AEE 672 BHPD LECTURE 1 (Introduction and Classification of Aircraft Propellers)

Propellers

Their core function is to convert the engine's rotating power into forward thrust

convert the engine's rotating power into forward thrust

What is a propeller's core function?

Early propeller designs

What propeller designs were essentially inefficient, flat paddles?

airfoil shapes

Propellers were eventually designed with____________ , similar to wings

aluminum alloys and composites

The use of new materials like __________ and ___________ has enabled the creation of thinner, stronger, and more efficient propeller blades

Hub

Blades

Shank/Root

Blade Tip

Blade Back

Blade Face

What are the basic components of a propeller?

Hub

this basic component of a propeller is the central component that connects the propeller to the engine crankshaft

Blades

This basic component of a propeller is the airfoil-shaped parts that produce thrust.

Shank/Root

This basic component of a propeller is the thick, cylindrical portion of the blade that fits into the hub.

blade tip

This basic component of a propeller is the outermost part of the blade.

blade back

This basic component of a propeller is the curved or cambered side of the blade, similar to the upper surface of a wing.

Blade Face

This basic component of a propeller is the flat surface of the blade, similar to the lower surface of a wing.

Blade Angle

This part of a propeller is The angle between the blade's chord line and the propeller's plane of rotation

Pitch Angle

Blade angle is also known as?

Blade Angle

This angle is critical for thrust generation and is measured at a specific station along the blade.

Chord Line

This is an imaginary straight line connecting the leading and trailing edges of the airfoil at any point along the blade.

Angle of Attack

The angle between the blade's chord line and the direction of the relative wind

typically 2-4 degrees

What is the optimal angle of attack that is needed for maximum efficiency?

Blade Station

This is A specific radial distance from the hub center, used to define the blade angle and other characteristics

Tip section

Mid section

Root section

What are the sections of a propeller?

Tip section

High airspeeds at this section require a thin aerofoil profile to minimise drag

Tip section

losses in this section cause an increasing loss in efficiency as the end of the blade is approached causing thrust production to drop-off towards the section

Tip section

velocities approaching the speed of sound dramatically increase both drag and noise production, so typically the overall propeller diameter is selected to avoid operating in this region

Mid Section

The bulk of the thrust is produced by the __________ section of the prop blade

Mid Section

In this section, The aerofoil profile and twist in this area are optimised for aerodynamic performance whilst still providing a large enough cross-sectional area to meet the structural strength and stiffness requirements of the blade

Root section

In this section, A thicker aerofoil provides the necessary blade strength and also gives a profile which stalls at a higher angle of attack

Root section

The inner 25% of the propeller's radius produces negligible thrust but high drag so providing shrouding with a spinner improves performance

Pressure Differential

Force Generation

The Corkscrew Analogy

In the propeller theory, what are the different ways thrust is generated?

Pressure Differential

In this propeller theory of how thrust is generated, As the propeller rotates, the blade's airfoil shape creates a low-pressure area in front of the blade and a high-pressure area behind it.

Force Generation

Thrust and Torque

In this propeller theory of how thrust is generated, This pressure differential creates a force, which can be resolved into two components

What are the components?

Thrust

In force generation, this component is the forward force that propels the aircraft

Torque

In force generation, this component is The resistive force that the engine must overcome

The Corkscrew Analogy

In this propeller theory of how thrust is generated, A propeller essentially "screws" its way through the air. The pitch of this "screw" determines how much air is moved backward for each rotation.

The rotational velocity of a propeller blade is not uniform; the tip moves much faster than the root

In propeller theory - pitch distribution, what is the problem stated?

Propeller blades are "twisted." The blade angle is high at the root and gradually decreases towards the tip

In propeller theory - pitch distribution, what is the solution to the problem stated?

The twist ensures that the blade's angle of attack remains relatively constant along its entire length, maximizing efficiency and preventing the outer sections from stalling

In propeller theory - pitch distribution, what is the result of the solution to the problem stated?

Propeller Slip

In propeller theory, this is The difference between the geometric pitch (the theoretical distance the propeller would advance in one revolution) and the effective pitch (the actual distance it advances).

geometric pitch

What is the theoretical distance the propeller would advance in one revolution?

effective pitch

What is the actual distance it advances?

False (A propeller can never be 100% efficient, so some slip is always present)

True or false

A propeller can sometimes be 100% efficient, so some slip is not always present.

Propeller Efficiency

In propeller theory, this is the ratio of the propeller's useful work (thrust power) to the work done by the engine (Torque power)

Efficiency

is a function of the angle of attack, forward speed, and RPM

Tractor Propellers

For this propeller classification, it is mounted on the front of the engine, pulling the aircraft

Tractor Propellers

For this propeller classification, it Operates in clean, undisturbed air, leading to higher efficiency and lower stresses on the propeller

Pusher Propellers

For this propeller classification, it is Mounted on the rear of the engine, pushing the aircraft

Pusher Propellers

For this propeller classification, they can allow for a cleaner wing design (without prop wash over the wing)

Pusher Propellers

For this propeller classification, they Operate in turbulent air, which can reduce efficiency

Pusher Propellers

For this propeller classification, they are More susceptible to damage from ground debris during takeoff and landing on unprepared surfaces

Fixed-Pitch Propellers

Ground-Adjustable Propellers

Controllable-Pitch Propellers

Constant-Speed Propellers

Reversible-Pitch Propellers

Feathering Propellers

What are the types of propellers classified by pitch?

