Lift

of the titles of this article is ambiguous. For further meanings see lift (term clarifying).

Lift one calls a Kraft, which exercises a liquid or a gas on a body (or on a gas volume).

One differentiates against thatThe force of gravity working static lift of right-angled the dynamic lift working for incident flow.

Drift is seen physical same Kraft as the lift, acts however in the opposite direction.

Static lift in the dead sea

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static lift

the static lift is a Kraft, which works against the force of gravity.

It develops, if itself a body in a fluid(thus a liquid or a gas), it finds thus displaced. This effect is described with the Archimedean principle.

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formula

< math> F = \ rho \ cdot V \ cdot g< /math>

Is <math> V< /math> the displaced volume, <math> \ rho< /math> is the density, therefore is <math> \ rho \ cdot V< /math> the displaced mass, and <math> \ rho \ V cdot \ cdot g< /math> their Gewichtskraft. The Archimedean principle is thus fulfilled.

Nevertheless the “displaced mass” is <math> m= \ rho \ cdot V </math> no actual body, but oneby the displacing body coined/shaped deformation (V) of the liquid (relative to their surface mirror), which a virtual density <math> \ rho </math> one measures out. The effect is to be observed thus also if the existing liquid possesses a smaller volume than thatimmersed part of the flotation chamber.


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examples of static lift

  • balloon ascend, because they are filled with a Traggas ( usually helium or is called air), which has a smaller density, as surrounding (cold) air. Altogether all haveComponents of the balloon (inclusive Covering, basket etc.) summed up a smaller and/or. the same density, as surrounding air.
  • Ships swim on the water, because the part of the ship immersed into the water is easier than the displaced waterand the total weight of the ship the total weight of the water displaced by it corresponds. Because of the large air spaces a ship has a smaller middle density than water despite the heavy building materials (steel etc.). Ships are with a certain depthin a stable equilibrium: If they dive in due to disturbances more deeply, the lift becomes larger and they again are raised, them too far raised, is reduced the lift, and the force of gravity lets them dive in again.
  • Submarines: With static dipping the ballast cells (or - tanks) are flooded and/or. aired out. If dynamic effects are missing such as currents or self-travel, it is possible to hold a submarine in purely static dipping by correct trim by means of rule or trim cells in a certain depth.In practice is however very difficult due to the waterproof one varying because of different Salzgehalte. It becomes somewhat simpler by driving out the Sehrohrs over the water surface, whereby a submarine like a surface vehicle into a stable equilibrium concerning the submerged depthone brings.
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dynamic lift

it develops, if the body moves relative to to the gas or the liquid. Kraft, which the fluid (gas or liquid) exerts on the body, consists in principle of two components:

1. that Strength F W (works toward the incident flow),

< math> F_ {\ rm W} = \ frac {1} {2} \ cdot \ rho \ cdot c_ {\ rm W} \ cdot A \ cdot v^2< /math>
C W = coefficient of drag (see also: Flow resistance coefficient and/or. C W - Worth]])
A = surface perpendicularly to the strength (cross sectional area/Projektionsfläche)
< math> \ rho< /math>= density of the medium
v = incident-flow velocity

2. the dynamic lift strength F A (English: elevator force, works right-angled for incident flow, whereby for the sake of the comprehensibility no forces of inertia are regarded here, those in the intermittent case, e.g. in the swell, additionally occur (hydrodynamic masses)).

<math> F_ {\ rm A} = \ frac {1} {2} \ cdot \ rho \ cdot c_ {\ rm A} \ cdot A \ cdot v^2< /math>
C A = coefficient of lift
A = surface, on that the lift works/bearing area
< math> \ rho< /math> = density of the medium
v = incident-flow velocity

contrary to the static lift is thoseDirection of the dynamic lift not by “above” and “down” in the sense of the force of gravity defines, but only by how bodies and current are to each other oriented. One calls nevertheless it also dynamic drift, if he works toward the Gewichtskraft, thusopposite to the static lift.

The dynamic lift depends on the size and direction of the incident-flow velocity relative to the body.

Examples of dynamic lift:

From the principle a profile disturbs itself in such a way with dynamic lift the current, as if an eddy would be there, that on the suction face with the incident flowdoes not turn and on the print page opposite - not enough in order to turn around the current, air really turns thus around an airplane bearing area. For developing this eddy forming of an eddy at the bearing area rear edge, the so-called is crucialStarting eddy. From movement of the bearing area from the peace (start) an instability of the air flow beginning and the occurrence of eddies result at the rear edge. If the current was at first nonvortical (peace), then leads to a Gegenwirbel, so that the total rotationthe vortex system (circulation) remains unchanged (sentence of Thomson). This Gegenwirbel provides then for a sufficiently large speed difference of currents on the upper and lower surface of a bearing area. After a regularity, which one calls the Helmholtz' eddy set, can a vortex filament not in the middle in the current suddenly to end its. The eddy, which carries an airplane, continues at both ends of the bearing areas u-shaped to the rear, as an enormous pair of eddies. It is at the airport of Rio de Janeiroalready occurred that someone forbid-proves a closed area at the airport fence drove on and by the pair of eddies of a landing airplane with its car meter far into air was hurled and heavily hurt - he did not know the Helmholtz' eddy set.

Example of oneCombination of static and dynamic lift:

  • Airships: They produce static lift by the gas filling and dynamic lift or if necessary drift by engine strength (tiltable propellers) and by the trunk with the help of the control surfaces.
  • Submarines: Dynamic dipping callsone the procedure of dipping with the help of the drive and the Tiefenruder (nose and tail). Without dynamic lift a submarine has always a tendency for the increase or sinking. When alarm dipping the drive on electrical and on maximum thrust becomes (AC = extreme Kraft) ahead switched. Nose the tiefenruder (e.g. 15°) downward posed and the tail depth rudder (e.g. 10°) upward posed. Thus develops an extreme inclination, which aired out ballast tank for water ballast fast sinking together with drive and effectuation.
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Drift

toward the force of gravity working lift strength is called with certain applications drift. Drift, which Kraft, with which a body is pressed on the soil, plays an important role in the autohaven, because there as high a contact pressure as possiblethe vehicle on the road is desired, in order to obtain a high road grip, and thus high rates of turn. Drift marks thereby the dynamic drift by aerodynamic surfaces, which are called with racing car wing. The spoiler likewise used in the automotive manufacture produce noneDrift, but prevent only the emergence of dynamic lift, which is produced by the aerodynamic characteristics of the body form. The more highly the drift is, the more stability has one in curves. One must lose however speed on the straight lines. If more speedon the straight line, reduces one is necessary the drift. One loses at stability in the curves.

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see also

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