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
Aerial advertising is a form of advertising that incorporates the use of flogos, manned aircraft, or drones to create, transport, or display, advertising media. The media can be static, such as a banner, lighted sign or sponsorship branding, it can be dynamic, such as animated lighted signage, skywriting, or audio. Prior to World War II, aviation pioneer Arnold Sidney Butler, the owner and operator of Daniel Webster Airport utilizing his fleet of J3 Cubs, created banner towing and was credited with a number of inventions and aircraft modifications used to pick up and release banners. At the start of World War II, the government took over the air strip for military training. Afterward, Butler moved his aircraft to Florida and formed Circle-A Aviation where he continued his banner towing business. Still today, many of his aircraft remain in service and can be seen in the skies over Miami and Hollywood, Florida. Aerial advertising is effective if a large target audience is gathered near the source of advertising.
Balloons and banner towing are strategically located. Long-range vehicles such as blimps and flogos can reach a broader audience along their flight route. Secondary distribution such as news media coverage, word of mouth and photos of aerial advertising can reach an extended audience. Due to safety and aesthetic reasons, the ability to perform aerial advertising is regulated by local and federal entities throughout the world. Advertising can be carried on the envelope or livery of the aircraft, or in the case of balloons the envelope can be constructed into a specific shape to advertise a product. Sky Sign Inc. created and holds various STC's for their aerial LED based signs. These signs attach to fixed wing aircraft. Banner Towing is a form of Skywriting. Dragged behind an aircraft; the banner itself can be of three kinds 5 foot high or 7 foot high letter were the traditional form of Banner towing for the past decades. 7 foot letter have the advantage of greater readability over a long distance, but incur a large drag penalty on the towing aircraft 5 foot letters on the other hand trade off some readability for the ability of the towing aircraft to tow longer messages A typical light aircraft would be able to tow 25 7 foot letter or 35 5 foot letters.
Advantages of standard letters are readability over flexibility. The letters being prefabricated means they can be made into messages with short notice and can be changed after each flight. Are a new form of Banner Towing. Billboards consist of a large area of nylon cloth. Similar in weight to a spinnaker on a sailing boat; this blank canvas allows vivid pictures to be digitally printed and towed behind an aircraft or below a helicopter. Helicopter Billboards tend to be square in shape to prevent the top corner sagging and becoming unreadable. Aircraft towed. 3 high to 1 long but sizes of 4 to 1 are becoming the norm. Advantages of Aerial Billboards is their visual impact. Disadvantages are once painted they can not be changes and lead times required to produce the Billboards This form of Banner Towing is a combination of the above types of Banners. An intermediate size area of nylon cloth is placed at the front of a Banner. Followed by standard letter; this combines the benefits of both banner styles to produce a Banner with a vivid digital printed area, giving impact.
Along with the flexibility and ease of changing message of standard letters. This technique involves printing a fabric to create an advertising banner, towed by an aircraft; this can be used to advertise a brand or be used as a marriage proposal or party invitation Flogos are stable foam shapes, customizable motifs made out of foam, which are suitable for both outdoor and indoor and once released into the air can float or fly into the air. In a special machine a patented foam fluid is combined with helium to make the foam; the generated foam gets pressed through a stencil. Flogos are customized to suit needs and can be shapes, logos and words; the machine can work far more complex motifs as well. They are produced continuously at a rate of one every 15 – 20 seconds in sizes of 100 cm, it can be written in the sky, the reason why they are linked to the term "skyvertising“ Sky-writing by fixed-wing aircraft, combined with the use of a vapor projector, remains popular with major advertisers. It is most effective in brand awareness with short, dramatic messages and for "spectaculars" such as marriage proposals.
