The Engineering Book: From the Catapult to the Curiosity Rover: 250 Milestones in the History of Engineering

1919

Under Friction Roller Coaster

John Miller (1872–1941)

If you think about a basic roller coaster, it is very simple. You take a free-rolling car up to the top of first hill and then let it roll down the hill’s other side. In the process, the car loses all of the stored potential energy and turns it into velocity. The next hill is a bit shorter to accommodate the losses from friction and drag. The process repeats.

If the builders are working with wood, a roller coaster will often be that simple.

But with the advent of the under friction roller coaster, patented by American entrepreneur John Miller in 1919, wheels under the cars facilitated even more creative routes. With the “Miller Under Friction Wheel,” the coaster could go through twists and spirals. Now, with the advent of steel tubular track, the only real barriers are the g-force limits that the human body imposes on the design.

The traditional way to get up the first hill is by using a chain. It allows the coaster to gather its potential energy slowly over a minute or more. But roller coasters like the Hulk in Orlando take a completely different approach. Riders launch from the bottom of the first hill using 230 large electric motors attached to rubber tires. The car goes from zero to 40 mph (64 kph) in less than two seconds and comes flying off the top of the first hill straight into an inversion and the first drop.

To take a fully laden car with 32 passengers up a hill and accelerate it that quickly requires something like 11,000 horsepower (8,000,000 watts). Engineers can’t just say to the average power grid, “I’d like eight megawatts for the next two seconds please” without some serious ramifications of the brownout variety. So the system uses flywheels to accumulate the needed power in the time between launches. Then the flywheels dump their accumulated power into the two-second launch. This evens out the load on the grid to a steady draw.

Ohio’s “Son of Beast” roller coaster at Kings Island.