The Air Speed calculator computes the air speed of an aircraft based on the static local atmospheric pressure (PS), the total pressure (PT) and the density of air (`rho`).
INSTRUCTIONS: Choose units and enter the following:
- (PT) Total Pressure measured by a pilot tube
- (PS) Total Static local atmospheric pressure
- (ρ) Density of Air
Air Speed (V0): The calculator returns the velocity in kilometers per hour. However this can be automatically converted to compatible units via the pull-down menu.
The Math / Science
The formula used in this calculator is the basis for airspeed measurement on aircraft which relies on reading the pressure at a pitot tube device mounted on the external surfaces of the aircraft.
This equation is derived from Bernoulli's equation's proposition that the total energy in the air flowing past the pitot tube is the sum of the potential energy due to air pressure and the kinetic energy due to motion of the air.
`E_Tot` = `E_"Potential"` + `E_"Kinetic"`
This translates to `P_"Total" = P_"Static" + 1/2*rho*V^2`
Solving for V gives us the formula used for Air Speed in this calculator:
`V = sqrt( (2*(P_"Total" - P_"Static"))/rho)`
where:
- V = Air Speed
- PTotal = Total Pressure Measured by a Pilot Tube (a pressure measurement instrument used to measure fluid flow velocity)
- PStatic = Total Static Local Atmospheric Pressure
- ρ = Density of Air
Static Local Atmospheric Pressure
Static Local Atmospheric Pressure refers to the pressure exerted by the atmosphere at a specific location, typically measured when the air is at rest relative to the measurement device. This pressure is influenced by factors such as altitude, weather conditions, and temperature.
Key points about Static Local Atmospheric Pressure:
- "Static": This term indicates that the pressure is measured in a stationary environment, unaffected by motion or dynamic forces like wind or airspeed.
- "Local": Atmospheric pressure varies depending on geographic location and altitude. For example:
- At sea level, the average atmospheric pressure is approximately 101.3 kPa (kilopascals) or 14.7 psi (pounds per square inch).
- At higher altitudes, atmospheric pressure decreases because there is less air overhead.
Influencing Factors:
- Altitude: Pressure decreases with elevation because the air column above the measurement point becomes shorter and contains less air mass.
- Weather Systems: High-pressure systems typically bring clear skies, while low-pressure systems are associated with storms and precipitation.
- Temperature: Warm air expands and reduces pressure, while cooler air contracts and increases it.
Static local atmospheric pressure is essential in various fields, including meteorology, aviation, and engineering, as it provides a baseline for understanding and predicting weather, calculating lift for aircraft, or calibrating pressure-sensitive instruments.
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