Fly system
[1] Theatrical rigging is most prevalent in proscenium theatres with stage houses designed specifically to handle the significant dead and live loads associated with fly systems.
Building, occupational safety, and fire codes limit the types and quantity of rigging permitted in a theatre based on stage configuration.
In large professional theatres, such as the Philadelphia Academy of Music, an electric may take the form of a flying bridge (catwalk) that provides a walkable platform for electrician access to fixtures and effects.
A flying rig typically allows horizontal as well as vertical movement by paying out individual lift lines to varying lengths and/or through the use of tracks.
Those substitutions permit the flying of greater loads with a high degree of control, but with a loss of flexibility inherent to most hemp systems.
Manual rigging is also possible with hand (and drill-operable) hoists (winches), but relatively limited operating speeds preclude their use for most running applications.
Other expressions and technology that overlap the nautical and theatrical rigging worlds include: batten, belay, block, bo'sun, cleat, clew, crew, hitch, lanyard, pinrail, purchase, trapeze, and trim.
A trim clamp or a "Sunday" (a circle of wire rope) is used to attach this sandbag to the "line set" to balance the load placed on the batten.
In a typical counterweight fly system, an arbor (carriage) is employed to balance the weight of the batten and attached loads to be flown above the stage.
The top of the arbor is permanently suspended by several wire rope lift lines, made of galvanized steel aircraft cable (GAC).
When the system is properly balanced, an unassisted operator (flyman) can lift the batten and its arbitrarily heavy load from the stage ("fly it out", in theatrical jargon), completely above the proscenium and out of view of the house, sometimes to heights in excess of 70 feet (21 m).
This often results in the arbors remaining well above the stage deck, leaving the otherwise occupied wing space usable for cast and crew.
Electrical hoists (also referred to as winches) can facilitate coordination with cues, move extremely heavy line-sets, and significantly limit the required population of the fly crew.
It is standard practice for overhead rigging lines and hardware to be rated with at least an 8-times safety factor to help ensure the protection of cast and crew.
The lift lines of a counterweight rigging systems are typically a specific type of steel wire rope known as galvanized aircraft cable (GAC).
The adjustable cam, or dog, inside the rope lock constricts and releases the operating line as the flyman lowers and raises a hand lever.
Turnbuckles are moused (secured against free rotation) to prevent the jaws from slowly unscrewing over time due to vibrations incurred during normal use.
A block consists of a grooved wheel, known as a sheave (pronounced "shiv"), steel side plates, spacers, shaft, flange bearings, mounting angles and clips, etc.
Tension blocks typically ride vertically along the arbor guide system tracks, instead of being fixed, to allow for variation in the length of the operating line.
Counterweights are stacked as required on the arbor's bottom plate to balance the line set load, with the weights held in place by the connecting rods.
Spreader plates serve to maintain consistent spacing between the arbor rods to ensure reliable containment of the counterweights under normal operating conditions.
Such arbors use multiple-width top and bottom plates with a tie bar and pair of connecting rods provided at each counterweight stack.
A worm gear is commonly used to provide mechanical advantage as the crank is turned, which coils a single line around a smooth or helically grooved drum.
This allows a full-height curtain or set piece to be located completely out of view of the audience without exceeding the travel distance of standard (single-purchase) counterweight arbors.
The grid deck surface is usually rated to support live loads as well as all anticipated dead-hung equipment and hemp and motorized (e.g., chain hoist) spot rigging.
For example, a particularly verbose call might be something like "lineset three, first electric flying in to the deck, downstage" (in USA) or "Heads onstage, Bar 3, LX 1 coming in."
However, as it is common for many thousands of pounds of equipment and scenery to be flown above cast and crew, major imbalance is a grave hazard, and, if left unaddressed, can result in runaways.
Where an engaging bar has been designed into the stage level locking rail, a portable electric capstan winch may be used to counteract an imbalanced counterweight line set.
Pulling on (constricting) a rope wrapped a few times around the capstan, a drum spinning at a constant rate, generates enough traction (through friction) to tug the imbalanced load.
The compensating chain is about half the length that the arbor travels, and sized to weigh twice as much as the combined weight of the lift lines per linear foot.
