People have been using lift for already more than a hundred years. Lift – is a component of the aerodynamic force which is perpendicular to the vector of the velocity of the motion of an object in the steam of liquid or of a gas which results from asymmetry of the body flow by a stream. It occurs at the motion of any object in the air, if the object has a shape conducive to this (the wing, for example).
Air flow around the wing is divided into two streams: over the wing and under it. Lower flow steams in a normal manner having no obstacles, and the upper is tapering. This is because of the shape of the wing – convex at the top. The object shall move faster to allow the same amount of air as under the wing to be transmitted above it. In accordance with Bernoulli's principle, the static pressure of the environment in the areas with higher velocity of flow is lower, and vice versa. For example, the wing has an asymmetrical profile (the upper part of the wing is more convex), so that the flow velocity above it is higher than under it. The difference of pressure that emerged generates lift. It pushes the wing up and, accordingly pushes the aircraft up. The higher the speed is, the greater is lift. In such a manner, when at a sufficient speed lift is higher than aircraft`s weight, the aircraft goes up – takes off, and if it is lower, the plane descends, at equilibrium – the flight is horizontal, as it should be in accordance with Newton's first law. In such a way, both the air that goes above the wing, and the one that goes under the wing are responsible for lift.
Newton`s Third Law also works: wind deflects downward because the wing is moving upwards, i.e. in the opposite direction. This upward movement is caused by the influence of energy of billions of tiny air molecules that hit the bottom of the wing. Furthermore, the molecules influence pressure to a large extent below the lower surface of the wing. Hence, a wing moves upwards, as if being pushed up from below.
Lift depends on the size and shape of the wing. Also of importance are the velocity at which air flows around the wing and the angle at which the air flow reaches the front edge of the wing. By varying the angle of inclination of the wing (in aviation it is called “angle of attack”), lift can be affected by the object.
Lift is widely used in modern technology. For example, thanks to lift during forward motion of the aircraft it becomes possible to maintain the aircraft in the air and its horizontal flight. The general theory of lift was established in scientific works by Joukowski, who laid the foundations of modern aerodynamics.
There are three basic principles of creation of lift: aeronautical, aerodynamic and reactive. Accordingly, all aircraft can be divided into three major groups. Aircraft, which lift is formed by the aerostatic principle, form a group of aircraft lighter than air. Aircraft based on the aeronautical principle are called aerostats. In the second group of aircraft, the most numerous one, lift is generated by aerodynamic principles when they move through the air. These aircraft are heavier than air. First of all, they include aircraft of various types and purposes. Aircraft, lift of which is created by jet principle, include rockets and spaceships of various types and purposes, rockets.
References
Aerodynamic Lift – How it is created. (n.d.) [PDF file]. Available from http://www.lets-go-fly.com/Aerodynamic%20Lift.pdf
Ali, J. (2011, November 29). Airplane Wings – How Lift is Created. Retrieved from http://www.decodedscience.com/airplane-wings-how-lift-is-created/6595
