CARS MYTH BUSTERS
CARS VRT personnel decided to do a little "Myth Busting" when we did this experiement. The myth being that when a wire-rope is under tension and suddenly breaks,
a coat or blanket placed on it will prevent it from flinging around. We also wanted to see if a wire-rope will actually whip around. The results are surpising!
We used a retired vehicle and old wire rope. The winch is rated at 12,000 pounds straight-line pull and the vehicle weighs 4,500 pounds. We used a large tree
for the anchor and a 15,000 pound dyno coupled to the wire-rope with webbing.
The first experiment involved hooking up the winch to the tree and seeing how much force it would take to move the car. At 3,500 pounds of tension, the vehicle moved. Next,
we placed wheel chocks in front of the rear wheels. It made no difference! We used several types/sizes wheel chocks and the vehicle just pushed the wheel chock along.
The wheel chock could not get a bite into the asphalt.
This picture shows the set-up we used.
The dyno we used is rated at 15,000 pounds. We allowed the winch cable to reach 10,000 pounds before we cut the webbing. Why not run it up to 12,000? It was decided that
at 10,000 we would see the same result and we didn't have to worry about breaking something important.
Once we tested just the car, we need more weight to continue. Squad 133 was attached to the car as an as a immovable anchor.
One the desired strain was reached, we cut the webbing. The result was the cable acting very much like a rubber band. It recoiled back towards the winch in a straight line.
The speed was the thing that surprised us, it was slow enogh that the winch operator could easily move out of its way. The cable did not whip around or up and it
landed underneath the car.
The last experiment involved putting a turnout coat over the wire cable. This is a standard practice in our area and the belief is that the cable stores energy and the when
something fails, the coat will drop the cable to the ground so it doesn't whip around.
Myth Busted! When the webbing was cut, the cable recolied much like it did without the coat. The one nice thing was the cable wrapped around the coat and the hook was
embedded in the coat so that it could not be a projectile.
The coat wound up underneath the car. Conclusion? Having a coat or blanket on a winch cable is worthwhile in that it allows you to see an otherwise
almost invisible wire and the weight will slow the cable's recoil somewhat. The weight will NOT drop the cable to the ground as everyone thought. Winch cable does not store as much energy as we thought simply because it does not stretch much.
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