Aircraft Propulsion Systems Quiz

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Questions and Answers

Which advantage is associated with propeller-driven aircraft?

Shorter takeoff and landing distances (correct)

Ability to fly at higher altitudes

Higher fuel efficiency

Faster cruising speeds

What has improved the efficiency of propellers in recent years?

New fuel types available for use

Advanced blade materials and manufacturing techniques (correct)

Increased engine horsepower

Lighter airframe materials

What type of aircraft will likely continue using propellers well into the future?

Large commercial airliners

Many smaller aircraft (correct)

Sleek jet fighters

Supersonic transport aircraft

What factors determine the development of different types of propeller systems?

Specific aircraft installation and type of operation Signup and view all the answers

What does the basic nomenclature of a simple fixed-pitch propeller include?

Terminology to describe parts of the propeller Signup and view all the answers

What is a major advantage of tractor propellers?

They operate in relatively undisturbed air. Signup and view all the answers

Where are pusher propellers typically mounted?

Behind the supporting structure. Signup and view all the answers

Which type of aircraft primarily utilizes pusher propellers?

Seaplanes. Signup and view all the answers

What is true about the construction of pusher propellers?

They can be constructed as fixed- or variable-pitch. Signup and view all the answers

What characteristic is common to tractor propellers used in most aircraft?

They come in all types of propellers. Signup and view all the answers

What is the primary force that moves the propeller blades toward high pitch?

Governor oil pressure Signup and view all the answers

Which component boosts the pressure of engine oil to operate the pitch-changing mechanism?

Gear pump Signup and view all the answers

The position of which valve regulates the quantity of oil flowing to and from the propeller?

Pilot valve Signup and view all the answers

What happens when oil pressure is removed from the governor?

Blades are rotated to low pitch Signup and view all the answers

What is the role of the flyweights in the governor mechanism?

Control the position of the pilot valve Signup and view all the answers

What maintains the operating oil pressures in the governor?

Relief valve system Signup and view all the answers

Which type of governor is described as engine-driven and single-acting?

Constant-speed governor Signup and view all the answers

What happens to the governor oil pressure in the presence of greater aerodynamic twisting force?

It increases proportionally Signup and view all the answers

What percentage of torque is constituted by thrust in a propeller system?

80% Signup and view all the answers

What happens to the horsepower required to turn the propeller as the blade angle increases?

It increases Signup and view all the answers

What effect does decreasing the propeller blade angle have on the engine RPM?

It speeds the propeller up Signup and view all the answers

What is the most efficient angle of attack (AOA) for propellers indicated in the content?

2° to 4° positive Signup and view all the answers

What causes the actual blade angle needed to maintain a small AOA to vary?

Changes in relative wind direction Signup and view all the answers

What impact does increasing the propeller blade angle have on lift and drag?

It increases both lift and drag Signup and view all the answers

Which factor is NOT mentioned as a consequence of increasing the propeller blade angle?

Decrease in thrust Signup and view all the answers

What percentage of total horsepower is lost in friction and slippage?

20% Signup and view all the answers

What happens when the flyweights of the governor mechanism turn faster than the tension on the speeder spring?

An over-speed condition occurs. Signup and view all the answers

How does the governor mechanism respond to an over-speed condition?

It increases the blade pitch. Signup and view all the answers

Which external factor can disturb the balance of forces in the governor mechanism?

Aircraft attitude changes such as climbing or diving. Signup and view all the answers

What function does the propeller control on the control quadrant serve regarding the governor mechanism?

It adjusts the maximum RPM in governor mode. Signup and view all the answers

What is the primary aim of increasing the propeller blade pitch during an over-speed condition?

To slow down the propeller until it reaches the correct speed. Signup and view all the answers

In the governor mechanism, what constitutes the state of being 'on-speed'?

Force on the flyweights and tension on the speeder spring are balanced. Signup and view all the answers

What adjustment must be made to the speeder spring to change the maximum RPM of the engine in governor mode?

Alter the tension on the speeder spring. Signup and view all the answers

What happens to the flyweights when the engine speed exceeds the governor's set rpm?

They move outward against the speeder spring. Signup and view all the answers

What occurs when the pilot valve opens the propeller-governor metering port?

Governor oil flows from the propeller piston. Signup and view all the answers

In an on-speed condition, what is true about the forces acting on the governor flyweights?

The centrifugal force balances the speeder spring. Signup and view all the answers

What occurs when the forces of the governor flyweights and the speeder spring are equal?

The propeller blades do not change pitch. Signup and view all the answers

What external forces can unbalance the conditions of the governor system?

Changes in aircraft altitude or attitude. Signup and view all the answers

What does the governor control to manage engine speed and propeller pitch?

The propeller blade angle and pitch. Signup and view all the answers

What is the function of the pilot valve in the governor system?

To direct oil to and from the hydraulic cylinder. Signup and view all the answers

What indicates that the governor is not functioning properly?

