dragpunkten

Dragpunkten is a theoretical point used in aerodynamics to describe the location where the resultant drag force on an object in a flow can be considered to act. It is a simplifying concept that aids in analysing how drag contributes to moments and stability, without tracking the distributed drag forces across the surface.

In practice, the drag force does not act as a single, physical pin at a precise spot, but its overall effect can be represented by a single force through the drag point. This concept is closely related to the center of pressure and, in many analyses, the drag point is approximated by or discussed alongside the center of pressure. For simple shapes and ordinary flight conditions, the drag point tends to align with the center of pressure, though it can shift with changes in angle of attack, speed, and Reynolds number.

Why it matters: The position of the drag point relative to the center of gravity determines the aerodynamic moment generated by drag. This moment affects pitch stability and control, influencing how tail surfaces or control surfaces must be sized and trimmed in aircraft design, automotive aerodynamics, and other applications with external flows.

Calculation and modeling: The drag force is proportional to dynamic pressure, reference area, and drag coefficient. When modeled as acting at the drag point, the moment about a chosen reference point equals the drag force times the lever arm to that point, enabling simpler stability and performance estimates.

See also: center of pressure, center of gravity, aerodynamic center, center of drag.