Found a Crack (Just in Time)

[SparWeb]

Last weekend I was getting ready to hoist the tower back in the air; giving it the last look-over.  And that's when I noticed a funny looking line.  Didn't believe my eyes at first, but it's a classic fatigue crack, right through the hinge of my tail arm hinge.  Moving the tail by hand I could force the crack to open simply by pushing the tail arm against the stop.



It's not so easily visible in the picture but it stood out pretty strongly to the eye.  I'm kicking myself that I didn't see it sooner - such as before mounting the new generator and wiring everything up!  So.... I spend some time deciding how to deal with it.  I even made a stop-drill hole to prevent it from spreading but I realized that I was giving in to my impatience instead of solving the problem.  The end of this crack was less than an inch away from the weld (read: zipper) joint that keeps the tail on.  And it's already longer than one inch.

It didn't take quite as long as I expected to pull the head off the tower (lots of wires to pull back through conduit).  Back in the garage I managed to cut it off and weld on a much beefier tube on the same arm.





Here's a picture of the crack in much closer detail.



If all goes well putting EVERYTHING back together again this weekend, I'll be ready to go by Monday or so.

Some future consideration of this problem is in order.  There's no guarantee the new part of the hinge won't develop its own crack in time.  I have been thinking of making a new genny mount for some time, to fit more wires inside, accomodate an anemometer "up top", maybe, aside from simply wanting to increase the size so that I can increase the tower size.  This event is like a a message saying "yeah do that".

[bj]

   A pain to have take it apart again, but worth it I'm sure.  The hole probably wouldn't have kept things going long.  My experience has
been that once steel gets like that, it progresses along fairly quickly.
   At least now you can sleep better.

[dnix71]

That's thin steel on the cracked part. I would find pipe that fits snug over and cut and weld a collar on the short section so you have at least double thickness metal in the stress cracked section.

[FishbonzWV]

Nice catch Stephen,
Just goes to show you, A good visual is 90% of your troubleshooting.
Hope you get her flying soon.
Bonz

[defed]

after today's winds are over, i'll have to lower mine down and see if any of my crappy welds are failing!  i think my materials are heavy enough to not fail w/ such a small turbine, but my welds are another story.

4' Piggott, 16' test tower, 25+ mph winds at the anemometer mounted under turbine.

[SparWeb]

That's thin steel on the cracked part. I would find pipe that fits snug over and cut and weld a collar on the short section so you have at least double thickness metal in the stress cracked section.

You're quite right.  Back when I originally made the mount, I started cutting pieces of thin 0.058" wall tube for the tail mount, then stepped back and said "nah", and made a bunch of heavy-walled parts.  I began welding the tail with the heavy-wall material, but one of the thin-walled pieces was still clamped on and I had it welded before realizing my mistake.  That's why there are 2 different OD's of tube in the top photo.  It took 2 years for this part to crack, but I guess it was inevitable, and I have paid for my carelessness.  The replacement part is 0.12" wall.

[luv2weld]

Glad you spotted that crack.
I guess that proves the theory that it is always worth the time and effort to look it over carefully
before putting it back to work.
But, Hey, you do good work if that thin stuff lasted for two years.

Ralph