Chairlift

A chairlift, more correctly known as an elevated passenger ropeway, is a type of aerial lift, which consists of a continuously circulating steel cable strung in a loop between two end terminals and generally over intermediate towers. They are found at many ski areas, amusement parks, at various tourist attractions, and increasingly, in urban transport.

Passenger ropeways are both safe and efficient; 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 m/s. The two-person double chair, which for many years was the workhorse of the North American Ski industry can move roughly 1200 people per hour at line speeds of up to 2.5 m/s. The four person detachle chair (or high speed quad), can transport 2400 people per hour with an average line speed of 5 m/s. Some bi and tri cable elevated-ropeways and reversible tramways acheive operating speeds much greater than this. Fixed-grip lifts are usually shorter and than detachable-grip lifts due to increased line load; the standard vertical rise for a fixed grip chairlift is in the range of 300-400m and usually under 1200 meters in length, while detachable quads can service a vertical rise of over 600 m and a line length of 2000m.

Design and Functions

Numerous components are necessary for elevated passenger ropeways to provide safe efficient transport.

Terminology

line speed: The speed in feet per minute or meters per sec that a lift can run at
interval: The distance between carriers in either distance or time. Often referred to as load interval, or the difference in time that two carriers pass a certain point (usually the loading point)
capacity: the number of passengers a lift can transport per hour.
efficiency: A percentage which represents how many carriers can be fully loaded during peak operation. Because fixed grip lifts load at a reasonably fast rate, misloads can be a regular occurence, reducing the efficiency of the lift to as low as 80%. Because detachable lifts load at speeds as low as 1 m/s, it is much easier for passengers to load, and misloads are much more infrequent.
fixed grip: the grip is fixed on the line; it should not move during regular operation.
detachable grip: the grip is able to open and close during regular operation allowing carriers to detach from the line and travel at a different speed. Detachable grips allow a greater line speed to be used, usually twice that of a fixed grip chair. There is a limit to how fast passengers can load a lift; a lift moving at greater than 2.5 m/s is very difficult to load, and a load interval of less than 5 seconds forces passengers to rush, and creates potential misload situations.

Capacity is a factor of both line speed and the load interval. The greater the line speed, the greater the distance between chairs must be, as a prime mover can pull either large loads or run at high speeds, but not both.

Rope

The rope is the defining characteristic of an elevated passenger ropeway; ropes are constructed of hundreds of steel fibres wound in strands, which are then wound around each other and a synthetic or natural fibre core. The rope is essentially a moving mechanical part; it streches and contracts as the tension exerted upon increases and decreases, and it bends and flexes as it passes over sheave and around the bullwheel. The fibre core contains a lubricant, which both protects the rope from corrosion, and also allows for smooth operation of the rope. The rope must be regularly re-lubricated to ensure safe operation and along life. Various construction techniques for constructing the rope. Each strand contains hundreads of individual steel threads, wound either clockwise or counter-clockwise. As the strands are wound around each other and the core, their twist can be oriented in the same or opposite direction as the twist of the individual strands; this is referred to as Lang Lay and Regular Lay respectively. Lay is further defined by specifying the overall direction of twist, either to the right or left. Obviously, rope is constructed in a linear fashion; before carriers can be affixed to it, it must be spliced together. Splicing involves un-winding 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 an indeterminate number of intermediate towers the support the line. A bullwheel in either terminal redirects the line either up or downhill, while sheaves (wheels) in assemblies on the towers support the rope above the ground. The number of towers is a factor of the length of the lift and the type of terrain it crosses. The Bullwheel that is attached to the Prime Mover is called the drive bullwheel, while the other bullwheel is known as the return bullwheel. Drive terminals can be located either at the top or the bottom of am installation; though top-drive configuration is more efficient, the installation of electricity to the top of a lift can often be prohibitively expensive.

braking systems

The drive terminal is the location of a lift's braking systems, of which there are at least three. The service brake is located on the driveshaft, before the gearbox, while the emergency brake must act directly upon the bullwheel. While not technically a brake, an anti-rollback device (usually a cam) also acts on the bullwheel. this prevents the potentially disasterous situation of reverse operation from occuring.

tensioning system

Because only one side of a lift carries wieght, the line is under a constantly varying load; to maintain friction between the drive bullwheel and the rope, the whole line must be under tension. Tension is provided either by a counterwieght system or by hydraulic rams, which adjust the position of the bullwhell carriage to maintain design tension.

Prime Mover and Gearbox

Both Diesel engines and electric motors can function as prime movers (PM), though alternating current electric motors are by far the most common. Recent technological advances have permitted the installation of direcdt current motors, though this is still rare and expensive The driveshaft of the PM turns at a high rpm, but with low torque. The gearbox interfaces between the PM and the bullwheel, and transforms high rpm/low torque rotation into low rpm/high torque that can drive the bullwheel. A higher horsepower PM is able to pull larger loads, or sustain a higher line speed.

secondary and auxiliary movers

By code in most countries, the PM must have a backup drive; this is usually provided by a diesel engine, which can operate during power outages. The purpose of the secondary is to permit clearing the line to ensure the safety of passengers; it is usually has much less horsepower than the PM and cannot be used for normal operation. The secondary drive connects with the drive shaftbefore the gear box, usually with a chain coupling. Some chairlifts are also equiped with an auxiliary drive, which can be used to continue regular operation in the event of a problem with the PM. Some lifts even have a hyrostatic coupling so snowcats can be hooked up the driveshaft to act as the PM.

Carriers and Grips

Carriers (which are usually chairs), can seat anywhere from one to eight people, and are connected to the cable with a steel grip that is either bolted or wound into the cable, or uses spring force to remain in place. The chairs can be removed from or relocated along the rope by loosening the grip for mainenance and servicing. Some lifts also come equiped with canopies, which can be lowered during inclement weather. The canopy, or bubble, is usually constructed of transparent plexiglass, and can be raised or lowered.

History

The first known chairlift was created for the ski resort in Sun Valley, Idaho in 1936. It was installed on Proctor Mountain, two miles east of the more famous Bald Mountain, the primary ski mountain of the Sun Valley resort since 1939. The chairlift was developed by James Curran of the Union Pacific's engineering department in Omaha during the summer of 1936. Prior to working for the Union Pacific, Curran worked for Paxton & Vierling Steel, also in Omaha, which had engineered installations for loading bananas on fruit boats. Curran took the mono cable tram idea and replaced the banana hooks with chairs. Thus he created a machine with a greater capacity than the up-ski toboggan (cable car) and more comfortable than the J-bar (rope tow), the two most common ways of transporting skiers up a mountain at the time short of actual mountain climbing. His basic design is still used for chairlifts today. W. Averell Harriman, the ski resort's creator and former mayor of New York City, financed the project. See and [http://www.gonorthwest.com/Idaho/central/Sun-Valley/svhistory.htm|Here

Future

Fixed-grip chairlifts are already less common-place at most major ski areas in North America, replaced by the faster Detachable chairlift. It is important to note however that the relative simplicity of the fixed-grip design results in lower installation, maintenance and other operational costs. For this reason they are likely to remain popular at smaller community hills, and for short distances such as beginner terrain.

External links

Skilifts.org An online community dedicated to documenting all types of Ski Lifts
Union Pacific Railroad The Chairlift's 70th Anniversary
Chairlift.org preservation society
Colorado Chairlift Locations
The Colorado Skier Newsletter archive

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