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The Kline–Fogleman airfoil or KF airfoil is a simple airfoil design with single or multiple steps along the length of the wing. It was originally devised in the 1960s for paper airplanes. In the 21st century the KF airfoil has found renewed interest among hobbyist builders of radio-controlled aircraft, due to its simplicity of construction. [1]
Airflow separating from an airfoil at a high angle of attack, as occurs at a stall.. In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack exceeds its critical value. [1]
Rotating stall arises when a small proportion of airfoils experience airfoil stall, disrupting the local airflow without destabilising the compressor. The stalled airfoils create pockets of relatively stagnant air (referred to as stall cells) which, rather than moving in the flow direction, rotate around the circumference of the compressor. The ...
Wingtip stall is unlikely to occur symmetrically, especially if the aircraft is maneuvering. As an aircraft turns, the wing tip on the inside of the turn is moving more slowly and is most likely to stall. As an aircraft rolls, the descending wing tip is at higher angle of attack and is most likely to stall.
Other types of foils, both natural and man-made, seen both in air and water, have features that delay or control the onset of lift-induced drag, flow separation, and stall (see Bird flight, Fin, Airfoil, Placoid scale, Tubercle, Vortex generator, Canard (close-coupled), Blown flap, Leading edge slot, Leading edge slats), as well as Wingtip ...
The aerodynamic center of an airfoil is usually close to 25% of the chord behind the leading edge of the airfoil. When making tests on a model airfoil, such as in a wind-tunnel, if the force sensor is not aligned with the quarter-chord of the airfoil, but offset by a distance x, the pitching moment about the quarter-chord point, / is given by
The angle at which maximum lift coefficient occurs is the stall angle of the airfoil, which is approximately 10 to 15 degrees on a typical airfoil. The stall angle for a given profile is also increasing with increasing values of the Reynolds number, at higher speeds indeed the flow tends to stay attached to the profile for longer delaying the ...
The effect of airfoil geometry on dynamic stall is quite intricate. As is shown in the figure, for a cambered airfoil, the lift stall is delayed and the maximum nose-down pitch moment is significantly reduced. On the other hand, the inception of stall is more abrupt for a sharp leading-edge airfoil. [8] More information is available here. [13]