Custom Search

Aerodynamics

Car Aerodynamics

Downforce

The same principles which allow aircraft to fly are similar in car aerodynamic, but the main focus is to produce downforce instead of lift. Depending on the exact requirement for the application, the set up can be modified to suit top speed (low drag) or high downforce (higher drag), while providing more grip for the corners by pushing down on the tyres. The ideal set up is normally to get the maximum amount of downforce, for the smallest amount of drag generated. Gear ratios, track configurations and regulations all have an effect on the overall package, which must be viewed as a whole.


 

escort cosworth

 

Most race cars aerodynamics will have a selection of different settings for the various aero aids (front wing, rear wing, and diffuser) to get the optimum set up for the highest lap times, depending on the requirements. While this might not always be the case with normal productions cars, some might be set up to produce real downforce (Ford Escort Cosworth for example) while other are more geared towards fuel efficiency and visual appealing looks. 


One of the main Physical forces involved in downforce generation is called the Bernoulli Effect, fundamentally meaning that if a fluid (gas or liquid) flows around an object at different speeds. The slower moving fluid will exert more pressure than the faster moving fluid on the object. The object will then be forced toward the faster moving fluid.

 

In car aerodynamics we need to force more high speed/ low pressure air to go under the car creating negative lift (downforce). The harder and faster you drive, the more downforce is produced and the more grip will be available to the tyres/ tires via the suspension and chassis, effectively sucking the car to the track with ever increasing speed. This results in higher grip levels for the tyres and more traction, especially going through the corners.

 

Car aerodynamic downforce can be achieved in a combination of ways. The easiest way to image this, is to turn an airplane wing upside down. The basic theory is that the faster the car can drive, the more downforce is generated and this pushes down on the tyres/tires of the car and produces higher grip and traction levels. A F1 car can produce enough downforce to drive upside down, so it can produce more downforce than the weight of the car and this force is the square of the object velocity (double the speed quadruple downforce and drag).

 

While this is desired if you going from 200 Mph straight into a sweeping corner, on a dragster or race car focused on top speed. This extra drag will hinder top speed and more engine power will be required to propel the car forward. It is a balancing act for top speed and downforce levels, hence the reason most competitive race cars will have adjustable aerodynamic aids to suit the best downforce levels for a given race track.

 

indycar aerodynamics

 

A Indy car for example would probably be generally set up to have a greater top speed then a F1 car, as the F1 car will require greater levels of grip and downforce for the corners, especially with its rapid directional changes to reduce lap times. Otherwise high downforce levels will compromise the rest of the course, for high top speed on the straights. It all comes down to different set ups for different race courses. Like a lot of components on race cars, it is possible to adjust the aerodynamic levels of the required downforce to yield greater top speeds depending on the circuit. But the introduction of Drag reduction System will somewhat change this situation for the 2011 F1 season, allowing for less downforce generation to aid overtaking.

These race teams normally have huge budgets and dedicated engineers striving to continually create more and more effective designs. Sometimes we are only talking about 0.1 or 0.2 of a second difference on a total lap. But over the course of a Race, this can make the difference between first and second place. As we can see the introduction of ground effects and downforce has made a big impact on the world of motorsport.

It is important to also reflect on the various aerodynamic advances over the last few decades, these have all been ways of conforming (to the extreme in most cases) to the various Governing bodies rules and regulations. I suspect with unlimited scope, Race cars pulling more than 6 g's in the corners are within technological sights.



Downforce Diagram

Here is an 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 downforce (0.20 psi difference in pressure) x 362 (number of square inches in a square yard)= 259.2 pounds of usable downforce. So these small little adjustments can yield impressive results.

 

 

 

You can see that huge amounts of potential downforce can be generated with a little thought and good design principles. This is an ever ongoing battle for engineers both in the world of production and motor sports cars. We have seen some weird and wonderful designs over the Years and the future of all Innovations in car design will always continue to evolve.

There are lots of areas of nature in which engineers and designers' draw inspiration from, especially true for birds and aquatic mammals and fish. The shape of wings and fins hold millions of years of evolutional engineering to overcome similar restraints, to the same laws of physics. I expect to see lots of continued develop in the Years to come emulating the natural world.

You can see that there are a lot of benefits that can be made in terms of aerodynamics and manufactures/race teams spend huge amounts of money testing in wind tunnels to develop the most efficient aerodynamic designs. It is an ever increasing battle for more downforce for as little drag as possible. 

