The Impact of the Chord Length of an Airfoil
Key Takeaways
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The distance from the leading edge to the trailing edge is called the chord length of an airfoil.
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To increase the aspect ratio, one method is to decrease the chord length. This technique is called tapering.
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The chord length of an airfoil, especially that of an aircraft wing, is a chief factor influencing the lifting force generated by it.
Decreasing chord length from the root of the wing to the tip is called tapering
Airplane wings are the most significant airfoil in aircraft, and they influence lift and drag. Aircraft wings are complex three-dimensional constructions with several associated components. Several terminologies are used to describe aircraft wing geometry: leading edge, trailing edge, angle of attack, chord length of the airfoil, etc. In this article, we will explore what the chord length of an airfoil is and how it impacts aerodynamic performance.
Chord Length of an Airfoil
The airfoil system in aircraft consists of an airfoil body and, at most, one flexible strip. In an airfoil body, there is a top surface, bottom surface, span, maximum thickness, and chord length. Let’s look at what chord length is in the context of aircraft wings.
In an aircraft wing, the front part is called the leading edge and the back end is called the trailing edge. The distance from the leading edge to the trailing edge is the “chord length” of an airfoil. The geometry of the aircraft wing, especially the shape and size, has a great impact on the coefficient of lift. The ratio given by the span (distance between the wing tips) to chord length is a parameter of interest in aircraft wings, especially rectangular wings.
Aspect Ratio and Chord Length
Aspect ratio is a ratio of the square of the span to the wing area. In rectangular wings, the chord length along the span at every location is the same. Therefore, when calculating the aspect ratio of the rectangular wing, it reduces to the ratio of span to chord length of the airfoil. For a high coefficient of lift, aviation planes need to have a high aspect ratio. For less lift reduction, high aspect ratio wings that are long and slender in construction are best.
Tapering of the Aircraft Wings
To increase the aspect ratio, one method is to decrease the chord length. Tapering is a technique that decreases the chord length from the root of the wing to its tip. Tapering of the wing decreases the drag and increases the lift, which is advantageous at high speeds. Along with enhancing lift, tapering reduces the weight of the wing.
More Chord Length Terminology
To summarize: the chord length is perpendicular to the span and is in the plane of the airfoil. The chord length is measured parallel to the normal airflow over the wing. As we already discussed in rectangular wings, the chord length is constant when leading and trailing edges are parallel.
However, for improved lift, wings are tapered and the width of the wing changes along its length. The width of the wing is maximum at its root (root chord). As it travels towards the tip, it reaches minimum length (tip chord). As a consequence of tapering, the chord length varies along the span of the wing. The average chord length is given by the standard mean chord (SMC).
The mean aerodynamic chord is the location where the aerodynamic forces are assumed to act. This chord coincides with another chord, the mean geometric chord, when the coefficient of lift is assumed to be constant over the semi-span.
The Chord Length of an Airfoil and Reynolds Number
The behavior of a fluid flow can be evaluated using the Reynolds number, especially in the boundary layer. Fluid flows with the same Reynolds number exhibit the same behavior. In aircraft, fluid flow characteristics are important for creating good aerodynamic performance. From the airflow in the aircraft wings, the Reynolds number can be calculated with the following equation:
Re = v * l * 70000
In the above equation, v is the flight speed, l is the chord length of the airfoil, and 70000 is a constant associated with air. When the chord length varies from root to tip, the mean aerodynamic chord length is used in the above equation for calculating the Reynolds number.
The chord length of an airfoil, especially that of an aircraft wing, is a chief factor influencing the lifting force generated by it. Decreasing the chord length of the airfoil is one of the techniques used for creating a high coefficient of lift in aircraft.
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