Aircraft Propeller MCQ Module 17

Questions and Answers

Which material is most affected by fatigue when used for propeller blades?

Composite

Wood

Carbon fiber

Aluminium alloy (correct)

What does a master spline determine during propeller installation?

The correct position the splines fit (correct)

The amount of interference allowed

The type of propeller used

The correct blade angle

When engine power increases, how does a constant-speed propeller adjust its function?

Decreases the RPM to increase thrust

Increases RPM to handle power

Increases the blade angle to decrease thrust

Decreases the blade angle to maintain RPM (correct)

What method should be used to clean an aluminum propeller for inspection?

Mild soap and water Signup and view all the answers

What effect does applying a force to the speeder spring have on the blade angle?

Makes it finer Signup and view all the answers

In what type of environment must variable pitch propellers be stored?

Damp and cool Signup and view all the answers

What does torque do relative to the direction of rotation?

Acts in the opposite direction Signup and view all the answers

Where is thrust on a propeller primarily produced?

Both surfaces of the blades Signup and view all the answers

At what propeller length percentage is thrust generally greatest?

70 to 80% Signup and view all the answers

What is the primary purpose of blade twist in a propeller?

To maintain angle of attack across the blade Signup and view all the answers

What is the primary purpose of a feathering propeller?

Eliminate drag from a windmilling propeller Signup and view all the answers

What causes the output of an anti-icing pump to be controlled?

A timer Signup and view all the answers

What advantage does a constant-speed propeller have compared to a fixed-pitch propeller?

Higher efficiency in all operating ranges Signup and view all the answers

What force acts on a propeller that tends to decrease the blade angle?

Centrifugal twisting force Signup and view all the answers

Which side of the propeller blade is known as the blade back?

Blade front Signup and view all the answers

What principle does the constant speed unit (CSU) governor operate on?

Spring pressure acting against centrifugal force Signup and view all the answers

During which phase of flight is the blade angle of a constant speed propeller the greatest?

Cruise flight Signup and view all the answers

What is the best method for inspecting an aluminium propeller for cracks?

Dye penetrant Signup and view all the answers

What angle is measured between the blade chord and the relative airstream?

Angle of attack Signup and view all the answers

What is the primary function of the centrifugal latches in a single acting propeller?

Prevent feathering of the propeller Signup and view all the answers

The blade angle at the root of a propeller is generally:

Greater than the tip Signup and view all the answers

Which range does the Beta mode of a propeller encompass?

Feather stop to the ground fine pitch stop Signup and view all the answers

What happens to the blade angle along a propeller blade?

Decreases from root to tip Signup and view all the answers

What does the angle of attack of a fixed-pitch propeller depend on?

Forward speed and engine rotational speed Signup and view all the answers

What is the term for the angle between the resultant airflow direction and the propeller blade plane of rotation?

Angle of attack Signup and view all the answers

What is the actual distance a propeller moves through the air during one revolution called?

Effective pitch Signup and view all the answers

What is the 'matrix' in a composite blade primarily composed of?

Bonding material Signup and view all the answers

What occurs when running an engine with a fixed-pitch propeller at full throttle while stationary into a strong wind?

A decrease in full throttle rev/min Signup and view all the answers

What is the purpose of synchronisation in propeller systems?

Reduce noise and vibration Signup and view all the answers

When dealing with stored propellers, what is a key maintenance requirement?

Restore them to 'zero time since overhaul' Signup and view all the answers

Which of the following relates to the blade angle of a propeller?

It increases from the root to the tip Signup and view all the answers

What is the proper condition of minor transverse cracks on an alloy blade?

They are not repairable Signup and view all the answers

What should the pilot valve in the governor of a constant speed propeller be activated by?

Governor flyweights Signup and view all the answers

For a conventional takeoff with a constant-speed propeller, which setting is common?

Low pitch, high RPM Signup and view all the answers

Which component provides oil pressure for propeller pitch actuation?

A pump in the governor Signup and view all the answers

What is an effective pitch defined as?

Geometric pitch minus slippage Signup and view all the answers

Which process is used to monitor the de-icing of the propeller?

Viewing the blade and observing ice falling off Signup and view all the answers

What is the main purpose of counterweights on constant-speed propellers?

To aid in unfeathering the propellers Signup and view all the answers

What happens during take-off when the propeller is too coarse an angle?

Reduced efficiency Signup and view all the answers

How does the centrifugal twisting moment (CTM) affect the pitch of a propeller blade?

It twists the blade to a coarse pitch Signup and view all the answers

What is the main purpose of a vibration analyzer in relation to propellers?

To assess dynamic balance Signup and view all the answers

What role does the speeder spring play in a constant-speed propeller system?

It adjusts the pitch of the propeller Signup and view all the answers

What does aerodynamic thrust imbalance refer to in a propeller system?

