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A vortex generator ( VG) is an aerodynamic device, consisting of a small usually attached to a lifting surface (or airfoil, such as an aircraft) or a rotor blade of a wind turbine. Wind Turbine Vortex Generators , UpWind Solutions. VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a vortex,Peppler, I.L.: From The Ground Up, page 23. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996. which, by removing some part of the slow-moving boundary layer in contact with the airfoil surface, delays local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators, , and .
Vortex generators are positioned obliquely so that they have an angle of attack with respect to the local airflow in order to create a tip vortex which draws energetic, rapidly moving outside air into the slow-moving boundary layer in contact with the surface. A turbulent boundary layer is less likely to separate than a laminar one, and is therefore desirable to ensure effectiveness of trailing-edge control surfaces. Vortex generators are used to trigger this transition. Other devices such as , leading-edge extensions, and leading-edge cuffs,A drooped leading edge presents a "vortex-producing discontinuity", in "Spin Resistance Development for Small Airplanes", SAE paper 2000-01-1691 also delay flow separation at high angles of attack by re-energizing the boundary layer.
Examples of aircraft which use VGs include the ST Aerospace A-4SU Super Skyhawk and Symphony SA-160. For swept-wing transonic designs, VGs alleviate potential shock-stall problems (e.g., Harrier, Blackburn Buccaneer, Gloster Javelin).
Owners fit aftermarket VGs primarily to gain benefits at low speeds, but a downside is that such VGs may reduce cruise speed slightly. In tests performed on a Cessna 182 and a Piper Cherokee, independent reviewers have documented a loss of cruise speed of . However, these losses are relatively minor, since an aircraft wing at high speed has a small angle of attack, thereby reducing VG drag to a minimum.Psutka, Kevin, Micro-vortex generators, COPA Flight, August 2003Kirkby, Bob, Vortex Generators for the Cherokee 235, COPA Flight, July 2004
Owners have reported that on the ground, it can be harder to clear snow and ice from wing surfaces with VGs than from a smooth wing, but VGs are not generally prone to inflight icing as they reside within the boundary layer of airflow. VGs may also have sharp edges which can tear the fabric of airframe covers and may thus require special covers to be made.
For twin-engined aircraft, manufacturers claim that VGs reduce single-engine control speed (V speeds), increase zero fuel and gross weight, improve the effectiveness of ailerons and rudder, provide a smoother ride in turbulence and make the aircraft a more stable instrument platform.
In the US from 1945USA Civil Air Regulations, Part 3, §3.85a until 1991,USA Federal Aviation Regulations, Part 23, §23.67, amendment 23-42, February 4, 1991 the one-engine-inoperative climb requirement for multi-engine airplanes with a maximum takeoff weight of or less was as follows:
where is the stalling speed in the landing configuration in miles per hour.
Installation of vortex generators can usually bring about a slight reduction in stalling speed of an airplane and therefore reduce the required one-engine-inoperative climb performance. The reduced requirement for climb performance allows an increase in maximum takeoff weight, at least up to the maximum weight allowed by structural requirements. An increase in maximum weight allowed by structural requirements can usually be achieved by specifying a maximum zero fuel weight or, if a maximum zero fuel weight is already specified as one of the airplane's limitations, by specifying a new higher maximum zero fuel weight. For these reasons, vortex generator kits for many light twin-engine airplanes are accompanied by a reduction in maximum zero fuel weight and an increase in maximum takeoff weight.
The one-engine-inoperative rate-of-climb requirement does not apply to single-engine airplanes, so gains in the maximum takeoff weight (based on stall speed or structural considerations) are less significant compared to those for 1945–1991 twins.
After 1991, the airworthiness certification requirements in the USA specify the one-engine-inoperative climb requirement as a gradient independent of stalling speed, so there is less opportunity for vortex generators to increase the maximum takeoff weight of multi-engine airplanes whose certification basis is FAR 23 at amendment 23-42 or later.
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