www.flyhouse.com: When you were a kid, did you ever try to make your own zip line between two trees? The likelihood of succeeding in this endeavor at that age was probably slim. But do you know why it didn't work? Flyhouse went into the shop to test the math behind this and we found out why.
6 comments:
I was not a kid that did this, but I could see kids trying this with everyday objects found around, like rope. My first thought was that the reason it would not hold up was because the wire was not pulled tight enough, that it needs as much tension as possible. However, it seemed at the end that the exact opposite is what zip lines rely on to hold a load. I am very proud that understood most of what he was taking about in term of the safety factor and where the load was coming from. The video itself was odd to me that it was in black and white, as their really is not much reason to be. I was also thinking this was going to be more of a Myth Busters set up where he actually set up a rig between trees, just like a child would have done.
I love these videos from Chicago Flyhouse videos. They’re always informative and thorough in their explanations without making it too hard to understand. The math in this situation makes sense, we know that a 50 pound point load in the center of a span doesn’t just translate to 25 on each end because of the angle at which it was pulling and the original tautness of the rope. However, I didn't really realize how much more stress the wire rope was experiencing even just with an average 100 pound kid. It was amazing to see how the rope was fine when he put on exactly the 100 pounds but one more click and the rope just snapped immediately. It really shows the difference between dynamic and static loads because when you're a kid you don't just gently and evenly pull on the zip line, you bounce around a bit and let your whole weight drop down at once. Lastly, I really appreciated how he talked about the purpose of the deforming thimbles and why they are so important.
Yeah, this is pretty scary to think about. During my last family trip, we were in Costa Rica where the whole family went on a ZIP line tour. The fascinating thing about it all was the whole rig looked as if it was put together with glue and popsicle sticks. Oh, and did I mention that this wasn’t your normal Zip Line. It is considered to be one of the longest zip lines in the world. Half a mile to be exact. And the whole time that I was on the attraction I was wondering what kind of engineering went into the structure and when the last time it had been serviced. I highly doubt these people are keeping their equipment up to an American standard. I must say that this video was very informative and eye-opening. Sometimes a visual is one of the only ways that you can really understand the breakdown of something and that what this video does.
This is a very interesting and informative video. Obviously, rigging safety is critical and this video demonstrates exactly why. The 100 pound load put on that line induced a force of over 500 pounds. We know that wire rope is strong, but it does have its limits. Zip lines, though they seem simple, are very complex mathematically with varying loads and forces. There is also a reason why I’ve never seen a zip line made with 1/8” aircraft cable. This video doesn’t even go into the concept of shock load. Typically, in theater we don’t pick from the middle of a piece of aircraft cable. We only attached to the end of a cable. This typically prevents the types of loading situations shown in the video. We should do more demonstrations like this in class. I also don’t know why this video was posted in black and white – but, whatever.
I remember talking about working load in one of Boevers’ classes once and being so surprised at how a person weighing only 125 pounds could exert forces well beyond their weight. I think in that story he mentioned an aerialist being able to produce almost 2,000lbs of downwards force on a drop. That’s a pretty crazy thing to consider when building/rigging for entertainment purposes because it feels like you just have to overbuild everything by a crazy 10x or 20x the assumed strength, which feels excessive but in reality could be very much what you need. I like this hometown zipline story and have always been a fan of the Chicago Flyhouse videos as they do a good job of explaining and showing what they’re actually talking about in terms of the science behind their projects. I had friends with ziplines growing up and I was always so interested in why the attachments to the trees had to be so intense and why the cable had to be so thick. Now I know!
We appreciate the thoughtful comments on our videos. It's always interesting to see how others interpret the subject matter. And to answer the one comment consistently coming up, we do the videos in black and white because of the vintage feel of an old theater. We actually even print our business cards using a letterpress technique on brown kraft paper.
Please keep commenting and let us know if there is a video idea you want us to explore.
www.flyhouse.com
Post a Comment