However a greater angle of attack also generates extra drag. Lift/drag ratio also determines the glide ratio and gliding range. Since the glide ratio is based only on the relationship of the aerodynamics forces acting on the aircraft, aircraft weight will not affect. The only effect weight has is to vary the time that the aircraft will glide for a heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time. 29 buoyancy edit main article: buoyancy air pressure acting up against an object in air is greater than the pressure above pushing down. The buoyancy, in both cases, is equal to the weight of fluid displaced - archimedes' principle holds for air just as it does for water.
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Large cargo aircraft tend to use longer wings with higher angles of attack, whereas supersonic aircraft tend to have short wings and rely heavily on high forward speed to generate lift. However, this lift (deflection) process inevitably causes a retarding force called drag. Because lift and drag are both aerodynamic forces, the ratio proposal of lift to drag is an indication of the aerodynamic efficiency of the airplane. The lift to drag ratio is the L/D ratio, pronounced "l over D ratio." An airplane has a high L/D ratio if it produces a large amount of lift or a small amount of drag. The lift/drag ratio is determined by dividing the lift coefficient by the drag coefficient, cl/CD. 26 The lift coefficient Cl is equal to the lift L divided by the (density r times half the velocity v squared times the wing area a). Cl l / (A *.5 * r * V2) The lift coefficient is also affected by the compressibility of the air, which is much greater at higher speeds, so velocity v is not a linear function. Compressibility is also affected by the shape of the aircraft surfaces. 27 The drag coefficient Cd is equal to the drag D divided by the (density r times half the velocity v squared times the reference area a). Cd d / (A *.5 * r * V2) 28 Lift-to-drag ratios for practical aircraft vary from about 4:1 for vehicles and birds with relatively short wings, up to 60:1 or more for vehicles with very long wings, such as gliders. A greater angle of attack relative to the forward movement also increases the extent of deflection, and thus generates extra lift.
This form of lift permits soaring and is particularly important for gliding. It is used by birds and gliders to stay in the air for long periods with little effort. Drag edit main article: Drag (physics) For a solid object moving through a fluid, the drag is the component of the net aerodynamic or hydrodynamic force acting opposite to the direction of the movement. Therefore, drag opposes the motion of the object, and in a powered vehicle it must be overcome by thrust. The process which creates lift also causes some drag. Lift-to-drag ratio edit Speed and drag relationships for a typical aircraft main article: Lift-to-drag ratio aerodynamic lift is created by the motion of an aerodynamic object (wing) through the air, which due to its shape and angle deflects the air. For sustained straight and level flight, lift must be equal and opposite to weight. In general, long narrow wings are able deflect a large amount of air at a slow speed, whereas smaller wings need a higher forward speed to deflect an equivalent amount of air and thus generate an equivalent amount of lift.
Reverse thrust can be generated to aid braking after landing by reversing the father's pitch of variable-pitch propeller blades, or using a thrust reverser on a jet engine. Rotary wing aircraft and thrust vectoring V/stol aircraft use engine thrust to support the weight of the aircraft, and vector sum of this thrust fore and aft to control forward speed. Lift edit main article: lift (force) Lift is defined as the component of the total aerodynamic force perpendicular to the flow direction, and drag is the component parallel to the flow direction In the context of an air flow relative to a flying body, the. 21 Aerodynamic lift results when the wing causes the surrounding air to be deflected - the air then causes a force on the wing in the opposite direction, in accordance with Newton's third law of motion. Lift is commonly associated with the wing of an aircraft, although lift is also generated by rotors on rotorcraft (which are effectively rotating wings, performing the same function without requiring that the aircraft move forward through the air). While common meanings of the word " lift " suggest that lift opposes gravity, aerodynamic lift can be in any direction. When an aircraft is cruising for example, lift does oppose gravity, but lift occurs at an angle when climbing, descending or banking. On high-speed cars, the lift force is directed downwards (called "down-force to keep the car stable on the road. Lift can also occur in a different way if the air is not still, especially if there is an updraft due to heat thermals or wind blowing along sloping terrain or other meteorological conditions.
