While we tend to think that...
While we tend to think that round is a smooth shape that would offer a good aero surface, it is clear that it is not. The airflow is very turbulent as it flows past the tube. This has a greater coefficient of drag. The turbulence is even greater as air flows past an open cage, as on a Sprint Car.
We have all seen the huge wings on the tops of Sprint Cars and the large side boards that the Late Model racers utilize. These aerodynamic devices are used to help keep the cars stuck to the track as they rotate through the corners. The Sprint Car has a wing that has the same general shape used on an airplane, except it is mounted upside down. So, instead of creating lift, it is creating downforce. In all actuality, it is still creating lift, but the force is in the opposite direction. The principle is the same, but we pay a price for generating that downforce-we get a great deal of drag. Consequently, it takes some very expensive engines to push the cars down the track. My dad always told me there is no such thing as a free lunch.
Remember, in race car design and application, we are not trying to create lift. We are creating downforce with very little drag. That is the key-low drag and high downforce. This should be your new mantra.
Laminar Flow: The air is moving in smooth layers around our car. In this case, the air can be likened to a gently curving country road. The curves are smooth and gentle, so it is not necessary to slow down as you progress through them. That is very much like laminar flow. The illustration is somewhat simplistic, but you get the general idea. Air takes less energy to move over smooth surfaces. That is why the bodies on race cars that race at high speeds are so sensitive to small changes in shape, such as the changes caused by contact (e.g., rubbing and bumping).
With the addition of a small...
With the addition of a small fairing to the tube, the airflow across the tube is much smoother. Consequently, the drag numbers go down and it takes less power to push this faired tube through the air.
Turbulent Flow: The flow is random in its shape. The air forms currents and erratic flow patterns that are contrary to the majority of the flow. The flow is disordered. Many times, this is the type of flow that our head porter brethren are trying to achieve. In actuality, they are trying to reach a balance between laminar and turbulent flow through the ports.
Boundary Layer: The molecules of air are not moving in this layer, which is usually adjacent to the surface of the body moving through the air. The depth of the boundary layer is dependent on several factors: the density or viscosity of the gas, the finish of the surface moving through the fluid, and the compressibility of the fluid (which in our case is air). For our uses, the thinner the boundary layer the better. A larger boundary layer impedes the progress of the air more than a thinner boundary layer. This is the reason that it is so important to keep the surface of the car as smooth as possible. On dirt, this is a great reason to keep the car as clean as possible between heats. A clean car not only makes your sponsor's logo more visible to the fans, it also makes a difference in performance.
Frontal Area: This is the first portion of the car the air contacts. It's a cross section of the frontal portion of the car. Visualize your race car backed up to a garage door. There are floodlights shining on the front end, and the shadow that the car casts against the garage door is the frontal area.
Notice how aero dirty the...
Notice how aero dirty the front of this Sprint Car is. The shock, axle, roll bars, brakes, and so on are hanging out in the wind. Rules may prevent some changes, but whatever we can do to clean up our cars in an aero sense would be worth it.
Anything within the structure and limitations of the rules that you can do to reduce the frontal area will improve the performance of the vehicle. If you can massage the roof line on your Modified or Stocker within the framework of the rules, it is a positive. If your racing division uses templates, make sure that your car fits the templates but is as close a fit as possible.
Racers tend to be very vocal when it suits them. There are many complaints about the cost of racing, and there is always someone or something to blame for the cost of speed. It would seem that if they could buy a few tenths for little or no money, it would generate some buzz. If you arrive early at any short track across the country and walk through the pits, you can see many racers giving away speed without even knowing it.
Ill-fitting body panels, large bolt heads in the air stream, exposed tubes, spoilers that are too large or have nothing to do with making the car go faster, suspension parts just hanging into the air stream, and tires sticking out past the edges of the fenders are all just waiting to rob you of the speed you work endless hours to achieve. Granted, many of these appendages are a required part of the car and serve a purpose, but some further thought could go into how these parts are integrated. It would be nice if, in addition to serving a valid function, they did not add to the overall drag coefficient of the car.