Editing Lift-induced drag (section)

==Explanation==
[[Image:Induce drag downwash.png|right|thumb|400px|Induced drag is related to the angle of the induced [[downwash]] in the vicinity of the wing. 
The grey vertical line labeled "L" is the force required to counteract the weight of the aircraft. The red vector labeled "L<sub>eff</sub>" is the actual lift on the wing; it is perpendicular to the effective relative airflow in the vicinity of the wing. The lift generated by the wing has been tilted rearwards through an angle equal to the downwash angle in three-dimensional flow. The component of "L<sub>eff</sub>" parallel to the free stream is the induced drag on the wing.<ref>Hurt, H. H. (1965) ''Aerodynamics for Naval Aviators'', Figure 1.30, NAVWEPS 00-80T-80</ref><ref name="Clancy">[[Laurence Clancy|Clancy, L.J.]] (1975) ''Aerodynamics''. Pitman Publishing Limited, London. {{ISBN|0-273-01120-0}}</ref>{{rp|Fig 5.24.}}<ref>Kermode, A.C. (1972). ''Mechanics of Flight'', Figure 3.29, Ninth edition. Longman Scientific & Technical, England. {{ISBN|0-582-42254-X}}</ref><ref name="McLean">{{cite conference |last=McLean |first=Doug |date=2005 |title=Wingtip Devices: What They Do and How They Do It |conference=2005 Boeing Performance and Flight Operations Engineering Conference |url=http://www.smartcockpit.com/docs/Wingtip_Devices.pdf }}</ref>{{rp|4.4|quote=While the air more than about one wingspan ahead of the wing is essentially undisturbed, the general flow pattern of Figure 3.1 reaches practically full strength at a distance of about one wingspan behind the wing and generally persists over long distances downstream. At the location of the wing itself, the flow pattern has reached roughly half of its maximum strength, and the wing is flying through air that is already moving generally downward between the wingtips. Thus the wing can be thought of as flying in a downdraft of its own making. Because of the apparent downdraft, or "downwash," the total apparent lift vector is tilted backward slightly. It is the backward component of the apparent lift that is felt as induced drag.}}]]

The total [[aerodynamic force]] acting on a body is usually thought of as having two components, lift and drag. By definition, the component of force parallel to the oncoming flow is called '''drag'''; and the component perpendicular to the oncoming flow is called '''lift'''.<ref name="Anderson">{{cite book |last1=Anderson |first1=John D. Jr. |title=Fundamentals of aerodynamics |date=2017 |publisher=McGraw-Hill Education |location=New York, NY |isbn=978-1-259-12991-9 |page=20 |edition=Sixth}}</ref><ref name="Clancy"/>{{rp|Section 5.3}} At practical [[Angle of attack|angles of attack]] the lift greatly exceeds the drag.<ref>[[Ira H. Abbott|Abbott, Ira H.]], and Von Doenhoff, Albert E., ''Theory of Wing Sections'', Section 1.2 and Appendix IV</ref>

Lift is produced by the changing direction of the flow around a wing. The change of direction results in a change of velocity (even if there is no speed change), which is an acceleration. To change the direction of the flow therefore requires that a force be applied to the fluid; the total aerodynamic force is simply the [[Newton's laws of motion#Third law|reaction force]] of the fluid acting on the wing.

An aircraft in [[slow flight]] at a high angle of attack will generate an aerodynamic reaction force with a high drag component. By increasing the speed and reducing the angle of attack, the lift generated can be held constant while the drag component is reduced. At the optimum angle of attack, total drag is minimised. If speed is increased beyond this, total drag will increase again due to increased [[profile drag]].