Aircraft Propeller Mechanics

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Questions and Answers

What is a function of the bronze bushing in a fixed-pitch wooden propeller hub?

To improve propeller laminar flow

To facilitate propeller removal (correct)

To serve as a front cone

To connect the two blades

Which type of propeller is designed to automatically adjust its pitch based on flight conditions?

Fixed-Pitch Propeller

Ground-Adjustable Propeller

Feathering Propeller

Constant-Speed Propeller (correct)

Which of the following types of propellers allows for reversing the pitch for negative thrust?

Constant-Speed Feathering Propeller

Reverse-Pitch Propeller (correct)

Metal Fixed-Pitch Propeller

Controllable-Pitch Propeller

What is the purpose of ice control systems in propellers?

To prevent the formation of ice on the blades Signup and view all the answers

Which of the following types of propellers is commonly used on general aviation aircraft?

Metal Fixed-Pitch Propellers Signup and view all the answers

What is the consequence of fluttering in a propeller blade?

It leads to blade failure due to weakening. Signup and view all the answers

What is the angle at which the air strikes the propeller blade called?

Angle of Attack (AOA) Signup and view all the answers

What does the downward and forward motion of a propeller blade create?

Increased dynamic pressure at the engine side of the blade. Signup and view all the answers

Why is it important for a propeller to be rigid?

To avoid fluttering vibrations. Signup and view all the answers

What phenomenon accompanies the vibration known as fluttering in propeller blades?

A unique sound often mistaken for exhaust noise. Signup and view all the answers

What is the primary function of a propeller in aviation?

To absorb engine power output Signup and view all the answers

What did the first propellers primarily consist of?

Wooden blades covered with fabric Signup and view all the answers

How has propeller development been influenced over time?

By the evolution of propulsion systems Signup and view all the answers

Which section of the FAA maintenance handbooks covers propeller location?

Powerplant Volume 2 Signup and view all the answers

What is the starting point for the discussion on propellers in the AVIA-1052 course?

General propeller information Signup and view all the answers

Which of the following is NOT included in the topics for today's AVIA-1052 class?

Aircraft design principles Signup and view all the answers

What is one reason propellers have evolved over time?

To improve propulsion efficiency Signup and view all the answers

What is the end objective of today’s discussion on propellers?

Grasping the basic controls of propellers Signup and view all the answers

What is the primary function of a propeller governor in constant-speed propellers?

To maintain a constant engine speed by changing the propeller blade angle. Signup and view all the answers

What happens to the blade angle when an airplane climbs?

The blade angle decreases to prevent the engine speed from dropping. Signup and view all the answers

When an aircraft is in a dive, what effect does this have on the propeller blade angle?

The blade angle increases to prevent engine overspeeding. Signup and view all the answers

If the throttle setting is changed while maintaining level flight, what happens to the propeller blade angle?

It varies to maintain constant RPM according to the new throttle setting. Signup and view all the answers

What directly influences the power output of the engine in a constant-speed propeller system?

The throttle setting and its adjustments. Signup and view all the answers

How is the pitch-changing mechanism of some constant-speed propellers typically operated?

Hydraulically using oil pressure and a piston arrangement. Signup and view all the answers

Which of the following is NOT a characteristic of constant-speed propellers?

They can require manual adjustment of blade angle to function effectively. Signup and view all the answers

What is the relationship between throttle setting and engine RPM in a constant-speed propeller system?

Throttle settings influence power output rather than engine RPM changes. Signup and view all the answers

What is the primary function of the retaining nut in a fixed-pitch wooden propeller hub?

It secures the hub in place on the tapered shaft. Signup and view all the answers

What is the purpose of the locknut in the propeller hub assembly?

To secure the retaining nut in place. Signup and view all the answers

Which component of the propeller hub is a steel disk that forms the forward face?

Faceplate Signup and view all the answers

How are the locknut and retaining nut secured together?

With lock-wire or a cotter pin. Signup and view all the answers

What feature of the flange plate aids in centering the hub on the propeller shaft?

External splines and cone seats. Signup and view all the answers

Which part of the propeller hub is explicitly mentioned to hold the propeller on the shaft?

Flange plate Signup and view all the answers

What type of shaft does the retaining nut typically correspond to?

Tapered shaft Signup and view all the answers

Which design feature helps maintain stability and balance in the hub assembly?

