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# 4. Speeds

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The ppt used in class

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### 4. Speeds

1. 1. SPEED = DISTANCE / TIMEThree 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
2. 2. 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
3. 3. 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
4. 4. 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
5. 5. 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 speed If ∆P > 0  ∆ℓ < 0 ASI will read a lower speed
6. 6. DEFINITION: Airspeed relative to the airmass in which the aircraft is actually flying. The EAS corrected for density error. ½ ℓ EAS² = ½ ℓh TAS² 0 NOTE: Must understand that density thermodinamyc charateristics vary in a “known” way through the atmosphere
7. 7. DEFINITION: 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. TAS M LSS TAS M 38 .92 T (º K )LSS 38.92 T (º K )