Car Aerodynamics are one of the top performance advantages any racecar can have over its competitors, especially in racing series like F1 or Indy Car and other open wheel race series- with limited set specifications.
Purely a science now, but with origins less defined with its early adaption as a result of trial and error and lots of inspiration from the aerospace sector. Aerodynamics were considered more of a black art until evolution of designs included foundation of fluid mechanics, downforce generation and ground effects.
Racing Car Aerodynamic History
During the early 20th century, racecar designers where focused on stream line configurations, with reduced frontal areas and shaped bodies to minimise drag. This resulted in increased top speeds compared to open wheeled designs, with out having to add engine power. Sadly early racing car aerodynamics were just in their infancy, with little research and development, unlike in today's Motorsport world with big money budgets. Designers had to rely on experience/ trial and error and this was considered somewhat a bit of a black art.
Due to stream line car bodies having increased weight compared to open wheel racing car designs, when it came to the twisty stuff, handling was normally an acceptable sacrifice. Resulting in racing focused on top speed to win races. This does not suit every circuit, especially tight and twisty tracks and was a compromise or weakness on early aerodynamic endeavours for the ultimate performance package.
High speed stability was also a major concern, with designers and engineers dialling in lots of understeer to try and counteract these tendencies which were commonplace. This dampened the instability to a certain degree at speed, but getting a good turn-in response, was hard and strong arms were needed to wrestle the cars to the apex on slower corners.
What caused this instability was a combination of things. Firstly flow separation was occurring over the top of the car causing reduced air pressure, resulting in lift at the rear of the car. This unloaded the rear tyres, resulting in poor cornering balance between the front and the rear.
If anything this interfered with the rear tyres contact patch, causing sudden extreme oversteer. In effect the air over the top of the car had to travel a longer distance, increasing velocity, reducing pressure and actually acting like a aeroplane wing to a certain degree- the opposite of modern downforce generation principles today. This sometimes also was in combination with air packing under the front nose resulting additional lift. The faster the cars drove, the more lift resulted and the more unstable the car became at higher speeds. Overall the car became harder to drive at speed and you needed nerves of steel to be competitive.
As time progressed even more sleek designs were developed, with lower centres of gravity and improved handling, compared to the boat like characteristics of earlier conceptions. Drag was still the primary factor in terms of aerodynamic developments, with top speed still winning races. As you can imagine the development of Motorsports was impacted during the Second World War and we reached a stall in this area of automotive development.
1960's Ground Effects Racing Car Application
Everything changed around the 1960's, where lift and drag began to be looked at as a whole. Instead of all the focus on drag reduction and top speed, negative lift (or down force as it would later be known) started to be explored with focus on cornering and handling characteristics.
In the beginning simple wing-lets and flat rear wings were incorporated into existing race car designs. Further steps forward began with Aerodynamic devices such as inverted wings, these were first mounted to struts high up above the race car's airflow, at the rear of the vehicle. This was to get maximum clean airflow and little consideration to drag was considered, until some time later, cable operated levers were fitted to reduce the angle of attack on the wings to gain higher top speed on the straights. These were mounted in the cock-pit and operated by the driver on the straights.
During the 1969 Spanish GP both Lotuses of Jochen Rindt and Graham Hill crashed in identical accidents, on a crest of a hill with Bi-winged cars. Due to safety concerns, legislation dictated that the rear wings must be located at the rear of the car just behind the back wheels and front wings also to be mounted just in front on the front wheels. All part of the overall bodywork. This was the blueprint for all open wheeled cars from the 1970's for this particular race specification. All due to earlier safety concerns of wings being mounted on tall struts, directly to the suspension- were to unpredictable and dangerous.
Later aerodynamic devices were incorporated into the bodywork and included in preliminary design concepts, rather than just a after thought or add on. Aerodynamics were now seen as the next big development area for future racing car design along with engine power alone, which also lead to ever increased tyre design to maximise traction and grip levels.
Moving Aerodynamic Racing Car Devices
American Jim Hall was another pioneered at early attempts at unleashing Downforce, using alternatives avenues. Realising the huge performance gains in this technology on the Motorsport world and reducing lap-times, The legendary Chaparral 2J Can-Am car showed the competition the path ahead in terms of future aerodynamic pursuit directions.
By effectively mounting 2 fans at the rear of the car to suck the car to the ground, by means of an auxiliary engine. Side skirts and front and rear sills were positions to maximise down force levels and help seal in low pressure air form the ambient high pressure air. While the car created huge down force levels, current tyre technology ultimately had an impact on the endurance levels of the machine. As ever this visionary design was some what limited by available technology limits of the time
Downforce levels were consistently generated, even when the car was stationary, providing a huge performance advantage other its competitors. No longer was down force generation linked to vehicle speed, with varying aerodynamic efficiency at different speeds. Very radical and genius in design, Jim Hall was a pioneer of this field of aerodynamics for racing cars and a true legend of American Ingenuity.
Downforce Generating Racing Car Underbodies
Colin Chapman and the iconic Lotus 79 make a big impact in F1 with the introduction of ground effects, with shaped under bodies. By effectively shaping the underside of the car like a giant wing, eliminating the need for high angle of attacks from drag inducing wings. Movable skirts were augmented into the design, to increase the performance potential and keep low pressure air levels.
This design along with so many other designs were eventually banned due to safety concerns. The skirts were subjected to wear and tear on camber changes and kerbs and this could result in sudden down force level drops, with the potential for huge safety concerns.
From 1983 ground effects design in F1 was banned with mandatory flat bottom configurations. Resulting in ever increasing focus from designers and engineers on more traditional aerodynamic devices, such as wings, but we have also seen rear diffusers playing a greater impact in recent Years.
Downforce vs Streamline Racing Car Design
If we look at the weight to performance trade off, compared to earlier aerodynamics designs, which were focused on stream line design for top speed (along with adding substantial weight gains to enclose the bodywork with early materials). By just adding adding aerodynamic devices for down force generation (substantially less weight), aerodynamic devices offer more performance per added mass.
Aerodynamic devices focused on downforce, having relatively small weight gains to the overall construction. Lightweight aerodynamic parts can reap big performance gains in reducing lap times, for small mass increases to the design. This lead to further research in stronger materials, which were lighter, with the dawn in the era of composites.
Downforce and Drag increases at the square of speed, divided by a constant. If we look a front wing for example, which produces say 10lbs (4.53kg) of down force at 40mph (64.3km/h).If the same wing increased speed to 80mph (128.74km/h), the amount of down force generated would be 40lbs (18.14kg).
Here is another interesting fact: the average atmospheric pressure at sea level is 14.7 psi on all sides of an object, even on our own bodies. By reducing the pressure under the bonnet/hood to 14.5 psi, over an area of just a square yard, we would generate about 260 pounds of down force (0.20 psi difference in pressure) x 362 (number of square inches in a square yard)= 259.2 pounds of usable down force. So these small little adjustments can yield impressive results.
This shows the huge potential that down force had on the world of Motorsports and the beginning of what now is one of the single biggest performance advantages to be had in racecar engineering, after engine and tyre technologies have reached acceptable levels. Rapid tyre development and material research followed, as the need to further enhance and maximise the potential gains which were now on offer.