The engineering aspects of flight are the purview ofaerospace engineering which is subdivided intoaeronautics, the study of vehicles that travel through the atmosphere, andastronautics, the study of vehicles that travel through space, andballistics, the study of the flight of projectiles.
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 and fly, due to theirbuoyancy in the air.
Anaerostat is a system that remains aloft primarily through the use ofbuoyancy to give an aircraft the same overall density as air. Aerostats includefree balloons,airships, andmoored balloons. An aerostat's main structural component is itsenvelope, a lightweightskin that encloses a volume oflifting gas[1][2] to providebuoyancy, to which other components are attached.
Aerostats are so named because they use "aerostatic" lift, abuoyant force that does not require lateral movement through the surrounding air mass to effect a lifting force. By contrast,aerodynes primarily useaerodynamiclift, which requires the lateral movement of at least some part of theaircraft through the surrounding air mass.
Some things that fly do not generate propulsive thrust through the air, for example, theflying squirrel. This is termedgliding. Some other things can exploit rising air to climb such asraptors (when gliding) andman-made sailplane gliders. This is termedsoaring. However most other birds and allpowered aircraft need a source ofpropulsion to climb. This is termed powered flight.
The only groups ofliving things that use powered flight arebirds,insects, andbats, while many groups have evolved gliding. The extinctpterosaurs, anorder of reptiles contemporaneous with thedinosaurs, were also very successful flying animals,[3] and there were apparently someflying dinosaurs. Each of these groups'wingsevolved independently, with insects the first animal group to evolve flight.[4] 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 ofarthropods.[3]
Bats are the onlymammals capable of sustaining level flight (seebat flight).[5] However, there are severalgliding 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 areflying lizards which fold out their mobile ribs into 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 bynatural selection because it was an effective means of escape from underwater predators. The longest recorded flight of a flying fish was 45 seconds.[6]
Most birds can fly, with some exceptions. The largest birds, theostrich and theemu, are earthboundflightless birds, as were the now-extinctdodos and thePhorusrhacids, which were the dominant predators ofSouth America in theCenozoic era. The non-flyingpenguins 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, thewandering albatross has the greatest wingspan, up to 3.5 meters (11 feet); thegreat bustard has the greatest weight, topping at 21 kilograms (46 pounds).[7]
Most species ofinsects 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 usingclap and fling, found in very small insects such asthrips.[8][9]
Mechanical flight is the use of amachine to fly. These machines includeaircraft such asairplanes,gliders,helicopters,autogyros,airships,balloons,ornithopters as well asspacecraft.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 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 anairfoil, which is a device that creates lift when air flows across it.
Supersonic flight is flight faster than thespeed of sound. Supersonic flight is associated with the formation ofshock waves that form asonic boom that can be heard from the ground,[10] 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 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 theSpace Shuttle andSoyuz.
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 termedballistic flight. Examples includeballs,arrows,bullets,fireworks etc.
A spaceflight typically begins with arocket launch, which provides the initial thrust to overcome the force ofgravity and propels the spacecraft from the surface of the Earth.[11] Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study calledastrodynamics. Some spacecraft remain in space indefinitely, some disintegrate duringatmospheric reentry, and others reach a planetary or lunar surface for landing or impact.
George Cayley studied flight scientifically in the first half of the 19th century,[16][17][18] and in the second half of the 19th centuryOtto Lilienthal made over 200 gliding flights and was also one of the first to understand flight scientifically. His work was replicated and extended by theWright brothers who made gliding flights and finally the first controlled and extended, manned powered flights.[19]
Lighter-than-airairships are able to fly without any major input of energy
There are different approaches to flight. If an object has a lowerdensity than air, then it isbuoyant and is able tofloat in the air without expending energy. Aheavier than air craft, known as anaerodyne, includes flighted animals and insects,fixed-wing aircraft androtorcraft. Because the craft is heavier than air, it must generatelift to overcome itsweight. The wind resistance caused by the craft moving through the air is calleddrag and is overcome bypropulsive thrust except in the case ofgliding.
Afixed-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 apropeller, or a rotatingfan pushing air out from the back of ajet engine, or by ejecting hot gases from arocket engine.[23] The forward thrust is proportional to themass of the airstream multiplied by the difference invelocity of the airstream. Reverse thrust can be generated to aid braking after landing by reversing the pitch of variable-pitch propeller blades, or using athrust reverser on a jet engine.Rotary wing aircraft andthrust vectoringV/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 is defined as the component of theaerodynamic force that is perpendicular to the flow direction, and drag is the component that is parallel to the flow direction
In the context of anair flow relative to a flying body, thelift force is thecomponent of theaerodynamic force that isperpendicular to the flow direction.[24] 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 withNewton's third law of motion.
Lift is commonly associated with thewing of anaircraft, although lift is also generated byrotors onrotorcraft (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 iscruising 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.
