From Encyclopedia Jr, free information reference for Kids
Drafting, or slipstreaming, is a technique in sports racing where competitors align in a close group in order to reduce the overall effect of drag or fluid resistance of the group. Especially when high speeds are involved, drafting can significantly reduce the average energy expenditure required to maintain a certain speed.
Drafting is usually to reduce wind resistance and is seen most commonly in bicycle racing, car racing, and speedskating though is occasionally used even in running. Some forms of triathlon allow drafting. Fluid resistance can also mean water resistance, however, and so drafting is sometimes seen in swimming as well, particularly in "open-water" swim events where competitors are not separated into distinct lanes.
In cycling, the main (largest) group of tightly packed cyclists in a race is called a peloton, while cyclists riding in straight-line formation, each (but the first) drafting behind the one in front of him, is called a paceline. Drafting can be cooperative, in which several competitors take turns in the lead position (which requires the most effort and energy consumption). Or, it can be competitive or tactical, where one competitor will try to stay closely behind another leaving him or her more energy for a break-away push to the finish line.
[edit] Drafting in nature
Cooperative fluid dynamics techniques like drafting are found in nature, as well. Flocks of geese and some other birds fly in a V formation that is believed to improve overall fluid dynamics, though not in the straightforward fashion of car racing, which involves close positioning in single file. Goose flocking is not fully understood, but probably involves the recovery of energy from vortices created by the leading birds' wingtips (see wingtip vortices). (For this reason, it may not meet some people's definition of drafting).
Other animals have been observed to use true drafting behavior reminiscent of auto racing or cycling. Lobsters, for example, are known to migrate in close single-file formation "lobster trains", sometimes for hundreds of miles.
[edit] Bump Drafting
Bump drafting is a tactic used in NASCAR races, it begins with standard drafting but the following car pulls up behind the lead car and bumps into the rear of it, pushing the lead car ahead, to maintain momentum. When done in side by side traffic on a straightaway this can assist the lead car in passing, and allows the following car to follow through. This tactic can destabilize the handling of the lead car, however, and if done roughly or in the wrong position (e.g. close to the entry of the turn) it can lead to a crash.
Bump drafting is most commonly used at the larger tracks of Talladega Superspeedway and Daytona International Speedway because a restrictor plate is used.
[edit] Simulation of Drafting
Computer simulation (Computational Fluid Dynamics or CFD) is increasingly being used to analyse drafting. It is important to understand the aerodynamic behaviour of a motor vehicle when drafting, for example if the rear car is too close to the front car, the air supply to its radiation will be reduced and there's a possibility of the engine overheating. Most motor sport aerodynamic analysis is performed using wind tunnel testing. This become difficult for drafting cases, if only because you need a very large wind tunnel. CFD, a kind of virtual wind tunnel, is used by race teams to understand the car's performance while drafting.
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