Chairlift

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Chairlift

[chair-lift]

A chairlift (technically, an elevated passenger ropeway), is a type of aerial lift, which consists of a continuously circulating steel cable loop strung between two end terminals and usually over intermediate towers, carrying a series of chairs. They are the primary onhill transport at most ski areas (in such cases referred to as 'skilifts'), but are also found at amusement parks, various tourist attractions, and increasingly, in urban transport.

Depending on carrier size and loading efficiency, a passenger ropeway can move up 4000 people per hour, and the fastest lifts achieve operating speeds of up to 12 meters/second (27 mph, 43 km/h). The two-person double chair, which for many years was the workhorse of the ski industry, can move roughly 1200 people per hour at rope speeds of up to 2.5 m/s. The four person detachable chairlift ("high-speed quad") can transport 2400 people per hour with an average rope speed of 5 m/s. Some bi and tri cable elevated-ropeways and reversible tramways achieve much greater operating speeds. Fixed-grip lifts are usually shorter than detachable-grip lifts due to rope load; the maximum vertical rise for a fixed grip chairlift is 300-400 meters and a length of about 1200 m, while detachable quads and "six-packs" can service a vertical rise of over 600 m and a line length of 2000 m.

Design and function

A chairlift consists of numerous components to provide safe efficient transport.

Terminology

Especially at ski areas, chairlifts are referred to with a ski industry vernacular. A one person lift is a "single", a two person lift is a "double", a three person lift a “triple”, four person lifts are “quads” and a six person lift is a "six pack". If the lift is a detachable chairlift, it is typically referred to as a “high-speed” lift, which results in a “high-speed quad” or “high-speed six pack”.rope speed: the speed in feet per minute or meters per second that the rope moves[load] interval: the spacing between carriers, measured either by distance or timecapacity: the number of passengers the lift transports per hourefficiency: the ratio of fully loaded carriers during peak operation, usually expressed as a percentage of capacity. Because fixed grip lifts move faster than detachables at load and unload, misloads (and missed unloads) are more frequent on fixed grips, and can reduce the efficiency as low as 80%.fixed grip: each carrier is fastened to a fixed point on the ropedetachable grip: each carrier's grip opens and closes during regular operation allowing detachment from the rope and travel slowly for load and unload. Detachable grips allow a greater rope speed to be used, usually twice that of a fixed grip chair, while simultaneously having slower loading and unloading sections. See detachable chairlift.

The capacity of a lift is constrained by the motive power (prime mover) versus the rope speed, the carrier spacing, the vertical displacement and the number of carriers on the rope (a function of the rope length). Human passengers can load only so fast before loading efficiency decreases; usually an interval of at least five seconds is needed.

Rope

The rope is the defining characteristic of an elevated passenger ropeway. The rope stretches and contracts as the tension exerted upon it increases and decreases, and it bends and flexes as it passes over sheaves and around the bullwheels. The fibre core contains a lubricant which protects the rope from corrosion and also allows for smooth flexing operation. The rope must be regularly lubricated to ensure safe operation and long life.

Various techniques are used for constructing the rope. Dozens of wires are wound into a strand. Several strands are wound around a textile core, their twist is oriented in the same or opposite direction as the individual wires; this is referred to as Lang lay and regular lay respectively.

Rope is constructed in a linear fashion, and must be spliced together before carriers are affixed. Splicing involves unwinding long sections of either end of the rope, and then winding each strand from opposing ends around the core. Sections of rope must be removed, as the strands overlap during the splicing process.

Terminals and towers

Every lift involves at least two terminals and—usually—intermediate supporting towers. A bullwheel in each terminal redirects the rope, while sheaves (pulley assemblies) on the towers support the rope well above the ground. The number of towers is engineered based on the length and strength of the rope, worst case environmental conditions, and the type of terrain traversed. The bullwheel with the prime mover is called the drive bullwheel; the other is the return bullwheel. Chairlifts are usually electrically powered, often with diesel or gasoline engine backup, and sometimes a hand crank tertiary backup. Drive terminals can be located either at the top or the bottom of an installation; though the top-drive configuration is more efficient, practicalities of electric service might dictate bottom-drive.

Braking systems

The drive terminal is also the location of a lift's primary braking system. The service brake is located on the driveshaft beside the main drive, before the gearbox. The emergency brake acts directly on the bullwheel. While not technically a brake, an anti-rollback device (usually a cam) also acts on the bullwheel. This prevents the potentially disastrous situation of runaway reverse operation

Many chairlifts have a braking system in the sheaves.

Tensioning system

The rope must be tensioned to compensate for sag caused by wind load and passenger weight, variations in rope length due to temperature and to maintain friction between the rope and the drive bullwheel. Tension is provided either by a counterweight system or by hydraulic rams, which adjust the position of the bullwheel carriage to maintain design tension. For most chairlifts, the tension is measured in tons.

