Properties of Airflow:

• The atmosphere us a uniform mixture of gases with the properties of a fluid. The flow of this fluid changes with static pressure, density, temperature and velocity
• Steady Airflow – exist if every point in the airflow consistently follow these four principles over time. A particle of air follows the exact same path and velocity as the particle in front of it
• Streamline – the path that air particles follow in steady airflow
• Streamtube – is a collection of many streamlines which contains a flow much like a tube with solid walls

Continuity Equation:

• An equation stating that the air flowing thru A₁ in a stream tube must equal the air flowing thru A₂ in a streamtube. The velocity and the area in a streamtube are inversely related

Bernoulli’s Equation:

• Gives the relationship between the pressure and the velocity of steady airflow
• Dynamic Pressure (q) – is the pressure of a fluid resulting from its motion and is equal to ½ p V ²
• Total Pressure (Pt) – also called the head pressure; the sum of the static and dynamic pressures

Airspeed Measurements:

• We need to know airspeed to find out if we have sufficient dynamic pressure to create lift but not so much as to damage and we need to know the velocity to navigate
• Pitot-Static System – the measure of total pressure and static pressure on the airplane, subtracting static pressure from the total pressure results in dynamic pressure
• Pitot Tube – is a device that collects total pressure. The static pressure port is the device that collects ambient static pressure. This results in a reading of the airplane’s knots of indicated airspeed
• Indicated Airspeed – is the instrumental indication of the dynamic pressure the airplane is creating during flight
• Instrumental Error – is caused by the ram effect of air in the pitot tube resulting in higher than normal airspeed indications at airspeeds approaching the speed of sound
• Calibrated Airspeed – the corrected airspeed taking in account the instrumental error
• Compressibility Error – caused by the ram effect of air in the pitot tube resulting in higher than normal airspeed indications at airspeeds approaching the speed of sound
• Equivalent Airspeed – the true airspeed at sea level on a standard day that produces the same dynamic pressure as the actual flight condition. Found by correcting calibrated airspeed for compressibility error
• True Airspeed – the actual velocity at which an airplane moves through an airmass. Found by correcting EAS for density. TAS will only equal IAS on standard days at sea level conditions. If IAS remains constant while climbing from sea level to a higher altitude, the TAS must increase
• ICE-T – used to remember the order of airspeeds
• Ground Speed – a measure of the airplane’s actual speed over the ground. It is the TAS of the plane through the air mass corrected with the movement of air.

Mach Number:

• As a plane approaches the speed of sound it begins to suffer from the effects of compressibility. The closer it gets, the greater the pressure wall forms called a shock wave. The Mach Number is the ratio of the airplane’s TAS to the Local Speed of Sound
• Critical Mach Number – the free stream Mach Number that produces the first evidence of local sonic flow