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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] |
Helicopter Rotor
On a helicopter, the main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift (force), lift force that supports the weight of the helicopter, and the thrust that counteracts aerodynamic drag in forward flight. Each main rotor is mounted on a vertical mast over the top of the helicopter, as opposed to a helicopter tail rotor, which connects through a combination of drive shaft(s) and gearboxes along the tail boom. The blade pitch is typically controlled by the pilot using the helicopter flight controls. Helicopters are one example of rotary-wing aircraft (rotorcraft). The name is derived from the Greek words ''helix'', helik-, meaning spiral; and ''pteron'' meaning wing. Design principles Overview The helicopter rotor is powered by the engine, through the transmission, to the rotating mast. The mast is a cylindrical metal shaft that extends upward from—and is driven by—the transmission. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lift (force)
When a fluid flows around an object, the fluid exerts a force on the object. Lift is the Euclidean_vector#Decomposition_or_resolution, component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag (physics), drag force, which is 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 is defined to act perpendicular to the flow and therefore can act in any direction. If the surrounding fluid is air, the force is called an aerodynamic force. In water or any other liquid, it is called a Fluid dynamics, hydrodynamic force. Dynamic lift is distinguished from other kinds of lift in fluids. Aerostatics, Aerostatic lift or buoyancy, in which an internal fluid is lighter than the surrounding fluid, does not require movement and is used by balloons, blimps, dirigibles, boats, and submarines. Planing (boat), Planing lift, in which only the lower po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Flying School
The Central Flying School (CFS) is the Royal Air Force's primary institution for the training of military flying instructors. Established in 1912 at the Upavon Aerodrome, it is the longest existing flying training school in the world. The school was based at RAF Little Rissington from 1946 to 1976. Its motto is ''Imprimis Praecepta'', Latin for "The Teaching is Everlasting". The school currently manages a series of training squadrons and the RAF Display Team. History The Central Flying School was established by the Royal Navy at Upavon Aerodrome, near Upavon, Wiltshire, on 12 May 1912. The school's strength at the outset was ten Staff Officers and eighty flying students, whose course lasted for sixteen weeks.Hugh Soar, ''Straight & True'' (2012), p. 87 Its first commandant was Captain Godfrey Paine RN, and it also trained pilots for the Royal Flying Corps, created in 1912, and the Royal Naval Air Service, 1914–1918. The school was transferred from the Southern Train ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airfoil
An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more Lift (force), lift than Drag (physics), drag. Wings, sails and propeller blades are examples of airfoils. Foil (fluid mechanics), Foils of similar function designed with water as the working fluid are called hydrofoils. When oriented at a suitable angle, a solid body moving through a fluid deflects the oncoming fluid (for fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as aerodynamic force and can be resolved into two components: lift (perpendicular to the remote freestream velocity) and drag (Parallel (geometry), parallel to the freestream velocity). The lift on an airfoil is primarily the result of its angle of attack. Most foil shapes require a positive angle of attack to generate lift, but Camber (aerodynamics), cambered airfoils can generate lift at zero ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Washout (aeronautics)
Washout is a characteristic of aircraft wing design which deliberately changes the lift distribution across the span of an aircraft’s wing. The wing is designed so that the angle of incidence is greater at the wing roots and decreases across the span, becoming lowest at the wing tip. This is usually to ensure that at stall speed the wing root stalls before the wing tips, providing the aircraft with continued aileron control and some resistance to spinning. Washout may also be used to modify the spanwise lift distribution to reduce lift-induced drag. Design considerations Washout is commonly achieved by designing the wing with a slight twist, reducing the angle of incidence from root to tip, and therefore causing a lower angle of attack at the tips than at the roots. This feature is sometimes referred to as geometrical washout, to distinguish it from aerodynamic washout. Wingtip stall is unlikely to occur symmetrically, especially if the aircraft is maneuvering. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chord (aeronautics)
