Homebrewed Electricity > Wind

Blades - lessons learned

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kitestrings:
Spar,

I believe you fashioned new blades for your "Spirit of Zubbly".  I guess new is relative, as I just realized this was done nearly five years ago now:

https://www.fieldlines.com/index.php/topic,149797.msg1048344.html#msg1048344

And, they were quite a bit longer than the set they replaced.  I'm curious how they are working out... if you have data before - and after, or any other observations.  How well is the finish holding up.

BigRock,

Similar questions.  I believe you also carved new blades late 2018/early 2019.  Curious what changes you made and whether they are performing the same, or better? 

https://www.fieldlines.com/index.php/topic,149712.msg1046882.html#msg1046882

Thanks for sharing what you may.  ~ks

bigrockcandymountain:
I have carved 4 sets so far.  The latest iteration are by far the best, but still not perfect.  The link you posted is my second set of blades.  They are still intact and hanging on the shop wall.  They were quite successful.  I took them down because they were quite unbalanced because one was a way less dense piece of wood than the rest.  The tower always shook when they were running. 

The newest ones are running now, and at 13' diameter, they peak about 3500w.  (If i was selling them on ebay, that number would be 15kw or so ;) ) In normal every day winds they make a steady 500w or so.  Lots of days they make 10kwh.  20kwh is about the highest I see in a 24 hour period.  Any windier than that and it is shut down.

In my case, I have learned a lower tsr works better for me.  I also like a thick airfoil.  I think these are over 20%.  I think the thick airfoil makes them less efficient at higher speeds, which i consider a good thing.  It also helps a lot with stiffness.

I also wouldn't recommend taking any pointers on blades from me.  I always look at yours and spar's posts to learn how to make perfect blades. 

We don't have any real rot issues here.  Bare spruce fence boards that are untreated last 30 or 40 years.  I know that is more of an issue where you're at.

Are you thinking of whittling out a new set?

kitestrings:
Hmm, I was (maybe still) confused.  I remember you had the rather catastrophic failure during a high wind event.  Then you had to carve a set in pretty-short order as I recall.  Are these you latest set:

https://www.fieldlines.com/index.php/topic,150690.msg1062013.html#msg1062013

So yes, I'm thinking probably next summer to do another set.  Ours have worked remarkably well - more by luck I suspect - but the moisture intrusion is not going to disappear.  Oddly, the balance now is the best we've ever had.

Just starting to think about it really...likely they'll be carved, but possibly modeled, or routed, or CNC.  We live in ski/snow board country (Burton, Rossignol), so it seems like there are lessons to learn from their efforts/successes.

I was also thinking some of a design where there would be no fastener penetrations; just a compression fit.

Those are impressive numbers.  We have higher peaks, but rarely do more than 8 kWh in a day, though I routinely shut down at night.

Perhaps a different post, but I'd be interested to hear how your furling actuator is working.  I'm convinced that automated furling is among the best things we ever did.  It doesn't get much acknowledgement here, as it wasn't proven by complex regression analysis, or tested in a wind tunnel; but it is passive, simple, and it works.
 

bigrockcandymountain:
Yes, that is the post about my current blades.  I'm really bad at being organised about pictures of a project.  They are good enough that when this set goes to pieces, i will likely just copy them and try to do a better job of finishing and leading edge protection. 

The furling actuator is a wonderful upgrade.  I absolutely wouldn't be without it now.  I used it last night.  I still haven't automated it.  It is just a manual switch, but in the basement instead of climbing the hill.  You have yours set up on aux 1 input voltage high or something like that right?

 I have a voltage monitoring relay that i might use to trigger it.  Then if the classic fails, or the rectifier, it will still shut down.

What wood did you use for your blades? 

I would love to see compression fit blades instead of through bolts.  That would be pretty unique and interesting to see how it would affect the rot resistance. 

One other thing i might try is wood stain instead of paint.  It allows moisture to escape, so anything that gets wet can dry again.  That is what we used on our house cedar siding.  It isn't as shiny or slippery as paint though, so the finish won't be as nice.

Would you do anything different size, airfoil, twist etc on the next set?

kitestrings:
Yes, we use Aux1 for furling.  You may know this, but for those who don't, Aux1 can be configured as a relay or logic output.  It is non-PWM (unlike Aux2), but can output 12V+, 0V, or continuity when used as a dry-type relay.  Ours is the latter, both jumpers (JP6 & JP8) are set to the right, so it is essentially an isolated switch up to 1A IIRC.  We use "PV V on Hi", so it will shut down if the voltage goes above the input V set-point, and of course you can manually turn it on or off.

Our blades are locally grown balsam fir.  I actually cut the trees these came out of.  These are single piece, without lamination.  Balsam is pretty strong relative to weight, straight grained, with small knots, especially nearest the trunk.  It is not rot-resistant like cedar.  The only local cedar we have is white-cedar, which is rot-resistant - it was used for rail fences for decades - but it is otherwise undesirable: twisting grain, lots of knots and not very strong in moment.

I don't think we will change size.  I'm pretty happy with performance.  Possibly a different airfoil, most likely with twist.

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