空速表

Leaks A leak in the pitot system causes the ASI to under-read,
whilst a leak in the static line causes the ASI to over-read in
an unpressurised fuselage (cabin pressure is usually lower
ASI FAULTS
Blockage of the static line
If the static line is blocked, the ASI over-reads altitudes at lower altitudes, and under-reads at higher altitudes than when the line became blocked.
than the atmospheric static pressure), and under-read in a
pressurised aeroplane (cabin pressure higher than static).
ASI ERRORS
Instrument Error
Pressure Error
Position of the Pitot-Static Sensors
Manoeuvre Induced Error
Compressibility Error
Density Error
Compressibility causes an increase in the measured value of dynamic pressure, which causes the ASI to over-read. Compensation for the error and correction is on some mechanical navigation Computers.
A useful formula for estimating TAS is: TAS = CAS + (1.75% of CAS per 1000 ft of altitude)
The relationship between the various airspeeds is as follows: Airspeed Indicator Reading (ASIR) + Instrument Error Correction = IAS IAS + Pressure Error Correction = CAS CAS + Compressibility Error Correction = EAS
Chapter 5 Airspeed Indicator 第5章 空速表
PRINCIPLE OF THΒιβλιοθήκη Baidu AIRSPEED INDICATOR (ASI) When an aeroplane is stationary on the ground it is subject to normal atmospheric or static pressure. In flight, the aeroplane experiences an additional pressure due to the aeroplanes motion through the air, which is known as dynamic pressure. PT=1/2V2 + Ps or PT - Ps =1/2V2
COLOUR CODING OF THE ASI
COLOUR CODING OF THE ASI
White arc This arc marks the flap operating speed range. Green arc This arc is the normal operating speed range. Yellow This arc denotes the cautionary speed range. Red Radial line This line marks VNE
EAS + Density Error Correction = TAS
In practice, the combined corrections give: ASIR + Instrument Error Correction + Pressure Error Correction = CAS CAS + Compressibility Error Correction + Density Error Correction = TAS
ASI FAULTS
Blockage of the pilot tube
A blockage of the pilot tube causes the ASI to not respond to changes of speed in level flight. If the aeroplane climbs, the ASI indicates an increase in airspeed (over-read) and if it descends, it indicates a decrease in airspeed (under-read).
airspeed and air density. Density also varies with temperature and pressure. The values used are the sea level values of the ICAO International Standard Atmosphere.
The airspeed indicator thus measures the pressure differential between the two sources, and provides a display indication graduated in units of speed.
OPERATION OF A SIMPLE ASI
CALIBRATION OF THE ASI Standard datum values are used in the calibration of
airspeed indicators since dynamic pressure varies with