The Full Wiki

Fly system: Wikis


Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.


From Wikipedia, the free encyclopedia

Fly gallery of the Theater Bielefeld in Germany

A fly system is a system of ropes, counterweights, pulleys, and other related devices within a theatre that enables a technical crew to quickly move components such as curtains, lights, and set pieces on and off stage by moving them vertically between the stage and the large opening above the stage.

The opening above the stage is known by various names including flyspace, flyloft, fly tower, and fly gallery. A component is said to be "flying in" when it is being lowered onto the stage, and "flying out" when it is being raised into the flyspace.


Types of fly systems

There are a number of types of fly systems. The most common is the counterweight fly system, in which a counterweight-carrying arbor moves up and down a track parallel to a wall. Some older theatres, which are sometimes called "hemp houses" (a reference to the material used in the ropes), lack counterweights and instead rely on skilled operators and human strength to fly theatrical scenery in and out. Other types include the pin-rail system—which uses sandbag counterweights and a single pulley for the control line—and systems that are powered by electric motors.

The use of a particular type of fly system in a theater does not preclude the use of other types of fly systems in the same theater. For example, theaters that incorporate built-in, grid-based counterweight fly systems often will also support additional, relocatable hemp system linesets for spot-rigging.


Counterweight fly system

Graphic depiction of a single lineset and the parts of a counterweight system. (A) Hoisting cables, (B) Turnbuckles, (C) Purchase line, (D) Arbor rod, (E) Spreader plates, (F) Cut steel counterweight, (G) Rope stop/lock (brake)/Lock rail, (H) Locking safety ring, (I) Tension sheave (block). Not shown: head sheave, loft sheaves, and batten.

In a typical counterweight fly system, an arbor is employed to balance the weight of loads that are to be raised and lowered above the stage. The arbor, which carries a variable number of counterweights, moves up and down a vertical track alongside a wall. In some fly systems, cable guide wires are used instead of tracks to guide the arbors and limit their horizontal movement.

The top of the arbor is permanently attached to several load bearing hoisting cables, known as lift lines, which are typically made of galvanized steel aircraft cable. The lift lines run from the top of the arbor up to the top of the fly tower, around the head sheave (pulley), across the stage to the loft sheaves, and then hang down at evenly spaced intervals across the width of the stage. The hanging ends of the lift lines are attached to a batten, which is a long, load-bearing pipe that spans the full width of the stage.

The arbor's vertical position is controlled by means of a long rope known as the purchase line. The purchase line forms a loop by running from the bottom of the arbor down to and around the tension sheave, through the lockrail, up and over the head sheave and back down with the lift lines, where it terminates by attaching to the top of the arbor. The head and tension sheaves are located at the top and bottom of the arbor's entire movement track, respectively, thereby enabling an operator to pull the purchase up or down to move the arbor. When the arbor is raised via the purchase line, the lift lines slacken, which causes the batten to lower due to its weight (and the weight of its load, if any). Conversely, when the arbor is lowered, it pulls the lift lines down, which in turn causes the batten to rise.

The combined weight of the arbor and its counterweights initially matches that of the batten so that when the batten is not being raised or lowered, it will tend to remain motionless at any arbitrary elevation above the stage. As more weight is added to the batten (in the form of curtains, scenery, lighting equipment, and rigging hardware), the system is rebalanced by adding more counterweights to the arbor. When the system is properly balanced, an unassisted operator can lift the batten and its arbitrarily heavy load off the stage ("fly it out", in theatrical terminology), completely above the proscenium and out of view of the house, sometimes to heights as great as 70 feet.

The mechanical system that raises and lowers a specific batten is called a lineset. Some large theatres, such as the Metropolitan Opera House (Lincoln Center), have more than 100 independent, parallel linesets, while smaller venues may only have a few linesets for the most commonly adjusted loads, such as electrics.


An arbor is a sturdy mechanical assembly that serves as a framework for holding counterweights. It consists of two horizontal steel plates, one at the top and the other at the bottom of the arbor assembly, connected together by two vertical steel rods. Counterweights are stacked as required on the arbor's bottom plate to balance the lineset load.

