In flight mechanics, the rate of change of the longitudinal aerodynamic force concerning airspeed is known as the “aerodynamic drag polar” or “drag curve.” This concept describes how the aerodynamic drag force experienced by an aircraft changes as its airspeed (or velocity) varies.
The aerodynamic drag polar is usually represented graphically with drag force (X) on the vertical axis and airspeed (u₀) on the horizontal axis. It helps illustrate how the drag force varies with airspeed under different flight conditions, such as different angles of attack, configurations, and altitudes.
- Xu: This represents the rate of change of the longitudinal aerodynamic force (often referred to as the drag force) concerning changes in airspeed (u₀). It quantifies how the drag force changes as the airspeed of the aircraft changes.
- Q: This typically represents the dynamic pressure, which is defined as (1/2) * ρ * u₀^2, where ρ is the air density at the altitude where the aircraft is flying and u₀ is the freestream airspeed.
- s: This represents the reference area, often associated with the frontal area of the aircraft or the area over which the drag force acts. It is used to calculate the drag force and is typically measured in square meters (m²).
- Cd: This is the drag coefficient, which quantifies the drag force experienced by the aircraft based on its shape and other aerodynamic characteristics. It is a dimensionless parameter.
- m: This represents the mass of the aircraft, which is a constant property of the aircraft, typically measured in kilograms (kg).
- u₀: This is the freestream airspeed or the initial velocity of the aircraft. It represents the speed at which the aircraft is traveling through the air and is typically measured in meters per second (m/s).