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66-450: Landing is the last part of a flight , where a flying animal , aircraft , or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting , although it is commonly called "landing", "touchdown" or " splashdown " as well. A normal aircraft flight would include several parts of flight including taxi , takeoff , climb , cruise , descent and landing. Aircraft usually land at an airport on

132-402: 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. Some things that fly do not generate propulsive thrust through the air, for example, the flying squirrel . This

198-451: A rocket launch , which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the Earth. 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

264-427: A firm runway or helicopter landing pad , generally constructed of asphalt concrete , concrete , gravel or grass. Aircraft equipped with pontoons ( floatplane ) or with a boat hull-shaped fuselage (a flying boat ) are able to land on water. Aircraft also sometimes use skis to land on snow or ice. To land, the airspeed and the rate of descent are reduced such that the object descends at a low enough rate to allow for

330-630: A flying fish was 45 seconds. Most birds fly ( see bird flight ), with some exceptions. The largest birds, the ostrich and the emu , are earthbound flightless birds , 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. Most small flightless birds are native to small islands, and lead

396-425: A gentle touch down. Landing is accomplished by slowing down and descending to the runway. This speed reduction is accomplished by reducing thrust and/or inducing a greater amount of drag using flaps, landing gear or speed brakes . When a fixed-wing aircraft approaches the ground, the pilot will move the control column back to execute a flare or round-out. This increases the angle of attack . Progressive movement of

462-474: A grid which allowed engine exhaust to be channeled away from the aircraft to avoid suckdown and HGI effects. Ventral strakes retroactively fitted to the P.1127 improved flow and increased pressure under the belly in low altitude hovering. Gun pods fitted in the same position on the production Harrier GR.1/GR.3 and the AV-8A Harrier did the same thing. Further lift improvement devices (LIDS) were developed for

528-427: A heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time. 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. A cubic meter of air at ordinary atmospheric pressure and room temperature has

594-564: A lifestyle where flight would offer little advantage. Among living animals that fly, the wandering albatross has the greatest wingspan, up to 3.5 meters (11 feet); the great bustard has the greatest weight, topping at 21 kilograms (46 pounds). 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 . Many species of spiders , spider mites and lepidoptera use

660-411: A mass of about 1.2 kilograms, so its weight is about 12 newtons . Therefore, any 1-cubic-meter object in air is buoyed up with a force of 12 newtons. If the mass of the 1-cubic-meter object is greater than 1.2 kilograms (so that its weight is greater than 12 newtons), it falls to the ground when released. If an object of this size has a mass less than 1.2 kilograms, it rises in the air. Any object that has

726-601: A mass that is less than the mass of an equal volume of air will rise in air - in other words, any object less dense than air will rise. Thrust-to-weight ratio is, as its name suggests, the ratio of instantaneous thrust to weight (where weight means weight at the Earth 's standard acceleration g 0 {\displaystyle g_{0}} ). It is a dimensionless parameter characteristic of rockets and other jet engines and of vehicles propelled by such engines (typically space launch vehicles and jet aircraft ). If

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792-468: A much more fluid ascent, which results in decreased noise, and decreased fuel consumption. The term "landing" is also applied to people or objects descending to the ground using a parachute . Some consider these objects to be in a controlled descent instead of actually flying. Most parachutes work by capturing air, inducing enough drag that the falling object hits the ground at a relatively slow speed. There are many examples of parachutes in nature, including

858-470: A pair of flat gliding surfaces. "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

924-534: A planetary or lunar surface for landing or impact. In 2018, researchers at Massachusetts Institute of Technology (MIT) managed to fly an aeroplane with no moving parts, powered by an " ionic wind" also known as electroaerodynamic thrust. Many human cultures have built devices that fly, from the earliest projectiles such as stones and spears, the boomerang in Australia , the hot air Kongming lantern , and kites . George Cayley studied flight scientifically in

990-626: A reality in the 20th century following theoretical and practical breakthroughs by Konstantin Tsiolkovsky and Robert H. Goddard . The first orbital spaceflight was in 1957, and Yuri Gagarin was carried aboard the first crewed orbital spaceflight in 1961. 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

1056-455: A retarding force called drag. Because lift and drag are both aerodynamic forces, the ratio 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

1122-411: A safe landing. Other factors affecting a particular landing might include: the plane size, wind , weight , runway length, obstacles, ground effects , weather , runway altitude, air temperature , air pressure , air traffic control , visibility , avionics and the overall situation. For example, landing a multi-engine turboprop military such as a C-130 Hercules , under fire in a grass field in

1188-465: A technique called ballooning to ride air currents such as thermals , by exposing their gossamer threads which gets lifted by wind and atmospheric electric fields . 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