Spreader plates, which are thin steel plates with holes through which the arbor rods pass, are lowered onto the counterweights in a distributed fashion as the counterweight stack is being built. Typically, one spreader plate rests on top of the semi-permanent counterweights that balance the batten, and another resides just below the topmost counterweight. Finally, a locking plate is lowered onto the completed stack of counterweights and spreader plates and secured in place with a thumbscrew. In the event of a "runaway" (loss of control of an unbalanced lineset), the spreader plates will prevent the arbor rods from bending, and thus releasing the counterweights upon arbor impact at the end of its travel.


Counterweights are made of lead or flame-cut steel. In any particular fly system all weights share a common, standardized footprint that matches the system's arbors. Although there is no unified dimensional standard for counterweight footprints, counterweight systems are most often designed to use either 4 or 6-inch (150 mm) wide plates. Weights vary in thickness, typically in half-inch increments ranging from 1/2 to 2 inches (51 mm), with each thickness corresponding to a different mass. Counterweights are sometimes also known as bricks or simply steel. Often a rigging worker will be asked to load a number of inches of steel, which correlates to a specific mass. Weights are usually loaded from the loading bridge, but can also be loaded from the fly gallery or locking rail.

When viewed from the top, a counterweight is fundamentally rectangular except for 45-degree angle cuts at two opposing corners. Also, a slot is cut into each end of the weight so as to enable the weight to straddle, and be locked in place by, the arbor rods. In order to facilitate removal, it is customary to stack weights in alternating orientations so that the square corners of any weight will be aligned with the angled corners of adjacent weights. This simplifies removal because the protruding square corners of the topmost weight effectively serve as "handles" that can be easily gripped, even with gloved hands.

It is customary to paint the weights that counterweight the batten (pipe) yellow to indicate that they should not be removed from the arbor. When draperies are permanently flown, their respective weights are also often painted yellow.


Battens near the grid in the flyspace.

A batten, or pipe batten, is a long steel pipe that is suspended by two or more lift lines that all belong to the same lineset. Various loads, such as lights, curtains, and scenery may be directly attached to a batten. A batten and its load can be raised up toward the flyspace ("flown out") or lowered near to the stage floor ("flown in") by its associated lineset. It typically spans the width of the stage and is usually maintained parallel to the stage floor, regardless of elevation.

Loads are attached to the batten in various ways. Most lights, for example, utilize a C-clamp to rigidly secure the light onto the batten, in conjunction with a safety cable that is looped around the batten to prevent the light from falling should the C-clamp connection fail. Non-traveling curtains often employ cloth ties, similar to shoestrings, that are hand tied onto the batten.

Locking rail

Locking rail with arbors, counterweights, rope locks (red) and pins for spot lines visible.

A locking rail is located on the stage deck or on a backstage catwalk, oriented perpendicular to the proscenium arch and extending from the proscenium to the back wall. It has a lever-operated rope lock, which clamps the rope so as to prevent a balanced load from drifting, and a safety lock for each lineset. In most cases the locking rail has a headset system or a cue light system to signal the flyrail crew. It is possible to load (add or remove counterweights) at the locking rail, but standard practice is to load at the loading bridge.

Single vs. double purchase

Single purchase systems are simpler and more common than double purchase systems. The difference is that instead of the lift lines (wire rope) and operation line (fiber rope) terminating at the arbor, they run through an extra set of blocks and terminate at the head block (above) and tension block (below). This has the effect of giving the arbor a mechanical disadvantage of 1:2 as compared to the batten. The arbor must carry twice the weight of the batten to remain balanced, but only travels half the distance. For every foot of hand line the operator pulls, the batten moves two; this allows for balanced systems to move in and out much more quickly. Because the travel of the arbor is half that of the fly tower, the loading rail could be placed only halfway up, but it is more common to raise the operating rail to that height and leave the loading rail at the top. This allows for open space underneath the entire lineset wall, so that the operating rail can be just offstage but the amount of useful floorspace is not reduced.

Note: The operating line is not actually required to pass through the extra blocks for the arbor/batten relationship to change; it is still helpful since it gives the operator a 2:1 advantage over the effective weight of the arbor, which is likely to carry more steel than in a single purchase system.

Hemp fly system

A small pin-rail at stage level.

