Carving Blades from wood

[imsmooth]

I am just about finished with my Cedar blades.  They are 5'  each, and I am attaching them to a marine plywood hub for a total rotor diameter of 10' 2".

I used a blade calculator to generate some numbers and carved them down.  They seem pretty strong, but the tips are about 1/4" to 3/16" thick for the last 6" of the blade.  I am afraid they may vibrate if they rotate very fast from strong winds.  I know the deed is done, but I am wondering what the rest of you have to say.

[niall7]

hi iamsmooth ..great that you,ve nearly finished those blades if the thickness increases  nice and pretty much linear down the blades to the 2.5 root (  according to the calculator) i wouldnt be to worried about the tip section you mentioned  ,...vibration (overspeeding ..stress...doubts in the middle of the night   ) would  be more related to what you attach them to  ..cedar is surprising strong ...its the  bits you  hang them on to you need to worry about ..any pics of those blades ?    

[Flux]

Stop worrying, you need blades not planks. If you make them an inch thick at the tip they will whistle and drag and be useless.

You are only running slowly, you are not building an Air403 or something that runs at half the speed of sound at the tip. It will not flutter or do anything silly. If you are only 3/16 thick you must be aiming for a higher tsr than I would have thought you needed from your alternator details but I really don't know what you are doing. If you have other troubles with high tsr that is another matter but the blade tips are not going to bother you.

Flux

[imsmooth]

thank you both for your comments.  I will post some pictures soon, but I have been busy at work.  I am looking for a higher tsr as this will allow my inverter to kick in sooner.  The alternator can then increase its load when the rotor has more power to deliver in stronger winds.  I have gotten my 5' 1" blades down to 2900 grams each.  My next step is staining and sealing.  I was planning on using some Western Red Cedar oil based stain, followed by two to three coats of exterior polyurethane.  Does this sound appropriate?

[jlt]

jacobs wind turbines had aluminum enamel brushed on them .and that's what i use.it drys fast ,and is very easy to use.and it holds up very well.also i put aluminum tape on leading edge to stop erosion.

[oregon wind]

Do you have a brand name for the aluminum enamel paint?

[imsmooth]

How does it compare to exterior polyurethane such as Spar Helmsman?  Can you post a picture of the painted blade?

[ghurd]

It doesn't seem to soak in.  The cherry furniture on the porch gets no direct sun, some wind blown rain.  Poly peels off in about 18~24 months. Tried several brands.

Worked the same.  Poorly.

G-

[birdhouse]

hello all-

i'm new and know very little.  i have been reading for quite some time and slowly learning about more of the technical end of wind generators.  

i do know a decent amount about wood, and finishes.  in my opinion cedar is not all that strong, however it does have natural oils in it that retard rot.  the problem is these oils inhibit catalizing finishes (anything polyurethane) from sticking over long periods of time.  cedar is very light however, which i think you folks prefer.  

are the blades "cvg" or knotty?  

cvg would be substantially stronger!

i believe clear fir or hemlock would be ideal blade materials.  they are both slighly heavier than cedar (cedar-23lbs per cu ft  hemlock-31lbs per cu ft   fir-33lbs per cu ft) however they are both substantially stronger.  they still have natural oils, but not near as much as cedar.  this makes them take finish much better.  i can't remember the brand, but most surf board epoxies (typically used to wet out glass) make great exterior finishes.  they go on thicker, have more uv blockers, will increase your blade strength and last way longer than any spar varnish ever could.  the down side s they aren't cheap.  a two part gallon kit is about $100.00 us.  

i like the aluminum tape idea on the leading edge!  that's genious and simple!

thanks

[oztules]

Hi Imsmooth,

As you know I carved mine from crappy radiata pine. I was concerned about the very very soft finish, so I mixed up some west systems epoxy, heated it up a bit ( to make it even runnier), and painted it on. It soaked into the wood very well.

Before the west systems, you could press the wood and leave an indent with your finger, after, it was quite solid... sort of like doping paper plane wings)

The blue paint on them is a dulux "luxepoxy" paint. It seems tough as nails.

My blades are 6'6" long (4m diameter), and have just under 1/4" tips, and seem strong enough to not vibrate etc.

After about 3 months, there is no sign of wear, or pitting. Look the same as the day they went up. (except for insects stuck to the leading edges)

.........oztules