Vortex generator
Small vanes that delay flow separation and improve control surface effectiveness.
A vortex generator (VG) is a small vane attached to a surface like an aircraft wing, a wind turbine blade, or even a vehicle's fuselage. As the surface moves through the air, the VG produces a vortex that pulls energetic air from outside into the sluggish boundary layer next to the surface. This process delays flow separation and stalling, making wings and control surfaces—such as flaps, ailerons, elevators, and rudders—more effective.
These devices are typically placed near the leading edge of an airfoil to keep airflow steady over trailing-edge controls. They are often rectangular or triangular, about as tall as the local boundary layer, and arranged in spanwise lines near the wing's thickest part. You can spot them on the wings and vertical tails of many airliners. By sitting at an angle to the local airflow, each VG creates a tip vortex that energizes the boundary layer, turning it turbulent. A turbulent boundary layer resists separation better than a laminar one, which helps trailing-edge controls work properly. Other devices, like vortilons or leading-edge cuffs, also re-energize the boundary layer to delay separation at high angles of attack. Aircraft such as the ST Aerospace A-4SU Super Skyhawk and Symphony SA-160 use VGs, and on swept-wing transonic designs like the Harrier, Blackburn Buccaneer, and Gloster Javelin, they help prevent shock-stall problems.
Many aircraft come with VGs from the factory, but aftermarket kits are available to improve short takeoff and landing (STOL) performance on light planes. Suppliers claim these kits lower stall speed, reduce takeoff and landing speeds, and boost the effectiveness of ailerons, elevators, and rudders, enhancing low-speed control and safety. For home-built or experimental aircraft, VGs are cheap and easy to install, but for certified planes, the certification costs can make the modification expensive. Owners mainly fit aftermarket VGs for low-speed benefits, though there is a downside: cruise speed may drop slightly. Tests on a Cessna 182 and a Piper PA-28-235 Cherokee showed a loss of 1.5 to 2.0 knots (2.8 to 3.7 km/h). This loss is minor because at high speed, the wing's small angle of attack reduces VG drag. On the ground, snow and ice can be harder to clear from wings with VGs, but the devices are not prone to inflight icing since they sit within the boundary layer.
- Cruise speed loss
- 1.5 to 2.0 kn (2.8 to 3.7 km/h)
- Noise reduction
- up to 2 dB
- One engine inoperative climb requirement
- 0.02(Vs0)^2 feet per minute
- Maximum takeoff weight threshold
- 6,000 lb (2,700 kg)
- Stalling speed threshold
- 70 miles per hour
Lore & Background
Vortex generators are most often used to delay flow separation and are placed on external surfaces of vehicles and wind turbine blades. On aircraft and wind turbine blades, they are usually installed close to the leading edge of the aerofoil to maintain steady airflow over control surfaces at the trailing edge. VGs are typically rectangular or triangular, about as tall as the local boundary layer, and run in spanwise lines near the thickest part of the wing. They can be seen on the wings and vertical tails of many airliners. Vortex generators are positioned obliquely to create a tip vortex that draws energetic outside air into the slow-moving boundary layer, triggering a transition to a turbulent boundary layer, which is less likely to separate. Other devices such as vortilons, leading-edge extensions, and leading-edge cuffs also delay flow separation at high angles of attack. Examples of aircraft using 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).
Reader's Guide
Vortex generators have significance in both original equipment and aftermarket installations. Many aircraft carry vane vortex generators from time of manufacture, but aftermarket suppliers sell VG kits to improve STOL performance of some light aircraft. Aftermarket claims include lower stall speed, reduced take-off and landing speeds, and increased effectiveness of ailerons, elevators, and rudders, improving controllability and safety at low speeds. For home-built and experimental kitplanes, VGs are cheap and cost-effective, but for certified aircraft, certification costs can be high. Owners fit aftermarket VGs primarily for low-speed benefits, though a downside is a possible reduction in cruise speed; tests on a Cessna 182 and Piper PA-28-235 Cherokee documented a loss of 1.5 to 2.0 kn. On the ground, it can be harder to clear snow and ice from wing surfaces with VGs, but VGs are not generally prone to inflight icing. VGs may have sharp edges that can tear airframe covers. For twin-engined aircraft, manufacturers claim VGs reduce single-engine control speed (Vmca), increase zero fuel and gross weight, improve aileron and rudder effectiveness, provide a smoother ride in turbulence, and make the aircraft a more stable instrument platform. Some VG kits for light twin-engine airplanes may allow an increase in maximum takeoff weight by reducing stall speed and thus the required one-engine-inoperative climb performance. After 1991, US certification requirements specify a climb gradient independent of stalling speed, reducing the opportunity for VGs to increase maximum takeoff weight. Most VG kits increase only takeoff weight, not landing weight, which is determined by structural considerations. Vortex generators have also been used on the wing underside of Airbus A320 family aircraft to reduce noise from airflow over pressure equalisation vents, with Lufthansa claiming a noise reduction of up to 2 dB.
Did You Know?
- Vortex generators are typically rectangular or triangular and about as tall as the local boundary layer.
- Tests on a Cessna 182 and Piper PA-28-235 Cherokee showed a cruise speed loss of 1.5 to 2.0 kn (2.8 to 3.7 km/h) with aftermarket VGs.
- Vortex generators on the wing underside of Airbus A320 family aircraft can reduce noise by up to 2 dB, according to Lufthansa.
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