Review

By Matt Gartner

Race Car Aerodynamics provides a comprehensive guide to how air flows around and through race cars. It is the most useful book on aerodynamics (of several) I have in my collection and covers nearly everything an amateur designer could want to know about aerodynamics.

The book is well organized, moving logically from beginning theory to detailed explanations of aerodynamic devices, their design and their behaviors. It is very focused on theory and design—you won't find any fabrication instructions on building the actual aerodynamic devices, and that is alright (There are many books that can show you how to fabricate with composites or sheet metal to produce aerodynamic shapes.)

It is written with a non-engineer in mind and avoids going too technical, yet it encompasses so many areas of aerodynamics that the reader will come away with a "big picture" engineering perspective on fluid flows to use in their own designs.

The book provides a huge range of diagrams, photographs and plots that demonstrate the theory and examples provided in the text. For the casual reader trying to understand the concepts of aerodynamics, these diagrams are like gold. Here is a sample diagram and excerpt:

Excerpt from "Race Car Aerodynamics" by Joseph Katz. © Bentley Publishers

Fig. 7-17. Schematic description of the flow field over a production car-based racer.

adjusting the length of the lower horizontal plate at the inlet, the front down-force can be trimmed as suggested by Fig. 6.46 (D). The rear wing has the maximum possible span (full width of the car) and its highly cambered airfoil shape was developed for this particular purpose. The flow over the wing was attached on the actual race car and its lift could have been varied by changing its angle of attack and by adding small Gurney flaps of various lengths.

The second part of Fig. 7.17 depicts the flow features under the car. Typical localized flow separation areas can be found behind all four wheels, and the flow under the car was somewhat restricted by the horizontal, front-inlet spoiler. As a result of the low base pressure at the back, which is enhanced by the rear wing, a lateral inward flow pattern is observed between the front and

Math formulas are shown alongside the theory to help provide estimations of the various coefficients and forces associated with aerodynamics like lift and drag. The formulas may sometimes seem intimidating, but are often shown with sample values and explanations that make understanding them much easier. In my opinion, the author has found a good balance of providing useful formulas without overwhelming the reader, even if they are not big on math. Here is the formula sidebar for Reynolds number:

Formula sidebar from "Race Car Aerodynamics" by Joseph Katz. © Bentley Publishers

Book Sections

The book includes the following sections:

Aerodynamic History

This section discusses some basic history of aerodynamic optimization, the basic forces of lift, drag and sideforce, and the effect race car aerodynamics has had on production cars.

Aerodynamic Theory (32 pages)

The Aerodynamic theory section delves heavily into the terminology, how air flows, properties of fluids, the boundary layer concept, Bernoulli's equation, and venturi tubes. It explains in detail the drag, lift and side force coefficients and their effects. Overall it provides a very concrete understanding of how aerodynamics work around a vehicle.

Measurement of Aero Forces

The author discusses testing and measurement techniques used to gauge the forces acting on cars. These include road testing, wind tunnel testing and CFD (computational fluid dynamics) computer-based simulation.

Airfoils and Wings

This section is the one-stop shop for everything wings. To give some idea, it has 45 pages (in my edition) just for wings, and it's not repetitive examples, but concise and to-the-point knowledge.

The diagrams, graphs, formulas and text are used to explain every aspect of wings theory, including lift coefficients, airfoil drag, angle of attack, center of pressure, and Reynolds number.

Single and Multi-element airfoils are also discussed in detail, with diagrams showing side views of the elements and their contribution to downforce. There are plenty of example wing profiles used in current race car applications.

The author goes on to explain the desirable pressure distribution over a wing, the potential wing planform shapes, high-lift wing designs, as well as wing performance enhancements such as vortex generators and end plates.

Finally, this section also looks at the interaction between wings and other surfaces, including ground proximity (how close to the ground the wing is).

Aerodynamics and Vehicle Performance

This section focuses on how aerodynamics affect the performance of the race car. The effect of downforce on tire adhesion, the effects of side winds, and lateral stability are discussed. As well, the sensitivity to aero forces of the suspension and vehicle pitch and even the interaction between race cars in situations such as drafting and passing maneuvers are explained and visually shown in diagrams.

Aerodynamics of the Complete Vehicle

Starting with the basic vehicle shapes, this section then looks at the overall aerodynamic flow around these shapes. It explains the effects of flow over open wheels as well as the use of side skirts, underbody venturis and spoilers.

Internal Flows

An area that I've seen very little information on in other books is covered reasonably well in this one. A variety of cooling system arrangements are explained and diagramed providing great ideas for the internal flow design of amateur cars, both scratch and production-based. The section also provides instruction on cooling system exit design and exhaust blowing for increasing downforce of wings and venturi tunnels.

Wing Design Examples

A wonderful resource this book provides is numerous examples of race car wings used today, and their downforce potential graphed for comparison. If you've ever seen the variations of wings between different racing series, or even F1 over time, this section is basically those variations compared side-by-side. The author provides amateur designers with a good starting point on their choices.

Excerpt from "Race Car Aerodynamics" by Joseph Katz. © Bentley Publishers

Various Airfoil Shapes

In this section a variety of airfoil shapes are presented along with their pressure distributions (two-dimensional pressures, except for the last three). In airplane applications, two-dimensional pressure distribution can help select the airfoil shape and estimate wing performance. Most race cars, though, have very small aspect-ratio wings (as low as b/c= 1.5), and the wings operate in close proximity to other body parts, such as wheels. Therefore, the following examples serve only to demonstrate the diversity of the various airfoil shapes. Their actual application to race cars requires three-dimensional pressure distribution data (which can be obtained either from experiments or computations).

When searching for a single-element airfoil shape, the simplest option is to examine the large variety of shapes developed by NACA, many of which are listed in Ref. 4.1. Most of these airfoils can be very efficient when used in the lower lift coefficient range (e.g., Cp< 0.8).

As a representative example, the NACA 64₂-415 airfoil is presented in Fig. 4.46. This airfoil will have a very low drag (as shown in Fig. 4.16) due to almost 40% laminar boundary layer in the lower range of angle of attack (up to a = 4°). At higher angles of attack, a suction peak develops near the leading edge (see pressure data for a = 5°), causing early transition in the boundary layer and a sudden jump in skin-friction drag. The pressure distribution, shown in the figure for Q ~ 0.90, corresponds to this condition with the higher drag. This can be verified by observing the Q = 0.90 point in Fig. 4.16, which is located at the higher drag range at the right-hand side of the low-drag bucket. At the lower lift coefficients, such as at a = 1° (Q = 0.46), the pressure distribution is favorable on both sides of the airfoil. This low-drag condition corresponds to the middle of the low-drag bucket in Fig. 4.16.

Fig,.4-46. Two-dimensional pressure distribution on a NACA 64₂-415 airfoil at a= 1° and 5° (effective Re number is over 2 x 10^e).

Historical Designs

Finally, this section discusses historically important aerodynamic designs including the Brabham BT46B fan car, Lotus 78 ground-effect side-skirt F1 car, and sports prototype Mazda RX-792P.

Helpfulness to amateur race car designers

This book provides everything an amateur race car designer could want in understanding aerodynamics. It provides the theory to understand, the formulas to estimate, and the examples from which to start designing. Even for those who are math challenged, it gives enough examples of applications that any amateur designer can, through the study of these examples, incorporate aero devices into their race car designs.