Prime mover and gearbox

Either diesel engines or electric motors can function as prime movers. The power can range from under ten horsepower (7.5 kW) for the smallest of lifts, to several hundred for a long, fast detachable eight-seat up a steep slope. AC electric motors were the most common, though direct current motors are now economically competitive.

The driveshaft turns at high RPM, but with low torque. The gearbox transforms high RPM/low torque rotation into low RPM/high torque to drive the bullwheel. Higher power is able to pull heavier loads, or sustain a higher rope speed.

Secondary and auxiliary movers

In most localities, the prime mover is required to have a backup drive; this is usually provided by a diesel engine, which can operate during power outages. The purpose of the backup is to permit clearing the rope to ensure the safety of passengers; it usually has much lower power and is not used for normal operation. The secondary drive connects with the drive shaft before the gear box, usually with a chain coupling. Some chairlifts are also equipped with an auxiliary drive, which can be used to continue regular operation in the event of a problem with the prime mover. Some lifts even have a hydrostatic coupling so the driveshaft of a snowcat can drive the chairlift.

Carriers and grips

Carriers are designed to seat 1, 2, 3, 4, 6 or 8 passengers. Each is connected to the cable with a steel cable grip that is either clamped onto or woven into the cable. Clamping systems use either a bolt system or coiled spring to provide clamping force. For maintenance or servicing, the carriers may be removed from or relocated along the rope by loosening the grip.

Restraining bar

Also called a retention bar or safety bar, these may help hold passengers in the chair in the same way as an automotive seatbelt or safety bar in an amusement park ride. If equipped, each chair has a retractable bar, sometimes with attached foot rests. In most configurations, a passenger may reach up and behind their head, grab the bar or a handle, and pull the restraint forward and down. Once the bar has rotated sufficiently, gravity assists positioning the bar to its down limit. Before disembarking, the bar must be rotated up, out of the way.

The physics of a passenger sitting properly in a chairlift do not require use of a restraining bar. If the chairlift stops suddenly (as from use of the system emergency brake), the carrier's arm connecting to the grip pivots smoothly forward—driven by the chair's inertia—and maintains friction (and seating angle) between the seat and passenger. The restraining bar is useful for children—who do not fit comfortably into adult sized chairs—as well as apprehensive passengers, and for those who are disinclined or unable to sit still. In addition, restraining bars with footrests reduce muscle fatigue from supporting the weight of a snowboard or skis, especially during long lift rides. The restraining bar is also useful in very strong wind and when the chair is coated by ice.

Restraining bars (almost always with foot rests) on chairlifts are more common in Europe and also naturally used by passengers of all ages. Some newer chairlifts have restraining bars that open and close automatically.

Canopy

Some lifts also have individual canopies which can be lowered to protect against inclement weather. The canopy, or bubble, is usually constructed of transparent acrylic glass or fiberglass. In most designs, passenger legs are unprotected; however in rain or strong wind this is considerably more comfortable than no canopy.

Control system

To maintain safe operation, the chairlift's control system monitors sensors and controls system parameters. Expected variances are compensated for; out-of-limit and dangerous conditions cause system shutdown. In the unusual instance of system shutdown, inspection by technicians, repair or evacuation might be needed. Both fixed and detachable lifts have sensors to monitor rope speed and hold it within established limits for each defined system operating speed. Also, the minimum and maximum rope tension, and speed feedback redundancy are monitored.

Many—if not most—installations have numerous safety sensors which detect rare but potentially hazardous situations, such as the rope coming out of an individual sheave.

Detachable chairlift control systems measure carrier grip tension during each detach and attach cycle, verify proper carrier spacing and verify correct movement of the detached carriers through the terminals.

Safety systems

Aerial lifts have a variety of mechanisms to ensure safe operation over a lifetime often measured in decades.

Braking

As mentioned above, there are multiple redundant braking systems. Turning off the main drive will normally bring the rope to a stop in installations where it is transporting passengers uphill. A service brake and emergency brake on the bullwheel as well as drum brakes in the sheaves can stop the ropeway quickly.

Brittle bars

Some installations use brittle bars to detect several hazardous situations. Brittle bars alongside the sheaves detect the rope coming out of the track. They may also be placed to detect counterweight or hydraulic ram movement beyond safe parameters (sometimes called a brittle fork in this usage) and to detect detached carriers leaving the terminal's track. If a brittle bar breaks, it interrupts a circuit which causes the system controller to immediately stop the system.

Cable catcher

These are small hooks sometimes installed next to sheaves to catch the rope and prevent it from falling if it should come out of the track. They are designed to allow passage of chair grips while the lift is stopping and for evacuation. It is extremely rare for the rope to leave the sheaves.

In May 2006, a cable escaped the sheaves on the Arthurs Seat, Victoria chairlift in Australia causing four chairs to crash into one another. No one was injured, though 13 passengers were stranded for four hours. The operator blamed mandated changes in the height of some towers to improve clearance over a road.

