Airfoil in the context of "Induced drag"

Terrestrial animals are animals that live predominantly or entirely on land (e.g., cats, chickens, ants, most spiders), as compared with aquatic animals (e.g., fish, whales, octopuses, lobsters, etc.), who live predominantly or entirely in bodies of water; and semiaquatic animals (e.g., crocodilians, seals, platypus and most amphibians), who inhabit coastal, riparian or wetland areas and rely on both aquatic and terrestrial habitats. While most insects (who constitute over half of all known species in the animal kingdom) are terrestrial, some groups, such as mosquitoes and dragonflies, spend their egg and larval stages in water but emerge as fully terrestrial adults (imagos) after completing metamorphosis.

Terrestrial animals conduct respiratory gas exchange directly with the atmosphere, typically via specialized respiratory organs known as lungs, or via cutaneous respiration across the skin. They have also evolved homeostatic features such as impermeable cuticles that can restrict fluid loss, temperature fluctuations and infection, and an excretory system that can filter out nitrogenous waste in the form of urea or uric acid, in contrast to the ammonia-based excretion of aquatic animals. Without the buoyancy of an aqueous environment to support their weight, they have evolved robust skeletons that can hold up their body shape, as well as powerful appendages known as legs or limbs to facilitate terrestrial locomotion, although some perform limbless locomotion using body surface projections such as scales and setae. Some terrestrial animals even have wings or membranes that act as airfoils to generate lift, allowing them to fly and/or glide as airborne animals.

A sail is a tensile structure, which is made from fabric or other membrane materials, that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments, usually in a three- or four-sided shape.

A sail provides propulsive force via a combination of lift and drag, depending on its angle of attack, its angle with respect to the apparent wind. Apparent wind is the air velocity experienced on the moving craft and is the combined effect of the true wind velocity with the velocity of the sailing craft. Angle of attack is often constrained by the sailing craft's orientation to the wind or point of sail. 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 from the apparent wind as a sailing craft turns downwind, the more drag increases and lift decreases as propulsive forces, until a sail going downwind is predominated by drag forces. Sails are unable to generate propulsive force if they are aligned too closely to the wind.

The throwing stick or throwing club is a wooden rod with either a pointed tip or a spearhead attached to one end, intended for use as a weapon. A throwing stick can be either straight or roughly boomerang-shaped, and is much shorter than the javelin. It became obsolete as slings and bows became more prevalent, except on the Australian continent, where the native people continued refining the basic design. Throwing sticks shaped like returning boomerangs are designed to fly straight to a target at long ranges, their surfaces acting as airfoils. When tuned correctly they do not exhibit curved flight, but rather they fly on an extended straight flight path. Straight flight ranges greater than 100 m (330 ft) have been reported by historical sources as well as in recent research.

An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or the dynamic lift of an airfoil, or, in a few cases, direct downward thrust from its engines. Common examples of aircraft include airplanes, drones, rotorcraft (including helicopters), airships (including blimps), gliders, paramotors, and hot air balloons. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapter I of Title 14 of the U. S. Code of Federal Regulations states that aircraft "means a device that is used or intended to be used for flight in the air."

The human activity that surrounds aircraft is called aviation. The science of aviation, including designing and building aircraft, is called aeronautics. Crewed aircraft are flown by an onboard pilot, whereas unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as lift type, aircraft propulsion (if any), usage and others.

A wing is a type of fin that produces both lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform. Wing efficiency is expressed as lift-to-drag ratio, which compares the benefit of lift with the air resistance of a given wing shape, as it flies. Aerodynamics includes the study of wing performance in air.

Equivalent foils that move through water are found on hydrofoil power vessels and foiling sailboats that lift out of the water at speed and on submarines that use diving planes to point the boat upwards or downwards, while running submerged. The study of foil performance in water is a subfield of Hydrodynamics.

Gliding flight is heavier-than-air flight without the use of thrust; the term volplaning also refers to this mode of flight in animals. It is employed by gliding animals and by aircraft such as gliders. This mode of flight involves flying a significant distance horizontally compared to its descent and therefore can be distinguished from a mostly straight downward descent like a round parachute.

Although the human application of gliding flight usually refers to aircraft designed for this purpose, most powered aircraft are capable of gliding without engine power. As with sustained flight, gliding generally requires the application of an airfoil, such as the wings on aircraft or birds, or the gliding membrane of a gliding possum. However, gliding can be achieved with a flat (uncambered) wing, as with a simple paper plane, or even with card-throwing. However, some aircraft with lifting bodies and animals such as the flying snake can achieve gliding flight without any wings by creating a flattened surface underneath.

Wingsuit flying (or wingsuiting) is the sport of skydiving using a webbing-sleeved jumpsuit called a wingsuit to add webbed area to the diver's body and generate increased lift, which allows extended air time by gliding flight rather than just free falling. The modern wingsuit, first developed in the late 1990s, uses a pair of fabric membranes stretched flat between the arms and flanks/thighs to imitate an airfoil, and often also between the legs to function as a tail and allow some aerial steering.

Like all skydiving disciplines, a wingsuit flight almost always ends by deploying a parachute, and so a wingsuit can be flown from any point that provides sufficient altitude for flight and parachute deployment – a drop aircraft, or BASE-jump exit point such as a tall cliff or mountain top. The wingsuit flier wears parachuting equipment specially designed for skydiving or BASE jumping. While the parachute flight is normal, the canopy pilot must unzip arm wings (after deployment) to be able to reach the steering parachute toggles and control the descent path.