Hydraulic
Highs
Hydraulic
propulsion rockets the world’s tallest, fastest roller coaster up a
420-ft hill
Forget
the old clackety-clack climb that traditional coasters take to the top
of the first big hill. Don’t expect a lot of time to enjoy the park’s
scenery on the way up. And don’t even think about letting go of the
safety bar to put your hands in the air. Top Thrill Dragster is not
that kind of roller coaster. Indeed, catapulting up a 420 ft hill, going
0-120 mph in just 4 seconds, is likely to leave even the bravest coaster
fanatics clinging for their dear life.
Top
Thrill Dragster, the newest among an army of giant coasters (including
a 300 ft steel monster called Millennium Force) in Sandusky, Ohio’s
Cedar Point Amusement Park, is making a name for itself in more ways
than one. The $25 million steel scream machine not only has the rights
to “world’s tallest, fastest roller coaster,” it lays claim to another
special feature: a hydraulic launch system.
For
years roller coasters have relied on chains to pull the cars to the
top of a lift hill and build a reservoir of potential energy. But new
propulsion systems have made it possible to launch coaster trains horizontally
into the ride’s elements rather than dragging them up a hill.
One
catapulting system that’s fast becoming a favourite uses linear-induction
motors (LIM). LIM powered coasters essentially ride a magnetic wave
down the track as metal fins attached to the bottom of the trains pass
stator coils anchored along the track. One such coaster at Cedar Point
blasts riders out of the station five times, at five different speeds,
topping out at 72 mph in 2.5 seconds. Wicked Twister, as it’s aptly
named, uses LIMs to shoot riders up and down a U-shaped track with 450°
corkscrews on top of each 215 ft vertical tower.
Another
type of launching system uses electric motors to power high-speed drive
tires; essentially dozens of rotating wheels arranged in rows along
the track that grips the train and pushes it forward.
Hydraulics
to the highest
This
newest launch method relies on hydraulics. Though hydraulics has seen
its share of amusement-ride applications, its use as a launching method
is special, says Cedar Point’s Rob Decker, Vice President (Planning
and Design). “We didn’t set out to build a roller coaster with a hydraulic
system. We left it up to the ride manufacturer - Switzerland-based Intamin
AG - to find a way to surpass the top speed, which at the time was 93
mph produced by our own roller coaster, Millennium Force. Our goal was
to set another world record, and our parameters were the tallest, fastest
roller coaster. Intamin looked at all of the known roller-coaster propulsion
systems and said that they could get the speed we wanted with less length
and in less time out of a hydraulic system,” says Mr Decker.
Intamin
went with the hydraulic approach for basically the same reason that
the technology is used on stamping presses: The ability to precisely
control applied force. In the case of Top Thrill Dragster, a hydraulic
launch made it possible to hit top speed faster and required less upfront
costs than a LIM coaster. And the hydraulic launch set-up helped Cedar
Point put the ride in a small footprint.
Though
the technical details are sketchy on Intamin’s proprietary hydraulic
launch system, the operating principle is fairly simple. Hydraulic oil
is pumped from a reservoir into storage cylinders filled with nitrogen.
“The nitrogen compresses and acts like a spring, and the hydraulic oil
acts like potential energy,” explains Cedar Point’s Monty Jasper, Vice
President (Maintenance and New Construction). The ride operator gets
a signal when pressure has built up and the train is ready to launch.
Pushing the start button opens high-speed valves at the storage cylinders
and sends the oil flowing into 32 hydraulic motors. Gears on each end
of the motors turn a large planetary gearbox. Planetary gearboxes sit
on either side of a cable-winding drum that turns at 500 rpm. “The drum
works like a big fishing reel, taking up cable as it turns,” Mr Jasper
explains. The launch cable attaches to a locking device called a catchcar
that, in turn, attaches to the coaster train. The catchcar runs in the
track and propels the train forward. Reaching the target speed of 120
mph, the catchcar disengages the cable from the train, closes the hydraulic
valves and restarts the process.
Hydraulics
also keeps riders secure in their seats. A redundant safety system including
interlocking seat belts and a hydraulic lap-bar assembly makes sure
that passengers stay in the train. Two hydraulic cylinders open and
close the padded lap bar and lock it in place.
Once
loaded and buckled in, the passengers are in for a wild ride. The trains
launch from a starting position and rocket straight up to 420 ft, rotate
90°, crest the top, and free fall 400 ft while spiraling 270°. Under
each car four road wheels ride on the track. Four side wheels position
the train to the left and right, and four up-stop wheels keep the train
from lifting off the track.
Unbelievably,
six 16-passenger trains run on the track simultaneously. Operators control
the traffic using programmable logic controllers (PLC) and an advanced
monitoring system. To keep trains from running into each other, the
track is divided into different zones, each with a stopping mechanism
and means of propulsion. Only one train at a time is allowed in a zone.
Oncoming trains are held up until a block is clear. “It’s a little like
juggling,” says Mr Decker. “The safety systems are quite sophisticated
and will not allow any human to override them,” adds Mr Decker.
Stop
that train!
Once
blasted from the starting position the last thing anybody wants, is
to see the train rolling backward after not making the 420 ft climb.
“That scenario is unlikely,” says Mr Decker. But Cedar Point officials
are prepared nonetheless....
....CONTD
