The Airco DH.9A was a British single-engined light bomber designed and first used shortly before the end of the First World War. It was a development of the unsuccessful Airco DH.9 bomber, featuring a strengthened structure and, replacing the under-powered and unreliable inline 6-cylinder Siddeley Puma engine of the DH.9 with the American V-12 Liberty engine. Colloquially known as the "Ninak", it served on in large numbers for the Royal Air Force following the end of the war, both at home and overseas, where it was used for colonial policing in the Middle East being retired in 1931. Over 2,400 examples of an unlicensed version, the Polikarpov R-1, were built in the Soviet Union, the type serving as the standard Soviet light bomber and reconnaissance aircraft through the 1920s; the DH.9A was planned as an improved version of the existing Airco DH.9. The DH.9 was a disappointment owing to its under-performing and unreliable engines, the DH.9A was to use a more powerful engine to resolve this.
As the Rolls-Royce Eagle engine used in the successful DH.4 was unavailable in sufficient quantities, the new 400 hp American Liberty engine was chosen instead. As Airco was busy developing the Airco DH.10 twin-engined bomber, detailed design was carried out by Westland Aircraft. The DH.9 was fitted with a strengthened fuselage structure. The first prototype flew in March 1918, powered by a Rolls-Royce Eagle as no Liberty engines were yet available; the prototype proved successful, with the first Liberty-engined DH.9A flying on 19 April 1918, deliveries to the Royal Air Force starting in June. By the end of the war, a total of 2,250 DH.9As had been ordered, with 885 being built by the end of the year. As it was decided that the DH.9A would be a standard type in the postwar RAF, the majority of outstanding orders were fulfilled, with 1,730 being built under the wartime contracts before production ceased in 1919. While the existing aircraft were subject to a programme of refurbishment, a number of small contracts were placed for new production of DH.9As in 1925–26.
These contracts resulted in a further 268 DH.9As being built. The new production and refurbished aircraft included batches of dual control trainers, as well as six aircraft powered by 465 hp Napier Lion engines, which were capable of a maximum speed of 144 mph; the Soviet Union built large numbers of an unlicensed copy of the DH.9A, the R-1. After the production of 20 DH.4 copies, followed by about 200 copies of the DH.9 powered by the Mercedes D. IV engine and a further 130 powered by the Siddeley Puma, a copy of the DH.9A powered by the M-5 engine, a Soviet copy of the DH.9A's Liberty, entered production in 1924. The United States planned to adopt the DH.9A as a replacement for the DH.4. Development work on the Americanization of the aircraft commenced at McCook Field in Ohio. Modifications included a new fuel system with increased fuel capacity, revised wings and tail surfaces, replacement of the Vickers machine gun on the port side of the British built aircraft with a Browning machine gun on the starboard side.
Plans called for Curtiss to build 4,000 modified aircraft, designated USD-9A. This order was cancelled with the end of the war and only nine were built by McCook Field and Dayton-Wright. One McCook aircraft was additionally modified with an enclosed, pressurised cockpit. In 1921, test pilot Lt. Harold R. Harris made the world's first high-altitude flight in a pressurised aircraft in the USD-9A at McCook Field in Dayton, Ohio; the DH.9A entered service in July 1918 with No. 110 Squadron RAF, moving to France on 31 August 1918 to serve with the RAF's Independent Air Force on strategic bombing missions. Its first mission was against a German airfield on 14 September 1918. A further three squadrons commenced operations over the Western Front before the Armistice, with 99 Squadron replacing DH.9s, while 18 Squadron and 216 Squadron replaced DH.4s. Despite the superior performance of the DH.9A over the DH.9, the DH.9A squadrons suffered high losses during their long range bombing missions over Germany.
Other squadrons flew coastal patrols from Great Yarmouth before the end of the year. The United States Marine Corps Northern Bombing Group received at least 53 DH-9As, commenced operations in September 1918. While the squadrons in service at the end of the First World War disbanded or re-equipped in the postwar dis-armament, the DH.9A continued in service as the RAF's standard light bomber, with 24 squadrons being equipped between 1920 and 1931, both at home and abroad. The first post war operations were in southern Russia in 1919, in support of the "White Army" against the Bolsheviks in the Russian Civil War. In September 1919, the RAF personnel were ordered leaving their aircraft behind. A squadron of DH.9As was deployed to Turkey in response to the Chanak Crisis in 1922, but did not engage in combat. The DH.9A was one of the key weapons used by Britain to manage the territories that were in its control following the collapse of the Ottoman Empire following the Great War. Five squadrons of DH.9As served in the Middle East carrying out bombing raids against rebellious tribesmen and villages.
