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Questions and Answers
In a normally aspirated engine, when does the maximum differential between manifold pressure and atmospheric pressure occur?
What is absolute pressure a measure of?
What does the long pointer on a three-pointer altimeter indicate?
What type of pressure does a Bourdon tube-type gauge measure?
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What is the most common differential pressure gauge found on an aircraft?
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What is gauge pressure defined as?
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What does the smaller pointer on a three-pointer altimeter indicate?
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Which instrument contains an electronic pressure sensor that communicates with the aircraft's transponder?
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What does the Manifold Pressure Gauge indicate?
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What is the primary function of the Engine Pressure Ratio Indicator?
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Which type of altimeter is commonly used in light general aviation aircraft?
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What does 'Hysteresis' refer to in the context of altimeter tests?
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What is the purpose of pressure switches in aircraft?
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What does the Radio Altimeter measure?
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What is the maximum allowable airspeed indicator used for?
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What testing is required for altimeters per FAR 91.411?
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What is the purpose of a true airspeed indicator?
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Which type of airspeed indicator incorporates accelerometers?
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What does the vertical speed indicator measure?
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What type of instruments measure changes in electrical resistance in relation to temperature changes?
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At what altitude should the altimeter not leak more than a specified amount?
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What is the delta T in temperature-measuring instruments?
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What phenomenon does liquid expansion in temperature measurement refer to?
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Which of the following best describes a machmeter?
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What principle does a gas expansion thermometer operate on?
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Which instrument is primarily used to measure the outside air temperature in aircraft?
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What does an accelerometer indicate regarding aircraft performance?
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Which of the following instruments helps synchronize propeller RPM in twin-engine aircraft?
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What characteristic allows a gyroscope to remain fixed in its plane during flight?
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Which type of thermometer relies on the pressure change detected through a Bourdon tube?
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What is the main purpose of a turn indicator in aviation?
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What type of thermometer is rarely used in aircraft but measures temperature change based on thermal expansion of solids?
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What is the primary function of the Heading Indicator in an aircraft?
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Which source of power is NOT typically used by gyroscopic instruments?
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What characteristic does the Attitude Indicator display?
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Which of the following is NOT a special pressure instrument?
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Which of the following errors is associated with altimeters according to FAR Part 43?
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What unit is modernly used to measure atmospheric pressure?
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What is the significance of the International Standard Atmosphere (ISA) in aviation?
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What type of pressure measuring technique is 'Absolute' pressure?
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Study Notes
Aircraft Instrument Systems Principles
- Pressure is the force differential between two points.
- Atmospheric Pressure is the force exerted by the air surrounding us.
- Absolute Pressure is measured relative to a total vacuum and often used for comparisons on aircraft.
- Gauge Pressure measures the difference between atmospheric pressure and the pressure being measured and is the most common type used.
- Differential Pressure compares two different pressures.
Measuring Instruments
- Aneroid Wafer measures the difference in pressure between a sealed chamber and the ambient pressure.
- Bellows-type measures the difference between the pressure inside a bellows and outside.
- Bourdon tube-type is commonly used to measure high pressure.
Aircraft Specific Instruments
- Manifold Pressure Gauge indicates the engine's power output.
- Engine Pressure Ratio Indicator measures thrust produced by axial flow turbine engines.
- Pressure Switches activate warning lights or sequence system activities based on fluid pressure changes.
Altimeters
- Altimeters are barometers that measure absolute air pressure.
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Types include:
- Three-Pointer Altimeter: Commonly used in general aviation aircraft.
- Encoding Altimeter: Contains an electronic pressure sensor that sends a digital code to the transponder.
- Servo Altimeter: Uses a built-in compensation system for specific aircraft and minimizes errors.
- Radio Altimeter: Displays altitude based on radio signals.
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Altimeter Tests:
- Scale Error: Altimeter must indicate the same altitude as a master indicator within a specified tolerance.
- Hysteresis: Altitude readings should match when increasing and decreasing at the same pressure level.
- After Effect: Altimeter should return to the same indication after testing.
- Friction: Must have minimal difference in readings before and after vibration.
- Case Leak: Altimeter should not leak more than a specified amount.
- Barometric Scale Error: Correlation between the barometric scale and altimeter pointers must be accurate.
Airspeed Indicators
- Airspeed Indicators measure the difference between pitot (ram air) pressure and static pressure.
- True Airspeed Indicator accounts for altitude and air temperature to display true airspeed.
- Maximum Allowable Airspeed Indicator shows the never-exceed speed of an aircraft with red markings on the indicator.
- Machmeter is an airspeed indicator adjusted for altitude, displaying airspeed relative to the speed of sound.
- Combination Airspeed Indicator displays airspeed, Mach, and maximum allowable airspeed.
Vertical Speed Indicator
- Vertical Speed Indicator measures the rate of change of static pressure and indicates climb or descent.
- Instantaneous Vertical Speed Indicator includes accelerometers for immediate indication of vertical speed changes.
Temperature Measuring Instruments
- Temperature Instruments measure temperature increase or decrease using expansion or contraction of liquids, solids, or gases.
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Non-Electrical Instruments:
- Liquid Expansion: Rarely used on aircraft.
- Solids Expansion: Bimetallic strip thermometers are commonly used for outside air temperature.
- Gas Expansion: Bourdon tube thermometers utilize expanding gas for temperature measurement.
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Electrical Instruments:
- Resistance Instruments: Measure changes in resistance of temperature-sensing bulbs.
- Voltage Instruments: Measure voltage produced by metals when exposed to heat.
- Thermocouple Instruments: Used for measuring high temperatures.
Mechanical Movement Measurement
- Accelerometer: Indicates G force acting on the aircraft, including maximum negative and positive Gs.
- Synchroscope: Syncs RPMs of twin-engine aircraft propellers.
- Tachometer: Displays engine RPMs.
Gyroscopic Instruments
- Gyro is a rotating mass, a key component in the early "blind flight" instruments.
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Spinning Gyroscope Characteristics:
- Rigidity in Space: A spinning gyro remains fixed in its spinning plane even when mounted on gimbals.
- Precession: When an outside force tries to tilt a spinning gyro, the response is as if the force was applied 90 degrees further in the direction of rotation.
- Heading Indicator (Gyrocompass): Shows the aircraft's heading relative to a fixed horizontal reference.
- Attitude Indicator (Artificial Horizon): Indicates the aircraft's orientation relative to the Earth's horizon.
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Turn Indicator: Measures the rate of rotation of an aircraft around its vertical axis.
- Turn and Slip Indicator: Includes "needle and ball" parts for indicating turning motion.
- Turn Indicator: Translates turning motion into a rate of turn indication.
Power Sources for Gyroscopic Instruments
- Vacuum: Used in older aircraft instruments.
- Electric: More modern instruments.
- Pressure: Some specialized instruments.
International Standard Atmosphere (ISA)
- A common reference for temperature and pressure in aviation.
Pressure
- Standard Pressure: Found at sea level and various elevations, subject to change with weather.
- Hectopascals (hPa): Modern term for "millibars".
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Description
This quiz covers the fundamental principles of aircraft instrument systems, focusing on various types of pressure measurements. You'll learn about different pressure types such as absolute, gauge, and differential pressure, along with specific measuring instruments used in aviation. Test your knowledge on how these instruments contribute to aircraft performance.
