One of the helpful elements used is called a bumper canard or dive plane. As seen on the DTM Touring Car above, the bumper canards are just above the front splitter and below the Dunlop sticker. These canards serve to add more downforce at the front increasing overall car balance in cars that have excessive rear downforce. This allows the car to be setup to maximum downforce without having to compromise the cars handling .

Also in prevalent use is the vortex generator. These devices create a venturi effect that keeps the air flowing closely together. This compressed flow allows the air to be directed much more accurately and in higher volume. You can see these devices on both the Mitsubishi Lancer Evolution MR (pictured) and the Subaru Impreza WRX STi. In these cars, the vortex generator sends more air over the rear wing, thereby increasing its efficiency.

In the past, other unusual designs were used to increase overall downforce. The most famous of these odd designs was the Brabham BT46B Formula 1 car, otherwise known as “the fan car”. This car had been designed by Gordan Murray to use a fan attached to the engine to suck air from underneath the car. This lead to a vacuum effect being created underneath the car which allowed it to stick to the road like glue. Niki Lauda and John Watson went on to pilot the fan car for only one race: the 1978 Swedish Grand Prix at Anderstorp. Watson DNF’d and Lauda went on to win comfortably. The fan car ended up being banned shortly thereafter.

This concludes our look at modern car aerodynamics. Please leave a comment to discuss your thoughts or opinions on this piece. Let us know what you’d like to hear about next time.

The diffuser works in two ways. First, it reduces the turbulent airflow.  Second, it slows down and pressurizes the air as it comes off the car.

Turbulent airflow is always problematic to aerodynamic efficiency. The diffuser reduces this turbulence. When the air hits the front splitter and is forced underneath the car it speeds up and decreases in pressure. When it enters the diffuser the air is allowed to expand and slow down increasing pressure to equate to the normal atmospheric pressure of the surrounding air. This is where the airflow is smoothed to decrease turbulence. If the air were to blast into the normal airstream at its high velocity, low pressure state, parasitic drag is created. This is air needing to fill the void left by the moving object it follows. The diffuser serves to eliminate the creation of parasitic drag and the air is replaced in the same state as the surrounding air.

The second function of a diffuser is a suction effect created by the pressure difference between the fast moving air under the car and the slow moving air in the diffuser. As the air slows, it decreases in pressure. This low pressure area will create a vacuum effect. This vacuum sucks the rear of the car closer to the ground (seeing as the it cannot really move the ground up to meet the car, all relativistic physics aside). It should be noted that most of the effectiveness of the diffuser is lost if there is too much clearance between the road and the underbody.

Come back next week for a look at the rest of the miscellaneous canards and fins that are also common in aerodynamics today.

Although not the first to dabble in aerodynamics in racing, Chaparral Cars is widely considered the first to do it successfully.  Jim Hall would race through the 60′s and 70′s radical new cars that he designed using his engineering background and an impressive hand behind the wheel of  a race car. His cars featured movable wings and, in one of his last cars, fans to suck air out from underneath the car. Hall’s cars were extremely successful in the Can-Am series and lived on in legend to this day.

Today, rear wings are a huge part of the aerodynamic success of vehicles simply because they can create huge amounts of downforce. Put together with the downforce created by the front splitter, at speed the car can have thousands of pounds of artificial weight added to it. This balance is very important because just like adjusting the suspension to account for handling, the aerodynamic elements will play a large role in the overall stability at speed. Having too much front downforce will cause the car to be very loose and vice versa. Also there is the element of drag to consider. The rear wing will cause massive amounts of downforce but also cause lots of drag, slowing the car down and making higher speeds much harder to attain. This balance between top speed and handling must also be considered when setting the car.

Next week: the venerable diffuser.

The leading edge of a car is generally called a splitter. This is due to the fact that at this point the air is split, with some of it having to go over the car and some under. This is important because of the differential in pressure that is created in this process. The air flowing underneath the car speeds up creating low pressure. The air flowing over the car encouters a surface with a high angle of attack and forces the car into the ground. The low pressure area under the car sucks it down and the high pressure area above pushes the car into the ground.

The math: D = 1/2 (WS x H x AoA) x F x ρ x V^2

Expressed as a sentence, it reads downforce is equal to one half of the width of the wing times the height of the wing times the angle of attack, the sum of which is multiplied by the coefficient of drag of the wing, times the air density, times the velocity of the airflow squared.

Unfortunately, there is more to a car than just airflow. Radiators, oil coolers, brake ducts, and ram air intakes are a few of a cars components that require airflow to provide cooling. In the picture above, cooling ducts account for a majority of the leading edge of that 911. So in many cases, figuring out a way to cool a car sufficiently and keep aerodynamic efficiency is of prime concern for a designer.

Next week: the rear wing.