 | This article needs additional citations for verification .(February 2018) |
A tailwind is a wind that blows in the direction of travel of an object, while a headwind blows against the direction of travel. A tailwind increases the object's speed and reduces the time required to reach its destination, while a headwind has the opposite effect.
The terms are also used metaphorically in business and elsewhere about circumstances where progress is made harder (headwind) or easier (tailwind).
In aeronautics, a headwind is favorable in takeoffs and landings because an airfoil moving into a headwind is capable of generating greater lift than the same airfoil moving through tranquil air, or with a tailwind, at equal ground speed. As a result, aviators and air traffic controllers commonly choose to take off or land in the direction of a runway that will provide a headwind. Aircraft carriers usually turn into the wind during takeoffs and landings, and may increase their own speed. While on take-off and landing, headwinds are good because they allow the aircraft to use a shorter runway, in flight, however, headwinds are bad because they reduce the ground speed of the aircraft, which requires more fuel to get to the destination. Conversely, tailwinds are bad on take-off and landing, but are good in flight.
In sailing, a headwind may make forward movement difficult, and necessitate tacking into the wind.
In motor vehicles, wind can affect fuel consumption and top speed but is usually ignored by the driver who chooses the speed from speed limits and road conditions.
In cycling, headwind is felt strongly by cyclists. It decreases the speed and increases the advantage of drafting, i.e. riding closely together in groups. This can affect tactics in road bicycle racing. The comedian Jacob Haugaard made a pointedly absurd campaign promise of more tailwind on bicycle paths when he successfully ran as an independent in the 1994 Danish parliamentary election. Cycling in Denmark is very popular.
Tailwinds and headwinds are commonly measured in relation to the speed of vehicles — commonly air and watercraft — as well as in running events — particularly sprints up to 200 metres where athletes run in the same or mostly same direction and wind assistance from a tailwind above two metre per second is not allowed in records. This limit also applies to long jump and triple jump.
Pilots calculate the Headwind or Tailwind Component and the Crosswind Component of local wind before takeoff. The direction of wind at a runway is measured using a windsock and the speed by an anemometer, often mounted on the same post. Headwind and Tailwind are opposite interpretations of the wind component which is parallel to the direction of travel, [1] while Crosswind represents the perpendicular component. Determining the ground speed of an aircraft requires the calculation of the head or tailwind.
Assume: [2]
Then
For example, if the wind is at 09015 that means the wind is currently from heading 090 degrees with a speed of 15 knots and the aircraft is taking-off from runway 24; having heading of 240. The pilot prefers the runway side with less than 90 difference from wind direction, in this case Runway 06; heading 060. Here, .
The aircraft is said to have 7.5 knots of crosswind and 13 knots of headwind on runway 06, or 13 knots of tailwind on runway 24.
Aircraft usually have maximum tailwind and crosswind components which they cannot exceed. If the wind is at eighty degrees or above it is said to be full-cross. If the wind exceeds 100 degrees it is common practice to takeoff and land from the opposite end of the runway, it has a heading of 060 in the above-mentioned example.
Rotation or rotational motion is the circular movement of an object around a central line, known as axis of rotation. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersecting anywhere inside or outside the figure at a center of rotation. A solid figure has an infinite number of possible axes and angles of rotation, including chaotic rotation, in contrast to rotation around a fixed axis.
In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna's directivity and radiation efficiency. The term power gain has been deprecated by IEEE. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, gain is understood to refer to the peak value of the gain, the gain in the direction of the antenna's main lobe. A plot of the gain as a function of direction is called the antenna pattern or radiation pattern. It is not to be confused with directivity, which does not take an antenna's radiation efficiency into account.
A windsock is a conical textile tube that resembles a giant sock. It can be used as a basic indicator of wind speed and direction, or as decoration. Windsocks are typically used at airports to show the direction and strength of the wind to pilots, and at chemical plants where there is risk of gaseous leakage. They are also sometimes located alongside highways at windy locations.
Apparent wind is the wind experienced by a moving object.
