Machmeter Local Speed of Sound Speed of sound is not constant but varies with temperature Sound travels slower in colder air and faster in warm air Speed of sound decreases with increase in altitude Local speed of sound (LSS) at sea level, in ISA (+ 15 deg C) is 661 knots Local speed of sound (LSS) at 30,000 ft, in ISA (-45 deg C) is 589 knots Calculation of Local Speed of Sound Formula for Local speed of sound in knots = 38.95 x Square root of Absolute Temperature In…
Vertical Speed Indicator (VSI)
Vertical Speed Indicator Principle of Vertical Speed Indicator VSI is also called Rate of climb or descent indicator (RCDI) Indicates rate of climb or descent by rate of change of static pressure Compares the present static pressure to that of 4 – 6 sec earlier Construction of Vertical Speed Indicator Air tight container with a metering unit retains past static pressure Pressure sensing capsule senses the current static pressure Static pressure differential between the capsule and container gives an indication of vertical speed Metering Unit of VSI Metering unit is…
Errors in Altimeter
Errors in Altimeter Position and Instrument Errors in Altimeter Position or Pressure error is caused due to location of pitot head Instrument Error is caused due to mechanical imperfections Position and Instrument error are corrected on ground Residual errors are listed on a correction card Manoeuvre and Time lag Errors in Altimeter Manoeuvre Induced Error causes temporary fluctuations in attitude indications Time Lag Error is caused due to sluggish response of capsule to pressure Servo assisted altimeter avoids time lag error Barometric Error Barometric error is caused due to change…