Concentric disk surface holes. Signup and view all the answers

What is the primary advantage of adjusting the blade angle of a propeller?

It maintains an efficient angle of attack. Signup and view all the answers

Which type of propellers is designed to achieve best efficiency at a single rotation speed?

Fixed-pitch propellers Signup and view all the answers

In what situation does a constant-speed propeller operate at a low blade angle?

During takeoff Signup and view all the answers

What happens to propeller efficiency when there is a change in conditions such as speed or load?

It lowers the efficiency of both propeller and engine. Signup and view all the answers

Why is a constant-speed propeller beneficial during flight?

It maintains maximum efficiency across various flight conditions. Signup and view all the answers

How does a low blade angle affect the angle of attack and air mass handled by the propeller?

It maintains a small angle of attack and reduces air mass. Signup and view all the answers

How does high engine rpm influence thrust during takeoff?

It creates maximum thrust despite low airplane speed. Signup and view all the answers

For which phases of flight might a specific propeller be optimized?

Takeoff, climb, cruising, and high speeds Signup and view all the answers

Study Notes

Week 1 Complete

AVIA-1052 course completed for week 1
Contact Matt C for any corrections or improvements needed

Week 1 of 1 Day 1

AVIA-1052 course, first class
First class overview
Initial topic overview for the day
Propeller overview

Previously On AVIA-1052

Topics covered in the previous class
General discussions on propellers
Aircraft Propeller Theory
Basic Propeller Controls

Today On AVIA-1052

Focus areas for the current class
Propeller Location
Types of propellers
Fixed-pitch propeller
Test Club propeller
Ground-adjustable propeller
Controllable-pitch propeller
Constant-speed propellers
Feathering propellers
Reverse-pitch propellers
Propeller Governor
Propellers used on General Aviation Aircraft

Where are we?

Powerplant (Vol. 2) 7-6 to 7-14
Start at
Propeller Location
Stop at
Metal Fixed-Pitch Propellers
FAA-H-8083-30A, General
FAA-H-8083-31A, Airframe Volume 1
FAA-H-8083-31A, Airframe Volume 2
FAA-H-8083-32A, Powerplant Volume 1
FAA-H-8083-32A, Powerplant Volume 2

Propellers

The unit that absorbs the power output of the engine
Development stages
Fabric-covered sticks were the first
Designed to force air in a rearward direction
Propellers started as simple two-bladed wood propellers, evolved to complex turboprop systems
Variable-pitch, constant-speed feathering, and reversing propeller system
Constant-speed systems (flyweight-equipped governor unit)
Control the pitch angle to maintain constant engine speed
Parts of the propeller
Normal movement with low and high pitch
Feather is used when the engine stops, reduces drag, zero to negative pitch reverse pitch

Aircraft Propeller Theory

Aircraft propeller consists of two or more blades
Each blade is similar to a rotating wing
Produce forces and create thrust
The power to rotate blades comes from engine
Central hub to which blades are attached

Basic Propeller Principles

Mounted on a shaft
Low-horsepower engines (extension of crankshaft)
High-horsepower engines (mounted on a propeller shaft geared to crankshaft)
Engine rotates airfoils of blades high speeds
Propeller transforms rotary power into thrust

Propeller Aerodynamic Process

An airplane creates drag force
There must be an equal and opposite force (thrust)
Work done by thrust equals thrust times distance
Power expended by thrust = thrust x velocity
Thrust horsepower if the power is measured in horsepower units
Engine supplies brake horsepower through a rotating shaft
Propeller converts brake horsepower into thrust horsepower
Some power is wasted in the conversion
Propeller efficiency is the ratio of thrust horsepower to brake horsepower (Greek letter n or eta)
Propeller efficiency = 50-87%, depends on slip
Pitch is different than blade angle
Geometric pitch: advance per one revolution (no slip) calculated by a formula
Effective pitch — considers slip (difference between geometric and effective pitch equals slip)
Chord line of the propeller blade is determined in a similar manner to an airfoil
Blade back (one side is cambered or curved); blade face (other side is flat)
Chord line, imaginary line through the blade (from leading edge to trailing edge)
Leading edge, thick edge of the blade the air as the propeller rotates

Principal forces acting on a rotating Propelller

Centrifugal force, tends to pull blades out of hub at high rpm
Blade weight important to propeller design
Excessive blade tip speed can lead to poor blade efficiency which leads to fluttering and vibration.