An additional radiator was fitted under the fuselage to cope with the high temperatures, while additional water containers and spares were carried in case the aircraft were forced down in the desert, the DH.9A's struggling under heavier loads. Despite this the aircraft served with the Liberty engine being picked out for particular praise for its reliability in such harsh conditions; some DH
Unmanned aerial vehicle
An unmanned aerial vehicle known as a drone, is an aircraft without a human pilot onboard. UAVs are a component of an unmanned aircraft system; the flight of UAVs may operate with various degrees of autonomy: either under remote control by a human operator or autonomously by onboard computers. Compared to manned aircraft, UAVs were used for missions too "dull, dirty or dangerous" for humans. While they originated in military applications, their use is expanding to commercial, recreational and other applications, such as policing and surveillance, product deliveries, aerial photography and drone racing. Civilian UAVs now vastly outnumber military UAVs, with estimates of over a million sold by 2015. Multiple terms are used for unmanned aerial vehicles, which refer to the same concept; the term drone, more used by the public, was coined in reference to the early remotely-flown target aircraft used for practice firing of a battleship's guns, the term was first used with the 1920s Fairey Queen and 1930's de Havilland Queen Bee target aircraft.
These two were followed in service by the similarly-named Airspeed Queen Wasp and Miles Queen Martinet, before ultimate replacement by the GAF Jindivik. The term unmanned aircraft system was adopted by the United States Department of Defense and the United States Federal Aviation Administration in 2005 according to their Unmanned Aircraft System Roadmap 2005–2030; the International Civil Aviation Organization and the British Civil Aviation Authority adopted this term used in the European Union's Single-European-Sky Air-Traffic-Management Research roadmap for 2020. This term emphasizes the importance of elements other than the aircraft, it includes elements such as data links and other support equipment. A similar term is an unmanned-aircraft vehicle system, remotely piloted aerial vehicle, remotely piloted aircraft system. Many similar terms are in use. A UAV is defined as a "powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, can carry a lethal or nonlethal payload".
Therefore, missiles are not considered UAVs because the vehicle itself is a weapon, not reused, though it is unmanned and in some cases remotely guided. The relation of UAVs to remote controlled model aircraft is unclear. UAVs may not include model aircraft; some jurisdictions base their definition on weight. For recreational uses, a drone is a model aircraft that has first-person video, autonomous capabilities, or both; the earliest recorded use of an unmanned aerial vehicle for warfighting occurred on July 1849, serving as a balloon carrier in the first offensive use of air power in naval aviation. Austrian forces besieging Venice attempted to launch some 200 incendiary balloons at besieged city; the balloons were launched from land. At least one bomb fell in the city. UAV innovations started in the early 1900s and focused on providing practice targets for training military personnel. UAV development continued during World War I, when the Dayton-Wright Airplane Company invented a pilotless aerial torpedo that would explode at a preset time.
The earliest attempt at a powered UAV was A. M. Low's "Aerial Target" in 1916. Nikola Tesla described a fleet of unmanned aerial combat vehicles in 1915. Advances followed including the Hewitt-Sperry Automatic Airplane; this developments inspired the development of the Kettering Bug by Charles Kettering from Dayton, Ohio. This was meant as an unmanned plane that would carry an explosive payload to a predetermined target; the first scaled remote piloted vehicle was developed by film star and model-airplane enthusiast Reginald Denny in 1935. More emerged during World War II – used both to train antiaircraft gunners and to fly attack missions. Nazi Germany used various UAV aircraft during the war. Jet engines entered service after World War II in vehicles such as the Australian GAF Jindivik, Teledyne Ryan Firebee I of 1951, while companies like Beechcraft offered their Model 1001 for the U. S. Navy in 1955, they were little more than remote-controlled airplanes until the Vietnam War. In 1959, the U.
