Drag

The aerodynamic resistance experienced as a solid object travels trough the air.
The remarkable speed of the F1 racecar is achieved from the careful combination of its powerful engine and expertly crafted aerodynamic body features. In the early years of F1 design, the engine was the primary variable in determining the racing success of a car. Applicable engine technology had far exceeded the maturity of vehicle aerodynamics.

Those historic years embodied a simple algorithm. Speed was nearly a direct function of horsepower. Although still improving almost annually, engine performance levels among the cars of each racing season today have comparable performance – record speed achievements now hinge on a different design issue - aerodynamics and drag plays a major role.
F1 aerodynamics engineer, Will Gray, has noted that "Top speed is determined other factors (car weight, fuel strategy, and good low-end engine power), but the main factor which separates the victors from the valiants in this area is aerodynamic performance – too much drag and you're pulling unvanted air along with you.

 

One form of drag occurs as air particles pass over a car's surfaces and the layers of particles closest to the surface adhere. It's known as Boundary layer drag or Skin Friction Drag.
The layer above these attached particles slides over them, but is consequently slowed down by the non-moving particles on the surface. The layers above this slowed layer move faster. As the layers get further away from the surface, they slow less and less until they flow at the free-stream speed.
The area of slow speed, called the boundary layer, appears on every surface, and causes one of the three types of drag.

The force required to shift the molecules out of the way creates a second type of drag, Form Drag. Due to this phenomenon, the smaller the frontal area of a vehicle, the smaller the area of molecules that must be shifted, and thus the less energy required to push through the air. With less engine effort being taken up in the moving air, more will go into moving the car along the track, and for a given engine power, the car will travel faster.

 

Another factor that plays a role in aerodynamic efficiency is the shape of the car's surfaces. The shape over which air molecules must flow determines how easily the molecules can be shifted. Air prefers to follow at surface rather than to separate from one. Interestingly, researchers of aerodynamics have found the 'teardrop' shape, round at the front and pointed at the back, to be most efficient at propelling through air while providing a suitable surface for the air to easily move across. With this shape there is little or no separation. It is important to note that sharp frontal areas, rounded ends, sharp curves or sudden directional changes in a shape should be avoided since they tend to cause separation, which increases drag.

 

 

Another type of drag is Induced Drag. It is noted as such because it is caused by or "induced" by the lift on the wings. Induced drag is an unfavorable and unavoidable byproduct of lift (or downforce). You can't do much about induced drag, since you wouldn't have "lift" without it. It occurs on wings of standard or inverted position. In fact, the potential of displaying induced drag exists for all bodies that exhibit opposite pressures on their top and bottom surfaces. Being that air prefers to move from high to low-pressure regions, air from low-pressure regions has a tendency to curl downward around the ends of a F1 car wings, for example. It travels down from the high-pressure region to the low-pressure region on the bottom of the wing (oposite direction in case of airplane wings) and collides with moving low-pressure air. Wingtip vortices are a result of this situation. Looking from the tail of the airplane, the vortices will circulate counterclockwise from the right wingtip and clockwise from the left wingtip because on airplane wing high pressure area is below the wing. In case of racing car, high pressure area is on the top of the wing, and vortices will circulate in oposite direction. The greater the size of the vortices, the greater the induced drag.

These vortices occur on both airplane wings and F1 car wings even though end plates may be used to reduce this type of drag . It should be noted that the kinetic energy of these turbulent air spirals acts in a direction that is negative relative to the direction of travel intended. In the case of induced drag on F1 cars, the engine must compensate for the losses created by this drag.

A rectangular wing produces much more severe wingtip vortices than a tapered or elliptical wing, therefore many modern airplane wings are tapered. Typically, straight wings produce between 5–15% more induced drag than an elliptical wing. Some early aircrafts and some sport car wings and spoilers has fins mounted on the tips of the wing which served as endplates. More recent aircraft have wingtip mounted winglets or wing fences to oppose the formation of vortices. Designs such as winglet, wing fence , modified wing tip, etc all reduce induced drag. But there is not a system invented yet to prevent it completely.

Understanding the relationship between speed and drag is important in calculating maximum endurance and the range of the airplane or racing car. When drag is at a minimum, power required to overcome drag is also at a minimum. 

 

Vortex drag is product of Induced drag. It can be created by both lifting and non lifting bodies (usually of the bluff variety, ex. road vehicles, airships). Vortices are released during flow separation and trail downstream to form structured or unstructured wake patterns.

 

There is another drag tipe very preset in car racing, and discused, especialy in F1 racing. Interference drag is the effect of the interference of one body on the aerodynamics of a second body. The interference drag is a system drag that is present even in absence of viscous effects (ideal fluid) and non lifting conditions. Since interference occurs in many practical situations interference drag is a separate topic.

The F1 racecar is a complicated aerodynamic system – composed of skin friction, form and induced drag. Resultantly, aerodynamicists typically find it sufficient to estimate an overall coefficient of drag for these cars. The following equation, which incorporates the effects of all three drag types, is used to determine this data.

F = 0.5CdAV2, where is F - Aerodynamic drag Cd- Coefficient of drag D- Air density A- Frontal area V- Object velocity

 

Interestingly, modern F1cars are reported to have Cd values of about 0.85 with corresponding CdA[m2] values near 1.2.1. These values are approximately tiple of those for the modern road car, and only a bit higher then typical bus. This is primarily due to three reasons.
The first is that regulations specify features that deter from the ability of a designer to achieve relatively low drag coefficients (i.e. open cockpits and running exposed wheels).
The second reason is likely due to be the fact that F1 cars rely on a balance between drag and downforce in which drag is often sacrificed for necessary downforce. In order to make up for the speed losses due to drag, engine power is increased if possible. Lastly, unlike family sedans, low fuel consumption is not a paramount concern. Therefore, drag coefficients are allowed to be somewhat large, especially since the importance of other factors (i.e. downforce) takes priority.

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