Aircraft Instrument Systems Midterm Reviewer PDF

Chapter 11: AIRCRAFT 1. Absolute Pressure INSTRUMENT SYSTEMS - measurement of pressure relative to a total vacuum. Section A: PRINCIPLES OF - often used on the...

Chapter 11: AIRCRAFT 1. Absolute Pressure INSTRUMENT SYSTEMS - measurement of pressure relative to a total vacuum. Section A: PRINCIPLES OF - often used on the aircraft in comparison INSTRUMENT SYSTEMS to other pressures. Aneroid Wafer General Information: - measures the difference in pressure 1. In a normally aspirated (no- between the vacuum inside a sealed supercharged) engine, the maximum chamber and the ambient pressure differential between the manifold around it. pressure and atmospheric pressure will occur when the engine is what? a. Bellows-type - At idle. - measures the difference between the pressure inside a bellows and the 2. The three-pointer altimeter is a pressure outside of the bellows. commonly used altimeter in light, general aviation aircraft. Describe what does b. Bourdon tube-type each of these pointers indicate. - to measure high pressure. - Long Pointer: Hundreds of ft. 2. Gauge Pressure - Fat Pointer: Thousands of ft. - most commonly used type of - Smaller Pointer: Tens of Thousands of pressure. ft. - difference between atmospheric I. PRINCIPLES OF PRESSURE pressure and the pressure being measured. MEASUREMENT - Pressure is the force differential 3. Differential Pressure between two points. - the comparison between two different pressures. Atmospheric Pressure - the most common differential - force exerted by the air that constantly pressure gauge found on an aircraft is surrounds us. the airspeed indicator. - can be measured with a mercury barometer. - can be measured in inches of mercury, hectopascals (hPa), or pounds per square inch (psi). II. SPECIAL PRESSURE b. Encoding Altimeter INSTRUMENTS - contain an electronic pressure - to measure the specific values that sensor that sends a digital code to provide the flight crew with the the aircraft's transponder. information needed to operate the aircraft safely and efficiently. c. Servo Altimeter - utilizes a built-in compensation 1. Manifold Pressure Gauge system, tailoring the instrument to - gives the pilot an approximation of the the particular aircraft and power the engine is producing. minimizing error for the full range of flight speeds and altitudes. 2. Engine Pressure Ratio Indicator d. Radio Altimeter - measures the thrust produced by an axial flow turbine engine by using a - displays the aircraft's altitude as differential pressure gauge. measured by a radio signal, instead of by atmospheric - the best indication of the thrust pressure. produced in an axial flow turbine engine. Altimeter Tests 3. Pressure Switches - required by FAR 91.411 every 24 - A microswitch activated by the calendar months to comply with movement of a bellows under the Appendix E of FAR Part 43. pressure applied by a fluid. - used to activate warning lights or to a. Scale Error sequence system activities. - The altimeter must indicate the same altitude as the master indicator 4. Altimeters or manometer within a specified tolerance. - simply a barometer that measures the absolute pressure of the air. b. Hysteresis Types of Altimeters: - Altitude readings must match when increasing and decreasing at the a. Three Pointer Altimeter same pressure level, within a - commonly used altimeter in light, specified tolerance. general aviation aircraft.  c. After Effect b. Maximum Allowable Airspeed Indicator - The altimeter must return to the same indication, within tolerance, - for airplanes with structural speed after the test. limits is marked by a fixed red radial line on the airspeed indicator to show d. Friction the never-exceed speed. - Two readings are taken at each 6. Machmeter pressure level before and after the instrument is vibrated, with no more - is an airspeed indicator that is adjusted than a specified difference. for altitude in order to indicate airspeed in relation to the speed of sound. e. Case Leak Combination Airspeed Indicator - At an altitude of 18,000 feet, the altimeter should not leak more than a - indicates airspeed, Mach, and specified amount within a specified maximum allowable airspeed. time. 7. Vertical Speed Indicator f. Barometric Scale Error - measures the rate of change of static - The correlation between the pressure and indicates the result as a barometric scale and the altimeter rate of climb or descent. pointers must be correct within an allowable tolerance. Instantaneous Vertical Speed Indicator 5. Airspeed Indicators - indicator incorporates accelerometers - measures the difference between the to help the instrument immediately pitot, or ram air pressure, and the static, indicate changes in vertical speed. or ambient, air pressure. III. TEMPERATURE-MEASURING a. True Airspeed Indicator INSTRUMENTS - contains altitude and air temperature - All temperature indicators measure the correction devices in order to indicate amount of temperature increase or true airspeed. decrease. - can be non-electrical or electrical. Delta T - change in temperature. 