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Disc Loading
In fluid dynamics, disk loading or disc loading is the average pressure change across an actuator disk, such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including helicopter main rotors and tail rotors; propellers typically have a higher disk loading. The V-22 Osprey tiltrotor aircraft has a high disk loading relative to a helicopter in the hover mode, but a relatively low disk loading in fixed-wing mode compared to a turboprop aircraft. Rotors Disc loading of a hovering helicopter is the ratio of its weight to the total main rotor disc area. It is determined by dividing the total helicopter weight by the rotor disc area, which is the area swept by the blades of a rotor. Disc area can be found by using the span of one rotor blade as the radius of a circle and then determining the area the blades encompass during a complete rotation. When a helicopter is being maneuvered, its disc loading changes. The higher the loading, the more po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MV-22B Osprey (USMC) 008
The Bell Boeing V-22 Osprey is an American multi-mission, tiltrotor military 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 (aeronautics), cruise performance of a turboprop aircraft. In 1980, the failure of Operation Eagle Claw (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 Department of Defense (DoD) initiated a program to develop an innovative transport aircraft with long-range, high-speed, and vertical-takeoff capabilities, and the Joint-service Vertical take-off/landing Experimental (JVX) program officially commenced in 1981. A partnership between Bell Textron, Bell Helicopter and Boeing Rotorcraft Systems, Boeing Helicopters was awarded a development contract in 19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autorotation (helicopter)
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Igor.How they fly – Bensen explains all" ''Gyrocopters UK''. Accessed: 10 April 2014. Quote: "air.. (is) deflected downward"Charnov, Bruce HCierva, Pitcairn and the Legacy of Rotary-Wing Flight ''Hofstra University''. Accessed: 22 November 2011. The term ''autorotation'' dates to a period of early helicopter development between 1915 and 1920, and refers to the rotors turning without the engine."Autorotation", ''Dictionary.com Unabridged (v 1.1)''. Random House, Inc. 17 April 2007 It is analogous to the [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mass Flow
Mass flow, also known as mass transfer and bulk flow, is the movement of fluids down a pressure or temperature gradient,Moyes & Schulte (2008). Principles of Animal Physiology. Pearson Benjamin Cummings. San Francisco, California particularly in the life sciences. As such, mass flow is a subject of study in both fluid dynamics and biology. Examples of mass flow include blood circulation and transport of water in vascular plant tissues. Mass flow is not to be confused with diffusion which depends on concentration gradients within a medium rather than pressure gradients of the medium itself. Plant biology In general, bulk flow in plant biology typically refers to the movement of water from the soil up through the plant to the leaf tissue through xylem, but can also be applied to the transport of larger solutes (e.g. sucrose) through the phloem. Xylem According to cohesion-tension theory, water transport in xylem relies upon the cohesion of water molecules to each other and adhesio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conservation Of Linear Momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass and is its velocity (also a vector quantity), then the object's momentum is : \mathbf = m \mathbf. In the International System of Units (SI), the unit of measurement of momentum is the kilogram metre per second (kg⋅m/s), which is equivalent to the newton-second. Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a ''conserved'' quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change. Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum mechanic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lift-induced Drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars with airfoil wings that redirect air to cause a downforce. It is symbolized as D_\text, and the ''lift-induced drag coefficient'' as C_. For a constant amount of lift, induced drag can be reduced by increasing airspeed. A counter-intuitive effect of this is that, up to the speed-for-minimum-drag, aircraft need less power to fly faster. Induced drag is also reduced when the wingspan is higher, or for wings with wingtip devices. Explanation The total aerodynamic force acting on a body is usually thought of as having two components, lift and drag. By definition, the component of force parallel to the oncoming flow is called drag; and the component perpendicular to the oncoming ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinetic Energy
In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body when decelerating from its current speed to a state of rest. Formally, a kinetic energy is any term in a system's Lagrangian which includes a derivative with respect to time. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2. In relativistic mechanics, this is a good approximation only when ''v'' is much less than the speed of light. The standard unit of kinetic energy is the joule, while the English unit of kinetic energy is the foot-pound. History and etymology The adjective ''kinetic'' has its roots in the Greek word κίνησις ''kines ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicopter Rotor
