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True wind (V T) is the same everywhere in the diagram, whereas boat velocity (V B) and apparent wind (V A) vary with point of sail. Forces on sails result from movement of air that interacts with sails and gives them motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles.
The dolphin flipper at bottom left obeys the same principles in a different fluid medium; it is an example of a hydrofoil. Streamlines on an airfoil visualised with a smoke wind tunnel. An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more lift than drag. [1]
On points of sail where it is possible to align the leading edge of the sail with the apparent wind, the sail may act as an airfoil, generating propulsive force as air passes along its surface, just as an airplane wing generates lift, which predominates over aerodynamic drag retarding forward motion. The more that the angle of attack diverges ...
Airfoil – An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section). Airlock – is a device which permits the passage of people and objects between a pressure vessel and its surroundings while minimizing the change of ...
The distribution of forces on a wing in flight are both complex and varying. This image shows the forces for two typical airfoils, a symmetrical design on the left, and an asymmetrical design more typical of low-speed designs on the right. This diagram shows only the lift components; the similar drag considerations are not illustrated.
The apparent wind on the sail creates a total aerodynamic force, which may be resolved into drag—the force component in the direction of the apparent wind—and lift—the force component normal (90°) to the apparent wind. Depending on the alignment of the sail with the apparent wind, lift or drag may be the predominant propulsive component.
A sail batten is a flexible insert in a fore-and-aft sail that provides added stiffness and definition to the sail's airfoil cross-section. [1] The most common use of sail battens is in the roach of a mainsail. The batten extends the leech past the line that runs from the head and the clew of the sail to create a wider sail towards the top.
Streamlines around a NACA 0012 airfoil at moderate angle of attack. A foil generates lift primarily because of its shape and angle of attack. When oriented at a suitable angle, the foil deflects the oncoming fluid, resulting in a force on the foil in the direction opposite to the deflection. This force can be resolved into two components: lift ...