A hemp fly system, so named for the type of rope that was once used for rigging, is both the oldest and simplest type of fly system.[1] A purchase line (rope) is run to the grid, with one end dangling for the operator and one end holding sandbag counterweights. A trim clamp, commonly known as a "knuckle-buster", is attached to both the purchase line and the lift line (or lines), which in turn attaches to the batten. In cases where the lineset lacks a rope to raise the sandbags, the batten is kept a few pounds heavier than the counterweight so that it can be flown in. In some hemp systems a separate line (often called a "bag line") is attached to the sandbags and rigged through a sheave above the operating rail; this is used to pull the sandbags upward and cause the batten to fly in. A pin rail is used to tie off, or belay the hauling end of a rope so as to keep the batten in place when it is not moving.

Hemp systems can be easily configured for spot rigging, where lift lines must be frequently relocated. They are generally less expensive and easier to install than counterweight fly systems, though somewhat more difficult to operate.

Pin rail

A pin-rail above stage level.

A pin rail is a large, horizontal wooden beam or steel pipe (the "rail") which has holes that accept belaying pins. Depending on the pin rail design, the pins, which are typically made from hardwood or steel, may be removable or they may be permanently fixed to the rail. Some theaters have permanent pin rails installed along the edge of the loading gallery, while others have mobile pin rails which can be bolted down.

Each belaying pin serves as an anchor to which the loose end of a rope may be quickly secured. A standardized method is used to tie off the rope so that it is subjected to friction from itself as well as from the pin rail, thus ensuring a secure connection that is unlikely to fail.

Motorized fly systems

There are two predominant varieties of winch-driven fly systems, both of which are similar to the counterweight fly system described above. One of these is fundamentally a classic counterweight system with the addition of a winch motor, located below the locking rail, that drives the purchase line. In this type of system, motors may be attached to linesets as needed. The other type of system is more like an elevator winch, with a cable drum that directly drives the lift lines, and no purchase line is involved. Winches are helpful for moving extremely heavy linesets. Electric linesets, for example, may be loaded with batten, circuit raceway, and lighting instruments that can weigh upwards of 1,500 lb (680 kg). Many winches, however, can only move linesets at speeds that are a fraction of that delivered by an experienced flyman and thus are not used unless high power or remote operation is needed.

Many modern large theatres use motorized systems without the aid of counterweights at all. In such systems, the batten is connected via wire rope directly to a drum, which in turn is powered by a geared motor. Speeds in excess of 2000mm/s, with loads greater than 1000 kg are possible and only limited by the availability of power and space for larger motor gear box units. Digital control systems incorporating computers or programmable logic controllers (PLCs) have become commonplace as well, bringing their advantages of high accuracy, safety and repeatability to fly systems.

Parts of a fly system


The flyrail is a locking rail or pin rail that is used by a fly crew to operate the fly system. A deck rail is a stage-level flyrail, whereas a mid rail is located above the stage, giving the fly crew a good view of the stage and also serving to increase off-stage space for performers and scenery.

Loading bridge

Specific to a counterweight system, the loading bridge is a catwalk located directly above the flyrail at grid level. Technicians reside on and are supported by the loading bridge while adding or removing counterweights from linesets. The floor of the loading bridge is also typically used as a storage area for uncommitted counterweights that are available for loading onto lineset arbors.


The grid is a steel lattice or slotted wood or steel beam floor found at the top of some flyspaces. It enables technicians to walk over the fly loft so they can easily configure lift lines and loft-blocks (pulleys that drop lift lines down to battens) and thus change the stage locations where the battens will fly in. Due to height limitations in some theaters, not all fly systems are equipped with a grid. In gridless fly systems, the battens typically have fixed fly-in locations and spot-rigging is not possible.

Fly tower

The fly tower is the large space above the stage into which fly system loads are raised. In a full size flyspace, the tower is at least 2.5 times as tall as the proscenium, thereby allowing a full-height set piece to be stored completely out of view of the audience. The loading bridge and, if present, the grid, are located at the top of the fly tower.

Parts of a fly system
Linesets are manually operated from a lock rail such as this one.  
Loading bridge. Weights are seen on floor.  
Gridless fly tower. Battens (yellow), under hung pulleys and cables are visible.  
Steel lattice grid with top mounted pulleys and cables visible.  
Steel lattice grid, viewed from below with drapes, battens, and electrics visible.  
Loft blocks on a steel lattice grid.  

