is 314.16 sq feet area.
    
20. 6' circle is 333.29 sq feet area.
    
    

By extending the blade 0.6 feet you can skip the first 2.5 feet from the center.

This eliminates most of the blade flaring at the hub.

Have fun,

Scott.

[Ungrounded Lightning Rod]

Note, however, that you need signifiacnt fore-and-aft thickness of the blade near the hub to supprt the bending moment from the wind loading.  Bending stress increases as you move from the tip to the hub, both because you have more blade to support and because you're at the "short end" of a progressively longer lever.  Make it too thin along the axis direction near the hub and it can snap, or bend back.

Some bending back is OK (if you left enough clearance between the blade and the mast).  Indeed, it's unavoidable, since materials don't have infinite strength.  But you don't want it to bend enough that it pases the yeild strength of your material.  Then your blade starts taking a permanent bend, breaking fibers, or stress-hardening (which will lead to fractures and breakage), depending on your material.

The thickening from the blade twist does roughly the right thing.  As scottsAI says, you can leave it out near the hub because you don't need efficiency (or even any power pickoff at all) in the small swept circle near the hub.  But you have to make sure your material is strong enough at the thickness where you stop implemeting the twist to take the progressively-increased-by-leverage stress all the way from there down to where you support and clamp it.

[Len Von Speedcult]

Peter, 4130 is quite flexible. Its used extensively in dragster chassis which flex and twist with a 6,000 h.p V8 thumpin on it. The only metal better would probably be stainless which is used quite a bit in helicopter roter blades which encounter

blade flapping with every revolution in forward flight. I'm still researching the feasibility of all this. As far as it being a more complicated way to do it? Not for me. I've been immersed in metal and race car fabrication /building,for the last 20 years so building it wouldn't be the challenge. Knowing if it will hold up for 10-20 years is another question. Thats what I'm trying to nail down here and appreciate everyones constructive opinions.  len

[wdyasq]

Len,

My tech library has been destroyed more than twice.  I quit keeping them... BUT, as I remember the first reports I read on material fatigue as in Wind Turbines was done by the Gougeon Brothers out of Bay City MI in the late 80's or early 90's.

As I have mentioned Sandia Labs has a lot of information on material fatigue. You may be amazed at the information that has been collected and made availabe to the public. They have published tons of data there. Of course, I recommend it as one of the few government services that actually might have a positive effect (although doubtful).

They really have had rocket scientists working on problems. But, they have failed to solve problems on the VAWTs. They did not fail to spend a lot of money not comming up with the solution. They did solve the "teetering" problems and "tower shadow" problems of HAWTs (they went back to three blades ie, they gave up). Anyway, you can read all about it there. Lots of engineeze talk.

Well, have lots of fun.  And when metal fatigue causes a blade to fall off, and the vibration takes the turbine down kiling your favorite chicken, duck, cow, goat or sheep, don't forget to report it to the new National Animal Identification System (NAIS) database. Your goobernment is at work, making you safer and lining the pockets of the elected.

Ron

[irishlad]

Hello Len

I have built a set of blades using a similiar method and they came out perfect, I used flexible high quaility steel for the inside of the blades where I attached cross sections and set the frame in Polyeuthrane foam and just sanded the foam down to the shape I needed. I simply laid fibre glass over the blades. They came out very good. What airfoil section are you intending to use?

[Len Von Speedcult]

Ron, I hope you tech library wasn't destroyed by blades constructed with metal parts flying apart (hence your disdain for the concept.) Can you tell me what length you feel is the maximum one could go with carved wood blades ? Expected life expectancy ? Do you encapsulate

the wood blades in fiberglass ? Thanks, Len

[Len Von Speedcult]

the only airfoil I've really looked at so far is the NACA 4412. Is there something better? What length are the individual blades ? How much time are on them? Did you use a tube spar? Method for attaching to hub ?? Have pics?  Any help is appreciated.

len@speedcult.com

[JF]

Dear Mr Speedcult and other friends

When considering blade construction and especially

in larger sizes it is advisable to consider other

options - and as you correctly suggest the steel spar

system is a good option for the those who wish a larger

rotor with minimal operational risk and likewise with a

relative easier construction.

I have many times on this board emphasied the good work

done in this respect by Prof Horst Crome from The

Technical University in Bremen.