In aeronautics, the chord is an imaginary straight line segment joining the leading edge and trailing edge of an aerofoil cross section parallel to the direction of the airflow. The chord length is the distance between the trailing edge and the leading edge. L. J. Clancy (1975), ''Aerodynamics'', Section 5.2, Pitman Publishing Limited, London. The point on the leading edge used to define the main chord may be the surface point of minimum radius. p.18 For a turbine aerofoil, the chord may be defined by the line between points where the front and rear of a 2-dimensional blade section would touch a flat surface when laid convex-side up. The wing, horizontal stabilizer, vertical stabilizer and propeller/rotor blades of an aircraft are all based on aerofoil sections, and the term ''chord'' or ''chord length'' is also used to describe their width. The chord of a wing, stabilizer and propeller is determined by measuring the distance between leading and trailing edges in the direc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tiltrotor
A tiltrotor is an aircraft that generates lift (force), lift and thrust, propulsion by way of one or more powered Helicopter rotor, rotors (sometimes called ''proprotors'') mounted on rotating shaft (mechanical engineering), shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a transverse rotor design, with a few exceptions that use other multirotor layouts. Tiltrotor design combines the VTOL capability of a helicopter with the speed and range (aircraft), range of a conventional fixed-wing aircraft. For vertical flight, the rotors are angled so the plane of rotation is horizontal, generating lift the way a normal helicopter rotor does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical. In this mode the rotors provide thrust as a propeller (aircraft), propeller, and the airfoil of the fixed wings takes over providing the lift via the forward motion of the entire aircra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell Boeing V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-use, tiltrotor military transport and cargo aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionality of a conventional helicopter with the long-range, high-speed cruise performance of a turboprop aircraft. The V-22 is operated by the United States and Japan, and is not only a new aircraft design, but a new type of aircraft that entered service in the 2000s, a tiltrotor compared to fixed wing and helicopter designs. The V-22 first flew in 1989 and after a long development was fielded in 2007. The design combines the vertical takeoff ability of a helicopter with the speed and range of a fixed-wing airplane. The failure of Operation Eagle Claw in 1980 during the Iran hostage crisis underscored that there were military roles for which neither conventional helicopters nor fixed-wing transport aircraft were well-suited. The United States Dep ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coning (aerodynamics)
Coning is a phenomenon which affects helicopter rotor discs, where the blades describe a cone shape as they rotate. For a helicopter on the ground, as the blades rotate, they describe a horizontal disc due to centrifugal force. However, as the helicopter generates lift, the blades are pulled upwards into a cone shape.Central Flying School: Manual of FlyingVolume 12: Helicopters Section 1-17. Coning results from the balancing of centrifugal and aerodynamic forces. The coning angle depends on RPM, gross weight and g-force. The ratio of aerodynamic forces to inertial forces is called the Lock number. Excessive coning can occur if the RPM is allowed to drop too low or the helicopter is operated at an excessive gross weight, or under turbulent conditions or if the helicopter experiences excessive g-force. An excessively coned disc will generate less lift due to reduced disc area. If rotor RPM drops too low, the centrifugal force will reduce until is no longer sufficient to balance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
Blade Element Theory
Blade element theory (BET) is a Mathematics, mathematical process originally designed by William Froude (1878), David W. Taylor (1893) and Stefan Drzewiecki (1885) to determine the behavior of propellers. It involves breaking a blade down into several small parts then determining the Force, forces on each of these small blade elements. These forces are then integrated along the entire blade and over one rotor revolution in order to obtain the forces and Moment (physics), moments produced by the entire propeller or Rotorcraft, rotor. One of the key difficulties lies in modelling the induced Velocity-addition formula, velocity on the Disk loading, rotor disk. Because of this the blade element theory is often combined with momentum theory to provide additional relationships necessary to describe the induced velocity on the rotor disk, producing blade element momentum theory. At the most basic level of approximation a uniform induced velocity on the disk is assumed: :v_i = \sqrt. Alter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
