Airspeed Indicator and Aviation Speeds

Overview

• Discussion on airspeed indicators and aviation speeds
• Divided into two videos: this part focuses on the workings, errors, and definitions of speeds
• Next part: color-coded markings, reactions to pitted tube and static port blockages

Airspeed Indicator (ASI)

• One of the six basic flight instruments
• Connected to the pitted static system
• Measures air pressure
• Only instrument connected to both pitted tube (total pressure) and static port (static pressure)

Pressure Definitions

• Static Pressure: Atmospheric pressure exerted equally in all directions
• Dynamic Pressure: Pressure produced by air movement, proportional to speed and air density
• Total Pressure: Sum of static and dynamic pressure

How ASI Works

• Measures dynamic pressure to indicate airspeed
• Total Pressure (from pitted tube) – Static Pressure (from static port) = Dynamic Pressure
• Mechanism inside ASI includes static port connected to the instrument case and pitted tube connected to a diaphragm
  • Diaphragm expansion/contraction moves the needle to indicate speed

Errors and Corrections

• Indicated Airspeed (IAS): Speed indicated on the instrument, not corrected for errors
• Instrument Error: Due to manufacturing imperfections and wear
• Position Error: Changes in flaps, gear, and maneuvers
• Calibrated Airspeed (CAS): IAS corrected for instrument and position errors
  • Determined using calibration tables from aircraft manual
• Compressibility Error: Air compresses at high speeds (>300 knots), not considered in small aircraft
• Equivalent Airspeed (EAS): CAS corrected for compressibility errors
• Density Error: Related to air density, affects dynamic pressure and thus airspeed
• True Airspeed (TAS): EAS corrected for density error, reflects actual speed relative to the air
  • Calculated using formula or flight computer
• Ground Speed (GS): TAS corrected by wind effects, actual speed relative to the ground
  • Tailwind increases GS, headwind decreases GS

Summary of Speed Terms

• IAS: Direct reading from airspeed indicator
• CAS: IAS + corrections for instrument/position errors
• EAS: CAS + corrections for compressibility errors
• TAS: EAS + corrections for density errors
• GS: TAS + wind correction

Practical Applications

• IAS: Structural limitations, take-off/landing speeds, stall speeds, performance speeds
• TAS: ATC flight plans, Mach speed, endurance, wind correction, flight planning
• GS: Flight time, fuel consumption, climb/descent parameters, general flight planning

Conclusion

• Understanding each speed is crucial for various flight operations
• Some aircraft have automated systems to handle these calculations
• Importance of practical knowledge for day-to-day flight operations