Airspeed Indicator

Question 1

How does the Airspeed Indicator work?

Answer 1

It measures the difference between ram pressure from the pitot head and atmospheric pressure from the static source.

The greater the difference between ram air pressure and static pressure the greater the speed.

Question 2

What are the limitations the airspeed indicator is subject to?

Answer 2

It must have proper flow of air in the pitot/static system.

Question 3

What are the errors that the airspeed indicator is subject to?

Answer 3

• Position error* - coused by the static ports sensing erroneous static pressure; slipstream flow causes disturbance at eh statc port preventing actual atmospheic pressure measurement. It varies with airspeed, altitude, configuration and may be a plus or minus value.
• Density error* - Changes in altitude and temperature are not compensated for by the instrument.
• Compressibility error* - Caused by the packing of air into the pitot tube at high airspeeds, resulting in highter than normal indications. It usually occurs above 180 KIAS.