Power Tower Cable Snap

Kevinj:

As an aside, what do those cables do, exactly?

I'm going to try to look and see if our alive and breathing (and hopefully recovering) RideMan has done one of his awesome breakdowns of the workings of Power Tower. I thought I saw a section of his stuff somewhere.

Basically there's a cable between the underside of the carriage and the underside of the piston inside the long tube up the tower, then the same above. Multiply times four, one for each side of the column. I'm sure it's over-simplifying it, but compressed air is flooded above or below the piston, depending on whether it's drop or launch, forcing the piston up/down and the carriage in the opposite direction. It's kind of a genius design in its simplicity and redundancy. The best part is that the direction reversal and bounce is caused by the compression of the air on the far side of the piston when it gets close to the top/bottom, and by gently bleeding air out, it comes to a soft stop at the bottom. I suspect the biggest complexity is trying keep the pressure close to the same in all four tubes.

What surprises me about this is that it appears the end of the cable tying into the piston above totally separated, and escaped the tube completely. I don't know how it was attached, but I am surprised it took decades to break.

From DRE420's picture, it looks like the failure was at the coupling and not the cable itself. Unless that was cut or moved away in the aftermath. If that's the failure, wasn't that similar to Skyhawk's in 2014?

I barely remember that. The giant swings work on a similar principle though, pushing a piston up and down through a tube. Where things got weird on those (as I understand it) is that because the tubes operated at an angle, the seals on the pistons would frequently fail from the friction on the inside of the slope. The solution, if I remember correctly, was a narrower piston that had some kind of durable cap on each end that led to a better seal around it, far less prone to failure. I believe they retrofitted all of them this way.

In 2007 at six flags Kentucky kingdom a girl lost both feet when a cable snapped on superman power of tower.

Thanks for posting that picture, I hadn't seen that one yet. The piece that fractured is one end of a turnbuckle. Turnbuckles are used to tension cables. A turnbuckle is similar to a coupling but a little different. A coupling will be threaded the same from one end to the other and a turnbuckle will have opposite threads on each end (one end "righty tighty" the other end "lefty tighty"). If you look closely at the middle of the thickest part in the photo you can see what looks like a space between two large threaded rods. One of the threaded rods (the one on the right) is crimped onto the cable which appears to be in tact, the other end (on the left) was likely connected to the carriage. It would make sense to have a turnbuckle connecting the cable to the carriage. It would be the perfect place to locate them as it's hidden behind the seats/vinyl banners yet easily accessable to work on them when adjusting the cable tension. When a turnbuckle is rotated one way the two threaded rods will move towards each other and the cable will become tighter. When turned the opposite way the threaded rods will move away from each other and the cable will loosen up. It looks like the threaded rod/bolt on the left side (a lot of times it's an eye bolt) fractured. The other end of the bolt that fractured was likely attached to the carriage. The question is why did the bolt fracture like that.

Right, and it doesn't look as if there is any rust where it snapped to indicate a potential crack or weak point in the bolt, at least not that we can see from my Pic. Usually in that situation, over tightened bolts are one potential candidate. Not saying thats what happened here, just my experience with these things from my auto repair knowledge.

Clean break, and it looks like what broke was whatever was threaded into that turnbuckle. My question is where was that turnbuckle located. I'm going to disagree with Jeff in that I don't think it makes sense to use that kind of connection inside the cylinder; instead the rope would connect to the cylinder with the sort of non-adjustable connection as we see on the unbroken end of the turnbuckle; I presume that's probably crimped somehow to the end of the rope.

To avert panic, I should mention that apparently there is a failure mode where something jams up and one jammed assembly can keep the carriage from coming down (there's that redundancy Jeff mentioned), and the solution S&S offered is to...cut the offending rope.

Oh, someone mentioned Skyhawk. That one was also NOT a wire rope failure. On that one, if I remember correctly, nothing actually broke, but the retaining nut backed off from the pin holding the rope to the upper frame. I'll bet there is a discussion somewhere on this site with all the details.

--Dave Althoff, Jr.

If the turnbuckle isn't in the cylinder, wouldn't it be visible on the outside? I suppose it could be connected to the back side of the carriage, hadn't thought about that.

Did Skyhawk separate a cable at some point? I don't recall that, only the leaky stuff around the piston seals. Cables break though. I think every ride other than Sky Ride (which is extremely improbable) with a cable has broken one.

Oh no, after reading that I feel the beginning stages of "SkyRide paranoia". gulp...

^ exactly this.

On Skyhawk there are those stabilizer ropes that run from the gondola support arm up to a cross piece on the axle. At the top, those ropes are secured to a bolt. The bolt let loose and the rope came down and took out the fence on the midway side. The park added a safety rope up top to keep that from happening again.

I am not aware of any Skyhawk incident involving a separation of a drive rope, but my knowledge of incidents isn’t comprehensive, either.

—Dave Althoff, Jr.