The practice of sky-writing is known to be one of the safest forms of flying as it is only done in clear skies with smooth air and in controlled airspace, where radar separation is provided between planes. Aerostats are effective carriers of mobile billboards due to their slow speed, long loiter time and inexpensive fuel costs; the first British airship, built by Stanley Spencer in 1902, was funded by an advertisement for baby food carried on its envelope. Research from the United States suggests that the direct cost of balloon advertising "per thousand opportunities to see" is lower than for newspapers, radio or television; the most common type of fixed-wing aircraft used for mobile billboards and aerial advertising are single reciprocating engine aircraft, such as converted crop dusters. While on the ground, operators attach a towline to the rear of the aircraft. Once in flight, the operator comes back and links the grapple hook to the banner, billboard, or streamer while in flight; the wind resistance created during the natural course of flight cau
A helicopter is a type of rotorcraft in which lift and thrust are supplied by rotors. This allows the helicopter to take off and land vertically, to hover, to fly forward and laterally; these attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of VTOL aircraft cannot perform. The English word helicopter is adapted from the French word hélicoptère, coined by Gustave Ponton d'Amécourt in 1861, which originates from the Greek helix "helix, whirl, convolution" and pteron "wing". English language nicknames for helicopter include "chopper", "copter", "helo", "heli", "whirlybird". Helicopters were developed and built during the first half-century of flight, with the Focke-Wulf Fw 61 being the first operational helicopter in 1936; some helicopters reached limited production, but it was not until 1942 that a helicopter designed by Igor Sikorsky reached full-scale production, with 131 aircraft built. Though most earlier designs used more than one main rotor, it is the single main rotor with anti-torque tail rotor configuration that has become the most common helicopter configuration.
Tandem rotor helicopters are in widespread use due to their greater payload capacity. Coaxial helicopters, tiltrotor aircraft, compound helicopters are all flying today. Quadcopter helicopters pioneered as early as 1907 in France, other types of multicopter have been developed for specialized applications such as unmanned drones; the earliest references for vertical flight came from China. Since around 400 BC, Chinese children have played with bamboo flying toys; this bamboo-copter is spun by rolling a stick attached to a rotor. The spinning creates lift, the toy flies when released; the 4th-century AD Daoist book Baopuzi by Ge Hong describes some of the ideas inherent to rotary wing aircraft. Designs similar to the Chinese helicopter toy appeared in some Renaissance paintings and other works. In the 18th and early 19th centuries Western scientists developed flying machines based on the Chinese toy, it was not until the early 1480s, when Italian polymath Leonardo da Vinci created a design for a machine that could be described as an "aerial screw", that any recorded advancement was made towards vertical flight.
His notes suggested that he built small flying models, but there were no indications for any provision to stop the rotor from making the craft rotate. As scientific knowledge increased and became more accepted, people continued to pursue the idea of vertical flight. In July 1754, Russian Mikhail Lomonosov had developed a small coaxial modeled after the Chinese top but powered by a wound-up spring device and demonstrated it to the Russian Academy of Sciences, it was powered by a spring, was suggested as a method to lift meteorological instruments. In 1783, Christian de Launoy, his mechanic, used a coaxial version of the Chinese top in a model consisting of contrarotating turkey flight feathers as rotor blades, in 1784, demonstrated it to the French Academy of Sciences. Sir George Cayley, influenced by a childhood fascination with the Chinese flying top, developed a model of feathers, similar to that of Launoy and Bienvenu, but powered by rubber bands. By the end of the century, he had progressed to using sheets of tin for rotor blades and springs for power.
His writings on his experiments and models would become influential on future aviation pioneers. Alphonse Pénaud would develop coaxial rotor model helicopter toys in 1870 powered by rubber bands. One of these toys, given as a gift by their father, would inspire the Wright brothers to pursue the dream of flight. In 1861, the word "helicopter" was coined by Gustave de Ponton d'Amécourt, a French inventor who demonstrated a small steam-powered model. While celebrated as an innovative use of a new metal, the model never lifted off the ground. D'Amecourt's linguistic contribution would survive to describe the vertical flight he had envisioned. Steam power was popular with other inventors as well. In 1878 the Italian Enrico Forlanini's unmanned vehicle powered by a steam engine, rose to a height of 12 meters, where it hovered for some 20 seconds after a vertical take-off. Emmanuel Dieuaide's steam-powered design featured counter-rotating rotors powered through a hose from a boiler on the ground. In 1887 Parisian inventor, Gustave built and flew a tethered electric model helicopter.
