Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 69

True airspeed (TAS) is obtained when EAS has been corrected for density ratio, the airspeed indicator measures dynamic pressure and is calibrated for sea level standard day density. As altitude increases, the density ratio decreases and a correction must be made. The correction factor is :

(2.12)

Values of can be found in the ICAO Standard Altitude Chart (Table 2.1); values of 1/ can be found in Figure 2.13.

Due to the decrease in air density with an increase in altitude, for any given TAS, CAS will decrease as altitude increases. As higher altitudes are attained, the aircraft must fly faster to obtain the same pressure differential. For a given CAS, as an aircraft increases in altitude, the TAS will increase. The higher the aircraft travels in altitude, the greater the difference between CAS and TAS.

Figure 2.13 Altitude and EAS to TAS correction chart.