1254-463: A war zone, requires different skills and precautions than landing a single engine plane such as a Cessna 150 on a paved runway in uncontrolled airspace, which is different from landing an airliner such as an Airbus A380 at a major airport with air traffic control . Required Navigation Performance (RNP) is being used more and more. Rather than using radio beacons, the airplane uses GPS-navigation for landing using this technique. This translates into

1320-418: Is perpendicular to the flow direction. 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

1386-439: Is a system that remains aloft primarily through the use of buoyancy to give an aircraft the same overall density as air. Aerostats include free balloons , airships , and moored balloons . An aerostat's main structural component is its envelope , a lightweight skin that encloses a volume of lifting gas to provide buoyancy , to which other components are attached. Aerostats are so named because they use "aerostatic" lift,

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1452-425: Is adjusted to control airspeed, although theoretically they must be adjusted together. In a light aircraft, with little crosswind , the ideal landing is when contact with the ground occurs as the forward speed is reduced to the point where there is no longer sufficient airspeed to remain aloft. The stall warning is often heard just before landing, indicating that this speed and altitude have been reached. The result

1518-404: 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 * V^2)] 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

1584-413: 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, and is frequently startling. The creation of this shockwave requires a significant amount of energy; because of this, supersonic flight is generally less efficient than subsonic flight at about 85% of the speed of sound. Hypersonic flight

1650-440: Is para-sailing, where a parachute-like object is pulled by a boat. In an 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 it. Supersonic flight

1716-450: 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 . The forward thrust is proportional to the mass of the airstream multiplied by the difference in velocity of the airstream. Reverse thrust can be generated to aid braking after landing by reversing

1782-648: Is termed ballistic flight . Examples include balls , arrows , bullets , fireworks etc. 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 . A spaceflight typically begins with

1848-493: 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 . However most other birds and all powered aircraft need a source of propulsion to climb. This is termed powered flight. The only groups of living things that use powered flight are birds , insects , and bats , while many groups have evolved gliding. The extinct pterosaurs , an order of reptiles contemporaneous with

1914-410: Is the reduced aerodynamic drag that an aircraft's wings generate when they are close to a fixed surface. During takeoff , ground effect can cause the aircraft to "float" while below the recommended climb speed . The pilot can then fly just above the runway while the aircraft accelerates in ground effect until a safe climb speed is reached. For rotorcraft , ground effect results in less drag on

1980-407: Is the result of entrainment of air around aircraft by lift jets when hovering. It also occurs in free air (OGE) causing loss of lift by reducing pressures on the underside of the fuselage and wings. Enhanced entrainment occurs when close to the ground giving higher lift loss. Fountain lift occurs when an aircraft has two or more lift jets. The jets strike the ground and spread out. Where they meet under

2046-480: Is used by many jet aircraft to help slow down just after touch-down, redirecting engine exhaust forward instead of back. Some propeller -driven airplanes also have this feature, where the blades of the propeller are re-angled to push air forward instead of back using the 'beta range'. Factors such as crosswind where the pilot will use a crab landing or a slip landing will cause pilots to land slightly faster and sometimes with different aircraft attitude to ensure

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2112-519: Is used to control airspeed and pitch is used to control rate of descent. The airspeed is kept well above stall speed and at a constant rate of descent. A flare is performed just before landing, and the descent rate is significantly reduced, causing a light touch down. Upon touchdown, spoilers (sometimes called "lift dumpers") are deployed to dramatically reduce the lift and transfer the aircraft's weight to its wheels, where mechanical braking , such as an autobrake system, can take effect. Reverse thrust

2178-455: 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 primarily by reentering spacecraft such as the Space Shuttle and Soyuz . 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

2244-457: Is very light touch down. Light aircraft landing situations, and the pilot skills required, can be divided into four types: In large transport category (airliner) aircraft, pilots land the aircraft by "flying the airplane on to the runway." The airspeed and attitude (pitch angle) of the plane are adjusted for landing. Thrust and pitch must be adjusted together, however the technique is reversed compared to light aircraft. In large aircraft, thrust

2310-492: The Gulfstream G650 business jet the test aircraft rotated to an angle beyond the predicted IGE stalling angle. The over-rotation caused one wing-tip to stall and an uncommanded roll, which overpowered the lateral controls, leading to loss of the aircraft. A few vehicles have been designed to explore the performance advantages of flying in ground effect, mainly over water. The operational disadvantages of flying very close to

2376-708: The Surveyor uncrewed lunar probe craft and the Apollo Lunar Module used a rocket deceleration system and landing gear to soft-land on the moon. Several Soviet rockets including the Soyuz spacecraft have used parachutes and airbag landing systems to dampen the landing on earth. In November 2015, Blue Origin 's New Shepard became the first rocket to cross the Kármán line (edge of space at 100 km altitude) and land vertically back on Earth. In December 2015, SpaceX 's Falcon 9 became