In July 1901, the maiden flight of Hermann Ganswindt's helicopter took place in Berlin-Schöneberg. A movie covering the event was taken by Max Skladanowsky. In 1885, Thomas Edison was given US$1,000 by James Gordon Bennett, Jr. to conduct experiments towards developing flight. Edison built a helicopter and used the paper for a stock ticker to create guncotton, with which he attempted to power an internal combustion engine; the helicopter was damaged by explosions and one of his workers was badly burned. Edison reported that it would take a motor with a ratio of three to four pounds per horsepower produced to be successful, based on his experiments. Ján Bahýľ, a Slovak inventor, adapted the internal combustion engine to power his helicopter model that reached a height of 0.5 meters in 1901. On 5 May 1905, his helicopter flew for over 1,500 meters. In 1908, Edison patented his own design for a helicopter powered by a gasoline engine with box kites attached to a mast by cables for a rotor, but it never flew.
In 1906, two French brothers and Louis Breguet, began experimenting with airfoils for helicopters. In
ISM Raceway is a 1-mile, low-banked tri-oval race track located in Avondale, near Phoenix. The motorsport track opened in 1964 and hosts two NASCAR race weekends annually. ISM Raceway has hosted the CART, IndyCar Series, USAC and the WeatherTech SportsCar Championship; the raceway is owned and operated by International Speedway Corporation. The raceway was constructed with a 2.5 miles road course that ran on both the inside and the outside of the main tri-oval. In 1991 the track was reconfigured with the current 1.51 miles interior layout. ISM Raceway has an estimated grandstand seating capacity of around 51,000. Lights were installed around the track in 2004 following the addition of a second annual NASCAR race weekend. ISM Raceway is home to two annual NASCAR race weekends, one of 13 facilities on the NASCAR schedule to host more than one race weekend a year. Phoenix International Raceway was built in 1964 around the Estrella Mountains on the outskirts of Avondale; because of the terrain and the incorporation of a road course and drag strip, designers had to build a "dogleg" into the backstretch.
The original roadcourse was 2 miles in length and ran both inside and outside of the main oval track. The hillsides adjacent to the track offer a unique vantage point to watch races from. "Monument Hill", located alongside turns 3 and 4, is a favorite among race fans because of the unique view and lower ticket prices. At the top of this hill lies a USGS bench marker known as Gila and Salt River Meridian, now listed on the National Register of Historic Places. Long before Phoenix Raceway existed, this spot was the original land survey point for all of what became the state of Arizona. Phoenix International Raceway was built with the goal of being the western home of open wheel racing. Sports cars and USAC began racing at the track in 1964, the track became a favorite of drivers and soon replaced the old track at the Arizona State Fairgrounds. In 1977, the first Copper World Classic was held, a marque event for USAC midget and Silver Crown cars. NASCAR began racing at Phoenix International Raceway in 1978.
However, it was not until 1988 when NASCAR's premier series, now the Monster Energy NASCAR Cup Series, began racing at the track. Following the announcement of NASCAR being added to the track schedule, Phoenix International Raceway built a 3-story suite building outside of turn 1 and increased grandstand capacity to 30,000. A year prior, the track's main grandstand was struck by lightning and burned to the ground, reconstruction was finished in time for the first NASCAR cup race; that first race was won by Alan Kulwicki where in his celebration he performed the first "Polish Victory Lap". In 1991, the old 2.5 miles road course was replaced by a 1.51 miles infield road course. In 1996 the grandstand capacity was increased to 65,000. International Speedway Corporation took ownership of Phoenix International Raceway from Emmett "Buddy" Jobe in April 1997. Racing at Phoenix International Raceway began to change in 2003. Turn 2 was reconstructed by pushing back the outside wall to make racing safer.
