1. Pitot-Static System:
* Most common method: Used for measuring indicated airspeed (IAS).
* How it works: Two tubes are used:
* Pitot tube: Points directly into the airflow, measuring total air pressure (static pressure + dynamic pressure).
* Static port: Measures static air pressure.
* Difference: The difference between these pressures is proportional to the dynamic pressure, which is related to the aircraft's speed relative to the air.
2. Air Data Computer (ADC):
* Calculates true airspeed (TAS): Uses IAS from the pitot-static system, along with altitude, temperature, and air pressure data to calculate TAS, which is the aircraft's actual speed relative to the air mass.
3. Global Positioning System (GPS):
* Provides ground speed: Measures the aircraft's speed relative to the ground, considering the effects of wind.
* More accurate than pitot-static system: Especially at higher altitudes.
4. Doppler Radar:
* Used for ground speed: Sends radar pulses to the ground and measures the Doppler shift (frequency change) of the reflected signal, which is related to the aircraft's ground speed.
* Accurate even in turbulent conditions: Can be used for navigation and landing systems.
5. Inertial Navigation System (INS):
* Provides ground speed and heading: Uses sensors to measure accelerations and rotations, which are then integrated over time to calculate position, speed, and heading.
* Autonomous: Does not rely on external references like GPS.
6. Other Techniques:
* Flight Data Recorders (FDR): Store data including airspeed, ground speed, and other parameters.
* Cockpit Displays: Provide pilots with speed information from various sources, such as the airspeed indicator, GPS, and INS.
Understanding the Different Speed Measurements:
* Indicated Air Speed (IAS): Speed relative to the air, based on the pitot-static system, not corrected for factors like altitude or temperature.
* True Air Speed (TAS): Actual speed relative to the air mass, corrected for altitude and temperature.
* Ground Speed: Speed relative to the ground, considering wind effects.
Important Considerations:
* Calibration: Aircraft instruments need to be calibrated regularly to ensure accurate speed readings.
* Wind: Wind conditions significantly affect ground speed and require adjustments to be made for navigation.
* Altitude and Temperature: Affect the relationship between IAS and TAS, and these factors are taken into account by the ADC.