Common uses

Electrical devices

Electrical battens, which are commonly called Electrics, are battens that are specifically designed to support lighting instruments and, in some cases, microphones and special effects equipment as well. Electrics have integral electrical conduits to convey wiring between the lighting instruments, which hang from the batten, and remote, programmable dimmer controls. There are normally three or four electrics in a theater, with the one furthest upstage being the cyclorama.

In most cases, electrics are assigned to dedicated linesets as they have permanent connections to cables that hang from the grid. Additional battens may serve as electrics as well, although doing so can be problematic as non-electrical battens usually lack provisions for electric wiring. Multicable is one solution to the problem of wiring to these battens.[2]

Set pieces

In many productions, set pieces are flown in and out so as to quickly change the scenery during the course of a performance. For example, soft painted drops are commonly used to depict backgrounds. Also, solid, three-dimensional sets may be flown in and hung above the stage or set in contact with the deck.

It is not uncommon to see an entire orchestra shell being manipulated by a fly system. Larger, multi-use theaters that must frequently convert the stage from a drama theatre to a concert hall often make use of the fly system in this way.


Fly systems are often used to manipulate theater drapes and stage curtains such as teasers, travelers, legs, cycs and scrims in order to mask the stage or provide backgrounds.


Because fly systems involve large amounts of weight, and particularly because the weight is usually suspended above people, there are a number of common precautions taken to ensure safety and prevent injuries. Communication, inspection, and loading procedure are key to the safe operation of a fly system.

Calling movement

Except for during performances and some rehearsals, a standard practice in theatre is for the flyman to always call (shout) out a warning before moving a lineset so as to alert personnel (e.g., rehearsing performers and technicians) who are on the stage. People on stage typically acknowledge the operator's warning by yelling out a confirmation that the warning was heard.

The flyman's warning specifies what is moving and its direction of movement. For example, a particularly verbose call might be something like "lineset three, first electric flying in to the deck, downstage." In many theaters, all people on stage are expected to respond with "thank you." Upon completion of the lineset motion, some operators may call again (e.g., "lineset three locked") to announce that the lineset has stopped moving.


A runaway is a moving lineset that cannot be safely controlled by its operator. Runaways can occur when the weight on the arbor is not equal to the weight of the batten and its load. Linesets are often intentionally unbalanced to facilitate quick flying in one direction and, in such cases, runaways are more likely to occur.

In the rare event that an unbalanced lineset gains so much momentum that the operator cannot stop it, a specified safety procedure is usually followed. Venues typically establish a standard call for this event, which might sound something like "Runaway 47, upstage, heads." Operators are trained not to attempt to stop a runaway lineset but rather to warn others and safely escape. The reason for this is that it is unlikely that they will be able to stop it, and very likely that they will burn their hands or be lifted up by the lineset, potentially injuring themselves on the structure above them. Furthermore, this might position the operator in the path of the batten, arbor, or sandbag as they accelerate downward. Spreader plates are used in counterweight arbors to keep the arbor's vertical rods from bending and releasing the counterweights in the event of a runaway, while the locking plate prevents the counterweights from bouncing out of the arbor.

Loading procedure

When loading a batten, or arbor in a counterweight system, it is imperative to control the balance of a set. The lineset should be balanced before loading begins, then the batten flown in, the set added, and then the counterweight added from the loading bridge. The specific order is important because it keeps the set from being unbalanced in a position where it could run away. When it is batten-heavy (after the set is added, but before the counterweights) the arbor does not have anywhere to run away to as it is already at its grid stop (the upper end of the track). In cases where the set is too tall for the batten to be all the way in, it should be kept as far down as possible. It is always best to add the load in pieces as small as practical and counterweight them one at a time so the system can never get too out of balance. Improper loading procedure is a common cause of accidents in many theaters.


  1. ^ Jay O. Glerum (2007). Stage Rigging Handbook, Third Edition. Southern Illinois University Press. p. 65. ISBN 978-0809327416. 
  2. ^ Gillette, J. Michael (2003). Designing With Light: An Introduction to Stage Lighting, Fourth Edition". McGraw Hill. p. 84. ISBN 0-7674-2733-5. 


Got something to say? Make a comment.
Your name
Your email address