Understand the Concept of Relative Wind in Aircraft

Relative wind, an important factor to consider during flight, refers to the relationship between the wing of an aircraft and the direction of airflow over said wing. In normal flight, the airflow of relative wind is in the opposite direction of the aircraft flight path. This means that if the aircraft flight path is forward, the relative wind is backwards and vise versa. Additionally, if the aircraft is ascending, the relative wind is downward.

Relative wind can also be created by the air moving around a stationary object, like an aircraft on the runway. Just prior to takeoff, when the aircraft is still stationary, the relative wind is measured as the speed and direction of the airflow around the aircraft caused by wind conditions. As the airplane accelerates down the runway, the wind and motion of the aircraft combine to form the relative wind. Once the aircraft takes flight, only the motion of the aircraft produces relative wind.

Just like fixed-wing aircraft, rotary-wing aircraft such as helicopters also experience relative wind. The difference is that, because the rotor is moving horizontally, the relative air is mostly displaced downward. This airflow is known as induced flow and is most predominant when a helicopter is hovering in still wind conditions.

One factor that affects relative wind is the aircraft’s angle of attack. The angle of attack is a term used to describe the angle between the wing chord and the flight path. Angle of attack is often mistaken for the attitude, which is the position of the aircraft relative to the earth’s surface. The angle of attack and attitude are almost never the same. Relative wind and angle of attack are both variables that can affect the amount of lift generated by a wing. This is not just a phenomenon experienced by aircraft. Any object in freefall through the atmosphere, like a skydiver, will be subject to relative wind.

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