In the past few weeks we've had good winds around here. Sometime in the last 4 weeks also the botched blade repair I had done last years summer had given up, and the tip of one blade had flown off. Back then, one blade tip twisted 90 degrees 30cm from the tip, as the tower came down blade tip first. Bad design on the tower support, there was room for the rotor only to come down in one position.
Surprisingly, with one blade short it was still making power, but shaking really bad. I had to wait for winds to calm down before I found the courage to go to the tower base to shut it down. No pictures of that, it was pitch black when I found out about it. Luckily, the unbalanced running had caused no extra damage, all nuts & bolts still accounted for and no signs of stator rubbing etc.
After it got bent, I just stuck some wood glue to the splinter and pressed it back together. Considering the dirtyness of the fix, it worked surprisingly long.
I figured it was easiest if I'd just make a completely new blade set, so to get it running quickly again I just decided to saw off all the blades. My heart was almost crying with blood as I had to cut down the 2 good blades. Hopefully I will find time next spring to carve a new blade set. At least this time I have some proper laminated wood available for carving the new blades. And this time I will know better to make one spare blade, just in case
The grain orientation on the blades wasn't the best to start with. Don't know if it would have helped with the accident, though.. Might have been too much stress to a properly oriented blade too. On the good side, the stuff (some sort of heat treated linseed oil)I used to treat the blades had worked well, no evidence of rotting. And the cut still smelled fresh of the stuff I used.
Using cheap plastic boxes for junction boxes wasn't such a bright idea, wrong place to be skipping. My only excuse is that at the time of build I had much more time than money to spend on this project.
Rattle can paint also needs to come off and replaced with something better.
If you're short on real estate, it's a good idea to grow your mushrooms on the gin pole
Last check that no cables are tangled, before it goes back up.
It sure does look puny with the shortened blades.
After chopping the blades, I updated the load curve on the MPPT box. I figured, that as the blades were designed with spreadsheets to work best at TSR 7, they would still retain the same RPM vs. windspeed characteristic. So, I just decreased the power level for each corresponding rotor rpm to 66% of what it used to be - the same amount the swept area was reduced. (Old diameter 3.2m new diameter 2.6m)
It will be interesting to see, at what power level it will furl after the modification. Will it be the same power level as before, same windspeed as before, or something from between? One interesting thing I noted with the smaller rotor. It will now stay seemingly better to the wind, before it would turn to the direction of furling, when the wind sped up, now it seems to hold the direction quite much better. It probably means, that the tail is too small for the 3.2m rotor, and I will probably increase the size of it when I will install the new rotor.
So in conclusion, I seem to have my work cut out for me for the spring;
-Completely new rotor
-New bigger tail, maybe slightly heavier too.
-New junction and rectifier boxes, both up and down the tower.
-New pendant cables + socket / plugs at the bottom for easy untwisting.
-New gin pole from some better rot-resistant wood.
-New paint job for the generator.
-Fix the anemometer, and install back to the tower to make datalogging worth while again.
(more & higher resolution pics:
http://pics.ww.com/v/Janne/Windmills/axial/?g2_page=7)
