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Dissymmetry Of Lift
Dissymmetry of lift (also known as asymmetry of lift or asymmetric lift) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros in forward flight. A rotor blade that is moving in the same direction as the aircraft is called the ''advancing blade'' and the blade moving in the opposite direction is called the ''retreating blade.'' When viewed from above, most American helicopter rotors turn counter-clockwise; French and Russian helicopters turn clockwise. Balancing lift across the rotor disc is important to a helicopter's stability. The amount of lift generated by an airfoil is proportional to the square of its airspeed (velocity). In a hover, the rotor blades have equal airspeeds and therefore equal lift. However, in forward flight the advancing blade has a higher airspeed than the retreating blade, creating uneven lift across the rotor disc. Analysis Consider ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Blade Sides
A blade is the sharp, cutting portion of a tool, weapon, or machine, specifically designed to puncture, chop, slice, or scrape surfaces or materials. Blades are typically made from materials that are harder than those they are intended to cut. This includes early examples made from flaked stones like flint or obsidian, evolving through the ages into metal forms like copper, bronze, and iron, and culminating in modern versions made from steel or ceramics. Serving as one of humanity's oldest tools, blades continue to have wide-ranging applications, including in combat, cooking, and various other everyday and specialized tasks. Blades function by concentrating force at the cutting edge. Design variations, such as serrated edges found on bread knives and saws, serve to enhance this force concentration, adapting blades for specific functions and materials. Blades thus hold a significant place both historically and in contemporary society, reflecting an evolution in material technolo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Angle Of Attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and 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 simply defined. Often, the chord line of the Wing root, root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Unequal Rotor Lift Distribution
Unequal rotor lift distribution is an effect where the blades of a helicopter rotor generate more lift at the rotor tips than at the rotor hub. A helicopter rotor blade is an airfoil, which is driven through the air to create lift. The lift generated is proportional to the square of the speed. Because the tips of the rotating blades travel much faster through the air than the parts of the blades near the hub, they generate much more lift. If not mitigated, this effect would cause large bending stresses in the blade. In addition, the tip would have to be made stronger to handle the increased load. Helicopter manufacturers use the following techniques to equalise lift across the blade: * Washout is a geometric twist in the blade, such that the blade root near the hub has a higher angle-of-attack, thus higher lift. * Varying the airfoil cross-section, such as flattening the airfoil towards the tip, or tapering the blade towards the tip, which reduces its surface area thus reduc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Cierva C
The Cierva Autogiro Company was a British firm established in 1926 to develop the autogyro. The company was set up to further the designs of Juan de la Cierva, a Spanish engineer and pilot, with the financial backing of James George Weir, a Scottish industrialist and aviator. History Juan de la Cierva's first British-built autogyro was the C.8 design. It and some other designs were built in conjunction with Avro. The pre-war Cierva C.30 proved popular. Nearly 150 were built under licence in the United Kingdom by Avro, in Germany by Focke-Wulf, and in France by Lioré-et-Olivier. On 9 December 1936, Cierva was killed in the Croydon KLM airliner accident when the aircraft in which he was a passenger crashed after taking off in fog. Dr. James Allan Jamieson Bennett was promoted to Chief Technical Officer of the company and remained in the position until leaving in 1939. In addition to making important contributions to autogyro controls while at Cierva Autogyro, Bennett carried ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
P-factor
Pfactor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller (aircraft), propeller,) wherein the propeller's center of thrust moves off-center when the aircraft is at a high angle of attack. This shift in the location of the center of thrust will exert a yawing moment on the aircraft, causing it to Aircraft principal axes, yaw slightly to one side. A rudder input is required to counteract the yawing tendency. Causes When a propeller aircraft is flying at cruise speed in level flight, the propeller disc is perpendicular to the relative airflow through the propeller. Each of the propeller blades contacts the air at the same angle and speed, and thus the thrust produced is evenly distributed across the propeller. However, at lower speeds, the aircraft will typically be in a nose-high attitude, with the propeller disc rotated slightly toward the horizontal. This has two effects. Firstly, propeller bla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Fuselage
The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as well, although in some amphibious aircraft the single engine is mounted on a hardpoint, pylon attached to the fuselage, which in turn is used as a floating Hull (watercraft), hull. The fuselage also serves to position the Flight control surfaces, control and Stabilizer (aeronautics), stabilization surfaces in specific relationships to Wing, lifting surfaces, which is required for aircraft stability and maneuverability. Types of structures Truss structure This type of structure is still in use in many lightweight aircraft using welding, welded steel tube trusses. A box truss fuselage structure can also be built out of wood—often covered with plywood. Simple box structures may be rounded by the addition of supported lightweight strin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
