Angle of attack

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In fluid dynamics, attack angle ( AOA , or ${\ displaystyle \ alpha}$ (alpha Greek letters)) is the angle between the reference line on the body (often the chord line of the airfoil) and the vector representing the relative motion between the body and the fluid in which it moves. The attack angle is the angle between the body reference line and the flow coming. This article focuses on the most common applications, angles of wings or airfoils moving through the air.

In aerodynamics, the angle of attack determines the angle between the wing chord of the fixed wing plane and the vector representing the relative motion between the plane and the atmosphere. Since the wings can have a twist, the chord line of the entire wing may not be determined, so the alternative reference line is simply defined. Often, the chord line of the wing root is selected as the reference line. Another option is to use a horizontal line on the fuselage as a reference line (as well as a longitudinal axis). Some authors do not use arbitrary chord lines but use a zero lift axis where, by definition, zero angle of attack corresponds to zero lift coefficients.

Some British authors use the term "incident angle" rather than angle of attack . However, this can cause confusion with the terms of the point of view riggers' which means the angle between the airfoil chord and some fixed datum on the plane.

Video Angle of attack

Hubungan antara angle of attack dan lift

The lift coefficient of the fixed wing aircraft varies with the angle of attack. Increasing angle of attack is associated with increasing the lift coefficient to the maximum lift coefficient, after which the lift coefficient decreases.

As the angle of attack of the fixed wing aircraft increases, the separation of airflow from the upper surface of the wing becomes more apparent, leading to a decrease in the rate of increase in lift coefficients. The image shows a typical curve for curved straight wings. The symmetrical wings have zero lift at an angle of 0 degrees of attack. The lift curve is also influenced by the shape of the wing, including the airfoil part and the wing planform. The swept wings have a lower and flat curve with a higher critical angle.

Maps Angle of attack

Angle of critical attack

critical attack angle is the angle of attack which results in the maximum lift coefficient. This is also called "corner kiosk attack". Under the critical angle of attack, as the angle of attack increases, the lift coefficient (Cl) increases. Conversely, above the critical angle of attack, as the angle of attack increases, the air begins to flow less smoothly over the top surface of the airfoil and begins to separate from the upper surface. In most forms of airfoil, when the angle of attack increases, the point of separation of the upper surface of the flow moves from the trailing edge to the leading edge. At the critical angle of attack, the upper surface flow is more separated and the airfoil or wing produces the maximum lift coefficient. As the angle of attack increases, the upper surface flow becomes increasingly separated and the airfoil/wing produces fewer lift coefficients.

Above this critical angle of attack, the plane is said to be inside a kiosk. A fixed-wing aircraft by definition stops at or above the critical angle of attack rather than at or below a certain airspeed. The airspeed at which the aircraft kiosk varies with the weight of the aircraft, the load factor, the center of gravity of the aircraft and other factors. But the plane always stalls at the critical angle of the same attack. The angle of critical attack or stalling is usually about 15 Â ° - 20 Â ° for many airfoils.

Some aircraft are equipped with built-in aviation computers that automatically prevent the aircraft from increasing the angle of attack even further when the maximum angle of attack is reached, regardless of the pilot input. This is called an 'angle of attack limiter' or 'alpha limiter'. Modern aircraft that have fly-by-wire technology avoid the critical angle of attack by using software in computer systems that regulate the flight control surfaces.

In the take-off and landing operations of short runways, such as the Navy's Naval Transport Operations and STOL's flying back state, the aircraft can be equipped with an attack angle or the Lift Backup Indicators. These indicators measure the angle of attack (AOA) or the Potential of Wing Lift (POWL, or Lift Reserve) directly and help pilots fly near the stalling point with higher precision. The STOL operation requires the aircraft to be able to operate close to the critical angle of attack during the landing and at the best climbing angle during takeoff. Angle of attack indicators are used by pilots for maximum performance during these maneuvers because airspeed information is only indirectly associated with stall behavior.

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Extremely high alpha

Some military aircraft are capable of achieving controlled flights at very high angle of attack, but with the cost of massive induced drag. It provides a plane with high agility. A famous military example is sometimes regarded as Cobra Pugachev. Although the aircraft suffered a high angle of attack across the entire maneuver, the aircraft was unable to control the aerodynamic direction or maintain the flight level until the maneuver ended. Cobra is a superman example when the plane's wings are far beyond the critical angle of attack for most of the maneuvers.

The additional aerodynamic surfaces known as "high lifter" includes the wing's leading root extension enabling a much larger, 'true' alpha flying fighter aircraft, up to 45 Â °, compared to about 20 Â ° for the aircraft without this device. This can help at high altitudes where even a bit of maneuver may require a high angle of attack due to low air density in the upper atmosphere as well as at low speeds at low altitudes where the margin between AoA and AoA stall levels is reduced. The high AoA capability of the aircraft provides the buffer for the pilot that makes the stalling of the plane (which occurs when AoA is critically exceeded) is more difficult. However, military aircraft typically do not gain a high alpha in combat, as it robs the aircraft of speed very quickly due to drag induction, and in extreme cases, an increase in the frontal and parasitic areas of drag. Not only do such maneuvers slow down planes, but they cause significant structural stress at high speed. Modern flight control systems tend to limit the angle of fighter attacks to well below their maximum aerodynamic limits.

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Sailing

In sailing, the physical principles involved are the same as the airplanes. The attack angle of the screen is the angle between the chord line and the wind direction.

The angle of attack boat is the angle between the direction of the boat and the direction of the wind. See the screen points.

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See also

• Ratio upfront
• Airfoil
• Side slot corner
• Bernoulli Principle
• Camber
• Drag equation
• Coefficient lift
• Raise (force)
• Pitch
• Stand (flight)
• Zero lift axis

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References

• Lawford, J.A. and Nippress, K.R.; Calibration of Air-Data Systems and the Flow Direction Sensors (NATO) Advisory Group for Aerospace Research and Development, AGARDograph No. 300 Vol. 1 (AGARD AG-300 Vol. 1); "Calibration of Water-Data Systems and Flow Sensors"; Establishment of Experimental Aircraft and Armament, Boscombe Down, Salisbury, Wilts SP4 OJF, United Kingdom
• USAF & amp; NATO Report RTO-TR-015 AC/323/(HFM-015)/TP-1 (2001).

Source of the article : Wikipedia