ON YOUR MARK…GET SET…DRAG!
An engineering consultant ensures safety of an amusement park ride with Algor FEA.
Located in amusement parks around the United States and in Japan, the Top Eliminator (TM) amusement ride was
created by ThrillTime Entertainment International, Inc., of Burnaby, British Columbia, Canada, with help from
engineering consultant Les Okreglak of Pol-X West, Inc., Carson City, Nevada. Mr. Okreglak used FEA software
from Algor, Inc., Pittsburgh, Pennsylvania, to analyze the frame of the dragster car. Photo courtesy of ThrillTime
Entertainment International, Inc.
September, 4 1998, Pittsburgh, Pennsylvania - It has a 350 cubic-inch engine with a four-barrel carburetor and a
horsepower rating of 300 bhp @ 5000 rpm, rear disc brakes, a tube steel space frame, drag slick rear tires and seating
capacity for one. No, it's not one of those new, compact high-performance sports cars -- it's a dragster, which anyone over
56 inches tall can drive at amusement parks around the United States and in Japan.
The Top Eliminator (TM) is a dragster racing simulation ride created and produced by ThrillTime Entertainment International,
Inc., Burnaby, British Columbia, Canada. It gives thrill-seeking drivers of all ages a license to "floor it" and experience the
adrenaline rush of drag racing without the danger associated with actual auto racing.
To ensure the safety of the ride, ThrillTime hired Les Okreglak, P.E., principal engineer and president of Pol-X West, Inc., an
engineering consulting firm in Carson City, Nevada, to analyze the dragster frame using FEA software. Mr. Okreglak chose
the linear static stress analysis capabilities of engineering software from Pittsburgh-based Algor, Inc.
Get Your Motor Running
Up to 10 dragsters are positioned on 200-ft. long parallel tracks. Each dragster has a 12-foot long guide blade bolted to the
frame that sets in an underground channel system to keep the dragster from leaving its lane. As green lights indicate the start of
the race, participants step on the gas pedal and feel the power of 1.1 g's of force as they accelerate from 0 to 75 mph in a few
seconds. At the finish line, a computer-controlled braking system causes roller coaster brakes to clamp onto the underground
guide blade and stop the car in less than 120 feet. Riders experience a decelerating force of -2.8 g's at normal operation.
Before green lights ever flashed "Go!" at a Top Eliminator track, Mr. Okreglak modeled and analyzed the dragster frame,
which supports a large Chevy engine, guide blade, fiberglass body and roll cage. "The goal of the analysis was to verify that
the existing frame design would be able to withstand stresses resulting from the acceleration and deceleration of the dragster,"
said Mr. Okreglak. He closely monitored stresses at the engine mounts in the rear of the car, as well as overall displacement.
Mr. Okreglak used AutoCAD to create a 3-D wireframe of the existing design and transferred the data in an IGES format to
Superdraw III, Algor's precision finite element model-building tool. The model was comprised of 340 beam elements, which
represented the 1.5-in. diameter round steel tubing used in the frame. According to Mr. Okreglak, he increased the number of
elements and nodes from the original model to enable more detailed analysis information.
Mr. Okreglak used several different models to address the acceleration and deceleration concerns. Using Algor's Beam
Design Editor, he applied acceleration loading to seven points in the model: at each of the wheel connections and at engine
mounts in the center of the frame. To account for the deceleration loading, Mr. Okreglak applied a boundary condition at the
point where the roller coaster brakes would clamp onto the guide blade during braking.
Next, a series of linear static stress analyses was performed to determine the maximum stresses resulting from acceleration
and emergency deceleration. Based on the von Mises and displacement results, Mr. Okreglak determined that stresses
resulting at the engine mounts exceeded the allowable limit. To correct this problem, he increased stiffness by adding an
additional support member to the frame.
Additional members were added to reinforce the tube steel space frame (optimized design shown left) based on
displacement (shown right) and stress results. Models courtesy of Les Okreglak, Pol-X West, Inc. Photo courtesy of
ThrillTime Entertainment International, Inc.
Further, Mr. Okreglak found displacements of the frame to be minor. Nonetheless, he still added small members throughout
the frame to reinforce it. Once the design was optimized, a prototype was built to test the dragster's reliability.
Taking a Test Drive
Acceleration and emergency braking tests were performed on the dragster prototype using Keithley data acquisition software
and an accelerometer. The accelerometer was fixed to the car, which was driven by a computer. According to Mr. Okreglak,
the accelerometer tests yielded a maximum deceleration force of 5.0 g's as compared to analysis results of 4.85 g's. The
stresses calculated by the Algor software were verified by strain gauging.
"By using Algor FEA, we optimized the design before producing prototypes of the dragster," Mr. Okreglak said. "Ultimately,
we built fewer prototypes and needed fewer test runs to ensure the safety of the design."
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