CH-47 Chinook
The Boeing CH-47 Chinook is a tandem-rotor helicopter originally developed by American rotorcraft company Piasecki Helicopter, Vertol and now manufactured by Boeing Defense, Space & Security. The Chinook is a Military transport helicopter, heavy-lift helicopter that is among the heaviest lifting Western helicopters. Its name, Chinook, is from the Native Americans in the United States, Native American Chinook people of Oregon and Washington (state), Washington state. The Chinook was originally designed by Vertol, which had begun work in 1957 on a new tandem-rotor helicopter, designated as the Vertol Model 107 or V-107. Around the same time, the United States Department of the Army announced its intention to replace the Radial engine, piston-engine–powered Sikorsky CH-37 Mojave with a new, gas turbine–powered helicopter. During June 1958, the U.S. Army ordered a small number of V-107s from Vertol under the ''YHC-1A'' designation; following testing, some Army officials consider ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Tandem Rotor
A tandem-rotor aircraft is an aircraft with two large helicopter rotor assemblies mounted one in front of the other in the horizontal plane. This configuration is mainly used for large cargo helicopters. Such aircraft are often informally referred to as "Chinooks," after the CH-47 Chinook, one of the first widely adopted heavy-lift helicopters with a tandem-rotor configuration. Design Single-rotor helicopters need a mechanism to neutralize the Aircraft principal axes, yawing movement produced by the single large rotor. This is commonly accomplished by a tail rotor, coaxial rotors, and the NOTAR systems. Tandem-rotor helicopters, however, use counter-rotating rotors, with each cancelling out the other's torque. Therefore, all of the power from the engines can be used for lift (force), lift, whereas a single-rotor helicopter uses some of the engine power to counter the torque. An alternative is to mount two rotors in a Coaxial rotors, coaxial configuration. The first successful ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Coaxial Rotors
A coaxial-rotor aircraft is an aircraft whose helicopter rotor, rotors are mounted one above the other on Concentric objects, concentric shafts, with the same axis of rotation, but turning in opposite directions (contra-rotating). This rotor configuration is a feature of helicopters produced by the Russian Kamov helicopter design bureau. History The idea of coaxial rotors originates with Mikhail Lomonosov. He had developed a small helicopter model with coaxial rotors in July 1754 and demonstrated it to the Russian Academy of Sciences. In 1859, the British Patent Office awarded the first helicopter patent to Henry Bright for his coaxial design. From this point, coaxial helicopters developed into fully operational machines as we know them today. Two pioneering helicopters, the Corradino D'Ascanio#Between the wars, Corradino D'Ascanio-built "D'AT3" of 1930, and the generally more successful French mid-1930s ''Gyroplane Laboratoire'', both used coaxial rotor systems for flight. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Flapback
Flapback or blowback is the tilting of a helicopter rotor disc, usually aft (backwards), which occurs in several circumstances. In normal operating circumstances, forward flight results in flapback caused by dissymmetry of lift and the transverse flow effect. Dissymmetry of lift is where the forward-moving rotor blade has a faster airspeed, so it generates more lift, which would cause the rotor disc to tilt to the side. To prevent this the forward-moving blade flaps up, which reduces its angle of attack and the corresponding lift. At the same time, the rearward-moving rotor blade flaps down thereby increasing its angle of attack and lift. Thus, lift is balanced on both sides of the rotor disc. However, since the rotor blades climb on the advancing side and descend on the opposite side, this also results in the rotor disk being tilted to the rear. The transverse flow effect is where the front of the rotor disc is moving into undisturbed air, whereas the rear of the rotor disc is movi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Relative Wind
In aeronautics, the relative wind is the direction of movement of the atmosphere relative to an aircraft or an airfoil. It is opposite to the direction of movement of the aircraft or airfoil relative to the atmosphere. Close to any point on the surface of an aircraft or airfoil, the air is moving parallel to the surface; but at a great distance from the aircraft or airfoil, the movement of the air can be represented by a single vector. This vector is the relative wind or the ''free stream velocity vector''.Clancy, L.J. (1975), ''Aerodynamics'', Section 5.2, Pitman Publishing Limited, London The angle between the chord line of an airfoil and the relative wind defines the angle of attack. The relative wind is of great importance to pilots because exceeding the critical angle of attack will result in a stall, regardless of airspeed. In freefall Relative wind is also used to describe the airflow relative to an object in freefall through an atmosphere, such as that of a person's ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Supersonic
Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights during which only some parts of the air surrounding an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.2. Sounds are traveling vibrations in the form of pressure waves in an elastic medium. Objects move at supersonic speed when the objects move faster than the speed at which sound propagates through the medium. In gases, sound travels longitudinally at different speeds, mostly depending on the molecular mass and temperature of the gas, and pressure has little effect. Since air temperature and composition varies significantly with altitude, the speed of s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
