The verb "to fly", like mhd. Viegen from ahd. Fliogan , goes like lit. plaũkti “swim” to an idg. root pleuk- back, which is expanded from pleu- rinnen , flow, swim, fly ”and originally meant“ to move [fast] ”in general.
Different types of flight
Different types of flight are distinguished according to the various forms of movement and underlying physical principles.
Active flight in the surrounding air
The movement of a body heavier than air with dynamic lift , which is created by bodies in a flow, is called aerodynamic flying. Aerodynamic flying is described in physics with the laws of aerodynamics , e.g. B. Flies with wings , flapping wings , fixed wings , rotary wings .
The movement of a body in the air that is filled with a gas with a lower density than the surrounding air and that experiences static buoyancy is called aerostatic flying. Aerostatic flying is described using the Archimedean principle , e.g. B. Flying a free balloon .
Active flight independent of the surrounding air
The flight of a body through space with recoil propulsion is realized with rocket propulsion . The recoil drive is the practical application of Newton's 3rd axiom , e.g. B. in space flight of a rocket .
Passive flying includes jumping, a form of locomotion that is widespread in the animal kingdom. The body snaps off the ground, flies passively through the air and lands again after a short time due to the effect of gravity. If one neglects the influence of air resistance and other aerodynamic effects, the body describes the trajectory of a trajectory parabola . Depending on the aerodynamic properties of the body, the trajectory parabola can be shortened, lengthened or changed asymmetrically.
Devices that are capable of flying not only in the air but also in space are called missiles . Rockets, artificial satellites , space probes and other spacecraft are always on ballistic trajectories when no engines are used. These trajectories can optionally be periodic orbits around a celestial body or around the Lagrange point of a three-body system.
Flight in nature
Buoyancy of plant seeds and spiders
Certain species of spider emit bundles of threads, which are then caught by the wind with them. You can cover several 100 kilometers in this way.
Most land animals that climb and run can jump in the air. A part of the species on land is winged , so that they can fly even greater distances: Insects ( class Insecta) make up the majority of land animals and most adult insects have two pairs of wings .
Among the reptiles (Reptilia class) which were extinct Flugsaurier ( Pterosauria ) capable of flight, under the recent only are kites ( genus Draco ) capable of gliding. Ornate tree snakes master the gliding flight.
Most birds (class Aves) and among the mammals (class Mammalia) the gliders (family Petauridae, limited to gliding), gliding squirrels ( tribe Pteromyini, limited to gliding) and bats ( order Chiroptera) are capable of flight.
In the embodiment of flying can be made between gliding, gliding , Gaukelflug , Rüttelflug , Schwirrflug , flapping flight or flight rudder and other flight forms. There are also special flight designs such as courtship flight z. B. with snipe , which are not primarily carried out as locomotion. In the case of some insects, the flight in swarms is used for mating , e.g. B. the wedding flight of some hymenoptera or the swarm dance ( English nuptial flight ) of some mayflies . The compensation flight serves to maintain the distribution in a habitat .
Insects use different techniques to fly. Depending on the size of the insect and the speed of movement of the wings, the air for the insect is differently "tough". Particularly small insects therefore “swim” in the air, which, due to their size, flight and wing speed, appears as tough to them as water. Their wings are therefore not aerodynamically shaped, but rather resemble a rapidly rotating “ paddle ”.
The flight of a bird is subject to the same basic aerodynamic laws as a hydrofoil aircraft. However, the principle of action is completely different. Moving the wings upwards creates less drag than moving the wings downwards. Thus, the wings push the bird more up (wing flap down) than down (when the wing flaps up). This is mainly achieved by a downward curvature of the wing tips when the wing flaps upwards. The forward movement is caused by a more or less strong curvature of the wings (think of the wings of a ship's propeller), depending on the bird's intention. In other words, the so-called hand areas at the wingtips are turned with the front edge facing downwards on the downstroke, on the upstroke the front edge of the hand area points upwards. This not only pushes the air down, but also backwards. Performing the up and down movement in an inclined and less vertical path can also be used to push the air not only downwards, but also backwards and thus generate a forward movement (see flapping flight ). The forward movement can also be brought about without flapping its wings by the fact that the bird converts the potential energy it has gained with its flight altitude into propulsion while gliding . One attempt to determine the performance of different bird species based on the ratio of the length of the hand wings to the total wing length is the hand wing index .
It is interesting that the frequency of the wing flapping of migratory birds during long-distance bird migration , e.g. B. over the Sahara , is not the same as with short-haul flights in their respective target region. In "everyday flying" their wing flapping frequency is higher because they want to move as quickly as possible. During the bird migration they divide their forces better, since a lower wing beat frequency means less energy expenditure. This has led to confusion among ornithologists for some time as they tried to use radar devices to identify birds in flight on bird migration based on the frequency of their flapping.
The energy- and energy-saving gliding and gliding can be observed especially in large birds. Their flight has long been considered a great (undiscovered) secret. There are a number of natural causes that make the drive unnecessary in gliding: updrafts on mountain slopes, heated and therefore rising air masses ( thermals ) or the gusty winds ( dynamic gliding ). Birds of prey can cover large distances on their prey flights within their extensive hunting ground, sometimes more than a hundred kilometers per day. The albatross with wingspan of up to 3.5 meters is able to stay almost motionless in the air for hours in the sea breeze. Some birds also master the shaking flight , in which they fly in place.
