Revolution was the first modern coaster to have a vertical loop. A couple of unsuccessful coasters had loops from 1895 to 1910, but those rides had circular loops which subjected riders to extreme g-forces. Revolution's 45-foot diameter loop has a larger curvature radius at the bottom of the loop than at the top, so it is more tear-drop shaped than the earlier unsuccessful circular loops. Modern loops have a clothoid shape, also referred to as a Euler spiral.
©2016 Joel A. Rogers.