Aneroid Barometer Principle Quiz & Flashcards

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Questions and Answers

What is the purpose of a strong leaf spring in an aneroid capsule?

To measure absolute pressure

To compress the capsule against atmospheric pressure

To indicate barometric pressure

To prevent the total collapse of the capsule (correct)

What happens to the aneroid capsule as atmospheric pressure increases?

It expands against the spring pressure

It loses its sensitivity

It compresses against the spring pressure (correct)

It remains unchanged

What is the purpose of calibrating an aneroid barometer?

To improve stability

To convert it into an altimeter

To indicate barometric pressure (correct)

To measure absolute pressure

What is the advantage of using multiple aneroid capsules in a stack?

Increased sensitivity and improved accuracy Signup and view all the answers

What is the purpose of extending the range of capsule movement?

To convert the aneroid barometer into an altimeter Signup and view all the answers

Why is magnification necessary in aneroid instruments?

To amplify the small expansions and contractions Signup and view all the answers

What is psid often referred to as?

psig Signup and view all the answers

What type of bellows is used in a manifold pressure gauge?

Sylphon-type Signup and view all the answers

Why do aneroid capsules need temperature compensation?

To correct for changes in material malleability with temperature Signup and view all the answers

What happens to a bimetallic strip when heated?

It curls Signup and view all the answers

What is the main purpose of temperature compensation in instruments?

To correct for changes in temperature affecting instrument readings Signup and view all the answers

What happens to a bimetallic strip when cooled?

It curls in the opposite direction Signup and view all the answers

What is the Mach number equivalent at 30 000 feet?

236 knots Signup and view all the answers

Why is high-speed flight concerning?

In-flight behaviour at high speeds Signup and view all the answers

What does the ratio V/α represent?

Mach number Signup and view all the answers

What is the effect of atmospheric temperature on the speed of sound?

It increases the speed of sound Signup and view all the answers

What is displayed by a Machmeter?

Mach number Signup and view all the answers

Why is overcoming airflow limitations crucial?

To ensure safe flight Signup and view all the answers

What is the relationship between altitude and flight levels above the transition altitude?

Altitudes become flight levels, multiplied by 100 Signup and view all the answers

What is the primary function of an airspeed indicator?

To provide information for maintaining control of the aircraft Signup and view all the answers

What happens to the dynamic pressure when an aircraft is stationary on the ground?

It is equal to static pressure Signup and view all the answers

What is the consequence of flying at too low an airspeed?

Aircraft stall Signup and view all the answers

What is the unit of measurement for indicated airspeed?

Nautical miles per hour Signup and view all the answers

What is the relationship between airspeed and aerodynamic loading?

Airspeed is directly proportional to aerodynamic loading Signup and view all the answers

What happens to the pressure inside the case when the aircraft levels off?

It equalises with the pressure inside the capsule Signup and view all the answers

What is the effect of the flow of static air on the capsule during descent?

It causes the capsule to expand Signup and view all the answers

What is the main limitation of a normal VSI?

It has a great deal of lag Signup and view all the answers

What happens to the pointer in a VSI during descent?

It moves to the descent section of the scale Signup and view all the answers

What is the purpose of calibration of the leak rate?

To maintain a difference between the pressure inside the capsule and that inside the case Signup and view all the answers

During climb, what happens to the pressure inside the case compared to the pressure inside the capsule?

It becomes higher Signup and view all the answers

Study Notes

Aneroid Capsule and Pressure

A strong leaf spring maintains the shape and responsiveness of an aneroid capsule, ensuring accurate pressure readings.
As atmospheric pressure increases, the aneroid capsule compresses and decreases in volume, which is vital for measuring changes in pressure.

Calibration and Multiple Capsules

Calibrating an aneroid barometer ensures that it provides precise pressure readings, crucial for reliability in various applications.
Using multiple aneroid capsules in a stack enhances accuracy and sensitivity, allowing the instrument to detect subtle pressure changes.

Extending Movement and Magnification

Extending the range of capsule movement increases the measurement range of the aneroid device, enabling it to detect a wider variety of pressures.
Magnification is necessary in aneroid instruments to translate small changes in capsule movement into more detectable readings on the display.

Pressure Measurement and Bellows

PSID is commonly referred to as "pounds per square inch differential," a unit measuring pressure differences.
A corrugated bellows is typically used in a manifold pressure gauge, allowing for precise pressure readings by expanding and contracting with pressure changes.

Temperature Compensation

Aneroid capsules require temperature compensation to ensure that pressure readings are accurate across varying temperatures, preventing erroneous measurements.
A bimetallic strip bends when heated due to differing expansion rates of the metals, which is a fundamental principle in temperature measurement devices.

Mach Number and Flight Concerns

At 30,000 feet, the Mach number equivalent varies based on atmospheric conditions, significantly impacting flight dynamics and performance.
High-speed flight raises concerns about aerodynamic stresses and potential structural failures, requiring careful monitoring.

Speed of Sound and Indicators

The ratio V/α represents the ratio of velocity to the speed of sound, quantifying how fast an object is moving relative to sound waves.
Atmospheric temperature affects the speed of sound; warmer air results in faster sound speeds, impacting aircraft performance.

Machmeter and Airflow Limitations

A Machmeter displays the current Mach number, essential for maintaining safe operating speeds during flight.
Overcoming airflow limitations is crucial to prevent stall conditions and ensure stable flight at high speeds.

Altitude and Functions

The relationship between altitude and flight levels becomes significant above the transition altitude, where pressure settings switch from standard atmospheric pressure to local altimeters.
The primary function of an airspeed indicator is to measure the dynamic pressure to determine the current airspeed of an aircraft.

Pressure Dynamics

When an aircraft is stationary on the ground, dynamic pressure is zero since there is no airflow over the wings.
Flying at too low an airspeed can lead to a stall, resulting in loss of lift and potential crashes, highlighting the importance of maintaining adequate airspeed.

Measurement Units and Aerodynamics

Indicated airspeed is measured in knots or miles per hour, crucial for pilot awareness and navigation.
There is a direct relationship between airspeed and aerodynamic loading; increased speed leads to higher loads on an aircraft’s wings.

Case Pressure and Descent Effects

When an aircraft levels off, the pressure inside the case equalizes with external pressure, stabilizing the instrument.
During descent, the flow of static air causes expansion in the capsule, modifying pressure readings and requiring adjustment.

Vertical Speed Indicator (VSI) Dynamics

The main limitation of a normal VSI is its response time; it may not provide immediate feedback in rapidly changing conditions.
During descent, the pointer in a VSI moves downward, providing pilots with necessary information about their rate of descent.

Leak Rate Calibration

Calibration of the leak rate is essential to ensure that the VSI functions accurately and responds properly to pressure changes during flight.
During a climb, the pressure inside the case decreases compared to the pressure inside the capsule, indicating rising altitude.

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Description

Learn about the working principle of an aneroid barometer, which involves a push-pull arrangement and an evacuated metal capsule called an aneroid capsule. Discover how pressure changes affect the capsule and how it is used to measure absolute pressure.

Aneroid Barometer Working Principle