Vertical Loop - Physics/Mechanics

Physics/Mechanics

In actuality, most roller coaster loops are not circular in shape. A commonly used shape for loops is the clothoid loop, which resembles an inverted tear drop and allows for less intense G-forces throughout the element for the rider. The name comes from the incorporation of sections from the mathematical clothoid spiral curve in the shape of the loop. The use of this shape was pioneered in 1975, on Revolution at Six Flags Magic Mountain, by Werner Stengel of leading coaster engineering firm Ing.-Büro Stengel GmbH.

On the way up, from the bottom to the top of the loop, gravity is in opposition to the direction of the cars and will slow the train. The train is slowest at the top of the loop. Once beyond the top, gravity helps to pull the cars down around the bend. If the loop's curvature is constant, the rider is subjected to the greatest force at the bottom. If the curvature of the track changes suddenly, as from level to a circular loop, the greatest force is imposed almost instantly (see jerk). Gradual changes in curvature, as in the clothoid, reduce the force maximum (permitting more speed) and allow the rider time to cope safely with the changing force.

Obviously this "gentling" runs somewhat contrary to the coaster's raison d'être. Schwarzkopf-designed roller coasters often feature near-circular loops (in case of Thriller even without any reduction of curvature between two almost perfectly circular loops) resulting in intense rides—a trademark for the designer.

It is rare for a roller coaster to stall in a vertical loop, although this has happened before. The Turbine coaster (then known as Sirocco) at Walibi Belgium once stranded riders upside-down for several hours. The design of the trains and the rider restraint system (in this case, a simple lap bar) prevented any injuries from occurring, and the riders were removed with the use of a cherry picker. A similar incident occurred on Demon at Six Flags Great America.