Aero Handbook

Introduction to Sub-Aero

Design Methods

Manufacturing Methods

General Advice

Sub-Aero History

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Introduction

Hello and welcome to the Georgia Tech Motorsports Sub-Aero Handbook! Building race cars is hard, as SuperFastMatt showed with Car 7 . Doing so on a team of students that has completely new members every four years is near impossible. This document intends to make that task slightly less daunting by officially documenting best practices in an organized and efficient manner. While it is impossible to document all the knowledge currently on our sub-system, my hope is to get as close as possible. To future members, please update this. What we consider best practices now are not optimal, and there are far better solutions out there for nearly everything we do. Once you find the better solution, add it, but document what we did prior to avoid regression.

General Resources

Design Reviews: These are always good places to start, as their real benefit is documentation. Design binders can be helpful as a single document outlines an entire design cycle, but sometimes they are done in different formats. Progress throughout a design cycle should be documented in preliminary, intermediary, and final design reviews. More importantly, these should show concepts that didn’t work and why they didn’t work to prevent repeating mistakes.

Mechanical/Manufacturing Resources

• Easy Composites: Tons of well-made videos on everything composites, including layups and mold design.
• FibreGlast: similar to Easy Composites but in article format.
• Guides and Resources: From our very own Sub-Composites.
• LittleMachineShop: Good source for using metal, including determining what size drill bit to use.

Aerodynamic Resources

• Kyle.Engineers: Former F1 Aerodynamicist turned Youtuber with tons of great videos analyzing different racecars, including an FSAE car.
• NASA: Great introductory articles on different topics in aerodynamics, both theoretical and applied.
• No One Can Explain Why Planes Stay in the Air: An explanation of why we have no concise, physical (non-math based), and general explanation of airfoil theory.

Introduction to Aerodynamic Theory

What We Try to Do

Race cars are built from the tires up; therefore, everything on a racecar is intended to manipulate the tires to make the car accelerate faster. Their grip is a product of the normal force and the coefficient of friction, both of which are constantly changing. Increasing the normal force allows for faster acceleration; however, simply adding mass adds inertial forces that slow the car down. Therefore, we want to increase the force pushing the tires down without increasing mass. There lays the goal of aerodynamics: using the car’s air speed to push it into the ground without adding much mass.

Aerodynamics has two downsides: drag and weight. The package must be designed to work efficiently, meaning the ratio of downforce to drag is high (somewhere between 2 and 3). While we have found an efficiency of 2 to still be beneficial versus having no aero, increasing efficiency can gain many points. F24 has an efficiency of 2.6 and F25 around 2.2. Secondly, as with anything on a racecar, reducing weight directly results in a faster car. F24’s full aero package weighed about 35 pounds; F25’s around 48 (see the lessons learned section for why).

General Sub-Aero terms

Airfoil

The cross-sectional shape of a wing which generates a pressure differential on either side.

Biplane

An airfoil or system of airfoils above the main airfoil system in a wing.

Camber

The curvature of an airfoil.

Chord Length

The distance from the LE to the TE of an airfoil.

Free Stream

The state of air infinitely ahead of a given aerodynamic system such that it is not affected by the system.

Leading Edge (LE)

The front edge of an airfoil.

Mainplane

The first, primary airfoil in a system/series of airfoils.

Ply

A layer of fiber in a composite material.

Ply Schedule

The construction of a composite skin as defined by individual plys.

Sandwich Panel

A composite board made of fibers on either end of a core material.

Secondary

The airfoil immediately preceding the mainplane.

Span Length

The length of an airfoil along its width (perpendicular its chord).

Tertiary

The airfoil immediately preceding the secondary airfoil.

Trailing Edge (TE)

The rear edge of an airfoil.

Up/Down/In/Out Wash

The movement of air in a respective direction.

Yaw

The crosswind experienced by the system, represented by an angle
or
the angular difference in the car’s velocity and wind speed brought on by rotation through a corner.

Core

The central section of sandwich panel; usually a honeycomb-shaped material or foam.

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