S. Air Force, concerned about losing pilots over hostile territory, began planning for the use of unmanned aircraft. Planning intensified after the Soviet Union shot down a U-2 in 1960. Within days, a classified UAV program started under the code name of "Red Wagon"; the August 1964 clash in the Tonkin Gulf between naval units of the U. S. and North Vietnamese Navy initiated America's classified UAVs into their first combat missions of the Vietnam War. When the Chinese government showed photographs of downed U. S. UAVs via Wide World Photos, the official U. S. response was "no comment". During the War of Attrition the first tactical UAVs installed with reconnaissance cameras were first tested by the Israeli intelligence bringing photos from across the Suez canal; this was the first time that tacti
Angle of attack
In fluid dynamics, angle of attack is the angle between a reference line on a body and the vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the oncoming flow; this article focuses on the most common application, the angle of attack of a wing or airfoil moving through air. In aerodynamics, angle of attack specifies the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is defined; the chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line; some authors do not use an arbitrary chord line but use the zero lift axis where, by definition, zero angle of attack corresponds to zero coefficient of lift. Some British authors have used the term angle of incidence instead of angle of attack.
However, this can lead to confusion with the term riggers' angle of incidence meaning the angle between the chord of an airfoil and some fixed datum in the airplane. The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases; as the angle of attack of a fixed-wing aircraft increases, separation of the airflow from the upper surface of the wing becomes more pronounced, leading to a reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. Cambered airfoils are curved such. A symmetrical wing has zero lift at 0 degrees angle of attack; the lift curve is influenced by the wing shape, including its airfoil section and wing planform. A swept wing has a lower, flatter curve with a higher critical angle; the critical angle of attack is the angle of attack. This is called the "stall angle of attack".
Below the critical angle of attack, as the angle of attack decreases, the lift coefficient decreases. Conversely, above the critical angle of attack, as angle of attack increases, the air begins to flow less smoothly over the upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, the upper surface separation point of the flow moves from the trailing edge towards the leading edge. At the critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum lift coefficient; as angle of attack increases further, the upper surface flow becomes more separated and the lift coefficient reduces further. Above this critical angle of attack, the aircraft is said to be in a stall. A fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed; the airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor, the center of gravity of the aircraft and other factors.
However the aircraft always stalls at the same critical angle of attack. The critical or stalling angle of attack is around 15° - 20° for many airfoils; some aircraft are equipped with a built-in flight computer that automatically prevents the aircraft from increasing the angle of attack any further when a maximum angle of attack is reached, regardless of pilot input. This is called the'angle of attack limiter' or'alpha limiter'. Modern airliners that have fly-by-wire technology avoid the critical angle of attack by means of software in the computer systems that govern the flight control surfaces. In takeoff and landing operations from short runways, such as Naval Aircraft Carrier operations and STOL back country flying, aircraft may be equipped with angle of attack or Lift Reserve Indicators; these indicators measure the angle of attack or the Potential of Wing Lift directly and help the pilot fly close to the stalling point with greater precision. STOL operations require the aircraft to be able to operate close to the critical angle of attack during landings and at the best angle of climb during takeoffs.
Angle of attack indicators are used by pilots for maximum performance during these maneuvers since airspeed information is only indirectly related to stall behaviour. Some military aircraft are able to achieve controlled flight at high angles of attack, but at the cost of massive induced drag; this provides the aircraft with great agility. A famous military example is sometimes thought to be Pugachev's Cobra. Although the aircraft experiences high angles of attack throughout the maneuver, the aircraft is not capable of either aerodynamic directional control or maintaining level flight until the maneuver ends; the Cobra is an example of supermaneuvering as the aircraft's wings are well beyond the critical angle of attack for most of the maneuver. Additional aerodynamic surfaces known as "high-lift devices" including leading edge wing root extensions allow fighter aircraft much greater flyable'true' alpha, up to over 45°, compared to about 20° for aircraft without these devices; this can be helpful at high altitudes where slight maneuvering may require high angles of attack due to the low density of air in the upper atmosphere as well as at low speed at low altitude where the margin between level flight AoA and stall AoA is reduced.
