What four airflow properties must remain constant on an airfoil to have steady airflow?

To achieve steady airflow over an airfoil, certain properties of the air must remain constant throughout the flow. The correct answer identifies four critical properties: velocity, temperature, pressure, and density.

Velocity refers to the speed of the air flowing over the airfoil. For airflow to be considered steady, the velocity must not change over time at a given point on the airfoil; it must remain consistent as the air passes over it.

Temperature is another property that must remain constant because variations in temperature can affect the air density and viscosity, both of which can influence how the air behaves around the airfoil.

Pressure is essential in defining the aerodynamic forces acting on the airfoil. Maintaining constant pressure helps ensure that the flow characteristics around the airfoil do not vary with time, which is vital for achieving predictable lift and drag behavior.

Density, which is influenced by both pressure and temperature, must also remain steady for similar reasons. Changes in density could lead to fluctuations in the airflow characteristics, which would prevent the airflow from being classified as steady.

In contrast, the other options incorporate factors that do not directly pertain to the steady-state characteristics of the airflow over the airfoil. For instance, the properties related to lift, weight, thrust, and drag represent