Propeller blade tip speed

Rotating the propeller too fast may result in poor blade efficiency
Flutter and vibration from excessive blade tip speed

Most Propellers

Two-bladed
Four- and six-bladed propeller types are developed due to increases in power output
Propeller-driven aircraft speed limited by rpm

Forces Acting on Rotating Propellers

Centrifugal force pulling blades outward.
Torque bends the blades in the opposite direction to rotation.
Thrust bends the blades forward as the aircraft pulls through the air.
Aerodynamic twisting force that rotates the blades into high pitch when the plane is in takeoff and climb mode.
Centrifugal twisting force, tends to force the blades toward a low blade angle.

Propeller Types

Fixed pitch
Ground adjustable
Controllable pitch
Constant speed

Propeller Governor

Engine rpm-sensing device and high-pressure oil pump
Responds to changes in engine rpm by directing oil to or releasing oil from the propeller hydraulic cylinder
In a constant-speed propeller system, the change in oil volume in the hydraulic cylinder maintains blade angle.
The two main instruments used: engine tachometer; manifold pressure gauge
Parts of the propeller governor
Fundamentals forces used to control blade angle
Centrifugal twisting moment
Aerodynamic twisting force
Forces on the rotating blades are not equal in strength, this creates a balance

Governor Mechanism

Constant-speed valve control consists of a gear pump, which increases engine oil pressure, and a pilot valve
The pilot valve is controlled by flyweights in the governor to control the oil flow to and away from propeller.
Governors regulate quantity of oil by controlling the position of the pilot valve (relative to metering port).
Relief valve system, regulates operating oil pressures in the governor.

Propeller Governor Operation

Underspeed conditions
Overspeed conditions
On-speed conditions

Feathering Propellers

Used in multi-engine aircraft to reduce drag during single-engine operation or failure.
By rotating the blade angle parallel to the line of flight.
The propeller ceases operation.
Windmilling is reduced or stopped
Methods involve oil pressure to move blades to a low pitch, and flyweights in the propeller

Reverse-Pitch Propeller

Change blade angle for negative value.
Provides an opposite thrust to normal forward direction.
Used for braking effect on the ground.
Loss of forward motion during engine failure.

Propeller Auxiliary Systems

Ice control systems
Anti icing fluid system (tank, pumps, forces, control systems)
Fluid types (isopropyl alcohol, phosphate compounds)
Feed shoes (narrow strip of rubber extending)
Slinger ring (transfers fluid to blades)

Ice Control Systems

Prevents the buildup of ice on blades
Ice formation causes: distortions in blade section, causes loss of propeller efficiency collecting asymmetrically, produces propeller imbalance, destructive vibration which increases weight of blades

Deicing Systems

Electric propeller
Electrical energy source
Resistance heating element
Mounted internally on propeller spinner and blades
Necessary wiring for the deicing system

Propeller Removal, and Installation

To remove and install propellers, follow the manufacturer guidelines to properly support the propeller.
Ensure correct identification of the propeller parts

Propeller Overhaul

Checks for and corrects blade, spinner, and hub defects

Propeller Balancing

Static balancing: when the center of gravity of the propeller and its parts don't coincide with the axis of rotation
Dynamic balancing: when the CG of component parts of the propeller and accessories do not lie in the same plane of rotation

Propeller Vibration

Caused by several problems
Imbalance in the blades, incorrect blade angle, or tracking problems
The intensity of the vibration can vary with the rpm.
Propeller hub checks are helpful if suspected of unbalance issues

Blade Tracking

The path/position of propeller blades when rotating at the same plane of rotation
The difference in track at like points is checked for issues by the manufacturer's tolerance specs.

Checking and Adjusting Propeller Blade Angles

Follow the guidelines from the appropriate manufacturer.
Using measuring инструменты to pinpoint blade issues
Protractor tool used

Composite Propeller Inspection

Look for nicks, gouges, loose material, erosion, cracks, and debonds.
A metal coin is used to tap composite blades for sound and determine if delamination or debonding is likely

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Description

This quiz tests your knowledge of aircraft propeller mechanics, focusing on fixed-pitch wooden propellers, pitch adjustment, and ice control systems. Understand the types of propellers, their functions, and the effects of fluttering. Perfect for aviation enthusiasts and students in aerospace engineering.