Atlas F1   Taking the Lid Off F1

Formula One Technical Analysis

  by Will Gray, England

Atlas F1 presents a series of articles by certified engineer Will Gray, that investigates in greater depth all the technical areas involved in design, development, and construction of a Formula One car.

7c. Underfloor aerodynamics

Why is an F1 car shaped the way it is? It's not because the Technical Director likes the curves (although to some extent it can be!), it's because that is the shape that, with the resources the team has to explore the area, is the most efficient at getting through the air obstacle. Rules and regulations help to clone the cars, with 'no-go boxes' stipulated all around the car - rules declaring where bodywork can and can't exist, but ingenious designers can always spot loopholes in these!

Car side-on, showing airflow from front to rear

The flow of air underneath the car is one of the most important areas of the aerodynamic design. Air travels under the nose and the underside of the front chassis to the chin, which splits the air between that which travels through the sidepods for cooling, and that which goes under the car's floor. At the end of the floor, the air meets the diffuser, which returns it to the outer airstream. This route will now be described in more detail.

The Nose and Chin:
Chin splitting air into sidepods In 1990, Tyrrell, often the innovators in F1 design, came up with a revolutionary high nose - contrary to the low nose trends of the time. The 019 slipped into the F1 field with some interest, but at the time it wasn't clear that the design would change the look of the F1 car for at least the next ten years.

The raised nose - which when it first came out looked like a handlebar mustache - allows the air to flow, undisturbed, to an air splitter (the chin) positioned under the cockpit, at the start of the floor. Before, the front chassis and nose ran flat to the floor, with the aim of obtaining downforce from this area. Instead, Tyrrell saw that by moving these obstacles out of the way, better airflow to the floor created more downforce. The nose was raised, the front wing suspended on pylons, and the front of the chassis was smoothly curved from the high nose down to the chin at floor level. The chin, shown in the diagram, is a semi-circular scolloped face, with a flat, horizontal surface sticking out underneath it. The face guides the undisturbed air around and under the sidepods, and the flat surface prevents the air from being encouraged to go anywhere else. The current school of designers are always looking for more air under the floor, as it is here that the greatest and most efficient downforce can be produced - the nose is now something they want to get out of the way.

Front Chassis:
Jean Alesi at Loews in his Tyrrell 019 In 1999, every car in the field has some kind of raised nose, but these have been honed from the Tyrrell Original, to provide very different interpretations of the same thing. It is interesting to see that the McLaren (the most victorious car of recent times), has a relatively low nose. This confirms the view of many designers that the raised nose is not so important, and that what is, is the raised front chassis - the area behind the nose, but in front of the driver, and the entrance to the chin. By curving the chassis up from behind the nose, then back down to the chin in a slight banana shape, the designer can get clean air to the floor without having too high a nose. However, the Jury is still out on this issue!

This flat section, close to the ground, is where most downforce is obtained. However, it is not, in itself, a magic surface. It works in the manner of a duct, and requires good inflow and outflow - obtained through good chin and diffuser design. In a duct, there exists a mouth (entrance), a throat (main body of the duct), and a diffuser (exit). The air accelerates in through the mouth, continues to speed up in the throat, and is decelerated to return to the speed of the free-stream flow in the diffuser. On an F1 car, the lower leading edge of the sidepod (coming off the edge of the chin) acts as the mouth, and the flat bottom is the throat. As explained previously, high speed air has low pressure, so the air under the car works to suck the car down. The size of the floor, however, is limited to a maximum width in the rules, but teams tend to vary its length.

The closer the floor is to the track, the more downforce it will produce due to ground effect, so to reduce the downforce created by the floor, the rulemakers stipulate that it is raised from the track. This is enforced by a plank of wood (yes, wood!), positioned underneath the car at cockpit width, running from the chin to the rear.

The Nose and Chin:
Diffuser airflow The better the diffuser works, the more efficient downforce you have - it is an important area of the 'duct' system. Forming an upsweep from the floor to just under the rear wing, the diffuser decelerates the air towards its original speed. Its design includes vertical fences, some of which are curved, some stepped, and some angled, but all are developed through constant tweaking and evolution in the wind tunnel. The basic job of these fences is to keep apart the many different types of flow found at the rear end of an F1 car - areas of low pressure air due to the rear wheels, and the rear wing, and the air coming under the floor. All these different air flows have different energy levels and different speeds, and their separation makes them easier to deal with.

The main aim in diffuser design is to take it to its limit, and not beyond. If the slope of the diffuser is too steep, we will have flow separation (the flow will no longer follow the surface), causing extra drag. This may not occur in all areas, however. In the outer edges of the diffuser, the air, which has traveled under the car along the outer part of the floor, will have mixed with, and been slowed by, air from outside the floor. Towards the centre, however, the air flows faster, as no extra air has reached that area. For this reason, the diffuser consists of varying slopes, depending on the curve the air can follow before separation.

With rear wing elements helping suck the air from under the car, and the close-packed nature of the car in this area, it tends to be knowledge-inspired trial and error development which changes the shapes of the diffuser - to get a good one takes a lot of time and effort...and a touch of luck!

Previous Parts in this Series: Parts 1 & 2 | Part 3 | Part 4A | Part 4B | Part 4C | Part 5A | Part 5B | Part 6A | Part 6B | Part 7A | Part 7B-1 | Part 7B-2

Will Gray© 2000 Kaizar.Com, Incorporated.
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