A helicopter main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic 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. At the top of the m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alfred George Greenhill
Sir Alfred George Greenhill, FRS FRAeS (29 November 1847 in London – 10 February 1927 in London), was a British mathematician. George Greenhill was educated at Christ's Hospital School and from there he went to St John's College, Cambridge in 1866. In 1876, Greenhill was appointed professor of mathematics at the Royal Military Academy (RMA) at Woolwich, London, UK. He held this chair until his retirement in 1908. His 1892 textbook on applications of elliptic functions is of acknowledged excellence. He was one of the world's leading experts on applications of elliptic integrals in electromagnetic theory. He was a Plenary Speaker of the ICM in 1904 at Heidelberg (where he also gave a section talk) and an Invited Speaker of the ICM in 1908 at Rome, in 1920 at Strasbourg, and in 1924 at Toronto. Greenhill formula In 1879, Greenhill developed a rule of thumb for calculating the optimal twist rate for lead-core bullets. This shortcut uses the bullet's length, needing no allowanc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William John Macquorn Rankine
William John Macquorn Rankine (; 5 July 1820 – 24 December 1872) was a Scottish mechanical engineer who also contributed to civil engineering, physics and mathematics. He was a founding contributor, with Rudolf Clausius and William Thomson (Lord Kelvin), to the science of thermodynamics, particularly focusing on the first of the three thermodynamic laws. He developed the Rankine scale, an equivalent to the Kelvin scale of temperature, but in degrees Fahrenheit rather than Celsius. Rankine developed a complete theory of the steam engine and indeed of all heat engines. His manuals of engineering science and practice were used for many decades after their publication in the 1850s and 1860s. He published several hundred papers and notes on science and engineering topics, from 1840 onwards, and his interests were extremely varied, including, in his youth, botany, music theory and number theory, and, in his mature years, most major branches of science, mathematics and engineering. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mathematical Model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, biology, earth science, chemistry) and engineering disciplines (such as computer science, electrical engineering), as well as in non-physical systems such as the social sciences (such as economics, psychology, sociology, political science). The use of mathematical models to solve problems in business or military operations is a large part of the field of operations research. Mathematical models are also used in music, linguistics, and philosophy (for example, intensively in analytic philosophy). A model may help to explain a system and to study the effects of different components, and to make predictions about behavior. Elements of a mathematical model Mathematical models can take many forms, including dynamical systems, statisti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airbus A400M
The Airbus A400M AtlasNamed after the Greek mythological figure. is a European four-engine turboprop military transport aircraft. It was designed by Airbus Military (now Airbus Defence and Space) as a tactical airlifter with strategic capabilities to replace older transport aircraft, such as the Transall C-160 and the Lockheed C-130 Hercules. The A400M is sized between the C-130 and the Boeing C-17 Globemaster III; it can carry heavier loads than the C-130 and is able to use rough landing strips. In addition to its transport capabilities, the A400M can perform aerial refueling and medical evacuation when fitted with appropriate equipment. The A400M's maiden flight, originally planned for 2008, took place on 11 December 2009 from Seville Airport, Spain. Between 2009 and 2010, the A400M faced cancellation as a result of development programme delays and cost overruns; however, the customer nations chose to maintain their support for the project. A total of 174 A400M aircra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contra-rotating Propellers
Aircraft equipped with contra-rotating propellers, also referred to as CRP, coaxial contra-rotating propellers, or high-speed propellers, apply the maximum power of usually a single piston or turboprop engine to drive a pair of coaxial propellers in contra-rotation. Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear or spur gear transmission. Contra-rotating propellers are also known as counter-rotating propellers, although counter-rotating propellers is much more widely used when referring to airscrews on separate non-coaxial shafts turning in opposite directions. Operation When airspeed is low, the mass of the air flowing through the propeller disk (thrust) causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-propeller design, and causes handling problems at low speed as the air strikes the vertical st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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