Inability to adjust propeller pitch. Signup and view all the answers

Study Notes

Week 1 Complete

AVIA-1052 course is complete
Contact Matt C for corrections or improvements

Week 1 of 1 Day 1

AVIA-1052 course
First class session of the course

Previously On AVIA-1052

No prior sessions
First class session

Today On AVIA-1052

Topic will be propellers
General propeller topics will be discussed
Topics include: Aircraft propeller theory and basic propeller controls

Where are we?

Powerplant (Volume 2) pages 7-2 to 7-6
FAA Handbooks (specific volumes and numbers are listed)
Propeller Location

Propellers

The unit that must absorb the power output of the engine
Propeller development covered many evolutionary stages.
The first propellers were fabric-covered sticks.
Designed to force air rearward
Propellers started as simple two-bladed wood propellers.
Advanced to turboprop aircraft system which has more than just the propeller.
More complex propeller designs like a variable-pitch, constant-speed feathering and reversing propeller system exist.
Allows engine RPM to be changed slightly during different flight conditions.
Increases flying efficiency.
Constant-speed systems consist of a flyweight-equipped governor unit that controls the pitch angle of the blades so the engine speed remains constant.
A governor unit can be regulated by a cockpit controls that set the desired blade angle setting of the blade and engine operating speed for takeoff, low-pitch, high-rpm settings, flight, higher pitch, and lower rpm settings.
Figure shows normal propeller movement with low and high pitch positions.
Feather: used if engine quits to reduce drag; zero to negative pitch, then reverse pitch.
Common propeller types: Constant Speed and Fixed Pitch. Charts show efficiency vs speed for both.
Most propellers are two-bladed, but greater power outputs have resulted in four and six-bladed propellers of large diameters.
Forces acting on propeller as it turns include centrifugal force.
Blade weight is a vital factor in design.
Excessive blade tip speed may result in poor blade efficiency, fluttering, and vibration.
The speed of a propeller-driven aircraft is limited approximately 400 mph.
As aircraft sped up, turbofan engines are used.
Propeller-driven aircraft have advantages in takeoff and landing and are less expensive to maintain.
New blade materials and manufacturing techniques increased efficiency.
Widely used in turboprops and reciprocating engine installations.
Smaller aircraft continue to use propellers in the future.
Multiple different types of propeller systems are used for specific aircraft, speed, and type of operation.
Basic nomenclature for parts of a simple fixed-pitch, two-bladed wood propeller.
Aerodynamic cross-section of a blade (next slide)
Includes terminology to describe certain areas.
Blade back: cambered or curved side of the blade, comparable to the upper surface of an aircraft wing.
Blade face: flat side of the blade.
Chord line: imaginary line drawn through blade, from leading edge to trailing edge.
Leading edge: thick edge of blade that meets the air as the propeller rotates.

Aircraft Propeller Theory

The aircraft propeller consists of two or more blades.
Each blade is essentially a rotating wing.
Propellers produce forces to create thrust to push the airplane through the air.
Engine power is needed to rotate the propeller blades.
A central hub is attached to the blades.
Low-horsepower engines have the propeller mounted on a shaft, which can be an extension of the crankshaft.
High-horsepower engines have a propeller shaft that is geared to the engine crankshaft.

Basic Propeller Controls

Fixed-pitch propellers have no controls
Required no adjustments in flight
Constant-speed propellers have a propeller control in the center pedestal
Two positions:
- increase RPM
- decrease RPM

Basic Propeller Principles

Mounted on a shaft
Low-horsepower engines
- extension of the crankshaft
High-horsepower engines
- mounted on a propeller shaft
- geared to engine crankshaft
- engine rotates airfoils.
- propeller transforms rotary power into thrust

Propeller Aerodynamic Process

Airplane moving through air creates a drag force.
Equal force is applied to oppose the drag (thrust)
Work done (by thrust) equals thrust × distance.
Power expended by thrust equals thrust × velocity.

