Wing

The wing, also wings, or wing is a component of a vehicle, whose main task is the generation of dynamic lift. The function of the airfoil is to be produced by interference of the flow around a sufficient force normal to the flow direction. This force is the buoyancy that keeps an airplane in the air, or lifts a hydrofoil boat from the water.

On aircraft wings are generally equipped with flaps by which the attitude of the lifting or or air resistance can be influenced. For large aircraft engines attached to them, in addition, the fuel tanks are in the wings. The distance between the left and right wing tip is referred to as a span.

Principle of operation

The mass of the deflected air per time unit depends on its density, the size (area ) of the wings and the flight speed: the faster the aircraft flies, the more air is deflected in the same time. Accelerating the deflected air flow is dependent on the air speed and the angle of attack of the wing.

At a constant air density, wing size and a constant angle of attack, the lift force is proportional to the square of the airspeed: because both the deflected air mass per unit time and the vertical acceleration grow proportionally with the airspeed. At twice the airspeed and otherwise identical flow to the air, both the accelerated downward air flow as well as its speed is doubled. This means that the buoyancy quadrupled. To keep at twice the speed, the height is based on the zero-lift angle, requires about a quarter of the angle of attack.

However, since the deflection velocity quadratically in the required drive for power, the power required for the generation of lift is inversely proportional to the air speed and the size of the wings. That is, the higher the flying velocity or the larger the airfoils, the lower the driving power required for the lift. This surprising at first glance fact you can be illustrated by the notion that the crossed airflow with increasing speed "harder" and therefore is " greater awareness ."

The mechanism described above is part of the induced resistance: he cut the buoyancy flow system supplying the energy needed for this in the form of flow resistance. This part of the induced drag can in principle not be removed because it physically takes into account the energy and momentum conservation law.

Another form of induced drag caused by wingtip vortex on the wing ends: as a real airfoil has a limited range, a pressure equalization can not avoid the vertical wingtips around. The result at each wing tip a vortex around the longitudinal axis of the aircraft, whose kinetic energy is removed from the lift-generating flow system and is thus wasted. The tip vortex can be described by a high aspect ratio ( = ratio of the span to the mean chord ) reduce, but not entirely eliminated in principle at finite wings. The winglets on the wing tips of modern aircraft are used to reduce this form of resistance by the pressure balance across the flight direction (and thus the vortex formation ) partially inhibit, respectively, the cross- flow as "Sailing " redirect turn into usable thrust. It should be noted that the total vorticity of the tip vortex can not be influenced by winglets because of Helmholz 's vortex theorem. A reduction in the vorticity would mean according to the set of Kutta - Joukowski also a reduction in the overall buoyancy of the aircraft. However, the winglets can by skilful shifting of the vertebrae have a positive impact on the distribution of lift and so reduce induced drag. Furthermore, it is to affect the flight characteristics at low speeds positive possible by winglets.

In addition to the induced drag increase other forms of resistance to flow the power requirements of an aircraft:

The frictional resistance on the surface of the wing, the aircraft brakes, by the kinetic energy in the boundary layer, it converts into thermal energy. It can be mitigated by a high surface quality ( smoothness), but not completely eliminated. Riblets can also reduce the frictional resistance.

The form or pressure drag comes from the fact that a real airfoil can not guarantee completely laminar flow. Where the flow turns into turbulence - generally at the trailing edge of the wing, but for example, also to the edges of the flaps and ailerons, etc. - created a braking suction, corresponds to the cross -section of the stall. The form drag can be minimized by a sensible choice and careful shaping of the airfoil profile.

The characteristic impedance finally comes in supersonic flight to the fore: here induces the supersonic collision of air particles on the front of the aircraft a conically propagating shock wave (Mach shear cone), which is perceived as a sonic boom on the ground.

The flow resistance (and hence the power requirement for the overcoming ) increases with the square of the airspeed. Together with the inversely proportional to flight speed performance required for the generation of lift is obtained depending on the construction for each airplane, a certain speed at which - based on the flight time - the energy required for level flight is lowest. On the flight path relative, however, the minimum energy consumption is at a significantly higher speed because the airplane then the same distance must be kept in the air less long. The speed with the lowest energy consumption per distance is called cruising speed.

Stall

, The required angle of attack to the lift generation is inversely proportional to the square of the flight speed: since at a higher speed in the same time more air mass flow is deflected and the magnitude of vertical acceleration is also increased, it is sufficient to produce a lesser angle of deviation of the same lift. Conversely, the angle of attack must be increased all the more, the slower the aircraft is flying.

The Coanda effect may provide a concern of the flow at the top of the support surface up to a specific profile shape, surface quality and Reynolds number dependent angle. Beyond this angle of attack breaks off the flow from the surface. This causes a drastic increase in resistance of the mold, at the same time interrupts the greater part of the buoyancy together, since the profile in the flow state of the air flow at the top of the support surface can not effectively deflect, but essentially only swirled. The air velocity at the flow stalls due to the increased angle of attack, called stall speed or stall speed; the resulting flight condition in which sags the plane and only a very limited is controllable, the (English) house. The stall speed is, the lowest speed at which an aircraft can just keep in the air; it is design dependent and ranges in practice from about 20 km / h ( paragliding) up to about 300 km / h ( fast jet aircraft without activated landing aids ).

