Chairlift
An elevated passenger ropeway, or chairlift, is a type of aerial lift, which consists of a continuously circulating steel wire rope loop strung between two end terminals and usually over intermediate towers. They are the primary on-hill transport at most ski areas, but are also found at amusement parks and various tourist attractions.
Depending on carrier size and loading efficiency, a passenger ropeway can move up to 4,000 people per hour, and the fastest lifts achieve operating speeds of up to or. The two-person double chair, which for many years was the workhorse of the ski industry, can move roughly 1,200 people per hour at rope speeds of up to. The four-person detachable chairlift can transport 2,400 people per hour with an average rope speed of. Some bi- and tri-cable elevated ropeways and reversible tramways achieve much greater operating speeds.
Design and function
A chairlift consists of numerous components to provide safe, efficient transport.Terminology
At American 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 is 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" or "express" lift, which results in an "express quad" or "high-speed six pack".;rope speed: the speed in meters per second or feet per minute/second at which the rope moves
; interval: the spacing between carriers, measured either by distance or time
;capacity: the number of passengers the lift transports per hour
;efficiency: 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 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 rope
;detachable 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, the rope speed, the carrier spacing, the vertical displacement, and the number of carriers on the rope. Human passengers can load only so quickly until 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 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 may also have intermediate supporting towers. A bullwheel in each terminal redirects the rope, while sheaves 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 a 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 drive shaft beside the main drive, before the gearbox. The emergency brake acts directly on the bullwheel. While not technically a brake, an anti-rollback device also acts on the bullwheel. This prevents the potentially disastrous situation of runaway reverse operation.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 or pneumatic 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 7.5 kW for the smallest of lifts, to more than 750 kW for a long, swift, detachable eight-seat up a steep slope. DC electric motors and DC drives are the most common, though AC motors and AC drives are becoming economically competitive for certain smaller chairlift installations. DC drives are less expensive than AC variable-frequency drives and were used almost exclusively until the 21st century when costs of AC variable-frequency drive technology dropped. DC motors produce more starting torque than AC motors, so applications of AC motors on chairlifts are largely limited to smaller chairlift installations, otherwise the AC motor would need to be significantly oversized relative to the equivalent horsepower DC motor.The driveshaft turns at high RPM, but with lower torque. The gearbox transforms high RPM/low torque rotation into a low RPM/high torque drive at the bullwheel. More 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 that can operate during power outages. The purpose of the backup is to permit clearing the rope to ensure the safety of passengers; it usually is much less powerful and is not used for normal operation. The secondary drive connects with the drive shaft before the gearbox, usually with a chain coupling.Some chairlifts are also equipped with an auxiliary drive, to 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 or magnets 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 a safety bar in an amusement park ride. If equipped, each chair has a retractable bar, sometimes with attached footrests. 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 swung sufficiently, gravity assists positioning the bar to its down limit. Before disembarking, the bar must be swung 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, the carrier's arm connecting to the grip pivots smoothly forward—driven by the chair's inertia—and maintains friction 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.
Some ski areas mandate the use of safety bars on dangerous or windy lifts, with forfeiture of the lift ticket as a penalty. Vermont and Massachusetts state law also require the use of safety bars, as well as most Ontario and Quebec in Canada.
Restraining bars on chairlifts are more common in Europe and also naturally used by passengers of all ages. Some 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. Among more notable bubble lifts are the Ramcharger 8 at Big Sky Resort, North America's first high speed eight pack; and the longest bubble lift in the world is the American Flyer high speed six pack at Copper Mountain.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.