Aircraft Engine Bypass Ratios

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Questions and Answers

What is the primary source of power for a gas turbine engine during flight?

Ram effect of the incoming air (correct)

Electric motor

Turbine wheel

Compressor impeller

What type of turbine wheel is used in the pure reaction turbojet engine?

Radial turbine wheel

Multi-stage turbine wheel

Single-stage turbine wheel (correct)

Axial turbine wheel

What is the purpose of the combustion chamber in a gas turbine engine?

To burn the air/fuel mixture (correct)

To extract energy from the exhaust gases

To compress the air

To generate electricity

What is the name of the British Royal Air College cadet who patented the first turbojet aircraft engine?

Frank Whittle Signup and view all the answers

What is the working fluid used in an aircraft gas turbine engine?

Air Signup and view all the answers

What is the primary function of the compressor in a gas turbine engine?

To compress the air Signup and view all the answers

What is the primary function of the gas generator in a turboshaft engine?

To extract energy from the combustion process Signup and view all the answers

What is the main difference between a fixed turbine and a free turbine turboshaft engine?

The power take-off mechanism Signup and view all the answers

Which of the following is NOT a common application of turboshaft engines?

Commercial airliners Signup and view all the answers

What is the primary purpose of an aircraft auxiliary power unit (APU)?

To drive generators and hydraulic pumps Signup and view all the answers

How many types of gas turbine-powered jet engines are commonly used in today's aircraft?

4 Signup and view all the answers

What is the name of the turbine that drives the free turbine system in a turboshaft engine?

Power turbine Signup and view all the answers

What is the primary purpose of the compressor in a turbojet engine?

To increase the air pressure Signup and view all the answers

What is the result of the heat generated by the burning fuel in a turbojet engine?

The air expands and flows towards the rear of the engine Signup and view all the answers

What is the ratio of airflow in a low-bypass engine?

1:1 Signup and view all the answers

What is the main advantage of the turbojet engine?

Enhanced efficiencies at high-speed, high-altitude operations Signup and view all the answers

What is the term for the air that passes through the core engine in a low-bypass engine?

Hot gas stream Signup and view all the answers

What is the advantage of a mixed exhaust design in a low-bypass engine?

Noise suppression Signup and view all the answers

What is the primary difference between a turbojet engine and a turbofan engine?

The ability to use higher turbine temperatures without a corresponding increase in jet velocity Signup and view all the answers

What is the result of the air exiting the engine at a higher velocity than the incoming air?

The engine produces more thrust Signup and view all the answers

What is the fan ratio of a high-bypass engine?

4:1 to < 9:1 Signup and view all the answers

What is the current trend in commercial and business jets in terms of engine choice?

Turbofan engines are becoming more popular Signup and view all the answers

What is required to accomplish the high-bypass ratio in a high-bypass engine?

A large-diameter fan Signup and view all the answers

What is the term for the air that is discharged by the fan and ducted overboard from a short duct?

Cold gas stream Signup and view all the answers

What percentage of the airflow accelerated by the fan rotor blades is ducted past the core engine?

Up to 90% Signup and view all the answers

What is the purpose of the pressure within the fan duct in ducted fan engines?

To reduce airflow separation from the blades at speeds over Mach 1 Signup and view all the answers

Why do high-bypass engines and ducted fan engines produce more fan thrust than low-bypass engines?

Because they suffer less loss through skin friction with their short ducts Signup and view all the answers

What is the purpose of the engine station reference system?

To identify the location of a component or fitting along the axis line of the engine Signup and view all the answers

What is the term for the airstream that is ducted overboard, either directly behind the fan or at the rear of the engine?

Bypass airstream Signup and view all the answers

What is an alternative arrangement of the fan, where it is powered by a shaft from the turbine or is an extension of the turbine blades?

Aft-fan arrangement Signup and view all the answers

Study Notes

Bypass Ratios

Low-bypass engine: airflow is divided approximately into two halves between the fan and compressor
Medium-bypass engine: 2:1 or 3:1 ratio
High-bypass engine: 4:1 to < 9:1 ratio
Ultra-high-bypass engine: > 9:1 ratio

Low-Bypass Engine

Air is divided into two halves: fan and compressor
Fan air may be ducted overboard or pass through the core engine
Core engine air is compressed, combusted, and discharged through the hot exhaust nozzle
Turbofan engine can have non-mixed or mixed exhaust
Mixed exhaust design offers noise suppression by diluting hot gases

High-Bypass Engine

Fan ratio: 4:1 to < 9:1 (four to nine parts of air go through the fan for every part that goes to the core engine)
Requires a large-diameter fan
Example: diagram showing changes in pressure, velocity, and temperature during ground run-up

History of Propulsion

Frank Whittle, British Royal Air College cadet, wrote a thesis advocating for the use of gas turbine engines in 1930
Whittle patented the first turbojet aircraft engine, which used a compressor impeller driven by a turbine
The engine developed was a pure reaction turbojet, where total thrust came from reaction to the hot gas stream

Gas Turbine Engine

The aircraft gas turbine is a heat engine using air as a working fluid
Consists of a compressor, combustion chamber, and turbine
Four types of gas turbine engines: turboshaft, turbo-propeller, turbojet, and turbofan

Turboshaft Engine

Delivers power through a shaft to operate something other than a propeller
Can be a fixed turbine or free turbine turboshaft engine
Free turbine turboshaft engine has two major sections: gas generator and free turbine
Used in industrial applications, such as electrical power-generating plants and surface transportation systems
Also used in aviation, particularly in helicopters and aircraft auxiliary power units (APUs)

Turbojet Engine

Uses the acceleration of airflow throughout the engine to produce thrust
Well suited for high-speed, high-altitude operations
Basic operating principles: air enters through an inlet duct, is compressed, mixed with fuel, and ignited
Expanding air spins turbine wheels, which drives the compressor, and exits the engine at a higher velocity

Turbofan Engine

Consists of a multi-bladed ducted propeller driven by a gas turbine
Up to 90% of airflow accelerated by the fan rotor blades is ducted past the core engine
Fan tip speed may exceed Mach 1 to deliver the correct amount of air
High-bypass engines and ducted fan engines produce more fan thrust than low-bypass engines

Engine Stations

Reference system using engine stations to identify the position of a component or fitting
Engine stations follow the gas path and refer to basic locations such as the compressor inlet, compressor outlet, and turbine inlet and outlet
Number of designated stations varies according to engine complexity

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Description

This quiz covers the different types of bypass ratios in gas turbine engines, including low, medium, high, and ultra-high bypass ratios.