# Relative wind

﻿
Relative wind

=Relative wind in aeronautics=

In aeronautics, the relative wind is the direction of airflow over the airfoil, i.e. in vector terms it is the vector sum of the ambient air past the aircraft: Most usefully, it is the direction of the air over the aircraft's wings and control surfaces. The angle between the wing chord line and the relative wind defines the angle of attack for an airfoil. Note that the relative wind can be in any direction at any velocity, and not necessarily parallel to the surface. The relative wind is of great importance to pilots because exceeding the critical angle of attack will result in a stall, regardless of airspeed.

Relative wind in freefall

Relative wind is also used to describe the airflow relative to one's body during freefall i.e. during a skydive or BASE jump. In a normal skydive the vertical descent of the skydiver creates an upward relative wind. The relative wind strength increases with increased descent rate.

The relative wind is directly opposite to the direction of travel.

Therefore, when a skydiver exits a forward-moving aircraft such as an aeroplane, the relative wind eminates from the direction the aeroplane is facing due to the skydiver's initial forward ( horizontal ) momentum. As gravity gradually overcomes this forward momentum and attracts the skydiver downward, the relative wind alters proportionally into an upward ( vertical ) direction. This creates an arc of travel for the skydiver similar to water flowing from a low pressure hose held horizontally and creates a variation in the pitch of the relative wind from horizontal to vertical.

When exiting the plane during a normal belly-to-earth skydive, the skydiver must arch his body in the direction of travel which is initially horizontal. If the skydiver continues to arch, his belly will gradually alter pitch until he is belly-to-earth. This section of the jump is commonly referred to as "the hill"

Relative wind differs from the wind we refer to in meteorology in that the object ( e.g. the skydiver ) moves past the air, as opposed to the air moving past the object.

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• relative wind — /wind/ the velocity or direction of airflow with respect to the body it surrounds, esp. an airfoil. [1915 20] * * * …   Universalium

• relative wind — i. The velocity and direction of the wind with reference to the body over which it is flowing. Also the relative airflow against an airfoil. In aircraft, it is normally the same as the TAS (true air speed) but seldom aligned with the longitudinal …   Aviation dictionary

• relative wind — noun : the motion of the air relative to a body in it usually determined so as to exclude disturbance at the surfaces of the body * * * /wind/ the velocity or direction of airflow with respect to the body it surrounds, esp. an airfoil. [1915 20] …   Useful english dictionary

• Relative Wind — (Airplanes) wind created during the movement of a surface (such as a wing) through the air (the speed of the wind is equal to the speed of the wing but in the reverse direction) …   English contemporary dictionary

• relative wind — noun Date: 1915 the motion of the air relative to a body in it …   New Collegiate Dictionary

• Relative — can refer to: *Kinship, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are said to be relatives Physics*Relativity as a concept in physics (for example Albert Einstein s… …   Wikipedia

• wind scale — /wind/ a numerical scale, as the Beaufort scale, for designating relative wind intensities. [1905 10] * * * …   Universalium

• wind scale — n. a scale used in meteorology to designate relative wind intensities, as the Beaufort scale …   English World dictionary

• Wind turbine design — An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines Wind turbines History Design …   Wikipedia

• wind scale — noun an international scale of wind force from 0 (calm air) to 12 (hurricane) • Syn: ↑Beaufort scale • Hypernyms: ↑scale, ↑scale of measurement, ↑graduated table, ↑ordered series …   Useful english dictionary