The wind resistance caused by the craft moving through the air is called drag and is overcome by propulsive thrust except in the case of gliding. Some vehicles also use thrust for flight, for example rockets and Harrier Jump Jets. Finally, momentum dominates the flight of ballistic flying objects. Forces edit main forces on a heavier-than-air aircraft main article: Aerodynamics Forces relevant to flight are 19 These forces must be balanced for stable flight to occur. Thrust edit main article: Thrust Forces on an aerofoil cross section A fixed-wing aircraft generates forward thrust when air is pushed in the direction opposite to flight. This can be done in several ways including by the spinning blades of a propeller, or a rotating fan pushing air out from the back of a jet engine, or by ejecting hot gases from a rocket engine. 20 The forward thrust is proportional to the mass of the airstream multiplied by the difference in velocity of the airstream.
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A spaceflight typically begins with a rocket launch, which provides the samarkand initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the earth. 10 Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics. Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact. History edit many human cultures have built devices that fly, from the earliest statements projectiles such as stones and spears, 11 12 the boomerang in Australia, the hot air Kongming lantern, and kites. Aviation edit main article: aviation history george cayley studied flight scientifically in the first half of the 19th century, and in the second half of the 19th century Otto lilienthal made over 200 gliding flights and was also one of the first to understand flight. His work was replicated and extended by the Wright brothers who made gliding flights and finally the first controlled and extended, manned powered flights. 16 Spaceflight edit main article: History of spaceflight Spaceflight, particularly human spaceflight became a reality in the 20th century following theoretical and practical breakthroughs by konstantin Tsiolkovsky and Robert.
The first orbital spaceflight was in 1957 17, and Yuri gagarin was carried aboard the first manned orbital spaceflight in 1961. 18 Physics edit lighter-than-air airships are able to fly without any major input of energy main article: Aerodynamics There are different approaches to flight. If an object has a lower density than air, then it is buoyant and is able to float in the air without expending energy. A heavier than air craft, known as an aerodyne, includes flighted animals and insects, fixed-wing aircraft and rotorcraft. Because the craft is heavier than air, it must generate lift to overcome its weight.
Supersonic edit main article: Supersonic speed Supersonic flight is flight faster than the speed of sound. Supersonic flight is associated with the formation of shock waves that form a sonic boom that can be heard from the ground, 9 and is frequently startling. This shockwave takes quite a lot of energy to create and this makes supersonic flight generally less efficient than subsonic flight at about 85 of the speed of sound. Hypersonic edit main article: Hypersonic speed Hypersonic flight is very high speed flight where the heat generated by the compression of the air due to the motion through the air causes chemical changes to the air. Hypersonic flight is achieved by reentering spacecraft such as the Space Shuttle and soyuz.
Ballistic edit main article: Ballistics Atmospheric edit some things generate little or no lift and move only or mostly under the action of momentum, gravity, air drag and in some cases thrust. This is termed ballistic flight. Examples include balls, arrows, bullets, fireworks etc. Spaceflight edit main article: Spaceflight Essentially an extreme form of ballistic flight, spaceflight is the use of space technology to achieve the flight of spacecraft into and through outer space. Examples include ballistic missiles, orbital spaceflight etc. Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications. Additional non-commercial uses of spaceflight include space observatories, reconnaissance satellites and other earth observation satellites.