The high AoA capability of the aircraft provides a buff
Stall (fluid dynamics)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs; the critical angle of attack is about 15 degrees, but it may vary depending on the fluid and Reynolds number. Stalls in fixed-wing flight are experienced as a sudden reduction in lift as the pilot increases the wing's angle of attack and exceeds its critical angle of attack. A stall does not mean that the engine have stopped working, or that the aircraft has stopped moving—the effect is the same in an unpowered glider aircraft. Vectored thrust in manned and unmanned aircraft is used to maintain altitude or controlled flight with wings stalled by replacing lost wing lift with engine or propeller thrust, thereby giving rise to post-stall technology; because stalls are most discussed in connection with aviation, this article discusses stalls as they relate to aircraft, in particular fixed-wing aircraft. The principles of stall discussed here translate to foils in other fluids as well.
A stall is a condition in aerodynamics and aviation such that if the angle of attack increases beyond a certain point lift begins to decrease. The angle at which this occurs is called the critical angle of attack; this critical angle is dependent upon the airfoil section or profile of the wing, its planform, its aspect ratio, other factors, but is in the range of 8 to 20 degrees relative to the incoming wind for most subsonic airfoils. The critical angle of attack is the angle of attack on the lift coefficient versus angle-of-attack curve at which the maximum lift coefficient occurs. Stalling is caused by flow separation which, in turn, is caused by the air flowing against a rising pressure. Whitford describes three types of stall, trailing-edge, leading-edge and thin-aerofoil, each with distinctive Cl~alpha features. For the trailing-edge stall separation begins at small angles of attack near the trailing edge of the wing while the rest of the flow over the wing remains attached; as angle of attack increases, the separated regions on the top of the wing increase in size as the flow separation moves forwards and this hinders the ability of the wing to create lift.
This is shown by the reduction in lift-slope on a Cl~alpha curve as the lift nears its maximum value. The separated flow causes buffeting. Beyond the critical angle of attack, separated flow is so dominant that additional increases in angle of attack cause the lift to fall from its peak value. Piston-engined and early jet transports had good stall behaviour with pre-stall buffet warning and, if ignored, a straight nose-drop for a natural recovery. Wing developments that came with the introduction of turbo-prop engines introduced unacceptable stall behaviour. Leading-edge developments on high-lift wings and the introduction of rear-mounted engines and high-set tailplanes on the next generation of jet transports introduced unacceptable stall behaviour; the probability of achieving the stall speed inadvertently, a hazardous event, had been calculated, in 1965, at about once in every 100,000 flights enough to justify the cost of development and incorporation of warning devices, such as stick shakers, devices to automatically provide an adequate nose-down pitch, such as stick pushers.
When the mean angle of attack of the wings is beyond the stall a spin, an autorotation of a stalled wing, may develop. A spin follows departures in roll and pitch from balanced flight. For example, a roll is damped with an unstalled wing but with wings stalled the damping moment is replaced with a propelling moment; the graph shows that the greatest amount of lift is produced as the critical angle of attack is reached. This angle is 17.5 degrees in this case. In particular, for aerodynamically thick airfoils, the critical angle is higher than with a thin airfoil of the same camber. Symmetric airfoils have lower critical angles; the graph shows that, as the angle of attack exceeds the critical angle, the lift produced by the airfoil decreases. The information in a graph of this kind is gathered using a model of the airfoil in a wind tunnel; because aircraft models are used, rather than full-size machines, special care is needed to make sure that data is taken in the same Reynolds number regime as in free flight.
The separation of flow from the upper wing surface at high angles of attack is quite different at low Reynolds number from that at the high Reynolds numbers of real aircraft. High-pressure wind tunnels are one solution to this problem. In general, steady operation of an aircraft at an angle of attack above the critical angle is not possible because, after exceeding the critical angle, the loss of lift from the wing causes the nose of the aircraft to fall, reducing the angle of attack again; this nose drop, independent of control inputs, indicates the pilot has stalled the aircraft. This graph shows the stall angle, yet in practice most pilot operating handbooks or generic flight manuals describe stalling in terms of airspeed; this is because all aircraft are equipped with an airspeed indicator, but fewer aircraft have an angle of attack indicator. An aircraft's stalling speed is published by the manufacturer for a range of weights and flap positions, but the stalling angle of attack is not published.