An airfield traffic pattern is a standard path followed by aircraft when taking off or landing while maintaining visual contact with the airfield.
Cruise is the phase of aircraft flight that starts when the aircraft levels off after a climb, until it begins to descend for landing. Cruising usually comprises the majority of a flight, and may include changes in heading, airspeed, and altitude.
A crosswind is any wind that has a perpendicular component to the line or direction of travel. This affects the aerodynamics of many forms of transport. Moving non-parallel to the wind direction creates a crosswind component on the object and thus increasing the apparent wind on the object; such use of cross wind travel is used to advantage by sailing craft, kiteboarding craft, power kiting, etc. On the other side, crosswind moves the path of vehicles sideways and can be a hazard.
A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow or relative wind. In other words, for a conventional aircraft, the nose will be pointing in the opposite direction to the bank of the wing(s). The aircraft is not in coordinated flight and therefore is flying inefficiently.
Ground speed is the horizontal speed of an aircraft relative to the Earth’s surface. It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight.
Projectile motion is a form of motion experienced by an object or particle that is projected in a gravitational field, such as from Earth's surface, and moves along a curved path under the action of gravity only. In the particular case of projectile motion on Earth, most calculations assume the effects of air resistance are passive and negligible. The curved path of objects in projectile motion was shown by Galileo to be a parabola, but may also be a straight line in the special case when it is thrown directly upward or downward. The study of such motions is called ballistics, and such a trajectory is a ballistic trajectory. The only force of mathematical significance that is actively exerted on the object is gravity, which acts downward, thus imparting to the object a downward acceleration towards the Earth’s center of mass. Because of the object's inertia, no external force is needed to maintain the horizontal velocity component of the object's motion. Taking other forces into account, such as aerodynamic drag or internal propulsion, requires additional analysis. A ballistic missile is a missile only guided during the relatively brief initial powered phase of flight, and whose remaining course is governed by the laws of classical mechanics.
The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is gross lift-off mass, or GLOW. MTOW is usually specified in units of kilograms or pounds.
In plane geometry, Morley's trisector theorem states that in any triangle, the three points of intersection of the adjacent angle trisectors form an equilateral triangle, called the first Morley triangle or simply the Morley triangle. The theorem was discovered in 1899 by Anglo-American mathematician Frank Morley. It has various generalizations; in particular, if all the trisectors are intersected, one obtains four other equilateral triangles.
Screw theory is the algebraic calculation of pairs of vectors, such as angular and linear velocity, or forces and moments, that arise in the kinematics and dynamics of rigid bodies.
A banked turn is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. For a road or railroad this is usually due to the roadbed having a transverse down-slope towards the inside of the curve. The bank angle is the angle at which the vehicle is inclined about its longitudinal axis with respect to the horizontal.
Antenna measurement techniques refers to the testing of antennas to ensure that the antenna meets specifications or simply to characterize it. Typical parameters of antennas are gain, bandwidth, radiation pattern, beamwidth, polarization, and impedance.
Marin County Airport or Gnoss Field, formerly O56, is a public airport two miles northeast of Novato, California, United States. It covers 90 acres (360,000 m2), and has one runway and one helipad.
In aviation, a crosswind landing is a landing maneuver in which a significant component of the prevailing wind is perpendicular to the runway center line.
China Airlines Flight 605 was a daily non-stop flight departing from Taipei at 6:30 a.m. and arriving at Kai Tak Airport in Hong Kong at 7:00 a.m. local time. On November 4, 1993, the plane went off the runway and overran while landing during a storm. It was the first hull loss of a Boeing 747-400.
In orbital mechanics, a frozen orbit is an orbit for an artificial satellite in which perturbations have been minimized by careful selection of the orbital parameters. Perturbations can result from natural drifting due to the central body's shape, or other factors. Typically, the altitude of a satellite in a frozen orbit remains constant at the same point in each revolution over a long period of time. Variations in the inclination, position of the apsis of the orbit, and eccentricity have been minimized by choosing initial values so that their perturbations cancel out. This results in a long-term stable orbit that minimizes the use of station-keeping propellant.