Fixed-Pitch Propellers

This propeller classification by pitch is The simplest type; the blade angle is permanently set during manufacturing and cannot be changed

Climb propeller and Cruise propeller

What are the types of fixed pitch propellers?

Climb Propeller

This type of fixed pitch propeller is A propeller with a low blade angle

Cruise Propeller

This type of fixed pitch propeller is A propeller with a high blade angle,

Fixed-Pitch Propellers

This propeller classification by pitch is a compromise and is only efficient at one specific RPM and airspeed

Ground-Adjustable Propellers

This propeller classification by pitch is when the blade pitch can be manually changed, but only when the aircraft is on the ground and the engine is off

Ground-Adjustable Propellers

This propeller classification by pitch allows the pilot or mechanic to set the propeller for either climb or cruise, but not both during a single flight

Controllable-Pitch Propellers

for this propeller classification by pitch, The pilot can change the blade pitch in flight using a control lever

Controllable-Pitch Propellers

for this propeller classification by pitch, it Allows the pilot to optimize performance for various flight conditions (takeoff, climb, cruise).

Constant-Speed Propellers

for this propeller classification by pitch, it is an advanced type of controllable-pitch propeller which automatically adjusts the blade pitch to maintain a constant engine RPM.

Constant-Speed Propellers

for this propeller classification by pitch, it uses a governor or a Constant Speed Unit (CSU).

Constant-Speed Propellers

for this propeller classification by pitch, it Allows the engine to operate at its most efficient RPM regardless of airspeed, resulting in better overall performance and fuel efficiency.

Reversible-Pitch Propellers

for this propeller classification by pitch, this is A type of constant-speed propeller where the blade angle can be rotated to a negative pitch

Reversible-Pitch Propellers

for this propeller classification by pitch, it Produces reverse thrust, which helps shorten landing rolls and provides better ground maneuvering

Reversible-Pitch Propellers

for this propeller classification by pitch, it is Commonly found on large multi-engine aircraft and turboprop engines

Feathering Propellers

for this propeller classification by pitch, it is A type of constant-speed propeller that can rotate the blades to a zero-lift position (pointing into the wind)

Feathering Propellers

for this propeller classification by pitch, This is used in the event of an engine failure to stop the propeller from windmilling, which would create significant drag

Feathering Propellers

for this propeller classification by pitch, it Reduces drag, allowing the pilot to maintain better control and glide performance

Wood

Metal

Composite materials

What are the types of propeller construction?

Wood

This is the first reliable material for propellers

Wood

This material has

○ Excellent vibration absorption properties.

○ Lightweight.

○ Easy to manufacture and repair.

Wood

This material is

○ Susceptible to moisture damage.

○ Lower tensile strength compared to metals.

○ Vulnerable to damage from rain, hail, and ground debris.

Metal

This type of propeller construction material uses Primarily aluminum alloys, but steel was used in some older aircraft

Aluminum Alloy

this type of metal propeller construction material, it has High strength-to-weight ratio, allows for thin and efficient airfoil shapes, highly durable

Aluminum Alloy

this type of metal propeller construction material, it is Susceptible to fatigue cracking over time, less effective at absorbing vibration than wood

Steel

this type of metal propeller construction material, is Used for hollow-bladed propellers on some vintage aircraft

Steel

for this type of metal propeller construction material, it has High strength and durability

Steel

for this type of metal propeller construction material, it is Very heavy, difficult to repair

Composite Materials

This type of propeller construction material is Typically a composite of fiberglass or carbon fiber reinforced with plastic resins

Composite Materials

For This type of propeller construction material, it is

○ Extremely lightweight and strong.

○ Excellent fatigue and corrosion resistance.

○ Superior vibration absorption.

○ Allows for advanced aerodynamic designs.

Composite Materials

For This type of propeller construction material, it

○ Can be more expensive to manufacture than aluminum.

○ Can be more complex to repair.

Propeller Icing

This operational consideration is needed because of ice accretion on the propeller blades which can disrupt airflow, reduce efficiency, and can cause severe vibration

Propeller De-icing Systems

Propeller Anti-icing Systems

What are some solutions to propeller icing?

Propeller De-icing Systems

This solution to propeller icing uses electrical heating elements in the blade leading edge.

Propeller Anti-icing Systems

This solution to propeller icing uses a fluid (often an alcohol mixture) pumped onto the blades to prevent ice from forming

What is the