The wall came to an end where the old road course crossed the oval track. At the same time, an access tunnel was built under turn 4. Vehicles had to use crossover gates and pedestrians used a crossover bridge. In 2004, NASCAR announced it would give a second annual race weekend to Phoenix International Raceway starting with the 2005 season. Following the announcement, the track installed lights to allow the newly scheduled NASCAR race to be run in the evening; the addition of a second NASCAR racing weekend had dramatic effects on the economy of the state of Arizona. A study at Arizona State University estimated that Phoenix International Raceway brings in nearly $473 million annually to the state. 2005 would become the last year that a major open-wheel racing series would race at PIR, until it was announced that the track will return to the schedule for the 2016 IndyCar season. Despite the 2006 departure from the schedule, the track was still used by IndyCar for testing purposes. In 2006, the Allison Grandstand was expanded from turn 1 to turn 2, increasing the reserved seating to 76,800.
Included with the expansion is "Octane", an exclusive lounge on top of the grandstands overlooking turn 1. In 2008 Phoenix International Raceway added the SPEED Cantina, a one-of-a-kind at-track sports bar and grill, outside turn 2. In early 2010, some of the grandstands along the backstretch were removed to allow additional room for recreational vehicles, thus the seating capacity dropped to around 67,000. In November 2010, ISC and the Avondale City Council announced plans for a $100 million long-term development for Phoenix International Raceway. $15 million would go towards repaving the track for the first time since 1990 and building a new media center. The plans include a reconfiguration of the track; the front stretch was widened from 52 feet to 62 feet, the pit stalls were changed from asphalt to concrete, the dogleg was moved outward by 95 feet, tightening the turn radius of the dogleg from 800 feet to 500 feet. Along with the other changes, progressive banking was added to the turns: Turns 1 and 2, which had 11 degrees of banking, changed to 10 degrees on the bottom and 11 degrees on the top.
Turns 3 and 4, which had 9 degrees of banking, changed to 8 degrees on 9 on the top. Project leader Bill Braniff, Senior Director of Construction for North American Testing Corporation, a subsidiary of Phoenix International Raceway’s parent company International Speedway Corporation, said "A
In aeronautics and aeronautical engineering, camber is the asymmetry between the two acting surfaces of an aerofoil, with the top surface of a wing being more convex. An aerofoil, not cambered is called a symmetric aerofoil; the benefits of cambering were discovered and first utilized by Sir George Cayley in the early 19th century. Camber is designed into an aerofoil to increase the maximum lift coefficient; this minimizes the stalling speed of aircraft using the aerofoil. An aircraft with wings based on a cambered aerofoil will have a lower stalling speed than an aircraft with a similar wing loading and wings based on a symmetric aerofoil. An aircraft designer may reduce the camber of the outboard section of the wings to increase the critical angle of attack at the wing tips; when the wing approaches the stall this will ensure that the wing root stalls before the tip, giving the aircraft resistance to spinning and maintaining aileron effectiveness close to the stall. Some recent designs use negative camber.
One such design is called the supercritical aerofoil. It is used for near-supersonic flight, produces a higher lift-to-drag ratio at near supersonic flight than traditional aerofoils. Supercritical aerofoils employ a flattened upper surface cambered aft section, greater leading-edge radius as compared to traditional aerofoil shapes; these changes delay the onset of wave drag. Broadly, an aerofoil is said to have positive camber if, as is the case, its upper surface is the more convex, but camber is a complex property, that can be more characterized by an aerofoil's camber line, the curve Z, halfway between the upper and lower surfaces, thickness function T, which describes the thickness of the aerofoil at any given point. The upper and lower surfaces can be defined as follows: Z upper = Z + 1 2 T Z lower = Z − 1 2 T An aerofoil where the camber line curves back up near the trailing edge is called a reflexed camber aerofoil; such an aerofoil is useful in certain situations, such as with tailless aircraft, because the moment about the aerodynamic center of the aerofoil can be 0.