As speed reduces, angle of attack has to increase to keep lift
A wing is a type of fin that produces lift, while moving through air or some other fluid. As such, wings have streamlined cross-sections that are subject to aerodynamic forces and act as an airfoils. A wing's aerodynamic efficiency is expressed as its lift-to-drag ratio; the lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a smaller thrust to propel the wings through the air at sufficient lift. Lifting structures include various foils, including hydrofoils. Hydrodynamics is the governing science, rather than aerodynamics. Applications of underwater foils occur in hydroplanes and submarines; the word "wing" from the Old Norse vængr for many centuries referred to the foremost limbs of birds. But in recent centuries the word's meaning has extended to include lift producing appendages of insects, pterosaurs, some sail boats and aircraft, or the inverted airfoil on a race car that generates a downward force to increase traction.
The design and analysis of the wings of aircraft is one of the principal applications of the science of aerodynamics, a branch of fluid mechanics. The properties of the airflow around any moving object can – in principle – be found by solving the Navier-Stokes equations of fluid dynamics. However, except for simple geometries these equations are notoriously difficult to solve. However, simpler explanations can be described. For a wing to produce "lift", it must be oriented at a suitable angle of attack relative to the flow of air past the wing; when this occurs the wing deflects the airflow downwards. Since the wing exerts a force on the air to change its direction, the air must exert a force on the wing, equal in size but opposite in direction; this force manifests itself as differing air pressures at different points on the surface of the wing. A region of lower-than-normal air pressure is generated over the top surface of the wing, with a higher pressure on the bottom of the wing; these air pressure differences can be either measured directly using instrumentation, or can be calculated from the airspeed distribution using basic physical principles—including Bernoulli's principle, which relates changes in air speed to changes in air pressure.
The lower air pressure on the top of the wing generates a smaller downward force on the top of the wing than the upward force generated by the higher air pressure on the bottom of the wing. Hence, a net upward force acts on the wing; this force is called the "lift" generated by the wing. The different velocities of the air passing by the wing, the air pressure differences, the change in direction of the airflow, the lift on the wing are intrinsically one phenomenon, it is, possible to calculate lift from any of the other three. For example, the lift can be calculated from the pressure differences, or from different velocities of the air above and below the wing, or from the total momentum change of the deflected air. Fluid dynamics offers other approaches to solving these problems—and all produce the same answers if done correctly. Given a particular wing and its velocity through the air, debates over which mathematical approach is the most convenient to use can be mistaken by novices as differences of opinion about the basic principles of flight.
An airfoil or aerofoil is the shape of blade, or sail. Wings with an asymmetrical cross section are the norm in subsonic flight. Wings with a symmetrical cross section can generate lift by using a positive angle of attack to deflect air downward. Symmetrical airfoils have higher stalling speeds than cambered airfoils of the same wing area but are used in aerobatic aircraft as they provide practical performance whether the aircraft is upright or inverted. Another example comes from sailboats, where the sail is a thin membrane with no path-length difference between one side and the other. For flight speeds near the speed of sound, airfoils with complex asymmetrical shapes are used to minimize the drastic increase in drag associated with airflow near the speed of sound; such airfoils, called supercritical airfoils, are flat on top and curved on the bottom. Aircraft wings may feature some of the following: A rounded leading edge cross-section A sharp trailing edge cross-section Leading-edge devices such as slats, slots, or extensions Trailing-edge devices such as flaps or flaperons Winglets to keep wingtip vortices from increasing drag and decreasing lift Dihedral, or a positive wing angle to the horizontal, increases spiral stability around the roll axis, whereas anhedral, or a negative wing angle to the horizontal, decreases spiral stability.
Aircraft wings may have various devices, such as flaps or slats that the pilot uses to modify the shape and surface area of the wing to change its operating characteristics in flight. Ailerons to roll the aircraft clockwise or counterclockwise about its long axis Spoilers on the upper surface to disrupt the lift and to provide additional traction to an aircraft that has just landed but is still moving. Vortex generators to help prevent flow separation in transonic flow Wing fences to keep flow attached to the wing by stopping boundary layer separation from spreading roll direction. Folding wings allow more aircraft storage in the confined space of the hangar deck of an aircraft carrier Variable-sweep wing or "swing wings" that allow outstretched wings during low-speed flight and swept back wings for high-speed flight (includin
In aircraft design and aerospace engineering, a high-lift device is a component or mechanism on an aircraft's wing that increases the amount of lift produced by the wing. The device may be a fixed component, or a movable mechanism, deployed when required. Common movable high-lift devices include wing slats. Fixed devices include leading-edge slots, leading edge root extensions, boundary layer control systems; the size and lifting capacity of a fixed wing is chosen as a compromise between differing requirements. For example, a larger wing will provide more lift and reduce the distance and speeds required for takeoff and landing, but will increase drag, which reduces performance during the cruising portion of flight. Modern passenger jet wing designs are optimized for speed and efficiency during the cruise portion of flight, since this is where the aircraft spends the vast majority of its flight time. High-lift devices compensate for this design trade-off by adding lift at takeoff and landing, reducing the distance and speed required to safely land the aircraft, allowing the use of a more efficient wing in flight.
