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.

7b1. A lesson in Aerodynamics - Drag

The two main areas in aerodynamics are drag - which slows the car down, and downforce - which pushes the car onto the track. The aerodynamicist's aim is to maximize the downforce whilst minimizing the drag, but as it will become apparent, this ideal can never be achieved and a compromise must be met. We will start by looking at drag.

Aerodynamics is a confusing concept - how can you get a force when there's nothing there?! Well, a simple explanation can clear up this confusion, and make things much more understandable.

Imagine driving a car through a tank of treacle - it would slow you down a bit! Now imagine driving it through a big tank of water - you would still slow down, but not as much. Now consider a tank of air. Nothing to slow you down there? Well, actually there is! All liquids and gases are made up of particles which can slide over each other.

Pointed vs. Rounded vs. Teardrop Some particles are more sticky than others, and cannot slide as easily. This is viscosity. When the fluid or gas (be it treacle, water, or air) moves over a surface, the layer of particles closest to that surface sticks to it. The layer above this one slides over, but gets slowed down by the non-moving particles on the surface. The layer above these is also slowed, but not so much. As the layers get further from the surface, they slow less and less until they flow at the freestream (main airflow) speed. This area of slow speed, called the Boundary layer, appears on every surface, and causes one of the three types of drag - called Skin Friction Drag.

The force required to shift the molecules out the way creates the second part of the drag - called Form Drag. In aerodynamics, size does matter! Although you can't feel it, pushing the base of a saucer through the viscous air is easier than pushing a dinner plate through, simply because there are more molecules to shift with the larger dinner plate than the saucer. It is the same with the frontal area of a car (the area of the car you see when you look at it head on). The smaller the frontal area, the smaller the area of molecules it has to shift, and the easier it is. With less engine effort being taken up in moving the air, more will go into moving the car along the track, and for a given engine power, the car will travel faster.

Unfortunately, it isn't as simple as that. The shape of the object is also important, as it determines how easily the molecules can be shifted. Air likes to follow a surface, so pushing the flat surface of a plate through the air will be harder than pushing through a curved bowl with the same frontal area. The air is encouraged to roll around the sides of the bowl, but it will get stuck on the flat surface of the plate. Researchers of aerodynamics have found the 'teardrop' shape to be most efficient in getting through the air - round at the front, and pointed at the back. This comes as a surprise to most, as it seems obvious that it would be easier to pierce through the air with a pointed object rather than one which is fat and round. And so we come to the discussion of separation.

Schumacher in his Ferrari F399When air is asked to follow a curve (or a change of direction), as long as it is shallow, it won't have any trouble. However, when the curve is quite sharp, or the direction change sudden (which is the case when it meets a sharp pointed object), the air will separate from the surface, as it doesn't have the energy to follow it. This situation is undesired because the boundary layer will be larger, and so will slow the air in front, basically acting as a barrier to oncoming air - just like a solid surface would. So having a point supposedly piercing through the air actually increases the drag!

So a round shape is ideal aerodynamically, right? Wrong! With a ball moving through the air, the air initially follows the curve of the ball as it grows - the air finds this easy. However, when it passes the maximum radius of the ball, it must continue to follow the surface which is now decreasing in size. This, for the air, is more difficult, and soon after the point of maximum radius, it will give up! It will become detached from the surface, and the air will become turbulent.

This turbulent air swirls around randomly, and is low in pressure compared to the freestream air, so creates a suction force in the opposite direction to the ball's motion, slowing it down. With the previously mentioned teardrop shape, the air follows the frontal curve, similar to the ball, but where it would break away with the round ball, the teardrop offers the air a curve with a slope it can cope with. It follows this curve, and leaves the object cleanly, causing much less drag. An example of the use of the teardrop shape is in suspension members, which if simply round, would create far more drag.

The final type of drag is called Induced Drag. This comes as an unwanted but irremovable product of downforce, and is why it was stated earlier that the aerodynamicist's dream of maximum downforce with minimum drag is just that! More will be explained in the next section, however, and for now simply accept it exists as the third type of drag.

These three drags add up to create an annoying problem for the vehicle designer! The more drag a vehicle has, the harder its engine must work to move it along at the same speed. However, with the ever increasing power of engines, high speeds can be attained even with lots of drag, and this is why the aim of the F1 designers is, first and foremost, to obtain downforce and worry about drag later.

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

Will Gray© 2000 Kaizar.Com, Incorporated.
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