For decades, Formula 1 cars were designed with high aerodynamic performance in their mind. Even at the very dawn of F1, cars had slim streamlined bodywork – called cigar-cars from time to time these days. These future classics had one thing in mind – to generate the least possible amount of aerodynamic drag. This changed with introduction of inverted wings on cars – used to create negative lift, or what's now known as downforce.
In 1968 inverted wings were introduced to Lotus 49 and this changed the Formula 1 for good. In his typical fashion, Colin Chapman and his team bolted the wings directly to suspension parts, to have a direct load-path for these new aerodynamic loads. This also placed the wings in a near-horizontal position all the time, making them more efficient. Even with a great design, thin wing struts broke several times, leaving the engineers with a single solution – bring those wings down, closer to the car.
As usual, pretty soon all cars featured inverted wings and there was no use trying to ban them, as almost every driver loved having them on his car. This article isn't about history of F1 aero development, but a historic introduction is always preferred.
What is it that makes these wings create a force out of thin air? You’ve probably heard about air travelling faster on the upper side of an airplane wing to meet with the air from bellow, as upper side is a bit longer. This difference in speed creates a pressure difference as well and now you have a force all of a sudden. The first part is wrong, air on top of the wing is moving much faster than air bellow the wing and two particles having been together before being split by the wing will actually never meet again.
Invert your wing and angle of attack and you create downforce instead of lift. With this downforce, you create higher vertical loads on tyres which creates more friction between the tyre and the road, which allows you to go faster trough corners and counter the centrifugal force. Wings are all well and nice, but unlike airplanes – race cars can’t afford to have big-span wings and this has led to a design with two narrower wings – front and rear. Other than generating downforce, wings need to generate it in a balanced way, so the car wouldn’t have very different handling characteristics at different speeds. Very simply, downforce is proportionate to air velocity squared, so if you create downforce only on rear or front end of the car it will have even more under steer or over steer respectfully and this would make a car very tough to handle. You need an overall aerodynamic balance – in other words your centre of pressure (CoP) needs to be very close to car’s centre of gravity (CoG).
What is also affecting downforce generation? Surface of your wing (or any surface exposed to air flow) and lift coefficient, both directly proportionate. With bigger surface comes more downforce, as does with higher lift coefficient. Many factors influence lift coefficient, but two most important are wing camber and angle of attack. Thickness is somewhat less important, but it is also influential, as is the position of maximum thickness and maximum camber of the airfoil.
Some things became very obvious to designers – surface area of wings isn’t that big (low aspect ratio wings are very ineffective and create a lot more drag for downforce) as allowed by rules – from first rule set to manage wing design to latest Formula 1 rule set wings have been constrained in design (namely wing span, chord and the overall position of this type of bodywork). The usual bodywork of the car, however, has a very large surface. Soon, designers started design the bottom of the car to produce large amounts of downforce and this is still the biggest source of overall F1 car downforce.
Floor design has moved from ground effect design to flat-floor design with diffuser at the rear. Ground effect designs featured specific shapes of the floor that produced very large amounts of downforce. These shapes were very similar to upper side of a typical airfoil, but with some differences. There were a lot of specific developments aimed at improving aerodynamic performance of ground effect floors, but one very unfortunate aspect of these floors remained – if they choked (started letting more air in than they can force out from under them) they stalled (flow separation occurs and turbulent air lowers the downforce) and this had disastrous effects in mid-corner. Cars used to fly straight over the gravel into protective barriers at very high speeds. Eventually, this design was outlawed and flat floor design was introduced in 1983.
As seen on figure 5, second generation of ground effect floors had some distinctive marks – a large flat part at the front where most of the downforce was created and a down curve at the back to allow the rear wing to sit in cleaner air and produce more downforce. It is also worth mentioning the small front wing. Small size had a cause-effect loop in its design – the smaller the wing and the lower the angle of attack, the less upwash it causes and this allows for more effective floor. The benefit is a very small drag penalty of front wing and aerodynamic balance is good because ground effect floor creates the most downforce in front of the car’s CoG, thus balancing the rear wing.
Flat floor cars are mandatory since 1983; the first championship winning cars was Brabham BT52, driven by Nelson Piquet. BT52 didn’t feature a diffuser, but Lotus 94T did already in the first year following ground effect floor ban. However, Lotus used the 92 and 93T in 1983 as well, which featured diffuser-like extensions on the floor. In this season, only 94T scored points for Team Lotus.
Although same principles are at play with diffuser and ground effect floor, they work in a very different way. In general, diffusers and flat floor are less effective than ground effect floors at producing downforce, but they are more efficient – meaning they produce less drag for the same amount of downforce. In latest specification of F1 cars (from season 2017 onwards) this is very important, as cars are reaching very high speeds in corners and cars with less drag can accelerate faster trough a corner even if another car creates slightly more downforce.
When you look at 2018 F1 cars, you will notice a huge number of aerodynamic appendages all over them. Most of these are aimed at making the floor and diffuser work as hard as possible, as more than 50% of total downforce now comes from the floor of the car. The more air moves under the car, the faster it goes and the lower the pressure under the floor. This affects both front wing and rear wing in a very good way, improving their aerodynamic performance as well. For years now, F1 cars are so sophisticated in terms of aero that entire aero package has to work in harmony – in the straight and in the corner. Designers cannot just bolt a bigger front wing and hope to solve under steering issues. In fact, a smaller angle of attack on the wing may lead to more air entering the floor improving its performance, improving the front wing performance as well and thus solving some under steering problems of the car.
2018 Formula 1 cars have several important aerodynamic areas:
- front wing
- barge board area
- side pod area
- rear wing
- misc (brake ducts, nose cone area, engine cover and side pods etc)
All of these will have its own article in this upcoming series of F1 aero articles on F1 Technical. Before those, there will be explanations of general aerodynamic principles and some specific principles in race cars and F1 as well. If you are a keen fan of F1 tech, you will want to stay tuned for those.