The 3 main areas of the car which can be developed are: Front WingChassis or under body and Rear Wing, apart from the actual design of the car. Learn more about these different areas on this following: aerodynamic upgrades.

 

Racing cars and aerodynamics have come a long way in terms of development since basic ground effects where first applied to cars. In the early days of 1967, cars like the Lotus 49 and Lotus 79 for example, initially had huge rear wings, which were mounted on the rear suspension and even had cable operated wings to reduce the angle of attack on the straights to increase top speed, the same as DRS in F1 2011 season. Due to too many accidents with these high mounted wings, they were banned and engineers started to look at other areas of the car to create even more downforce levels. Most of the principals applied where taken from aeronautical design and modified for use in Motorsport.

Coefficient of Drag

Cd (Drag coefficient or coefficient of drag) is an aerodynamic term that describes the car ability to cut through the air and the shape of the car will ultimately affect the overall top speed. The lower the Cd level, the lower the drag and more aerodynamic efficiency of a cars design (this is focused on drag reduction and not downforce).

 

 If we look at the "drag coefficient values" diagram below, we can see the impact that different shapes have on the airflow over them. The lower the CD figure the more streamlined the shape is and also its increased aerodynamic efficiency. It takes ever increasing BHP engine power to overcome air resistance, this is effectively a ration of 1:4, meaning the required powered is ex-potentially squared to the target speed.

 

Boundary Layer:

We can also see that airflow that makes contact with a moving shape creates a boundary layer, which surrounds the object. Air molecules adhere to the objects surface through friction to a degree, although this is variable to due to different object materials. The further the airflow is from the object, the less the effect; so a car might typically have a boundary layer of some 20-25mm (0.78-0.98 inch).

Flow Separation:

We can see by the diagram that the boundary layer of air at some point begins to break away from the object, as the object punches through the air, this is called flow separation. Depending on the shape of the object, we can see that the more turbulent the airflow exits an object, the more the object suffers from drag as a result.

Drag:

This is the force acting in opposite to the object direction of movement. While this is a simplistic view and there are lots of other factors involved and types of drag. We for the illustration of this example only need to know that turbulent air filling in the gap left behind it, creates drag. 

Drag Coefficient Values

 Newtons Law of Motion identifies that :

" For every action, there is a equal and opposite re-action"

 

Let’s have a look at an example. Think of a generally squared/ flat car frontal area as a high CD level and a rounded smooth shape as a lower rated one. A car with a larger frontal area will require more of the engine BHP to continue to make the car accelerate and continue to gain speed. As the car continues to go faster, the required power to keep building speed increases significantly (squared).

Drag is proportionate to the square of the speed. Normally a smooth, low frontal area car will be able to produce better top speeds (if engine power is similar), this low Cd value combined with a good aerodynamics downforce aids will result in a true performance package.

But designers and engineers have a fine balancing act to combine good downforce for the corners and minimum drag for the straights. So you can see that just bolting on that fancy or cool looking spoiler or huge rear wing, could have huge affects on the overall performance of your car. That is why Motorsport is so expensive and teams end up spending huge sums of money for a competitive aerodynamic package, within the confines of their regulations and given goals.

  

Streamlined Design Cars

The aerodynamics of a car can also be developed to produce a more slippery streamlined designed shaped car, there will be a point where a car's design with a high downforce set up, will be good in the corners but will have compromised top speed. This is not a desired aerodynamic design for production cars, as it will lead to higher fuel and tyre/ tire consumption. It is always a balancing act to get the desired amount of downforce for the corners and also low drag levels for top speed, for out and out track focused cars, but production cars have their own set goals to achieve.

Some production car do have active car aerodynamics, where a wing pops up at a given speed, or in some cases appears under heavy braking acting as a air brake to stabilise rear traction and reduce high speed lift. This is mostly seen in Ultra cars likes the Bugatti Veyron. 

veyron pop up rear wing

This set up of the wing dropping down into the body work essentially follows the rule of a streamlined body design, as huge wings and spoilers will create drag which is the biggest killer in terms of top speed and aerodynamic efficiency. Also the majority of the required downforce levels are generated through underbody diffuser design, which produces low drag levels.

 

If we also look at the world speed record cars, they essentially look more like a rocket, or aeroplane with its wings cut off, then traditional cars designs. The design is predominately engineered to cut through the air, minimal drag levels. Although not practical in everyday production cars, we can see the relevance of a slippery design in achieving a streamlined design for maximum top speed.

 

  

Rapid-Racer.com
Protected by Copyscape Online Copyright Protection