#Whistler Blackcomb | Explore Tumblr posts and blogs

kxantares · 2 years ago

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So, I got this commentary in the tags:

Well, thanks for asking, because: I'll explain it.

Here's what each part is:

deeper blue: the rope (a big, thick metal cable)

white: the chair assembly; not really relevant for this discussion

olive: what we're defining as "static", for the purposes of this discussion — the block connecting the chair assembly to the grip mechanism

magenta: the grip jaws

dark green: a hinge (one on each side)

cyan: the grip opening mechanism, which is only engaged upon entering the station

purple: the bar which pushes back against the springs

yellow: rubber springs

And here's how it works in practice:

The operation of the grip centres around the "static" part, which serves two purposes: both holding all the dynamic parts in place, and also carrying a fair portion of the grip force to the cable-grip interface, where friction is what *directly* holds it all in place.

So the elastic component of the force works roughly like this:

Screws (olive) hold the bar (purple) in place.

The bar is under some degree of compression, pushing back against (and, due to its shape, in an inward direction) relative to the springs (yellow).

The springs, in turn being pushed by the bar, push down against the grip jaws (magenta).

The grip jaws, attached to the fixed assembly by hinges (dark green), respond to this downward force by rotating up.

By rotating up, the jaws push the rope (blue) up against the fixed assembly. The rope is now subject to force both from roughly the bottom left and bottom right as well as the direct top.

And the gravitational component of the force works a bit like this:

The fixed assembly (olive) presses down on the rope (blue).

The rope presses up against the upper part of the grip jaws (magenta).

The upper part of the grip jaws, being pushed up in that fashion, undergoes a rotational force around the hinges (dark green), which pulls the lower part of the grip jaws in against the cable from below.

This additional force itself causes further force against the fixed assembly.

So this sounds all fine and dandy, but what if you…

…damage the sources of that elastic force by means of, say, cooling them repeatedly to a temperature where they gradually become permanently less elastic?

The screws (olive) are probably still just fine, and the bar (purple), being metal, is pretty resilient to the unimpressively cold temperatures the lower half of Whistler Mountain gets — say, basically never below –15°C.

The bar does its thing, pressing against the springs (yellow)…

…which are putting out far less force than they should be, given their currently low temperature and frequent cycling between cold and colder, which means they aren't pushing as hard as they should be against the grip jaws (magenta).

The grip jaws, pivoting around those hinges (dark green), respond to this below-spec downward force by rotating up with below-spec force.

By rotating up too weakly, the jaws don't provide as much force against the rope (blue) as they need to to withstand certain conditions, resulting in a situation where the friction at the top, bottom right, and bottom left of the rope could, due to some other force being removed, for some reason, could become insufficient to keep the chair on the rope.

…take gravity out of the equation?

It's probably worth noting here that the section of the rope where the failure occurred at was at an angle of about 40°, where a fair portion of gravity's force, under perfect conditions, would already not be pressing in the right direction, directly fighting the grip's friction rather than assisting the grip's gravitational redundancy.

Oh no, there's been an emergency stop, and the chair is just coming down from the apex of a particularly sharp bounce! This means that the fixed assembly (olive) is currently applying exactly zero force down on the rope (blue).

Due to the lack of gravity, the rope isn't pushing up against the upper part of the grip jaws (magenta).

The upper part of the grip jaws, being subject to no force at all, do not have any gravity helping them rotate inward more forcefully, thus leaving the only force in that direction being the already dangerously weak force of the springs (yellow).

There is now basically no force between the rope and the fixed assembly, absolutely no force between the upper parts of the grip jaws and the rope, and just a bit between the lower parts and the rope. The freefall that the chair enters as it returns from the apex of that bounce translates into downward acceleration which overcomes the friction remaining against the rope, and the chair subsequently accelerates right into the chair ahead of it.

And that's what that diagram was getting at.

What the heck's the deal with tower 6 on the Big Red Express (1997–2022) at Whistler-Blackcomb?

So, on Whistler Mountain, there was this one chairlift, the Big Red Express (due to be replaced in time for the 2022–2023 ski season with a new lift by the same name), which was notable for, mostly, being remarkably miserable to ride on snowy, windy days; being ten minutes long; and:

This is a rare design feature on ropeways, which only really happens when there's a serious elevation differential across the several metres separating each side of the ropeway. Usually, they'll just build a tower tall enough to support both sides of the cable, unless it's way cheaper to not do that. Which, well, it is here.

But there's another thing that's weird about that tower. Like, here, let me show you a basically identical lift built by the same company, Doppelmayr, around the same year:

Check the tower heads on both — the ones on the second picture are normal for that manufacturer in that era. So where did the Big Red get its weird towers from?

