16 replies to this topic

[liftmech]

We were getting off topic in the compression assembly thread, so here's a more focused one.
As Ryan and I have touched on, Riblet used a design wherein the weight of the towerhead was kept light so that the tower could lean more and place the load directly on the foundation. The load, in this case, offsets the weight of the tower. Hall, Thiokol, CTEC and Yan depended on the weight of the tower to offset tle direction of the load, however, and placed more sheaves on the cap than Riblet. They put their towers completely vertical no matter the direction of load. Doppelmayr, Poma, and Heron designed their towers somewhere in the middle of this range, with slight tower anles on steeper sections and vertical towers on flatter parts. Doppelmayr in particular used the caternary (sag) of the rope to contain it on the tower.

I hope this attached sketch sheds a little more light on this. The solid lines represent the stronger force; the dashed lines the weaker (relatively speaking).

Attached File(s)

•  tower_loading.JPG (29.64K)
  Number of downloads: 61

[Allan]

Very interesting! There must be exceptions to the leaners - some of our Thiokol towers lean slightly downhill, as with many of the YAN towers on the steep sections of Motherlode - and all the leaners on Motherlode are 8ers.

[floridaskier]

Thanks for the drawing and info, Ryan

CTEC has just about every single tower completely vertical, especially at DV on the Empire lift. The towers are so perfectly vertical, even on the really steep section at the end, so that in relation to the chair it almost feels like the towers are angled back uphill. CTEC has only 3 angled towers that I've seen, and only one of them is not right on the edge of a cliff (Baldy at Snowbird, but that lift is different in more ways than that)

Here's a picture of the breakovers on DV's Empire lift, from the front page of skilifts.org:

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•  top_background_home.jpg (37.48K)
  Number of downloads: 45

[SkiBachelor]

Here is the Tower Placement page on Skilifts.org: http://www.skilifts....erplacement.htm

If anyone feels like they can add onto that article, that would be appreciated.

[KZ]

Ive also seen several leaning yan towers on various lifts around the tahoe area. Sometimes the vertical CTEC towers annoy me, especially on Lookout at Northstar becasue the entire line is steep, and it just looks kinda funny.

[Allan]

Here's a Thiokol leaner... It doesn't lean that much though.

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•  Tower3.jpg (57.97K)
  Number of downloads: 40

[Allan]

One of the breakovers on Motherlode - the crossarms are even with flat ground. The next two towers down from this one lean quite heavily.

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•  MotherLode___Breakover_Tower_1.JPG (143.58K)
  Number of downloads: 44

[CAski]

KZ: A few towers at the top of Lookout lean a little bit. However, you are right that the majority of the line does look a bit funny with mostly vertical towers.

[liftmech]

Allan, on Apr 24 2004, 12:15 PM, said:

One of the breakovers on Motherlode - the crossarms are even with flat ground.  The next two towers down from this one lean quite heavily.

I had forgotten about that vintage of Yans- there are exceptions to every rule. Were those by any chance new when you guys bought the lift from Blackcomb? I ask because those two are three years older than S-lift, and even on its steepest section it still has vertical towers.

[Allan]

The towers are from the Cruiser chair at Blackcomb - maybe they re-engineered them when they were installed here!

[floridaskier]

When was the Motherlode lift built?
Was it around 1991? Because there are 2 Yans at DV that had been moved and they both have a bunch of leaners with level crossarms like the ones in Allan's picture. They all seem to be leaning at about the same angle regardless of the line slope

[KZ]

On the hsq at sierra it reuses old yan towers from their hsq, and probably more then half of them lean at some angle or another. Some even seem to lean to the right when you go up.

[floridaskier]

When was the original Yan HSQ at Sierra built? Because all the towers on DV's 91 Yan retrofit are completely vertical.

Could it be something the resort can choose, whether or not to have leaning towers for whatever reason?

[Allan]

Finally the internet works properly again!! Motherlode was built in 95.

[partek]

Towers are inclined for several reasons. Foundation loading, limited travel of the sheave assembly main axle pivot, swing clearance, tower vibration and ease of climbing. In early years catwalks were very rare, today most lifts have them. Chairs must clear all cross arm components when swung 15 degrees as per A.N.S.I. code. As a chair traveling uphill exits a vertical tower the clearance is less than when it entered and vice versa in the downhill direction. By inclining the tower the clearance is improved. Otherwise the hangers would need to be longer and therefore the line gauge would have to be wider.

My personal favorite reason is ease of climbing :D

[floridaskier]

Why was it that just about every tower was angled on older lifts, but on new lifts, it isn't nearly as steep? Is it because the towers are heavier now, or stronger so they won't need it?

[liftmech]

Could be that the manufacturers who followed the steeper tower philosophy are all out of business...