"Handbuch Windenergie Technik" - by Prof. Horst Crome

available from - http://www.oekobuch.de - is possibly

only marginally bested by Hugh Piggott's series of books

and manuals.  

1:  I enclose an illustration of the Crome "KUKATE" tower

and rotor construction - please note the use of a side

overspeed-vane

2:  This shows the profile and construction of the GOE 624

aerofoil.

Please note the usual traditional method of construction

with a 4mm marine-plywood covering and wooden leading and

trailing edges.

Likewise please note the round steel spar.

3:  This shows another illustration of the blade construction

 - please note the two small plates welded to the blade spar.

It will be noticed that a section of allthread is passed

through two aerofoil sections to prevent movement of the blade

itself.

   

4:  A more advanced aerofoil section is as follows:

Please note the use of alumimium aerofoil profiles -

these are either in profile sections or as longer extruded

blades - screwed directly onto the steel spars. It can be

noticed on the first image that the stress forces on the

blades are relieved by the use of stays.

5: Likewise the mounting of the spars or rotor arms can be

made using the traditional hub construction

 

6: - I have also followed the discussion concerning the use

of alumimum extruded or covered blades -

As for me personally I have no definate position on this

matter at all and am fully aware of the known problems with

this material However - and for the record - I will remark

that in Michael Hacklemann's good book -

"The Home-built Wind-generated Electricity Handbook" -

Earthmind/Peace Press USA 1975

- concerning the re-conditioning and re-building of WINCHARGER

and JACOBS rural power-systems [with up to 1.5 kW units]

from the 1930's and 1940's - of which the 4-bladed WINCHARGER's

utilized alumimium blades - no dire warnings or serious comments

are made concerning the use of this material [page 31].

I can only suggest that the unusal longlivity of these blades

is possibly due to their efficient blade-angle governing-system.

With best wishes to all - JF

[willib]

something better is a very debatable question.

the 4412 is optimized for low drag , ive seen some similar but with a slight concave curve on the leeward edge.

check out the shape in got root?

http://www.fieldlines.com/story/2006/4/19/7542/40189

[wdyasq]

Wooden blades have been successfully built larger but - from the Gougeon Brother's site :

The success of the wood/epoxy blades led to multi-million dollar contracts with General Electric, Westinghouse, and Bendix. 4,300 blades, from 10 to 70 feet long, were produced between 1979 and 1993.

I figure you can read as well as I can. I have sent pointers toward a possible resource. AND, no it was the failure of a metal blade that causes my distain. It is the fact someone will likely get killed and the polidictators will pass laws keping folks from building their own. As far as I am conserned anyone stupid enough to use metal blades after they have been advised there may be problems and then not verifying the FACTS doesn't need to be swimming in the gene pool.

Folks on this forum bitch that epoxy resin is more expensive than polyester resin, fail to put structural fibers in their stators and generally try to do things on the cheap. To most "fiberglass" encompasses all and is one product.  I have no idea of your knowledge or skills in the materials. Again, if you do a bit of research, you will begin to understand the processes it takes to build proper blades.

Ron

[Len Von Speedcult]

thats what I'm here for. I agree with your references to government and how they react.Always thinking they know whats best..yet cannot take care of their own household. Keep in mind, at no time was I thinking about using all metal blades. I was just curious as to what others thought of using a fiberglass/metal spar combination as seen on the Australian website I sited as a reference. Its just research at this point.   Len

[Len Von Speedcult]

Ron, By the way, I do quite a bit of reading and read the part you cut and pasted

here about the Gougeon Brother's this morning after your post mentioning there name. Have a beer man...I'm not your enemy

[hvirtane]

Yes you can certainly do it with

a method of

"a round steel tube spar

and thin metal airfoils tacked

along the length at different angles (twist)

filled with expanding foam"

1)

I've got one friend here, who has got blades

like that 10 m diameter. They have been in use

more than ten years.

The exact details of these blades are not

known to me.

2)

You might also consider using a thin

airfoil like K2 and making solid

fiberglass blades. With such a thin

airfoil they wouldn't become so heavy?

3)

There are also other ways.

Instead of covering the blades with

fiberglass you could also use

strong cloth.

I've been working with a friend of mine

reinstalling a wind turbine using

special really successful blades

with a steel tube inside,

the leading edge made of polyurethane,

the trailing edge made of a steel

wire and covered with plastic cloth.

They have been in use 6 years in

really rough conditions in Finland.

Details below.

- Hannu