Lift (force)
The lift force, lifting force or simply lift is the sum of all the forces on a body that force it to move perpendicular to the direction of flow.
The most common type of lift is that of a wing of an aircraft. But there are many other common uses such as propellers on both aircraft and boats, rotors on helicopters, fan blades, sails on sailboats, and wind turbines.
While the common meaning of the term "lift" suggests an "upwards" action, lift can be in any direction. For instance, for a sail the lift is horizontal, and for the wing on a race car the lift is down.
There are a number of ways of explaining the production of lift; some are more complicated than others, some have been shown to be false. The simplest explanation is that the wing deflects air downward, and the reaction pushes the wing up.
Lift (force) Media
The 1902 Wright Glider shows its lift by pulling up
Lift is defined as the component of the aerodynamic force that is perpendicular to the flow direction, and drag is the component that is parallel to the flow direction.
A cross-section of a wing defines an airfoil shape.
When a wing generates lift, it deflects air downward, and to do this it must exert a downward force on the air. Newton's third law requires that the air must exert an equal upward force on the wing.
An illustration of the incorrect equal transit-time explanation of airfoil lift.
Streamlines and streamtubes around an airfoil generating lift. The flow is two-dimensional and the airfoil has infinite span. Note the narrower streamtubes above and the wider streamtubes below.
Angle of attack of an airfoil
An airfoil with camber compared to a symmetrical airfoil
Airflow separating from a wing at a high angle of attack
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Other websites
- How Airplanes Fly: A Physical Description of Lift
- NASA tutorial, with animation, describing lift Archived 2009-03-09 at the Wayback Machine
- Description on one very common incorrect explanation of lift Archived 2014-04-27 at the Wayback Machine
- Discussion of the apparent "conflict" between the various explanations of lift Archived 2006-02-07 at the Wayback Machine
- Explanation of Lift with animation of fluid flow around an airfoil
- A treatment of why and how wings generate lift that focuses on pressure.