Difference in thrust produced by propeller blades Signup and view all the answers

In a propeller's BETA range, what is produced?

Negative thrust Signup and view all the answers

When tracking a propeller, what is the recommended method to prevent injury?

Standing clear of the propeller arc Signup and view all the answers

What follows after pulling back the power lever on a turbo-prop aircraft for reverse thrust?

Propeller angle moves to negative pitch Signup and view all the answers

What is the primary use of a universal propeller protractor?

To ensure the blade is at the horizontal position Signup and view all the answers

What may cause a vibration frequency problem when installing a propeller?

Higher than turbine vibration frequency Signup and view all the answers

What is typically checked during a scheduled service of a propeller spinner?

Surface cracks Signup and view all the answers

What is a characteristic of wooden propellers?

More efficient blade construction Signup and view all the answers

Study Notes

Propeller Materials and Fatigue

Aluminium alloy propeller blades are particularly affected by fatigue compared to wood and composite materials.

Propeller Fitting to Engine

A master spline ensures the correct positioning of splines in the hub on a splined shaft.
Front and rear cones must not touch to avoid interference.

Constant-Speed Propellers

When engine power increases, the constant-speed propeller adjusts by decreasing the blade angle to maintain RPM.
The propeller aims to maintain RPM by decreasing the blade angle under increased engine power conditions.

Cleaning and Maintenance

When cleaning aluminium propellers, use mild soap and water to ensure safe inspection.

Speeder Spring Function

Applying force to the speeder spring causes the blade angle to go finer.

Variable Pitch Propeller Storage

Variable pitch propellers require a dry environment to prevent corrosion of seals.

Torque and Thrust

Torque acts in opposition to the direction of rotation.
Thrust arises due to low pressure on both surfaces of the propeller blades, especially significant at the rear face.

Thrust Distribution

The thrust on a propeller blade is greatest at 70-80% of its length.
Blade stations are crucial for tasks like measuring blade angle and indexing blades.

Propeller Anatomy

The thrust face of a propeller blade refers to the rear face or flat side.
The synchronisation governor is responsible for monitoring RPM and tip speeds.

Propeller Lifespan and Repairs

Fixed pitch propellers have a typical shelf life of up to 5 years, while the shank can only have minor repairs allowed.

Blade and Pitch Angle

Propeller twist or pitch is designed to ensure consistency in Angle of Attack across the blade.
Blade twist equalizes thrust distribution by reducing the angle of attack at the blade root.

Propeller Balancing and Accumulator

An arbor assists in balancing a propeller by marking where weights are attached.
An accumulator in a double-acting propeller system provides backup to the governor pump during feathering.

Measurement of Propeller Tip Clearance

For single-engine tailwheel aircraft, propeller tip clearance is measured with the tailwheel on the ground.

Propeller Spinner and Control

The spinner is essential for reducing drag and may distribute anti-ice fluid.
The governor controls oil for the pitch-changing mechanism and regulates engine RPM through the control lever.

Pitch Angle and Geometric Pitch

Pitch angle is determined by the acute angle between the airfoil section chord line and the propeller's plane of rotation.
Geometric pitch is defined as the distance the propeller would advance in one revolution at a given blade angle.

Force Dynamics in Propellers

Forces affecting propellers include centrifugal twisting force, aerodynamic twisting force, thrust bending force, and torque.
The operational force causing the greatest stress is aerodynamic twisting force.

Constant-Speed vs Fixed-Pitch Propellers

A constant-speed propeller provides higher efficiency across varied operating ranges compared to fixed-pitch designs.

Inspection Methods

Eddy current and dye penetrant methods are effective for inspecting aluminium propellers for cracks.

Angle of Attack Measurement

The angle-of-attack for a rotating propeller blade is measured between the blade's chord or face and the relative airstream.### Propeller Operation and Mechanics
Angle of attack for a fixed-pitch propeller is influenced by forward speed and engine rotational speed.
The angle between airflow and the propeller blade plane of rotation is termed the helix angle or angle of advance.
Alpha range of a variable pitch propeller includes settings from feather to flight fine pitch, feather to ground fine pitch, and flight fine pitch stop to reverse stop.
Effective pitch describes the actual distance a propeller moves through the air during one revolution, as opposed to geometric or relative pitch.

Propeller Design and Materials

The matrix in a composite blade serves as the bonding material.
Propeller blades can be adjusted in flight or on the ground with engine running or stationary.
Blade stations are measured from the hub center line, with blade angle typically increasing from root to tip.

Synchronization and Maintenance

Synchronization presets the phase angle of propellers to minimize vibration and noise.
Stored propellers require regular maintenance such as replacing seals and checking torque loadings to ensure safety.

