Blade Runner…

[Greg S]

I’ve never heard or read of this happening to anyone else, so thought I’d check in with the forum.

Last spring we were anchored in the south Alligator River waiting for the winds to drop enough to let the Alligator Bridge open when we heard a very loud BANG! Running up the companionway my first thought was that we’d been hit by another boat, but looking around I saw nothing. It was then that I realized that the wind generator was no longer making any noise, a rare thing for our old Air-X in this much wind, about 22 knots at the time.

Peering out from under the bimini revealed that one of the Air-X blades had indeed went for a fly-by of the anchorage on its own. We were at once lucky and unlucky that the blade had flown off leaving us without “free” power, but its trajectory hadn’t been through the boat or crew. Thinking about what could have happened had it sliced down into the cockpit while we were there made me shudder.

It wasn't until we stopped in Hampton, VA, that I was able to remove the nose cone and check things out. Wow! The two remaining blade roots were broken into three or four pieces and being held on by the tiniest grip of one bolt.

What could have caused this to happen? True, a few days previous we had been through a night of 40-50 knots off the Georgia coast, but the wind gen was turned off and the blades should have just been idling away like they usually do when the gen is switched off. I wasn't looking at the time, but assumed that was the case.

Removing the hub, and then the blades revealed what may have been the problem. There was a fairly large amount of corrosion residue under the two remaining blades. This was probably caused by the blades being fastened with stainless steel bolts to an aluminum hub with out benefit of super lube or other isolating product. I'm guessing here, but I suspect that the corrosion enlarged the holes slightly and the residue that built up under the blade perhaps warped the blade slightly. Combined, they caused the damage. Does this sound right?

I was going to replace the blades with some of the newer, supposedly quieter ones, but the offer of an older, unused set for free changed my mind and, after cleaning up the old hub they were installed and ready for a wind test. Which it failed. Too loud, and way too much vibration. Down they came and after balancing them they went back up, and what a difference! They are so much quieter than the old ones I can hardly believe it. So now I'm thinking that I have to add - out of balance blades - to the reason for the blade coming off. I should add that the Air-X has been on the boat since we bought it five years ago and have never had a problem with it, but have also never done any maintenance to it either.

Anyone else out there have this happen to them? Any other thoughts as to why the blades failed?

[anjou]

Prolonged resonance and metal fatigue?
Over speeding and excessive torsional loading?

Many of the Chinese made wind turbines are failing, mainly caused by poor quality castings and innacurate ballancing.

It sounds as though you had a lucky escape.

[paradix]

Everything fails eventually, and for a moving system in a marine environment to go five years plus without maintenance is perhaps asking too much? Definitely being a little out of balance would have increased the stress on those blade attachment points. But it may not have just been balance: with all three being cracked, you would expect extra noise anyway from the extra movement around the single bolt now doing the holding. Either way the extra noise was a definite hint that you should check it... Of course until you've heard a quiet one, how do you know that your own is noisy!

This doesn't look like a recent, sudden problem but one which has been developing over time - and would have been spotted if the Air-X was examined regularly. Just another thing to add to the maintenance schedule I guess

[Greg S]

Originally Posted by paradix

Either way the extra noise was a definite hint that you should check it... Of course until you've heard a quiet one, how do you know that your own is noisy!

This doesn't look like a recent, sudden problem but one which has been developing over time - and would have been spotted if the Air-X was examined regularly. Just another thing to add to the maintenance schedule I guess

Yes, and yes. Lesson learned!

[delmarrey]

Once erosion starts to set in around the bolt holes it allows stress cracks to form, allowing more erosion to set in. It's a catch 22 situation. I would think a monthly inspection for corrosion would be in order.