This year, in order to improve the overall standing of Columbia University's Forumla SAE team, a group of dedicated seniors proposed a creative and ingenious way to drastically improve the performance of the car. Through an active rear wing system the team aims to maximize cornering velocity as well as minimize drag while accelerating between corners. By using accelerometer data, the controlling software will be able to decide the proper angle of attack of the wing to provide maximum downforce or minimum drag. Through our extensive background research on the topic, we have found that many companies and racing teams have discovered the benefit of aerodynamic systems that alter based on changing driving conditions. Formula 1, a pioneer in automotive technology, was the first to discover the improvements in lap times. Since their introduction in Formula 1, many automotive companies have adopted the practice, notably Porsche, Buggatti, McLaren, and Pagani.
The final design utilizes a three tiered wing system in which the upper two tiers are actuated by a single linear actuator. Through Creo's kinematic analysis the location of the mounting points for the wing, actuator, and link were designed to see the minumum amount of force and stress to the system. The system is controlled using an iPhone's accelerometer and GPS through an app developped by the team. When the accelerometer data determines the wing should be in the high downforce position the iPhone sends a 22kHz tone to an Arduino. The arduino contains the PID controlling software to place the wing in the exact location with 0% overshoot in under half a second. By doing so, we aim to have the wing in the full "up" position before entering the corner.
Aerodynamic efficiency is a major deciding factor in many racing series. With cars powered by similar engines and similar suspension kinematics, the aerodynamic profile of the car can lead to faster lap times than opponents. Due to the fact that most cars have similar power outputs and weights, cornering velocity usually becomes the difference. In order to increase cornering velocity aerodynamic downforce, or negaitve lift, helps add normal force to the tires increasing the friction force and therefore increae the tractive force from the tires. The increase of cornering forces comes with the cost of added drag, however, which decreases straight line speed. The ability to increase tractive forces while cornering without the high cost of drag would lead to an optimized racecar at every point on the track.
The team spent countless hours in the cad lab, mechatronics lab, and SAE shop developing this project. Development began through concept development and CFD to produce the most efficient airfoil possible. This process required a powerful computer to run continuously for 24 hours to provide a single analysis. After much testing, a standardized profile was chosen for each airfoil tier. This reduced the complexity of the system and allowed for optimization of the remaining geometric parameters. Numerous variations of profiles and chord lengths were tested before a final design was chosen. Following the wing profile design, the placement of each wing with respect to one another as well as the endplates required additional development work. Due to the fact that the team did not have access to a wind tunnel large enough for testing purposes, CFD work was the only method of developping the aerodynamic system. Through CFD analysis the team found the rear wing supplied 212 lbf of negative lift with 70 lbf of drag at 60 mph. With the wing open it only produced 12 lbf of drag, a decrease of over 80%.
Production began with test pieces. Using scrap foam and a hot wire cutter, multiple attempts at manufacturing a dimensionally accurate piece were completed, unsuccessfully. This wasn't a complete loss, however, as many lay-up techniques could be tested and perfected.
In the end, the team decided to purchase CNC hot wire cut foam profiles from Bob's Flying Foam in order to gaurantee the accuracy desired.
For mounting purposes, aluminum profiles were CNC machined to each airfoil shape. The profiles were then tapped in order to secure the wings to the endplates. The enplates themselves were CNC profiled foam with aluminum bearing housing inserts.
Following machining, all parts needed to be laid-up with carbon fiber. The unidirectional carbon fiber was graciously donated by Zoltek Companies, Inc., who made this entire project possible. In addition we recieved epoxy resin from Momentive. The resin required a 24 hour cure at an elevated temperature of 140° F to harden to full strength. We could not find an autoclave large enough for our wingspan and therefore were required to to get creative. In order to cook the wings, we decided to build our own oven out of cardboard, aluminum foil, and heat guns. Using thermistors, we were able to turn on or off the heat guns to keep the temperature of the oven within the necessary range.
The mounts were made of 3D printed ABS plastic with aluminum and carbon fiber support structure for additional strength. The mounts were attached to the wing with epoxy and carbon fiber. Six steel bars were required to hold the wing effectively. All six bars were manufactured to allow for turnbuckling, so the lengths could be altered while assembled to the car. This allowed us to place the wing in the exact location and allow for tuning while testing.
While design and manufacturing our project took nearly the entire year, we were able to get in one day of testing. Due to difficulties with vibration interacting with strain gauges, the team opted for a quick test of lap times with and without the wing. Driving the same track with the wing first we saw an average of 0.4 seconds per lap increase when we took the wing off. The track took approximately 30 seconds to complete. At the FSAE competition in Michigan, the average endurance lap time without the wing was 1:05. We would have expected to see a drop of almost a second per lap at competition.
In the future the team hopes to run strain gauge tests in order to see the forces acting through the support arms in order to validate the computer model. In addition, a "drag down" test could be performed with and without the wing in order to determine amount of drag the wing adds to the vehicle.
On this page you will find additional technical information on the project. A downloadable file of our second design review is available as well as our references. In addition, please take a moment to visit our sponsors pages.
Click Here to View / Download our Presentation File
Click Here to View / Download our Report File
In addition, we would like to thank Momentive for their generous contribution of epoxy resin. The high quality resin gave our project the results we desired. You can visit them here.
For his imense insight, knowledge, and enthusiasm he continously brought to our project.
Mohamed "Ali" Haroun:
For his limitless help machining.
For his expertise in electronics, controlls, and programming. Without Doug, we were lost.
For donating space, materials, and an amazing racecar to make this project possible.
For his expertise in composite materials.
For his help in developping our control program.
And Vinod Nimmagadda
For his time and energy spent in helping the Wingers.
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