5 replies to this topic

[Nor'eastSkier]

I'm sure many of you know about the indoor ski area in Dubai, which has a quad chair and a surface lift. I had a question about the midstation of the quad. There is a line turn at the midstation, however, it seems much less complex than most other line turns for fixed-grip lifts I've seen.

Ski Dubai midstation:
 ski_dubai_mid.jpg (46.6K)
Number of downloads: 386

Snowflake Double, Breckenridge:
 turn4.jpg (63.26K)
Number of downloads: 342

It seems that the former approach is much simpler and less expensive, so why isn't it the standard design?

I also was interested in learning more about Dubai's design, because it would seem that the springbox for the grip would cause trouble when traveling around the bullwheel.

Thank you for your time.

[Peter]

There is actually a cutout in the bullwheel for the grips to pass through. So the bullwheel circumference must exactly match the chair spacing. I suspect this setup requires constant monitoring and adjustment to make sure that the chairs don't get out of sequence with the hole in the bullwheel. This lift also runs at only 1.5 m/s which might have something to do with it.

[skiersage]

Skier, on 02 October 2011 - 07:52 AM, said:

There is actually a cutout in the bullwheel for the grips to pass through. So the bullwheel circumference must exactly match the chair spacing. I suspect this setup requires constant monitoring and adjustment to make sure that the chairs don't get out of sequence with the hole in the bullwheel. This lift also runs at only 1.5 m/s which might have something to do with it.

I remember there was a topic on this subject a while back. It is in this forum somewhere. The bullwheel has rollers built in so that it can spin independently of the rope. I believe there is a drive mechanism that makes sure the groove lines up with the chairs.

[Allan]

You can see it in this vid:
http://video.google.com/videoplay?docid=-4497380729948638464&q=ski+area#docid=5548158277633563582

[piotrek21]

It all about physics. On the chairlift in Breck, people never actually go around the bull wheel, only empty downhill chairs do, and there is a reason for that. A chairlift runs at a constant speed and never has an acceleration apart from loading and when it starts back up. However, once you go around a curve even though you do not have any tangential acceleration (acceleration of the line), you most certainly have normal acceleration (acceleration towards the center of rotation). Assuming that a normal quad FGC runs at 2.5 m/s (little on the high side probably), and the bullwheel has a diameter of 6m (some one comment on the accuracy of this please) then the normal acceleration would be 2.5^2/3 or 2.08 m/s^2 which is pretty significant. Anyone who has ridden the South Ridge Triple in Killington, Vt can tell you that that acceleration is not pleasant. You want to have as little of an acceleration on a chairlift as possible.

So what do we learn? We want to keep the normal acceleration as small as possible for the comfort and safety of the passengers. The acceleration depends on the radius of curvature and on the speed of the line. To decrease the value of a given fraction you can either decrease the numerator (top) while keeping the denominator (bottom) the same, or keep the numerator then same and increase the denominator. In Dubai they decrease the speed to 1.5 m/s, in Breckenridge they increase the radius of curvature of the turn that the uphill chairs take (notice that on the left side of the picture you posted).

So to answer your question, the reason why they do not use the design used in Dubai, is because at a reasonable chairlift speed, the passengers would be very uncomfortable and/or put in a dangerous situations going round such a small radius. So they keep their speed down and everyone is happy. In Breck, and probably most places that would have a kink in a FGC, there is more room to play with and a more elaborate system can be put into place to allow the chairs to have a higher line speed.


P.S. Also keep in mind stresses and forces experienced by the towers and bull wheels.

[floridaskier]

The South Ridge triple turn was pretty harrowing. It wasn't bad in the middle seat, but the outside and inside people needed to hold on tight to stay on the chair. They had a sign that said 'Hold On'