Profile

The profile of an airfoil, the cross- section therethrough in the flow direction. The shape of the profile is used on the one hand, to reach as much of a boost in as little flow resistance, and on the other hand, to provide a maximum angle of attack range without stalling. Depending on the design ( purpose, speed range, wing loading ) different profiles are used.

Wing floor plan

In the early days of aviation, the wing layouts were modeled in shape to the wings of a bird, because first was the arched profile of significance. For airfoil especially Otto Lilienthal significant contributions has done. Today's wings have a variety of different forms. In general, they are elongated and tapered outdoors ( worsening ) in order to achieve a better lift distribution.

In more modern airliners they go on in so-called winglets. Due to the reduced air pressure at the top of the wing, the air flowing to the tips of the bottom to the top. This creates air turbulence that go on among other things, in the dreaded wake vortices. The winglets reduce air turbulence at the ends of the wings, thus reducing the loss of energy, bringing the wake vortices with it, and so make the aircraft more economical.

Supersonic aircraft often delta wing, whose leading edges are straight, as a rule, in the extreme case, but also may be curved several times, such as at the " Ogival " wing Concorde. Delta wings are the effects occurring during supersonic flight better adapted than the tapered wing otherwise commonly used. When flying at supersonic speeds occur compression shocks. These are areas in which the pressure of the surrounding fluid, so the air rises suddenly. Some of these shocks propagate in a shape around the plane, which is adjusted the sweep of the wing. ( The higher the desired airspeed, the stronger the wing must be swept. ) When flying at supersonic speed occurs an ( oblique ) shock at the leading edge. When flying with transonic speed ( perpendicular ) shock occurs on the upper wing surface, behind which the velocity of the airflow suddenly drops in the subsonic, resulting in a reversal of some fluid mechanical effects. Thus, when combining by an incorrect wing configuration, these different effects on a wing to can eliminate each other. To obtain a homogeneous inflow velocity at the leading edge of the wing when the incident flow is adapted itself. By the sweepback this speed decreases with the cosine of the sweep angle and leads to loss of buoyancy. Another disadvantage is that in addition to these normal speed and a tangential component occurs, which increases accordingly. This causes a floating off towards the boundary layer to the outer wing area. Characterized the boundary layer is thickened, and it can cause a separation of the flow at the wing tips. This reduces the effectiveness of the aileron.

In addition are a number of other shapes, for example circular wings ( wing ring ) is possible, but so far have been implemented only for model and experimental aircraft.

In particular in jet aircraft ( " jets " ) to allow the wings of supersonic flight are often angled arrow-shaped towards the rear. A set of military aircraft, which were constructed in the 1960s and 1970s, may by a variable geometry sweep of their wings in flight adjustable (swing-wing ) to be optimized for the particular speed.

A team of researchers ( Miklosovic / Murray / Howle / Fish) has recently completed a wing shape tested on the model of the front flippers of the humpback whale in the wind tunnel that is curled at the front edge. Characterized could be increased relative to an otherwise similar wing with a straight leading edge of the lift by up to 8 percent, and at the same time, the air resistance to be reduced up to 32 percent. The angle of attack at which it came to stall (stall ), 40 percent higher. The reason for this good performance lies in the introduction of energy into the flow through the wavy leading edge (similar vortex generators ).

Arrangement

Depending on the height of attachment of the wing divides one aircraft in low wing ( the wings sit flush with the hull bottom edge ), mid-wing aircraft ( average height ), high-wing monoplane ( flush with the hull top ) and high-wing ( wing above the fuselage ) a. Aircraft in which the tailplane is located in front of the wing, hot duck or Canardflugzeuge, aircraft in which the tailplane is located behind the wings, hot dragon aircraft. Modern wide-body aircraft are designed as low-wing monoplane, with the two wings are connected by a center wing box to the fuselage.

Most modern aircraft have on each side of the fuselage, a wing panel. In the first decades of aviation biplanes were often above the other, each with two wings, isolated three-deckers were even built. Today biplanes are only built for aerobatics. There are only aircraft with an airfoil, without stabilizer. Such are called flying wing or tail lots. Aircraft with two or more consecutively arranged wings ( tandem ) remained a rarity. As another option, there is the Boxwing wing that is been used in practice only for model aircraft and ultralights Sunny.

The wing position is roughly characterized by the shape of its front view. They can be straight, have a more or less pronounced dihedral or present themselves as gull wing.

Drive

Unlike the wings of the animals producing propulsion and lift, wings provide lift only. The tunnel must be created by separate engines. At the beginning of aviation experimented with wings, which should mimic the flapping wings of birds and thereby generate propulsion. However, these structures ( wings aircraft or ornithopter ) were found for the man -carrying flying as inappropriate and have been implemented successfully only in the model airplane.

The only viable solution to a combination of pre-and buoyancy in the wing is to rotate the wings around a vertical axis. But in this case one speaks then of a rotor blade (refer to helicopter ).

Other Features

Wings of modern aircraft to fulfill a number of additional features:

• They contain large fuel tanks, z.T. self-sealing
• They carry a variety of valves to control, such as ailerons, spoilers, trim tab
• You have buoyancy aids
• By a resilient design, the wings are at the same time the " suspension " of the aircraft and cushion vertical forces such as air turbulence
• They form in many large aircraft the suspension for the engines (usually in gondolas below)
• They are used in some aircraft with retractable landing gear of recording the chassis.
• In the 20 years of the German aircraft manufacturer Junkers used the wing approaches ( wing root ) for passenger accommodation