For a solid object moving through a fluid, the drag is the component of thenetaerodynamic orhydrodynamicforce acting opposite to the direction of the movement.[25][26][27][28] Therefore, drag opposes the motion of the object, and in a powered vehicle it must be overcome bythrust. The process which creates lift also causes some drag.
Speed and drag relationships for a typical aircraft
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. 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 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.[29]
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.[30]
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 * V^2)][31]
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. 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 – a heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time.[32]
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 ordinaryatmospheric pressure and room temperature has a mass of about 1.2 kilograms, so its weight is about 12newtons. 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 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 instantaneousthrust toweight (where weight means weight at theEarth's standard acceleration).[33] It is a dimensionless parameter characteristic ofrockets and other jet engines and of vehicles propelled by such engines (typically spacelaunch vehicles and jetaircraft).
If thethrust-to-weight ratio is greater than the local gravity strength (expressed ings), 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 thentakeoff using aerodynamic lift is possible.
The upward tilt of the wings and tailplane of an aircraft, as seen on thisBoeing 737, is called dihedral angle
Flight dynamics is the science ofair andspace vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in threedimensions about the vehicle'scenter of mass, known aspitch,roll andyaw (SeeTait-Bryan rotations for an explanation).
The control of these dimensions can involve ahorizontal stabilizer (i.e. "a tail"),ailerons and other movable aerodynamic devices which control angular stability i.e. flight attitude (which in turn affectsaltitude,heading). Wings are often angled slightly upwards- they have "positivedihedral angle" which gives inherent roll stabilization.
To create thrust so as to be able to gain height, and to push through 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.[34][35]
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.[36]
For powered aircraft the useful energy is determined by theirfuel fraction- what percentage of the takeoff weight is fuel, as well as thespecific energy of the fuel used.
All animals and devices capable of sustained flight need relatively high power-to-weight ratios to be able to generate enough lift and/or thrust to achieve take off.
Vehicles that can fly can have different ways totakeoff and land. Conventional aircraft accelerate along the ground until sufficient lift is generated fortakeoff, and reverse the process forlanding. Some aircraft can take off at low speed; this is called a short takeoff. Some aircraft such as helicopters andHarrier jump jets can take off and land vertically. Rockets also usually take off and land vertically, but some designs can land horizontally.
In aircraft, successfulair navigation involves piloting an aircraft from place to place without getting lost, breaking the laws applying to aircraft, or endangering the safety of those on board or on theground.
The techniques used for navigation in the air will depend on whether the aircraft is flying under thevisual flight rules (VFR) or theinstrument flight rules (IFR). In the latter case, thepilot will navigate exclusively usinginstruments andradio navigation aids such as beacons, or as directed underradar control byair traffic control. In the VFR case, a pilot will largely navigate usingdead reckoning combined with visual observations (known aspilotage), with reference to appropriate maps. This may be supplemented using radio navigation aids.
Aguidance system is a device or group of devices used in thenavigation of aship,aircraft,missile,rocket,satellite, or other moving object. Typically, guidance is responsible for the calculation of the vector (i.e., direction, velocity) toward an objective.
A conventional fixed-wingaircraft flight control system consists offlight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight.Aircraft engine controls are also considered as flight controls as they change speed.
Air safety is a term encompassing the theory, investigation and categorization offlight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety ofair travel.
^"Sir George Cayley". Flyingmachines.org. Retrieved27 August 2019.Sir George Cayley is one of the most important people in the history of aeronautics. Many consider him the first true scientific aerial investigator and the first person to understand the underlying principles and forces of flight.
^"The Pioneers: Aviation and Airmodelling". Retrieved26 July 2009.Sir George Cayley, is sometimes called the 'Father of Aviation'. A pioneer in his field, he is credited with the first major breakthrough in heavier-than-air flight. He was the first to identify the four aerodynamic forces of flight – weight, lift, drag, and thrust – and their relationship and also the first to build a successful human-carrying glider.
^"U.S. Centennial of Flight Commission – Sir George Cayley". Archived fromthe original on 20 September 2008. Retrieved10 September 2008.Sir George Cayley, born in 1773, is sometimes called the Father of Aviation. A pioneer in his field, Cayley literally has two great spurts of aeronautical creativity, separated by years during which he did little with the subject. He was the first to identify the four aerodynamic forces of flight – weight, lift, drag, and thrust and their relationship. He was also the first to build a successful human-carrying glider. Cayley described many of the concepts and elements of the modern aeroplane and was the first to understand and explain in engineering terms the concepts of lift and thrust.
^Sutton and Biblarz 2000, p. 442. Quote: "thrust-to-weight ratio F/W0 is a dimensionless parameter that is identical to the acceleration of the rocket propulsion system (expressed in multiples of g0) if it could fly by itself in a gravity free vacuum."
_arrives_London_Heathrow_11Apr2015_arp.jpg)
