4. Speeds
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Transcript of 4. Speeds
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4. SPEED
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INTRODUCTION
SPEED = DISTANCE / TIME
Three types of speeds:
• AIRSPEED: Rate of change of position in relation to time, of air molecules as they are flowing though
a certain passage • GROUNDSPEED: Relative velocity an aircraft has
in relation to the ground. (Being the ground considered still)
• RELATIVE SPEED: Relative change of position between any two objects
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INTRODUCTION
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INTRODUCTION
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INTRODUCTION
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AIRSPEED INDICATOR READING (ASIR)
DEFINITION: The one measure by the pitot-static system without any corretions
INSTRUMENT ERROR: All inaccuracies shown on an airspeed indicator due to the inherent
imperfections of the instrument. (Frictions, readablity, timming, accuracy, scale reading,…).
Usually considered negligible
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INDICATED AIRSPEED (IAS)DEFINITION: Airspeed shown on an airspeed indicator
whenever the actual incoming from the pitot-static system indication is corrected for INSTRUMENT ERROR.
The one actually shown on a usual ASI
POSITION ERROR: Missinterpretation of the real airspeed due to the fact of the pitot-static system’s incoming not being undisturbed. (Drifting, turbulence, water, maneuvreing,…). Taken into account for certain maneuvres and situations
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CLIBRATED AIRSPEED (CAS)DEFINITION: Sometimes called Rectified airspeed (RAS) Stands for the IAS corrected for position error.
DENSITY ERROR: Due to the fact of the Pitot-Static system only being able to measure dynamic pressure the systems takes into account a constant value for the air density. This mistake increases as density decreases, and so, as altitude increases. ≈2% each 1000ft AMSL
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EQUIVALENT AIRSPEED (EAS)DEFINITION: Calibrated Airspeed (CAS) of an airflow
taking into account compressibility of the air.
Must take into account that the air is taken as not compressible bellow ≈300Kts
DENSITY ERROR: Density varies in accordance with the Ideal Gases Formula P/ℓ = MRT. So temperature and pressure will affect the
airspeed indicator reading
If ∆T > 0 ∆ℓ < 0 ASI will read a lower speedIf ∆P > 0 ∆ℓ < 0 ASI will read a lower speed
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TRUE AIRSPEED (TAS)DEFINITION: Airspeed relative to the airmass in which
the aircraft is actually flying.
The EAS corrected for density error.
½ ℓ0 EAS² = ½ ℓh TAS²
NOTE: Must understand that density thermodinamyc charateristics vary in a “known” way through the atmosphere
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MACH NUMBERDEFINITION: Adimensional number that relates the
actual airspeed of a body to the speed that the sound would have inside the airmas (with its thermodinamyc charateristics) through wich the body is moving.
LSSTAS
M
)(º92.38 KTLSS )(º92.38 KT
TASM