• power expended by thrust is termed thrust horsepower if the power is measured in horsepower units • the engine supplies brake horsepower through a rotating shaft • the propeller converts it into thrust horsepower • some power is wasted in this conversion • the propeller must be designed to keep this waste as small as possible for maximum efficiency • propeller efficiency is the ratio of thrust horsepower to brake horsepower • the efficiency of any machine is the ratio of the useful power output to the power input • the usual symbol for propeller efficiency is the Greek letter η (eta) • propeller efficiency varies from 50-87%, depending on how much the propeller slips • pitch is not the same as blade angle, the two terms are often used interchangeably. • An increase or decrease in one usually results from an increase or decrease of the other • blade angle is the angle between the blade section or chord/chord line and the plane in which the propeller rotates • usually measured in degrees • geometric pitch is the distance a propeller moves in one revolution with no slippage. • Usually expressed in pitch inches. • calculated by using the formula (GP = 2 × π × R × tangent of blade angle at 75% station), where: • R = radius at the 75% blade station and π = 3.14. • The formula is based on no slippage • effective pitch is the distance the blade advances during one revolution, when taking slippage into account • geometric pitch – effective pitch = slip • the chord line of the propeller blade is determined in about the same manner as the chord line of an airfoil. • A propeller blade can be considered as being composed of an infinite number of thin blade elements • The typical propeller blade can be described as a twisted airfoil of irregular planform •the cross-sections of each 6-inch blade segment are shown as airfoils. • blade shank, thick and rounded portion near the hub, that supports strength to the blade • blade butt, also referred to as the blade base or root • blade tip, part of propeller that is farthest from the hub; usually the last 6 inches of the blade • Blade back: cambered or curved side of the blade; Upper surface of the wing. • Blade Face: flat side of the blade. • Chord line: imaginary line drawing though the blade. Leading edge to trailing edge. • Leading edge: thick edge of the blade as the propeller rotates. • centripical force: physical force acting on propeller that causes the blades to move away from the hub. • torque bending force: tends to bend the blades in the direction opposite to the direction of the rotation • thrust bending force: loads that bend the propeller blades forward as the aircraft is pulled through the air. • aerodynamic twisting force: force to turn the blades into a high-angle blade • propeller must be capable of withstanding severe stresses greater near the hub • caused by centrifugal force & thrust; increase proportionally to RPM • blade face is subjected to tension from centrifugal force • Nicks & scratches cause consequences like cracks & blade failure • excessive blade tip speed, rotating the propeller too fast could result in poor blade efficiency, fluttering and vibration • since the propeller speed is limited, the aircraft speed of a propeller driven aircraft is also limited approximately 400 mph (644 kilometers per hour) • as aircraft speeds increased, turbofan engines were used for higher speed aircraft • propeller efficiency is more than just the ratio of thrust horsepower to brake horsepower but also the ratio of the useful power output to the power input to the ratio of the useful power output to the power input η= Thrust horsepower /Brake horsepower

Propeller Types

Fixed-pitch
Ground-adjustable
Controllable-pitch
Constant-speed

Propeller Governor

an engine rpm-sensing device that boosts oil pressure to operate the pitch-changing mechanism.
a gear pump increases the pressure.
a pilot valve that regulates the flow of oil through the governor.

Propeller Auxiliary Systems

Ice control systems

Ice Control Systems

Ice formation produces a distorted propeller blade airfoil section causing a loss in the propeller efficiency.
Asymmetrical collection produces propeller unbalance leading to destructive vibration and increasing the weight of the blade.
Fluid anti-ice system
- typically includes a tank, a pump, and control system
- variations in pumping rate permit varying quantities of fluid delivered
An example fluid type is isopropyl alcohol.
Has high availability, low cost, reduced flammability but is not widely used.
Feed shoes: narrow strips of rubber on the blades
Slinger ring: transfers fluid from a stationary nozzle in the engine nose case.

Deicing Systems

electric propeller-icing control system
a source of electrical energy
a heating element mounted on the blades of the propeller
a master switch and optional toggle switches
control the amount of time the system applies power to the blades
a timer determines the sequence of which blades are being deiced
electric motor-driven contactors that control the power contactors in separate sections of the circuit.

Propeller Synchronization and Synchrophasing

Used on multi-engine aircrafts (mostly)
Provides a means of controlling and synchronizing engine RPM.
Reduces vibration and eliminates the unpleasant vibrations in unsynchronized propeller operation.

Autofeathering System

An auto-feather system is used during takeoff, approach and landing.
The system automatically feathers the propeller if engine power is lost using a solenoid valve.

Propeller Removal and Installation

removing the spinner dome
removing the safety wire
supporting the assembly with a sling
identifying marks on the hub and engine flange
cleaning the mounting hardware
Installation
- cleaning the engine flange and propeller flange with solvent
- installing the O-ring in the hub bore
- carefully mounting the propeller assembly on the engine mounting flange
- tightening mounting nuts evenly to avoid hub damage
- installing propeller mounting nuts with spacers and correct torque specifications

Servicing Propellers

servicing propellers includes:
cleaning
lubricating
replenishing operating fluids

Propeller Vibration

Excessive vibration often stems from blade imbalance, non-tracking, or faulty blade angle settings.
If vibration only occurs at a specific RPM, the problem is typically not with the propeller itself, but with the engine match

Blade Tracking

The procedure to determine the position of the propeller blades relative to one another.

Checking and Adjusting Propeller Blade Angles

Follow manufacturer instructions to check and adjust blade angles.

Propeller Balancing

Propeller unbalance can be either static (center of gravity of the propeller does not coincide with the axis of rotation) or dynamic (centers of gravity of similar propeller elements, such as blades or counterweights, do not follow the same plane of rotation).
Dynamic unbalance, resulting from improper mass distribution is negligible, provided track tolerance requirements are met.
Unequal thrust of blades can be eliminated by setting and inspecting blade configurations and blade angles.

Composite Propeller Inspection

The visual inspection of composite blades should be frequent and thorough.
The blades might show nicks, gouges, loose material, and erosion.

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Description

Test your knowledge on propeller-driven aircraft and their efficiency advancements. This quiz covers various aspects of propeller types, functionality, and their applications in aviation. Challenge yourself to understand the technical elements behind aircraft propulsion systems.