Engine and Propeller Interaction

Running a fixed-pitch propeller at full throttle while stationary in strong wind may yield an increase in full throttle RPM.
Reverse pitch propellers can provide aerodynamic braking and reverse rotation.

Repairs and Inspections

Removal of material from propeller blade tips, termed cropping, reduces diameter and may affect performance.
Propeller defects like nicks and scratches require prompt repairs to maintain aerodynamic performance and safety.
Blade tracking determines the position of blade tips relative to each other and the aircraft.

Speed and Control Mechanisms

For a constant speed propeller, RPM is adjusted via the prop control unit (PCU), allowing power adjustment while engine RPM remains constant.
Manifold pressure and engine RPM gauge are key metrics in controlling power on piston engine aircraft.

Pitch Regulation

Oil pressure for propeller pitch actuation is provided by the engine lubrication pump or a pump in the governor, enabling precise control of blade angle.
The pilot valve in a governor is influenced by oil pressure and governor flyweights.

Safety Considerations

Critical RPM ranges in engine-propeller combinations can lead to severe propeller vibrations, potentially causing inefficiencies.
In the event of engine failure, constant-speed propeller blades move to their lowest pitch position due to centrifugal force.

Ice Removal and Environmental Adjustments

Ice on propeller blades can be removed with heated boots or electrical systems to maintain performance, especially in adverse weather conditions.

Pitch Settings

For takeoff, a constant-speed propeller is generally set in a low pitch, high RPM position to optimize performance.

Performance Metrics

Geometric pitch is the distance a propeller moves in one revolution without slip, crucial for performance assessment in variable conditions.### Propeller Mechanics
Effective pitch combines geometric pitch and slip; it indicates the distance a propeller moves in one complete revolution.
Dynamic balance in propeller systems can be confirmed using knife edges, mandrel tracking checks, or vibration analyzers.
Fixed-pitch propellers should have an optimum angle for maximum efficiency during take-off.

Propeller Behavior During Take-off

An increase in RPM without throttle increase leads to engine over-speeding or inefficient blade angles.
Propeller de-icing can be monitored using blade observation and ammeter readings; monitoring for ice buildup is crucial.

Propeller Design Features

Counterweights in constant-speed propellers are integral for adjusting blade angles, enhancing performance during various flight conditions.
Composite blades utilize carbon fiber spars to protect against electrostatic buildup, improving reliability and safety.

Pitch and Balancing Mechanics

Coarse pitch settings in propellers are employed during take-off and climb but not during maximum economical cruise.
Centrifugal twisting moment (CTM) acts on the blade to influence pitch, creating forces that affect flight dynamics.

Propeller Tracking and Safety Measures

When tracking propellers, safety measures include removing spark plugs and positioning oneself away from the blade arc.
Propeller blades transition through different pitch settings like feathering to optimize performance; this varies based on the application.

Anti-Icing and Electrical Systems

Anti-icing fluids are delivered to blades through pumps or gravity-fed systems; this is critical for maintaining performance in cold conditions.
Propeller de-icer electrical power is transferred to the hub assembly through slip-rings and brushes from the engine.

Vibration and Maintenance

Vibration frequency related to propeller installation issues will typically fluctuate and could be higher, lower, or equal to turbine vibrations.
Typical components of a propeller governor include oil pumps, speeder springs, and diaphragm systems.

Control Mechanisms

Reverse thrust in turbo-prop aircraft is achieved by manipulating the power lever, critical for landing scenarios.
Centralizing propellers involves using front and rear cones to ensure alignment on the shaft.

Propeller Performance and Engineering

During take-off or climbs, maintaining a balance between RPM and blade angle is vital for optimal performance.
Specific maintenance practices involve evaluating blade integrity and serviceability through various checks and measures.

Advanced Propeller Features

The profile of aluminum blades is finalized through a combination of chemical etching and milling processes.
In 'on-speed' conditions, oil flows to the propeller, ensuring effective operation without unnecessary wear.

Adjusting Operations and Performance

Adjusting throttle in constant speed range operations impacts the blade angle, necessitating careful management of thrust and pitch.
Synchronization between engines is crucial during flight operations, especially when landing or taking off to ensure uniform thrust distribution.

Propeller Physics

The aerodynamic twisting moment has significant effects on blade pitch, influencing performance during different flight phases.
Tension adjustments in the speeder spring impact blade angle and RPM; this dynamic must be understood for efficient propeller operation.

Maintenance Protocols

Regular inspections for cracks and lubrication checks on propeller spinners are essential for longevity and safety.
"Blending" defects in blades involves smoothing edges to reduce turbulence and enhance aerodynamic efficiency.

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Description

Test your knowledge with this practice MCQ quiz based on Module 17, focusing on aircraft propeller blades and their materials. This quiz covers topics such as fatigue effects on propeller blades and fitting propellers to engines. Perfect for those looking to enhance their understanding of aviation technology.