The camber line, or mean line, of an airfoil is a curved line running halfway between its upper and lower surfaces.

Usually the frame for such an airfoil was curved, or cambered. Pitch must be evaluated along with the forces of lift and drag.Įarly airfoil shapes were thin, essentially cloth stretched over a wood frame, a type of airfoil sometimes seen today in the wings of ultralight or hang glider-type aircraft. The amount of pitching movement, or tendency for the airfoil to rotate nose up or down, is also a function of the airfoil’s shape and the way lift is produced. An airplane designer tries to select an airfoil shape that will give the best possible lift-to-drag ratio at some desired optimum flight condition, such as cruise or climb, depending on the type of aircraft. The shape of the airfoil then determines the balance of lift and drag at various angles of attack. The shape of the upper and lower surfaces of the airfoil and the angle that it makes with the oncoming airflow, or angle of attack, determines the way the flow will accelerate and decelerate around the airfoil and, thus, determines its ability to provide lift.įlow around the airfoil also causes drag, and an airfoil should be designed to get as much lift as possible while at the same time minimizing drag. The higher-speed air on the top of the airfoil produces a lower pressure than the flow over the bottom, resulting in lift. Although airfoils come in many different shapes, all are designed to accomplish the same goal: forcing the air to move faster over the top of the wing than it does over the bottom. The shape revealed if a wing were to be sliced from its leading edge to its trailing edge is called the wing’s airfoil section. Significance: The shape of a wing’s airfoil section or sections determines the amount of lift, drag, and pitching movement the wing will produce over a range of angles of attack and also determines the wing’s stall behavior.

With simulations at a higher Reynolds number (1.5 million) showing very similar drag reductions, using reflex camber over inboard blade sections appears to have significant promise for alleviating reverse flow drag on edgewise rotors at high advance ratio.Definition: A two-dimensional, front-to-back section or slice of a wing. Even greater percentage reductions in drag (up to 70%) were observed with a larger 15° reflex angle (not tested experimentally) for nose-up pitch angles greater than 5°in reverse flow. This yielded maximum drag reductions near 60% for a 10° reflex camber, compared to reductions near 50% in experiments. The simulations (unsteady Reynolds-averaged Navier–Stokes with and without the Spalart–Allmaras turbulence model) captured the reduction in separation at the trailing-edge well, as there was good agreement between the velocity fields when compared to experiments. As expected, the flow was dominated by separation over the sharp trailing edge, where at moderate angles of attack ( α <190°), a separation bubble was observed the use of reflex camber reduced the extent of this separation. Particle image velocimetry and surface pressure measurements were utilized in experiment to directly compare with the results obtained through simulation. Of the three contributors to drag-ram pressure on the upper surface near the trailing edge, suction on the lower surface near the trailing edge, and bluff body separation at the rounded nose-reflex camber (where the camber line near the trailing edge of the airfoil is deflected upward) influences the first two, reducing exposure to ram drag on the upper surface while rotating the suction on the lower surface away from the direction of drag.

Through computational fluid dynamics simulations and wind tunnel tests, this study examines a NACA 63-218 airfoil in reverse flow at Re c=375,000 and demonstrates reduction in reverse flow drag through the introduction of reflex camber.

Camber airfoil