1. Non-Electrical Instruments 2. Electrical Instruments - depend on expansion or contraction of - measure changes in electrical liquids, solids, or gases to indicate a rise resistance, which are proportional to or fall in temperature. changes in temperature. a. Liquid Expansion a. Resistance Instruments - Refers to the phenomenon where a - measure the change in resistance liquid expands in response to an produced when a temperature- increase in temperature. sensing bulb is subjected to heat. Common Household or Medical b. Voltage Instruments Thermometer - instruments measure voltage - This type of thermometer is rarely used produced when certain metals are in aircraft. subjected to heat. b. Solids Expansion c. Thermocouple Instruments - Refers to the increase in size of a - typically used to measure relatively solid material as its temperature high temperatures. increases. IV. MECHANICAL MOVEMENT Bimetallic strip thermometer MEASUREMENT - Many aircraft use this type of thermometer to measure the outside air 1. Accelerometer temperature (OAT). - indicates the present G force acting on the aircraft, plus the maximum negative c. Gas Expansion and positive Gs experienced since the - Works on the principle of an accelerometer was last reset. expanding gas. 2. Synchroscopes Bourdon Tube - helps the pilot of a twin-engine airplane - Detects this pressure change and synchronize the R.P.M. of the propellers. straightens out proportionally to the increase in pressure, moving a pointer 3. Tachometer across a calibrated scale marked in - a mechanical or electrical instrument temperature units. that displays engine R.P.M. V. Gyroscopic Instruments 3. Turn Indicators - made it possible to fly an aircraft without - measure the rate of rotation of an outside visual reference. aircraft about its vertical axis. Gyro a. Turn and Slip Indicator - simply a rotating mass. - first "blind flight" instrument invented. Spinning Gyroscope Characteristics: - including "needle and ball" and a. Rigidity in Space "turn and bank indicator." - refers to the principle that a spinning b. Turn Indicator wheel with a weighted rim (gyroscope) remains fixed in the - translate an aircraft's turning plane in which it spins, even when motion into an indication of the mounted on gimbal rings that allow rate of turn. free rotation in any direction. b. Precession - is the effect where, when an outside force tries to tilt a spinning gyro, the gyro responds as if the force had been applied 90 degrees further in the direction of rotation. 1. Heading Indicator (Gyrocompass) - indicates an aircraft's heading relative to a fixed horizontal reference. 2. Attitude Indicator (Artificial Horizon) - indicates an aircraft's heading relative to the earth's horizon. - indicates an aircraft's heading relative to the earth's horizon.  Enumeration: Additional Information: I. Sources of Power of Gyroscopic - The Consolidated NY-2 airplane he flew Instruments: VEP had an artificial horizon, which gave him 1. Vacuum an indication of the pitch and roll attitude 2. Electric of the airplane relative to the earth's 3. Pressure surface. II. Special Pressure Instruments: - Many aircraft instruments rely on MAMAVEP measuring the pressures of fluids such 1. Manifold Pressure Gauges as air, fuel, and oil. 2. Altimeters 3. Mach Meters Pressure 4. Air-speed Indicators 5. Vertical Speed Indicators - always a comparison between two 6. Engine-pressure Ratio Indicators forces. 7. Pressure Switches International Standard Atmosphere III. Tests Required by FAR Part 43 (ISA) Appendix E for Altimeters Before Certifying for Instrument Flights: - common reference for temperature and SBCHAF pressure. 1. Scale Error 2. Barometric Scale Error Standard Pressure 3. Case Leak - exists at sea level and other elevations. 4. Hysteresis 5. After Effect - can change with weather patterns. 6. Friction Hectopascals (hPa) IV. Basic Ways of Measuring Pressure: GAD - modern term for an older measurement 1. Gauge called "millibars." 2. Absolute - Under standard day conditions, 3. Differential atmospheric pressure that equals 29.92 V. 6-Pack Basic Aircraft Instruments. inches of mercury equals 1013.2 hPa or Pilot Static and Gyroscopic 14.7 psi. Instruments: TAAAHV 1. Turn Coordinator Ram Pressure 2. Airspeed Indicator 3. Attitude Indicator - created by the aircraft's forward motion 4. Altimeter and static pressure is the atmospheric 5. Heading Indicator pressure outside the aircraft. 6. Vertical Speed Indicator Mean Sea-Level (MSL) Flight Level (FL) Reduced Vertical Separation Minimums (RVSM) Type Certificate Data (TCD) Density Altitude - pressure altitude corrected for non- standard temperature. - The speed of sound decreases as altitude increases due to the lower air temperature. Leon Focault - French physicist who devised a small wheel with a heavy outside rim. Gyroscope - Greek, meaning "to view the earth's rotation." Elmer A. Sperry - invented the turn and bank indicator in 1918.