Air Data Computer Requirement of Air Data Computer Avoid multiple Pitot and Static lines Provide centralized source of static and pitot pressure Convert pressure data in an electric or electronic format Advantage of Air Data Computer Provide pressure data to other equipments Flight data recorder Navigation computer Auto Pilot Equipments dependent on Air Data Computer ADC provides pressure data to Flight Data Recorder Electronic Flight Information System Warning Systems ATC Transponder Inertial Reference System Flight Control Computer Flight Management System Analogue ADC Analogue ADC E-I bar to convert pressure data…
Category: Flight Instruments
Aircraft are equipped with many instruments which assist pilots in safe and efficient flight operations. In this section, we will learn about the instruments used in modern aircraft.
Machmeter
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…
Altimetry
Altimetry Height Above Mean Sea Level Mean sea level (MSL) is the reference sea level taking the average of tides MSL is the datum for measuring altitude and elevation Altitude is the vertical distance of a movable object from MSL Elevation is the vertical distance of a point on surface of earth from MSL Altitude and elevation are referred as Above mean sea level (AMSL) Height Above Ground Level Airfield Reference Point (ARP) is the reference point for an airfield Height is the vertical distance from specified datum ARP is…
Pressure Altimeter
Pressure Altimeter Introduction to Pressure Altimeter Pressure altimeter is the basic instrument for measuring altitude It is basically an aneroid barometer which measures pressure Altimeter senses change in static air pressure and displays as altitude Principle of Pressure Altimeter Static or atmospheric pressure reduces with height at a non uniform rate This is due to the reduction in weight of air column at higher altitudes Static pressure is also affected by temperature and pressure variations These need to be understood and corrected during height measurement Construction of a Simple Altimeter…