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6 Most species of insects can fly as adults. Insect flight makes use of either of two basic aerodynamic models: creating a leading edge vortex, found in most insects, and using clap and fling, found in very small insects such as thrips. 7 8 Mechanical edit main article: aviation Mechanical flight is the use of a machine to fly. These machines include aircraft such as airplanes, gliders, helicopters, autogyros, airships, balloons, ornithopters as well as spacecraft. Gliders are capable of unpowered flight. Another form of mechanical flight is para-sailing where a parachute-like object is pulled by a boat. In an plan airplane, lift is created by the wings; the shape of the wings of the airplane are designed specially for the type of flight desired. There are different types of wings: tempered, semi-tempered, sweptback, rectangular and elliptical. An aircraft wing is sometimes called an airfoil, which is a device that creates lift when air flows across.
"Flying" snakes also use mobile ribs to flatten their body into an aerodynamic shape, with a back and forth motion much the same as they use on the ground. Flying fish can glide using enlarged wing-like fins, and have been observed soaring for hundreds of meters. It is thought that this ability was chosen by natural selection because it was an effective means of escape from underwater predators. The longest recorded flight of a flying fish was 45 seconds. 5 Most birds fly ( see bird flight with some exceptions. The largest birds, the ostrich and the emu, are earthbound, as were the now-extinct dodos and the Phorusrhacids, which were the dominant predators of south America in the cenozoic era. The non-flying penguins have wings adapted for use under water and use the same wing movements for swimming that most other birds use for flight. Citation needed most small flightless birds are native to small islands, and lead a lifestyle where flight would offer little advantage. Among living animals that fly, the wandering albatross has the greatest wingspan, up.5 meters (11 year feet the great bustard has the greatest weight, topping at 21 kilograms (46 pounds).
birds, insects, and bats, while many groups have evolved gliding. The extinct Pterosaurs, an order of reptiles contemporaneous with the dinosaurs, were also very successful flying animals. Each of these groups' wings evolved independently. The wings of the flying vertebrate groups are all based on the forelimbs, but differ significantly in structure; those of insects are hypothesized to be highly modified versions of structures that form gills in most other groups of arthropods. 3 Bats are the only mammals capable of sustaining level flight. 4 However, there are several gliding mammals which are able to glide from tree to tree using fleshy membranes between their limbs; some can travel hundreds of meters in this way with very little loss in height. Flying frogs use greatly enlarged webbed feet for a similar purpose, and there are flying lizards which fold out their mobile ribs into a pair of flat gliding surfaces.
Aerostats include free balloons, airships, and moored balloons. An aerostat's main structural component is its envelope, a lightweight legs skin that encloses a volume of lifting gas 1 2 to provide buoyancy, to which other components are attached. Aerostats are so named because they use "aerostatic" lift, a buoyant force that does not require lateral movement through the surrounding air mass to effect a lifting force. By contrast, aerodynes primarily use aerodynamic lift, which requires the lateral movement of at least some part of the aircraft through the surrounding air mass. Aerodynamic flight edit Unpowered flight versus powered flight edit main article: Unpowered flight Some things that fly don't generate propulsive thrust through the air, for example, the flying squirrel. This is termed gliding. Some other things can exploit rising air to climb such as raptors (when gliding) and man-made sailplane gliders. This is termed soaring.
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For other uses, see, flight (disambiguation). Flight is the process by which an object moves through an atmosphere (or beyond it, as in the case of spaceflight ) without contact with the surface. This can be achieved by generating aerodynamic lift associated with propulsive thrust, aerostatically using buoyancy, or by ballistic movement. Many things can fly, from mini natural aviators such as birds, bats, and insects, to human inventions like aircraft, including airplanes, helicopters, balloons, and rockets which may carry spacecraft. The engineering aspects of flight are the purview of aerospace engineering which is subdivided into aeronautics, the study of vehicles that travel through the air, and astronautics, the study of vehicles that travel through space, and in ballistics, the study of the flight of projectiles. Contents Types of flight edit buoyant flight edit main article: Aerostat An airship flies because the upward force, from air displacement, is equal to or greater than the force of gravity humans have managed to construct lighter than air vehicles that raise off the ground. An aerostat is a system that remains aloft primarily through the use of buoyancy to give an aircraft the same overall density as air.