The high-lift devices on the Boeing 747-400, for example, increase the wing area by 21% and increase the lift generated by 90%. The most common high-lift device is the flap, a movable portion of the wing that can be lowered to produce extra lift; when a flap is lowered this re-shapes the wing section to give it more camber. Flaps are located on the trailing edge of a wing, while leading edge flaps are used occasionally. There are many kinds of trailing-edge flap. Simple hinged flaps came into common use in the 1930s, along with the arrival of the modern fast monoplane which had higher landing and takeoff speeds than the old biplanes. In the split flap, the lower surface hinges downwards while the upper surface remains either fixed to the wing or moves independently. Travelling flaps extend backwards, to increase the wing chord when deployed, increasing the wing area to help produce yet more lift; these began to appear just before World War II due to the efforts of many different individuals and organizations in the 1920s and 30s.
Slotted flaps comprise several separate small airfoils which separate apart and slide past each other when deployed. Such complex flap arrangements are found on many modern aircraft. Large modern airliners make use of triple-slotted flaps to produce the massive lift required during takeoff. Another common high-lift device is the slat, a small aerofoil shaped device attached just in front of the wing leading edge; the slat re-directs the airflow at the front of the wing, allowing it to flow more smoothly over the upper surface when at a high angle of attack. This allows the wing to be operated at the higher angles required to produce more lift. A slot is the gap between the wing; the slat may be fixed in position, with a slot permanently in place behind it, or it may be retractable so that the slot is closed when not required. If it is fixed it may appear as a normal part of the leading edge of a wing, with the slot buried in the wing surface behind it. A slat or slot may be either full span, or may be placed on only part of the wing, depending on how the lift characteristics need to be modified for good low speed control.
Slots and slats are sometimes used just for the section in front of the ailerons, ensuring that when the rest of the wing stalls, the ailerons remain usable. The first slats were developed by Gustav Lachmann in 1918 and by Handley-Page who received a patent in 1919. By the 1930s automatic slats had been developed, which opened or closed as needed according to the flight conditions, they were operated by airflow pressure against the slat to close it, small springs to open it at slower speeds when the dynamic pressure reduced, for example when the speed fell or the airflow reached a predetermined angle-of-attack on the wing. Modern systems, like modern flaps, can be more complex and are deployed hydraulically or with servos. Powered high-lift systems use airflow from the engine to shape the flow of air over the wing, replacing or modifying the action of the flaps. Blown flaps take "bleed air" from the jet engine's compressor or engine exhaust and blow it over the rear upper surface of the wing and flap, re-energising the boundary layer and allowing the airflow to remain attached at higher angles of attack.
A more advanced version of the blown flap is the circulation control wing, a mechanism that ejects air backwards over a specially designed airfoil to create lift through the Coandă effect. Another approach is to use the airflow from the engines directly, by placing a flap so that it deploys into the path of the exhaust; such flaps require greater strength due to the power of modern engines and greater heat resistance to the hot exhaust. The effect can be significant. Examples include the C-17 Globemaster III. More common on modern fighter aircraft but seen on some civil types, is the leading-edge root extension, sometimes called just a leading edge extension. A LERX consist of a small triangular fillet attached to the wing leading edge root and to the fuselage. In normal flight the LERX generates little lift. At higher angles of attack, however, it generates a vortex, positioned to lie on the upper surface of the main wing; the swirling action of the vortex increases the speed of airflow over the wing, so reducing the pressure and providing greater lift.
LERX systems are notable for the large angles in which they are effective. A Co-Flow Jet wing has an upper surface with an injection slot after the leading edge and a suction slot before the trailing edge, to augment lift, increase the stall margin and reduce drag. CFJ