Stress Analysis of Two-Blade Propeller

Questions and Answers

What happens to a propeller's performance when it is operated outside its designed purpose?

It increases significantly.

It remains the same.

It becomes more efficient.

It drops off rapidly. (correct)

How can the pitch of a ground-adjustable propeller be altered?

Only on the ground by loosening the retaining clamps. (correct)

Automatically based on flight conditions.

By adjusting a control lever in the cockpit.

While in flight using a protractor.

What is a key feature of a controllable-pitch propeller?

It cannot vary the pitch during flight.

Its pitch can only be changed while on the ground.

It operates on fixed pitch settings.

The blade angle can be adjusted while it is rotating. (correct)

What transforms a controllable-pitch propeller into a constant-speed propeller?

Incorporating a speed-sensitive governor. Signup and view all the answers

What describes the limitations of a ground-adjustable propeller?

The blade pitch is fixed during flight conditions. Signup and view all the answers

What defines the pitch adjustment capabilities of the earliest adjustable propellers?

They are set to a fixed pitch after adjustment. Signup and view all the answers

Which type of propeller can change its blade angle to optimize performance?

Controllable-pitch propeller. Signup and view all the answers

What is the primary limitation of a fixed-pitch propeller?

It cannot adjust blade angle during flight. Signup and view all the answers

What primarily enables the counterweights to adjust the blade angle of the propeller?

Centrifugal force acting on the counterweights Signup and view all the answers

What happens when the blade angle is changed to a coarser pitch?

The propeller operates less efficiently Signup and view all the answers

Which component is necessary to convert a two-position propeller into a constant speed unit?

A speed-sensitive governor Signup and view all the answers

What role does the lever-operated control valve play in the operation of the propeller?

It regulates oil flow to the counterweights Signup and view all the answers

What physically connects the counterweights to the propeller blades?

A movable cylinder Signup and view all the answers

When oil pressure dissipates from the cylinder, what action occurs next?

The blades adjust to a coarser pitch Signup and view all the answers

What effect does adding a speed-sensitive governor have on the propeller's performance?

It maintains a constant rotation speed Signup and view all the answers

Which of the following statements about 'coarser pitch angle' is true?

It leads to a potential decrease in engine efficiency Signup and view all the answers

What is the expected angle of attack range for a properly designed fixed-pitch propeller at 1500 rpm and 50 kt forward velocity?

2° to 4° Signup and view all the answers

Which factor directly affects the performance (thrust) of a fixed-pitch propeller?

Rotational velocity Signup and view all the answers

What happens to the angle of attack when the rotational velocity of the propeller is increased from 1500 rpm to 2000 rpm while keeping forward velocity constant?

It increases. Signup and view all the answers

The lines drawn to scale in vector diagrams are used to represent which of the following?

Speed or force Signup and view all the answers

If both rotational velocity and forward velocity change simultaneously, how does this affect a propeller's thrust performance?

Thrust will vary. Signup and view all the answers

At what point will a propeller produce the required amount of thrust according to its design?

At its specified rotational and forward velocities. Signup and view all the answers

What is the primary condition for ensuring a propeller operates efficiently?

Correct angle of attack. Signup and view all the answers

When forward velocity is increased, what can be anticipated regarding the thrust produced by a propeller?

It will increase if the angle of attack is optimized. Signup and view all the answers

What is the primary purpose of anodising alloy blades?

To provide extra protection against corrosion Signup and view all the answers

How does shot peening improve the durability of metal propellers?

By distributing stresses evenly across the surface Signup and view all the answers

What is typically used as the shot material in the shot peening process?

Steel and glass beads Signup and view all the answers

Which statement about shot peening is incorrect?

It requires other treatments to enhance its effectiveness. Signup and view all the answers

What effect does increasing the velocity or size of the shot have during shot peening?

It increases the depth of work achieved. Signup and view all the answers

Why is shot peening particularly important for steel propellers?

Because steel propellers can exhibit brittleness changes. Signup and view all the answers

Which of the following is NOT a characteristic of anodised metal?

Lightweight Signup and view all the answers

What is the typical depth of plastic deformation caused by shot peening?

A few thousandths of an inch Signup and view all the answers

What consequence can occur if a propeller cannot absorb the power provided by the engine?

The propeller will race, leading to inefficiency. Signup and view all the answers

Which of the following factors is NOT considered when selecting a propeller?

Aircraft color and design Signup and view all the answers

What must be considered regarding aircraft design when selecting a propeller?

Clearances between various aircraft components Signup and view all the answers

In terms of propeller operation, what does a positive pitch angle indicate?

An increase in lift production Signup and view all the answers

Which engine characteristics are pivotal when choosing a propeller?

Engine power and torque absorption Signup and view all the answers

What is a critical factor in propeller selection related to aircraft performance?

Cruising speed and climbing rate Signup and view all the answers

Which attachment method might be considered when selecting a propeller?

Reciprocating or gas turbine engine type Signup and view all the answers

Why is it important to consider the effect of airflow over control surfaces when selecting a propeller?

It influences aircraft agility and response. Signup and view all the answers

Study Notes

Propeller Performance Factors

Propeller performance is influenced by thrust, which varies with rotational velocity (rpm) and aircraft velocity (True Airspeed in knots).
Aimed angle of attack for optimal thrust is between 2° to 4°; for example, at 1500 rpm and 50 knots, the thrust output is ideal until these parameters change.

Rotational and Forward Velocity Effects

Increasing rotational velocity (e.g., from 1500 rpm to 2000 rpm) without changing forward velocity raises the angle of attack.
Increasing forward velocity does not enhance thrust from the propeller but improves engine cooling airflow.

Anodising Process

Anodising provides a hard protective coating on alloy blades, enhancing corrosion resistance, waterproofing, and airtight qualities.
This electroplating process plays a pivotal role in extending the life of propeller materials.

Shot Peening Technique

Shot peening improves the fatigue strength of metal propellers by distributing surface stresses uniformly.
This finishing treatment mitigates the risk of stress cracking in steel propellers, often caused by nicks and gouges.
The technique involves high-velocity impact of shot beads (steel or glass) to induce plastic deformation of the blade surface.

Propeller Types

Ground-Adjustable Propeller: Pitch can only be changed when propeller is not rotating; adjustments are made manually on the ground.
Controllable-Pitch Propeller: Allows for blade angle adjustments during operation, optimizing performance across different flight conditions.
Constant-Speed Propeller: Equipped with a speed-sensitive governor, allowing automatic adjustments to maintain a specific speed.

Propeller Selection Considerations

Factors for selecting propellers include engine power, type of engine attachment, aircraft design, and performance requirements.
Proper alignment with engine power is essential to prevent propeller racing, which leads to inefficiency.

Blades and Pitch Control Mechanism

Blade angle adjustments can alter between fine and coarse pitches based on oil flow controlled by a lever-operated valve.
The introduction of a speed-sensitive governor converts a two-position propeller into a constant-speed propeller, enhancing operational efficiency.

Performance Requirements

The propeller must effectively absorb power from the engine to maintain efficiency. If not, it will exceed speed capabilities (race).

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Description

This quiz focuses on the stress analysis of a two-blade propeller, emphasizing the importance of understanding the angle of attack and performance variations. It requires a basic knowledge of vectors and their application in assessing propeller efficiency and stability.