A camber line for such an aerofoil can be defined as follows: Z ¯ = a An aerofoil with a reflexed camber line is shown at right. The thickness distribution for a NACA 4-series aerofoil was used, with a 12% thickness ratio; the equation for this thickness distribution is: T ¯ = t 0.2 Where t is the thickness ratio. Chord NACA airfoil Aerodynamic drag. Retrieved 9/7/08. Theory of Wing Sections, Ira H. Abbott and Albert E. Von Doenhoff ISBN 0-486-60586-8
A fluid flowing past the surface of a body exerts a force on it. Lift is the component of this force, perpendicular to the oncoming flow direction, it contrasts with the drag force, the component of the force parallel to the flow direction. Lift conventionally acts in an upward direction in order to counter the force of gravity, but it can act in any direction at right angles to the flow. If the surrounding fluid is air, the force is called an aerodynamic force. In water or any other liquid, it is called a hydrodynamic force. Dynamic lift is distinguished from other kinds of lift in fluids. Aerostatic lift or buoyancy, in which an internal fluid is lighter than the surrounding fluid, does not require movement and is used by balloons, dirigibles and submarines. Planing lift, in which only the lower portion of the body is immersed in a liquid flow, is used by motorboats and water-skis. A fluid flowing past the surface of a body exerts a force on it, it makes no difference whether the fluid is flowing past a stationary body or the body is moving through a stationary volume of fluid.
Lift is the component of this force, perpendicular to the oncoming flow direction. Lift is always accompanied by a drag force, the component of the surface force parallel to the flow direction. Lift is associated with the wings of fixed-wing aircraft, although it is more generated by many other streamlined bodies such as propellers, helicopter rotors, racing car wings, maritime sails, wind turbines in air, by sailboat keels, ship's rudders, hydrofoils in water. Lift is exploited by flying and gliding animals by birds and insects, in the plant world by the seeds of certain trees. While the common meaning of the word "lift" assumes that lift opposes weight, lift can be in any direction with respect to gravity, since it is defined with respect to the direction of flow rather than to the direction of gravity; when an aircraft is cruising in straight and level flight, most of the lift opposes gravity. However, when an aircraft is climbing, descending, or banking in a turn the lift is tilted with respect to the vertical.
Lift may act as downforce in some aerobatic manoeuvres, or on the wing on a racing car. Lift may be horizontal, for instance on a sailing ship; the lift discussed in this article is in relation to airfoils, although marine hydrofoils and propellers share the same physical principles and work in the same way, despite differences between air and water such as density and viscosity. An airfoil is a streamlined shape, capable of generating more lift than drag. A flat plate can generate lift, but not as much as a streamlined airfoil, with somewhat higher drag. There are several ways to explain; some are more physically rigorous than others. For example, there are explanations based directly on Newton’s laws of motion and explanations based on Bernoulli’s principle. Either can be used to explain lift. An airfoil generates lift by exerting a downward force on the air. According to Newton's third law, the air must exert an equal and opposite force on the airfoil, lift; the airflow changes direction as it passes the airfoil and follows a path, curved downward.
According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Newton's third law requires the air to exert an upward force on the airfoil. In the case of an airplane wing, the wing exerts a downward force on the air and the air exerts an upward force on the wing; the downward turning of the flow is not produced by the lower surface of the airfoil, the air flow above the airfoil accounts for much of the downward-turning action. Bernoulli's principle states that there is a direct mathematical relationship between the pressure of a fluid and the speed of that fluid, so if one knows the speed at all points within the airflow one can calculate the pressure, vice versa. For any airfoil generating lift, there must be a pressure imbalance, i.e. lower average air pressure on the top than on the bottom. Bernoulli's principle states that this pressure difference must be accompanied by a speed difference. Starting with the flow pattern observed in both theory and experiments, the increased flow speed over the upper surface can be explained in terms of streamtube pinching and conservation of mass.
For incompressible flow, the rate of volume flow must be constant within each streamtube since matter is not created or destroyed. If a streamtube becomes narrower, the flow speed must increase in the narrower region to maintain the constant flow rate, to satisfy the principle of conservation of mass; the upper streamtubes constrict as they flow around the airfoil. Conservation of mass says; the lower streamtubes expand and their flowrate slows. From Bernoulli's principle, the pressure on the upper surface where the flow is moving faster is lower than the pressure on the lower surface where it is moving slower; this pressure difference creates a net aerodynamic force. As explained below under a more comprehensive physical explanation, producing a lift force requires maintaining pressure differences in both the vertical and horizontal directions, thus requires both downward turning of the flow and changes in flow speed consistent with Bernoulli's principle; the simplified explanations given above are therefore incomplete because they define lift in terms of only one o