I went skiing last weekend and noticed that the chair lift really rolls along but as it approaches the load or unload point, it slows down until loaded or loaded, makes a U-turn, then speeds up again. The chairs get closer together at the turnaround to slow them down, since the cable moves at a constant speed.
The chairs appear to be attached quite securely to the cable, so it doesn’t seem possible that they are slipping their position at the turnaround points. But nonetheless, the somehow do.
How does this work? howstuffworks.com came up dry, as did various Googles.
In all chairlifts I have seen the chairs are un-clamped from the cable at either end. They then run around a fixed track where they bunch up and are then re-clamped to the main cable at a point past where you get on.
Actually, many, if not most, chairlifts built in the last ten years are designed so that they do detach from the main cable when they go around the turn. This makes loading and unloading a lot more pleasant, IMHO.
The new detachable quad at Snowbird doesn’t whack me in the back of the knees like the old fixed double used to.
As to the actual engineering involved, I’m not the one to ask. Try Googling “detachable chair lift”.
Those chair lifts detach the chair from the main cable and attach the chair to a slower cable to allow for easier loading and unloading. This allows you to get up the hill faster without getting smacked around when loading.
They detach from the cable. If you look at the jaw that holds the chair on the cable, you’ll see a couple of big springs which keep the jaws closed tightly. There’s a mechanism in the wheel house that releases those jaws so the chair is not on the cable when you load.
Even more interesting (to my easily-entertained mind) is a new lift at Breckenridge that has a midway loading point. In the old days, they didn’t bother to slow down for midway loading (and they typically only had midway loading on slower lifts). This lift pulls the chairs off the cable and routes them in a little arc so they’re moving slowly when you load and then reattach to the cable. I’m sure this isn’t unique and it’s basically the same mechanism as the endpoints, but it entertained me for a couple of rides.
I used to work on the ski lifts at Breckenridge. (micco, which lift are you talking about? I haven’t been back in a couple of years.)
There are actually two broad types of lifts: Detachable, which previous posters have explained, in which the chair detaches from the main cable to a slower-moving cable to facilitate loading and un-; and Attached, in which the chairs are essentially welded to the cable.
Obviously, detachable lifts can offer several advantages to attached lifts; since the attached lift has to run at a uniform speed that is slow enough to allow for loading and unloading, it can’t cart as many skiers up the mountain as a detachable lift given the same amount of time and distance and the same size chair.
However, detachable lifts have a hell of a lot of moving parts. Therefore, there are (obviously) more points of potential failure. They’re also more expensive to install, and tend to be used only on the main routes from the lodge to the top of the mountain.
But with more moving parts comes greater safety. During our training, we saw a movie depicting what happens when all of the safety brakes are disengaged on an attached chair. (This was done intentionally on a chair at, I think, Crested Butte, during the summertime.) The motor didn’t have enough horsepower to push the chairs up the mountain, so the chairs started moving backwards . . . and picking up speed. It didn’t take long for the chairs to gain enough momentum that when they reached the huge flywheel at the top, they were catapulted surprisingly large distances.
We were told, “If this happens to you, don’t think about the skiers on those chairs. They can’t be saved. Just run.” That point made an impression on us.
It’s a new lift, the Peak 8 SuperConnect. It runs from mid-mountain below the Beaver Run chair up to the Peak 8 powder house. It replaced the old #4 but starts much lower. The midway loading point is at the bottom of Shock where the #4 used to start.