2442-529: The dinosaurs , were also very successful flying animals, and there were apparently some flying dinosaurs (see Flying and gliding animals#Non-avian dinosaurs ). Each of these groups' wings evolved independently , with insects the first animal group to evolve flight. The wings of the flying vertebrate groups are all based on the forelimbs, but differ significantly in structure; insect wings are hypothesized to be highly modified versions of structures that form gills in most other groups of arthropods . Bats are

2508-429: The static source . When a hovering rotor is near the ground the downward flow of air through the rotor is reduced to zero at the ground. This condition is transferred up to the disc through pressure changes in the wake which decreases the inflow to the rotor for a given disc loading, which is rotor thrust for each square foot of its area. This gives a thrust increase for a particular blade pitch angle, or, alternatively,

2574-482: The thrust-to-weight ratio is greater than the local gravity strength (expressed in g s), then flight can occur without any forward motion or any aerodynamic lift being required. If the thrust-to-weight ratio times the lift-to-drag ratio is greater than local gravity then takeoff using aerodynamic lift is possible. Flight dynamics is the science of air and space vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are

2640-419: The "floating" effect. Ground effect also alters thrust versus velocity, where reduced induced drag requires less thrust in order to maintain the same velocity. Low winged aircraft are more affected by ground effect than high wing aircraft. Due to the change in up-wash, down-wash, and wingtip vortices, there may be errors in the airspeed system while in ground effect due to changes in the local pressure at

2706-428: The "ram" or "cushion" effect, and thereby improves the aircraft lift-to-drag ratio. The lower/nearer the wing is to the ground, the more pronounced the ground effect becomes. While in the ground effect, the wing requires a lower angle of attack to produce the same amount of lift. In wind tunnel tests, in which the angle of attack and airspeed remain constant, an increase in the lift coefficient ensues, which accounts for

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2772-561: The AV-8B and Harrier II. To box in the belly region where the lift-enhancing fountains strike the aircraft, strakes were added to the underside of the gun pods and a hinged dam could be lowered to block the gap between the front ends of the strakes. This gave a 1200 lb lift gain. Lockheed Martin F-35 Lightning II weapons-bay inboard doors on the F-35B open to capture fountain flow created by

2838-503: The air frame, fountain impingement on the underside of the fuselage and HGI into the engine causing inlet temperature rise (ITR). Suckdown works against the engine lift as a downward force on the airframe. Fountain flow works with the engine lift jets as an upwards force. The severity of the HGI problem becomes clear when the level of ITR is converted into engine thrust loss, three to four percent per 12.222 °c inlet temperature rise. Suckdown

2904-591: The air to overcome the drag associated with lift all takes energy. Different objects and creatures capable of flight vary in the efficiency of their muscles, motors and how well this translates into forward thrust. Propulsive efficiency determines how much energy vehicles generate from a unit of fuel. The range that powered flight articles can achieve is ultimately limited by their drag, as well as how much energy they can store on board and how efficiently they can turn that energy into propulsion. Ground effect in aircraft For fixed-wing aircraft , ground effect

2970-413: The airframe and loss in hovering thrust if the engine sucks in its own exhaust gas, which is known as hot gas ingestion (HGI). When an aircraft flies at or below approximately half the length of the aircraft's wingspan above the ground or water there occurs an often-noticeable ground effect. The result is lower induced drag on the aircraft. This is caused primarily by the ground or water obstructing

3036-601: The angles of rotation in three dimensions about the vehicle's center of mass , known as pitch , roll and yaw (See Tait-Bryan rotations for an explanation). The control of these dimensions can involve a horizontal stabilizer (i.e. "a tail"), ailerons and other movable aerodynamic devices which control angular stability i.e. flight attitude (which in turn affects altitude , heading ). Wings are often angled slightly upwards- they have "positive dihedral angle " which gives inherent roll stabilization. To create thrust so as to be able to gain height, and to push through

3102-400: The car stable on the road. 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. Aerodynamic lift is created by

3168-400: The control column back will allow the aircraft to settle onto the runway at minimum speed, landing on its main wheels first in the case of a tricycle gear aircraft or on all three wheels simultaneously in the case of a conventional landing gear -equipped aircraft, commonly referred to as a "taildragger". In a light aircraft , power is adjusted to control the descent rate, and pitch attitude

3234-486: The craft is heavier than air, it must generate lift to overcome its weight . 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 in the place of lift; for example rockets and Harrier jump jets . Forces relevant to flight are These forces must be balanced for stable flight to occur. A fixed-wing aircraft generates forward thrust when air

