Which statement describes the operational principle of an airspeed indicator?
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A
It measures total air pressure and compares it with static air pressure.
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B
It measures total air pressure via static ports and converts it into a speed indication.
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C
It measures dynamic air pressure using the Pitot tube and converts it into a speed indication.
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D
It measures static air pressure and compares it with a vacuum.
Refer to figure.
The ASI is an air pressure sensing instrument.
It is worth mentioning that an aircraft that is stationary on the ground will be subject only to ambient atmospheric pressure or static pressure. The aircraft will be subject to additional or dynamic pressure in forward motion.
Thus, the total pressure the aircraft will be subjected to will be the static and dynamic pressure. This is known as total pressure or P.
Total Pressure = Dynamic + Static
The dynamic pressure experienced by the aircraft will vary with its speed through the air, and mathematically, this relationship is expressed in the formula.
Dynamic Pressure = 1/2ρV2 , where V is the true airspeed, and ρ is the density of the air.
So, if dynamic pressure can be isolated from the total or P to pressure, it can be used to indicate airspeed.
Therefore, in the context of the previous information, the airspeed indicator's function is to isolate the dynamic pressure from the pitot pressure and display the dynamic pressure calibrated as airspeed.
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