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Aircraft and Spacecraft Instrumentation
Lecture Air and vertical speed measurements, Mach-number measurement, Machmeters and variometer constructions Aircraft and Spacecraft Instrumentation Radar altimeter Typical altitude range Typical accuracy Transmit power Pulse width MTBF 8000 ft (2.5 km) β 32 000 ft (10 km) ±5 ft (±1.5 m) 5 W peak 30-225 ns 5000 hours t+οt Real altitude (absolute altitude) Reflected signal Aircraft and Spacecraft Instrumentation t Sea surface Transmitted signal Barometric altitude (relative altitude) ground surface Principle of Laser altimeter Laser altimeter Imaging laser altimetry Laser altimeter 9201A (Goodrich Sensor Systems) Laser altimetry map Max. operating range Accuracy Update rate Power supply Operating temperature Light wavelength 2500 feet (850 m) ±6 inches (15 cm) at 100 feet up to 100 Hz 28 VDC, 100W -40 °C to 85 °C 1064 nm Aircraft and Spacecraft Instrumentation Air speed indicator Can you name and describe 5 different types of airspeed? 1. Indicated (IAS) 2. Calibrated (CAS) 3. True (TAS) 4. Equivalent (EAS) 5. Ground (GS) Bernoulli's principle states that total pressure is constant along a streamline. Pitot pressure is equal to total pressure so pitot pressure is constant all around the aircraft and does not suffer position error. Aircraft and Spacecraft Instrumentation Air speed indicator β speed definitions IAS - indicated airspeed reading by the instrument CAS - is indicated airspeed corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors. Pitot tube is at a fixed angle and therefore cannot be accurate at all AOA. TAS - is the physical speed of the aircraft relative to the air surrounding the aircraft. It is a calibrated airspeed corrected for altitude and nonstandard temperature. Given a calibrated airspeed as altitude increases true airspeed increases. GS - is the speed of the aircraft relative to the ground rather than through the air, which can itself be moving. Used for navigation and flight planning. EAS - is defined as the speed at sea level that would produce the same incompressible dynamic pressure as the true airspeed at the altitude at which the vehicle is flying. An aircraft in forward flight is subject to the effects of compressibility. In ISA conditions at MSL EAS=CAS Aircraft and Spacecraft Instrumentation Air speed indicator β errors 1. Instrument error 2. Pressure error 3. Position error 4. Compressibility error 5. Density error 6. Blockages Aircraft and Spacecraft Instrumentation Air speed indicator π£2 ππ β ππ» = ππ» = ππ 2 π£0 = 2ππ0 π0 π£π» = π£0 π£πΌπ΄π = π£πΆπ΄π = under incompressible conditions 2ο« ππ» ο« β 1 ππ» 2ο« π0 ο« β 1 π0 under incompressible conditions and H=0 π0 ππ» under incompressible conditions and Hβ 0 ο« ππ +1 ππ» ππ +1 π0 ο« β1 ο« ο« β1 ο« β1 β1 π£πΈπ΄π = π£ππ΄π = 2ο« ππ» ο« β 1 π0 2ο« ππ» π π0 ο« β1 π0 ο« = 1.4, π = 287.05 Aircraft and Spacecraft Instrumentation ππ +1 ππ» 2 π½ , ππ πΎ ο« β1 ο« β1 ππ +1 ππ» ο« β1 ο« β1 Air speed indicator β total pressure Compressible environment Incompressible environment Aircraft and Spacecraft Instrumentation TAS and CAS indicator Aircraft and Spacecraft Instrumentation Air speed indicator Aircraft and Spacecraft Instrumentation Vertical speed indicator What does a VSI show? Climbs Descents Level Flight Trend Information: shows an immediate indication of an increase or decrease in the airplaneβs rate of climb. Rate Information: shows a stabilized rate of change in altitude. Aircraft and Spacecraft Instrumentation Vertical speed indicator blockage Airspeed indicator will indicate zero, because there will be static pressure on both sides of the aneroid wafer. Acts like altimeter. Climbs show increase in airspeed Descent shows decrease in airspeed Aircraft and Spacecraft Instrumentation Machmeter Mach number is the speed of an object moving through air divided by the speed of sound. It is commonly used to represent the speed of an object when it is travelling close to or above the speed of sound. π ππππ ππ π‘βπ ππππππ‘ π= π ππππ ππ π ππ’ππ π ππππ ππ π ππ’ππ = π= 2 ο« β1 π ο« ππ» ππ +1 ππ» π» ο« β1 ο« (m/s; -,Pa,kg/m3) β1 for M β€ 1 Flight can be roughly classified in six categories: Aircraft and Spacecraft Instrumentation Ernst Mach (1838 β 1916) Austrian physicist Machmeter Aircraft and Spacecraft Instrumentation Machmeter Accuracy of the Machmater is under normal conditions ±0.01 M Aircraft and Spacecraft Instrumentation Mach airspeed indicator Aircraft and Spacecraft Instrumentation