Small birds can usually move about in both gliding and rowing flight . The very small hummingbird is one of the few birds that also masters the hovering flight , and it flies with a very high frequency of up to 80 wing beats per second. This technique makes it possible to fly backwards or sideways or to stand still in the air, similar to insects.
Through the formation of swarms and V-formation in flight, birds reduce the energy expenditure by - diagonally behind - birds following behind use the buoyancy zone of the tip vortex of the one flying ahead. In the case of large birds, synchronization of the flapping of the wings in a V-formation could also be advantageous.
The automation manufacturer Festo presented a robotic seagull for the first time at the Hanover Fair in 2011, which uses an active articulated torsion drive to fully reproduce the flight of birds and thus differs from simple flapping wing devices . Festos SmartBird can take off and land itself and generates its lift and thrust only with the wings (see below ornithopter).
Lighter than air
During the balloon flight , the aerostatic lift is generated by the lifting gas in gas cells or by hot air . In the technical jargon, the word “flying” is not applied to the ride in a balloon or an airship ; instead, the term “driving” is used. This could have historical origins, as the first balloonists adopted the vocabulary of seafaring.
Hybrid shapes use aerostatic lift plus aerodynamic forces. Airships generate a small part (about five percent) of the required lift aerodynamically by rotating propellers. Hybrid airships make greater use of aerodynamics and combine the properties of airships and aircraft.
A Kytoon - a hybrid of a kite and a balloon - uses the wind passively in addition to its buoyancy. Bionic flying objects use movement elements that are based on the flight of birds or the diving swimming of marine animals. The indoor flying object Air Jelly from Festo uses the recoil of eight paddles on tentacles similar to an octopus or a jellyfish . AirRay and AirPenguin , both also from Festo, are similar to rays and penguins .
Heavier than air
Being able to fly “like birds ” has always been a dream of mankind. The legend of Daedalus and Icarus is passed down from ancient Greek mythology , who moved through the air like birds using self-made wings. Even in this ancient legend, technical ignorance and high-spirited neglect of safety precautions are discussed as a human risk when flying (Icarus disregards the fact that the wings made by his father Daedalus with wax and bird feathers melt when approaching the sun and has a fatal accident).
In reality, people without knowledge of the physical fundamentals of aerodynamic flight were initially only able to move in the air with manned kites or, with mostly imaginative devices, at best by chance to get into a short-term lift phase without using it for a long time in flight can (see Albrecht Ludwig Berblinger ). The pre-Christian artefact of the dove of Saqqara may be a model of a glider. According to an Islamic chronicle, the scholar Abbas Ibn Firnas was the first person to develop a hang-glider (with vulture feathers) and attempted a flight in 875. However, he is said to have broken both legs during the rapid landing.
Despite the role models in nature, it took man a long time to understand the functional principle of the wing and to imitate it technically. The application of empirical and scientific methods ( Leonardo da Vinci , George Cayley ) brought the first usable insights and suggestions for empirical flight research, which, however, did not lead to an understanding of the operation of the wing and successful flight tests until the end of the 19th century. The first successful flights with apparatuses that were suitable for carrying the weight of a person were initially made in gliding flight (e.g. Otto Lilienthal , Octave Chanute , Wright brothers ).
It was only possible to cover longer distances with a controllable aircraft with the use of motorized fixed-wing aircraft at the beginning of the 20th century. With their successful powered flights, the Wright brothers laid the technical foundation for a rapid development in the history of aviation that continues to this day. It was only the knowledge gained during the development of modern motorized aircraft that made it possible to build functional, muscle-powered aircraft . The helicopter is subject to the same aerodynamic principles as the aircraft flight, although the vertical movement by rotating surfaces ( rotors is effected).
The generation of dynamic lift with wings or wings uses properties of the air ( mass , viscosity ). Due to these properties, incoming air is diverted by suitable profiling and adjustment of the wing; an impulse is transmitted to them perpendicular to the direction of flow. According to Newton's first law , this change in direction of the flow requires a continuously acting force. According to Newton's third law ( actio and reactio ), an equal and opposite force, the lift, acts on the wing.
The size of the lift force depends on speed, angle of attack and wing geometry. While the speed changes with the drive power and by changing the flight altitude , the angle of attack can be changed with the elevator . Even the wing geometry can be changed during flight, e.g. B. with the help of the landing flaps . Since the generation of lift as an induced drag counteracts the flight movement, forward movement (with the exception of gliders and gliders ) is maintained with aviation engines . This is partly done with the help of aircraft engines that drive one or more propellers , partly with jet engines , sometimes in combination ( turboprop drive ).
It was only recently that the biological models, birds , bats and insects , which have been moving with flapping wings for millions of years ( flapping flight ), have been able to function. A spectacular success was presented in 2011 with an artificial herring gull, the SmartBird . A very small ornithopter simulates the swimming of the jellyfish with 3 paddles that fold together (wings). It was developed by Leif Ristroph and Stephen Childress at New York University.
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