Slipstream - Drafting

Drafting

Slipstreaming, also known as drafting is important in a number of contexts, including:

• In fast bicycle races, competitors attempt to use one another's slipstream, or "draft", breaking out to overtake the leader only at the last possible moment. In recreational cycling, on the other hand, members of a group can take turns at the leading position, enabling one another to rest a little. In a group of cooperative cyclists with sufficient group-riding skill, stronger members can spend more time leading to give weaker riders more rest, enabling riders of different strengths to ride together, at least on relatively flat routes. On inclines, however, the benefit of drafting is relatively less, as speeds are slower and the cyclist's primary effort is working against gravity. The flat or hilly nature of a route has consequences for both racing and recreational cycling, with different types of routes favouring different types of cyclists.
• Following in the slipstream of another motor vehicle, or "drafting", allows for significantly improved fuel efficiency due to reduced atmospheric drag. Truck convoys are a common example, travelling highways in a single-file queue several vehicles long. Auto racing drivers also draft in order to conserve fuel, the better to gain competitive advantage by reducing the frequency of fuel stops or, more often, to reach a higher speed before pulling out to attempt to overtake another driver.
• A related effect used for lift rather than drag reduction is vortex surfing for airborne objects. The extended formations (V formation) or "skeins" in which many migratory birds (especially geese) fly enable the birds (except, of course, the bird at the front) to use vortex surfing to take advantage of one another's vortices. Other birds (for example cormorants) that typically fly in close formation, even on short journeys, are probably also exploiting this effect. Using wingtip vortices has been tested for aircraft, and could save 10%-29% fuel.