Collision

Passenger loading and unloading is supervised by lift operators. Their primary purpose to ensure passenger safety by checking that passengers are suitably outfitted for the elements and not wearing or transporting items which could entangle chairs, towers, trees, etc. If a misload or missed unload occurs—or is imminent—they slow or stop the lift to prevent carriers from colliding with or dragging any person. Also, if the exit area becomes congested, they will slow or stop the chair until safe conditions are established.

Communication

The lift operators at the terminals of a chairlift communicate with each other to verify that all terminals are safe and ready when restarting the system. Communication is also used to warn of an arriving carrier with a passenger missing a ski, or otherwise unable to efficiently unload, such as patients being transported in a rescue toboggan. These uses are the chief purpose for a visible identification number on each carrier.

Evacuation

Aerial ropeways always have several backup systems in the event of failure of the prime mover. An additional electric motor, diesel or gasoline engine—even a hand crank—allows movement of the rope to eventually unload passengers. In the event of a failure which prevents rope movement, staff may conduct emergency evacuation using a simple rope harness looped over the aerial ropeway to lower passengers to the ground one by one.

Grounding

A steel line strung alongside a mountain is likely to attract lightning strikes. To protect against that and electrostatic buildup, all components of the system are electrically bonded together and connected to one or more grounding systems connecting the lift system to earth ground. In areas subject to frequent electrical strikes, a protective aerial line is fixed above the aerial ropeway.

Load testing

In most jurisdictions, chairlifts must be load inspected and tested periodically. The typical test consists of loading the uphill chairs with bags of water (secured in boxes) weighing more than the worst case passenger loading scenario. The system's ability to start, stop and prevent reverse operation are carefully evaluated against the system's design parameters.

Rope testing

Frequent visual inspection of the rope is required in most jurisdictions, as well as periodic non-destructive testing. Electromagnetic induction testing detects and quantifies hidden adverse conditions within the strands such as a broken wire, pitting caused by corrosion or wear, variations in cross sectional area, and tightening or loosening of wire lay or strand lay.

Safety gate

If a passenger fails to unload, their legs will contact a lightweight bar or thin line which stops the lift. The lift operator will then help them disembark, reset the safety gate, and initiate the lift restart procedure. While possibly annoying to other passengers on the chairlift, it is preferable to strike the safety gate (that is, it should not be avoided) and stop the lift than be an unexpected downhill passenger. The majority of chairlifts are rated for zero downhill capacity, so the operator would eventually stop the lift and call for a time-consuming evacuation of the passenger.

History

Aerial passenger ropeways were known in Asia well before the 1600s for crossing chasms in mountainous regions. Men would traverse a woven fiber line hand over hand. Evolutionary refinement added a harness or basket to also transport cargo.

The first recorded mechanical ropeway was by Venetian Fausto Veranzio who designed a bicable passenger ropeway in 1616. The industry generally considers Dutchman Wybe Adam to have built the first operational system in 1644. Alpine regions of Europe developed the technology; progress rapidly advanced and expanded with the advent of wire rope and, especially, electric drive. World War I motivated extensive use of military tramways for warfare between Italy and Austria.

The first known chairlift was created for the ski resort in Sun Valley, Idaho in 1936. It was installed on Proctor Mountain, two miles (3 km) east of the more famous Bald Mountain, the primary ski mountain of Sun Valley resort since 1939. The chairlift was developed by James Curran of Union Pacific's engineering department in Omaha during the summer of 1936. Prior to working for Union Pacific, Curran worked for Paxton and Vierling Steel (www.pvsteel.com), also in Omaha, which engineered banana conveyor systems to load cargo ships in the tropics. (PVS manufactured these chairs in their Omaha, NE facility.) Curran reengineered the banana hooks with chairs and created a machine with greater capacity than the up-ski toboggan (cable car) and better comfort than the J-bar, the two most common skier transports at the time—apart from mountain climbing. His basic design is still used for chairlifts today. The patent for the original ski lift was issued to Mr. Curran along with Gordon H. Bannerman and Glen H. Trout (Chief Engineer of the Union Pacific RR) in March 1939. The patent was titled "Aerial Ski Tramway,' . W. Averell Harriman, Sun Valley's creator and former governor of New York State, financed the project. The original 1936 chair lift was later moved to Boyne Mountain, Michigan (U.S.A.) where parts of it are still in use.

The second was the Magic Mile chairlift on Mount Hood, Oregon in 1938 which was also the longest in the world.

Future

New chairlifts built since the 1990s are infrequently fixed-grip. Existing fixed-grip lifts are being replaced with detachable chairlifts at most major ski areas. However the relative simplicity of the fixed-grip design results in lower installation, maintenance and—in many cases—lower operation costs. For this reason, they are likely to remain at low volume and community hills, and for short distances, such as beginner terrain.