The Redline Express, installed in 1992. I'll get into why it only lasted five ski seasons in a bit, but basically, they ended up having to put that little side tower in because that lift was itself replacing the original Red Chair (1965–1992). Which was built, well, very differently from the big, beefy high-speed lifts that started to become the main workhorses of large ski resorts in the '80s, and which also had chairs that didn't require quite the same vertical clearance or other such space:

So, reusing the same alignment, which was the most direct route from "the top of whatever lift comes up from the base at Creekside" to "up a hill from the main lodge on the mountain, so that people can ski down to the ski racks", but with chairs that need way more vertical clearance and can support larger gaps between towers, meant sticking in a little side tower to make sure people's skis wouldn't brush against the snow (or worse!). Speaking of "worse", though, let's get into why the Redline was replaced maybe a sixth of the way into its theoretical service life:

Think about how it works in practice. For clarity, this is a device intended to secure hundreds of kilograms of metal and passengers to a rope, usually in temperatures below freezing, under conditions where forces on the cable, such as those that occur in the event of an emergency stop, can result in reduced or absent gravitational force acting on the chair.

And for more clarity, look at the upper part of the "jaws" on the cable, and where the hinges are relative to the "jaws". Just one more thing: those tension-providing devices aren't lazily drawn metal springs; they're rubber "marshmallow" springs.

Can you see where the problem might be with this setup? Because this guy didn't:

Meet Janek Kunczynski, the founder of Lift Engineering & Manufacturing Co., AKA Yan, who might as well be the Elon Musk of ropeways. Before I get deeper into just how disastrous his detachable grip design was, let me show you another Incredible™ (derogatory) example of his engineering sensibilities:

Allow me to remind you that this is usually operating in sub-zero temperatures, and that this specific lift was often subject to considerable wind and snow. As in, when mechanics were working on this chairlift, they'd have to do that with no protection from the elements. (It's also at least rumoured within the ropeway and ski resort industries that his lifts were routinely welded together in ski resort parking lots.) His whole thing was, basically, making lifts look cool and implementing them cheaply, to undercut his European competitors, which led not just to impractical designs that were hostile to the people maintaining them or prone to breaking down, but to his company's lifts killing at least five people and injuring at least seventy.

Which brings us back to Whistler:

Whistler, at the time in an arms race to outcompete Blackcomb, its neighbour, but lacking the sort of venture capital backing Blackcomb had, wanted to put in some high-speed lifts to be able to match the skiing experience at Blackcomb, which had already bought several such lifts from Doppelmayr (after buying several low-speed lifts from Yan). So they figured they'd take the cheap route, and get three high-speed lifts, of a fairly unproven design, installed. These were to replace three ancient lifts that were, at that point, constraining the resort's capacity.

While the Redline and Green both served through their five years of operation without any serious issues, the same can't be said for the Quicksilver Express, which was the only chairlift Yan ever built with "bubbles" on it — which required a slightly enhanced grip, to handle the additional weight.

It wasn't enhanced enough, though. On December 23rd, 1995…

The Quicksilver, specifically, was an unmitigated dumpster fire, even before any accidents happened. It was designed such that, in wind, grips could smack against towers, taking on damage in the process. It had a faulty brake system that would apply maximum braking force via the emergency brake when a normal stop is what the operator pressed the button for. At least a few empty chairs had straight up fallen off the cable before the accident. And then there were the grips.

These grips received multiple retrofits and rebuilds throughout the few years the lift was operating, which never seemed to help — they slipped so often that operators on the lift just stuffed paper into the grip force alarm to muffle it. The clearance between grips and towers was known to be below code, and Whistler stated that they simply couldn't fix it. Upon testing the grips after the accident, of 29 tested, every single one failed to perform adequately.

Furthermore, there was the whole thing with the rubber and the claws. Rubber springs lose performance at much less extreme temperatures than metal springs, and the way the grips were designed, a lot of their grip force relied on the chair applying force via gravity. Take away gravity, and the grip can slip. Take away gravity on a particularly steep section of the lift line, and you've got a cascade of chairs knocking each other off of the cable until they ram into a tower and fall to the ground.

So it was 1997, and Whistler, on the edge of going bankrupt from lawsuits and lost business, had to get rid of the other Yan high speed lifts, which were likely safer, but not safe enough. Some resorts retrofitted theirs to use a better grip design, but Whistler just got rid of them…

…other than the towers.

#ropeway #chairlift #skilift #engineering #deep dive #Whistler-Blackcomb #ropeway accident #Lift Engineering #Janek Kunczynski #chairlift accident #1995 #Whistler Mountain #detachable grip #longpost #Whistler BC

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