CPL » Principles – Aeroplane » Basic Aerodynamic Theory

22.6 Basic Aerodynamic Theory

22.6.2 Describe the terms freestream static pressure, dynamic pressure (including the term ½ρV²) and total (or pitot) pressure.

Static Pressure

Static pressure is the result of the weight of the atmosphere pressing down on the air beneath.

Static pressure will exert the same force per square metre on all surfaces of an aeroplane. The lower the altitude, the greater the force per square metre.

It is called static pressure because of the air’s stationary or static presence.

An aircraft always has static pressure acting upon it.

Dynamic Pressure

Because air has mass, air in motion must possess kinetic energy, and will exert a force per square metre on any object in its path.

It is called DYNAMIC pressure because the air is moving in relation to the object being considered, in this case an aircraft.

Dynamic pressure is proportional to the density of the air and the square of the speed of the air flowing over the aircraft.

Kinetic Energy = ½ m V².  Because air has mass and density, you can change the m to the symbol for density which is rho ρ.