3300-418: The creation of wingtip vortices and interrupting downwash behind the wing. A wing generates lift by deflecting the oncoming airmass (relative wind) downward. The deflected or "turned" flow of air creates a resultant force on the wing in the opposite direction (Newton's 3rd law). The resultant force is identified as lift. Flying close to a surface increases air pressure on the lower wing surface, nicknamed

3366-443: The drag coefficient, CL/CD. 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 * V^2)] 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. The drag coefficient Cd

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3432-525: The engine and fan lift jets and counter suckdown IGE. The stalling angle of attack is less in ground effect, by approximately 2–4 degrees, than in free air. When the flow separates there is a large increase in drag. If the aircraft overrotates on take-off at too low a speed the increased drag can prevent the aircraft from leaving the ground. Two de Havilland Comets overran the end of the runway after overrotating. Loss of control may occur if one wing tip stalls in ground effect. During certification testing of

3498-521: The engine is hotter and less dense than cold air. Early VTOL experimental aircraft operated from open grids to channel away the engine exhaust and prevent thrust loss from HGI. The Bell X-14 , built to research early VTOL technology, was unable to hover until suckdown effects were reduced by raising the aircraft with longer landing gear legs. It also had to operate from an elevated platform of perforated steel to reduce HGI. The Dassault Mirage IIIV VTOL research aircraft only ever operated vertically from

3564-411: The extent of deflection, and thus generates extra lift. 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 it. The only effect weight has is to vary the time that the aircraft will glide for –

3630-458: 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 scientifically. His work was replicated and extended by the Wright brothers who made gliding flights and finally the first controlled and extended, manned powered flights. Spaceflight, particularly human spaceflight became

3696-581: The first launch vehicle on an orbital trajectory to successfully vertically-land and recover its first stage, although the landed first stage was on a sub-orbital trajectory. Flight Many things can fly, from animal aviators such as birds , bats and insects , to natural gliders/parachuters such as patagial animals, anemochorous seeds and ballistospores , to human inventions like aircraft ( airplanes , helicopters , airships , balloons , etc.) and rockets which may propel spacecraft and spaceplanes . The engineering aspects of flight are

3762-413: The fuselage they mix and can only move upwards striking the underside of the fuselage. How well their upward momentum is diverted sideways or downward determines the lift. Fountain flow follows a curved fuselage underbody and retains some momentum in an upward direction so less than full fountain lift is captured unless lift improvement devices are fitted. HGI reduces engine thrust because the air entering

3828-427: The ground. Ground effect is at its maximum over a firm, smooth surface. There are two effects inherent to VTOL aircraft operating at zero and low speeds in ground effect, suckdown and fountain lift. A third, hot gas ingestion, may also apply to fixed-wing aircraft on the ground in windy conditions or during thrust reverser operation. How well, in terms of weight lifted, a VTOL aircraft hovers IGE depends on suckdown on

3894-663: 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. 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

3960-427: The only mammals capable of sustaining level flight (see bat flight ). 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

4026-410: The 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. In the context of an air flow relative to a flying body, the lift force is the component of the aerodynamic force that

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4092-399: The power required for a thrust is reduced. For an overloaded helicopter that can only hover IGE it may be possible to climb away from the ground by translating to forward flight first while in ground effect. The ground-effect benefit disappears rapidly with speed but the induced power decreases rapidly as well to allow a safe climb. Some early underpowered helicopters could only hover close to

4158-410: The purview of aerospace engineering which is subdivided into aeronautics , the study of vehicles that travel through the atmosphere, and astronautics , the study of vehicles that travel through space, and ballistics , the study of the flight of projectiles. Humans have managed to construct lighter-than-air vehicles that raise off the ground and fly, due to their buoyancy in the air. An aerostat

4224-591: The rotor during hovering close to the ground. At high weights this sometimes allows the rotorcraft to lift off while stationary in ground effect but does not allow it to transition to flight out of ground effect. Helicopter pilots are provided with performance charts which show the limitations for hovering their helicopter in ground effect (IGE) and out of ground effect (OGE). The charts show the added lift benefit produced by ground effect. For fan- and jet-powered vertical take-off and landing (VTOL) aircraft, ground effect when hovering can cause suckdown and fountain lift on

4290-427: 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

4356-422: The seeds of a dandelion . On the other hand, modern ram-air parachutes are essentially inflatable wings that operate in a gliding flight mode. Parachutists execute a flare at landing, reducing or eliminating both downward and forward speed at touchdown, in order to avoid injury. Sometimes, a safe landing is accomplished by using multiple forms of lift, thrust ( propulsive landing ) and dampening systems. Both

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