Formula SAE Aerodynamic Package; Design, Development and Validation - Luke Phersson, 2009

Monash Motorsport Final Year Thesis Collection

The Final Year Thesis, is a technical engineering assignment undertaken by students of Monash University. Monash Motorsport team members often choose to conduct this assignment in conjunction with the team. 

These theses have been the cornerstone for much of the team’s success. The purpose of the team releasing the Monash Motorsport Final Year Thesis Collection is to share knowledge and foster progress in the Formula Student and Formula-SAE community.

We ask that you please do not contact the authors or supervisors directly, instead for any related questions please email info@monashmotorsport.com

Summary:

This project covers four main areas, the first outlines the measurement of a number of physical attributes governing vehicle dynamics with and without an aerodynamic package, subsequently, analysis is performed with ChassisSim to quantify the effects these parameters have on vehicle performance at the Formula SAE competition. Further, the simulations performed with ChassisSim are correlated with experimentally determined data to validate their accuracy.

Secondly, an improved method for manufacturing composite aerofoils is presented, providing a 32% weight saving over the previous method as well as increased dimensional accuracy. 

Thirdly, a numerical and physical analysis of both 2008 and 2009 Monash Formula SAE car aerodynamic packages is performed, providing a number of parameters used in the initial modelling section as well as providing a solid basis for further 3D CFD development. 

Finally, a preliminary analysis of the 2010 vehicle is presented to assess the applicability of an aerodynamic package. The findings of this analysis are that the 2009 aerodynamic package will still provide a significant performance advantage.

Introduction:

The Formula SAE competition involves a team of university students who conceive, design, manufacture, and compete with formula style race vehicles in both dynamic and static events. The competition can trace its origins to the early 1980’s when it was hosted by the University of Texas, Austin, USA. Since then the competition has spread throughout Europe, Asia, South America, and Australasia with hundreds of teams and thousands of students competing worldwide.

Monash University has competed in Formula SAE since the inaugural Australasian competition in 2000 with mixed success. Our third car, the 2002 entry, was equipped with a full aerodynamic package, including front and rear wings in addition to a diffuser. This was an Australian first, and in the words of Carroll Smith (head judge of the Formula SAE competition and motorsport legend), Monash was only the third team in the world with “an intelligent use of downforce” (Australasia Formula SAE Competition, 2002).

Figure 1.1 - Breakdown of modes seen in 2008 competition (Juric, 2008)

Formula SAE events heavily favour small and nimble cars due to the low speed, tight and corner intensive nature of the tracks (See Figure ..1.1, showing relative significance of cornering). To be competitive, vehicles are required to have excellent transient cornering potential rather than outright maximum speed in a straight line. The controlling factors influencing cornering potential are weight and available lateral grip. If a car’s available lateral grip can be increased for only a small weight penalty, then the car will usually be faster on a Formula SAE specification track.

At present, only a few cars world-wide have implemented a cohesive aerodynamic package to increase their cornering potential. This is likely due to a number of reasons including insufficient resources available to the team, additional weight and complexity to the vehicle, as well as a wide spread opinion that due to the relative low speeds seen in Formula SAE, wings are not effective enough to justify their weight. This is disputed by the late motorsport great, Carroll Smith who is quoted saying – “As you know, for at least 12 years I’ve been saying the first car to intelligently apply ‘download’ at this competition will dominate, and Monash is pretty close” (Australasia Formula SAE Competition, 2002).

Additional static weight due to aerodynamic devices has a three stage effect on cornering potential. Most obvious is the additional lateral force required of the tyres to resist the centrifugal acceleration (inertia) induced by the wing mass. Secondly, the vehicle’s centre of gravity (CG) height will usually increase as a consequence of the addition of wings, which are commonly located above the CG height of the bare vehicle. This will facilitate more weight transferring to the outside laden wheels during cornering, and due to load sensitivity effects, this can result in a decrease of the average coefficient of friction for the four wheels  (Smith, 1978). Thirdly, and of particular importance for transient response, is the increase in yaw inertia (vertical polar moment about the centre of the car) caused by wing mass located away from the vehicle’s centre of rotation. This increased inertia slows the response of the car, particularly in fast slaloms by resisting rapid changes of direction and slowing down the car’s response to driver inputs (Milliken & Milliken, 1995).

Detrimental effects from the addition of aerodynamic devices have the potential to be offset through the enhanced grip produced by downforce generation. Downforce increases the normal force acting on the tyres resulting in an increase in total lateral grip. It is this balance that requires an aerodynamic package to be specifically designed for a certain environment to optimise the performance benefits gained.

A thorough investigation on the performance benefits achieved due to wings has not been performed since the vastly dissimilar 2003 car, thus there is no quantifiable data suggesting the current wing package on the 2008 car is beneficial. This paper aims to address this by comprehensive analysis using the Monash Wind Tunnel facility to determine the aerodynamic characteristics of the car with and without wings. Physical changes to the dynamic properties of the vehicle as a whole will also be analysed, specifically the effect upon vehicle centre of gravity height and yaw inertia with the addition of wings. This data will then be applied to vehicle dynamic simulators to predict the gains or losses incurred in the various dynamic events of the competition. Based upon these results it will be possible to make an informed decision regarding the inclusion of an aerodynamics package on the 2009 car.

With the aid of the information gathered through wind tunnel testing, the 2008 aerodynamic package will be further developed, primarily in regards to weight and construction technique as well as improving endplate design under yaw conditions. Further development will be limited as the current design philosophy employed for the 2008/2009 cars is at the end of its development cycle, resources will be primarily invested on the 2010 car. The 2010 vehicle will follow a new design philosophy, focusing on weight reduction and increasing fuel efficiency as a direct result of a Formula SAE rule change resulting in a 100% increase in fuel efficiency weighting.

Conclusions:

A number of physical attributes governing vehicle dynamics with the addition of an aerodynamic package has been physically measured, and subsequently analysed using ChassisSim to quantify their effect on vehicle performance at the Formula SAE competition. Wings were found to be advantageous in all scenarios with the exception of the acceleration event, where they were marginally worse, however due to the gains in other events; an informed decision has been made to retain an aerodynamic package for the 2009 vehicle. ChassisSim has also correlated well with logged competition data, giving confidence to its ability to accurately predict vehicle performance, this is an important tool to quantify design changes.

The 2008 aerodynamic package has been extensively tested in the Monash full-scale wind tunnel to provide aerodynamic properties used in the performance modelling section. Furthermore, the 2008 wings were further developed in the form of the 2009 aerodynamic package, giving significant gains in downforce of up to 20%.

A preliminary 3D CFD model of the entire 2009 car has been developed, setting a basis for any further CFD work.

Manufacturing improvements have resulted in more consistent profiles for the 2009 aerodynamic package as well as a 32% reduction in weight.

A preliminary study of the applicability of an aerodynamic package on the 2010 vehicle has been completed, with the finding that the current aerodynamic package on the 2009 vehicle is still a performance advantage.