In overhauling the rickety wooden Texas Giant roller coaster in Six Flags Over Texas amusement park, Arlington, Tex., Six Flags Chief Engineer Larry Chickola wanted to design a coaster that had exceedingly tall crests and sharp turns, and make riders hold on for their very lives. The high forces and extreme speeds he envisioned necessitated stronger and smoother rails than traditional wood or tubular metal tracks. He turned to roller-coaster manufacturer Rocky Mountain Construction in Hayden, Idaho, which had just designed an entirely new kind of steel track. The ride’s scaffolding would still be wood to retain the coaster’s old-time look, but the new rails would safely support the loads and accelerations necessary to provide the most thrilling ride possible.
“The rail technology is different from previous roller coasters in that it is a box-beam, square metal track,” says Rocky Mountain Construction Design Engineer Alan Schilke. “An older track-fabrication method — still in use today — is to build up tracks by laminating pieces of lumber together. Trouble is, today’s coasters hold such heavy loads and undergo such extreme forces that wooden track can no longer withstand the forces without frequent repair. We have laid traditional wood track, but I thought there must be a better method.”
The result was the box-beam track, says Schilke. “With this approach, we cut large, flat sheets of mild steel plate on large plasma cutters. We weld the flat shapes longitudinally with typical wire-feed equipment to produce a three-dimensional rail.” Automated buggies carry welding equipment and lay down the welds. The welds are cleaned and then inspected using magnetic particle testing for cracks, deviations, and pockets. Finished 3D lengths run from 40 to 50-ft long.
Traditional tubular steel tracks are really just pipe that has been measured, bent, and shaped. “Both the tubular steel tracks and the new box-beam rails can endure the same amount of force, which is much larger than wooden tracks can handle,” adds Rocky Mountain Technical Designer Jake Kilcup. “But the box-beam tracks arguably provide the smoothest ride. That’s because we build the track to engineered specs on high-tech CNC machines.”
In Rocky Mountain Construction’s method, bends in the track are cut directly in the flat metal. “Heat of welding causes the metal to slightly change shape. But the company’s patented technique restores the shape to the original engineering specs. In the field, bolted-connection plates attach the lengths together.
Says Kilcup, the design does include bolts that stick up on the outside of the rails. “However, the coaster wheels themselves only run on a smooth path. In general, roller coasters stay on their tracks with the help of a three-wheel locking configuration consisting of side wheels, a top running wheel, and an uplift wheel.”
“Of the products we have installed, there has been no maintenance work needed on the box-beam tracks,” says Kilcup. “In the future, we intend to help develop roller coasters where the cars run upside-down on box tracks.”