Thrust Reverser Quiz & Flashcards on Aircraft Engines

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Questions and Answers

What is the purpose of cascade vanes in a thrust reverser system?

To redirect the gas stream forwards to oppose the aircraft motion (correct)

To redirect the hot gas stream backwards

To mechanically block the fan airflow

To block the normal gas stream exit

What is the primary function of the post exit bucket type system?

To mechanically block the fan airflow

To block the normal gas stream exit

To reverse the hot gas stream and prevent hot gases from coming into contact with the fuselage (correct)

To redirect the fan airflow forwards

Which type of thrust reverser system uses a movable obstruction in the pre-exit fan airstream?

Cold stream mechanical blockage type (correct)

Cascade vane type

Aerodynamic blockage type

Post exit bucket type

What is the purpose of blocker doors in an aerodynamic thrust reverser system?

To redirect the fan airflow forwards Signup and view all the answers

What type of thrust reverser system is used in mixed low-bypass exhaust turbofans?

One reverser Signup and view all the answers

What is the purpose of a divergent nozzle in a helicopter tailpipe?

To nullify the thrust produced Signup and view all the answers

What is the purpose of a thrust reverser system in an aircraft?

To slow the aircraft during landing Signup and view all the answers

What happens to the exhaust gases in the converging portion of a convergent/diverging nozzle?

They are accelerated to sonic speed Signup and view all the answers

Why is a variable geometry nozzle necessary on engines that utilize an afterburner?

To increase the area of the exhaust nozzle Signup and view all the answers

What is the purpose of an afterburner?

To accelerate the exhaust gases and increase thrust Signup and view all the answers

What controls are typically used to operate variable nozzles?

Pneumatic, hydraulic, or electric controls Signup and view all the answers

What happens to the exhaust gases in the divergent portion of a convergent/diverging nozzle?

They are accelerated to supersonic speed Signup and view all the answers

What is the purpose of the radial struts between the outer shell and inner cone?

To support the inner cone and straighten the swirling exhaust gases Signup and view all the answers

What are the outer duct and exhaust cone commonly made of?

Nickel alloys or titanium Signup and view all the answers

What is the primary purpose of a jet pipe?

To direct exhaust gases safely from the exhaust cone to the exhaust nozzle Signup and view all the answers

What is the effect of using a jet pipe on an engine's operating efficiency?

It decreases the exhaust gas velocity and thrust due to heat and duct friction losses Signup and view all the answers

What happens if the exhaust nozzle is too small?

It restricts gas flow and causes a significant rise in jet pipe temperature and turbine temperatures Signup and view all the answers

What is the purpose of the exhaust nozzle?

To provide a final boost in velocity to the exhaust gases Signup and view all the answers

Why are hot stream reversers not used in high-bypass turbofans?

Because they would add weight and provide little additional thrust Signup and view all the answers

What is the function of the cascade vanes in a cold stream thrust reverser system?

To direct the airstream in a forward direction Signup and view all the answers

What must be true before the thrust reversal lever can be unlocked?

The main engine power lever must be in the idle position and the undercarriage squat switch must be closed Signup and view all the answers

What happens when the reverser control lever is fully deployed and locked in position?

The solenoid in the throttle quadrant is released Signup and view all the answers

What is the purpose of the blocker doors in a cold stream thrust reverser system?

To mechanically block the normal airstream exit Signup and view all the answers

What is the effect of moving the thrust reverser sleeve rearwards in a cold stream thrust reverser system?

The blocker doors close and the cascade vanes are exposed Signup and view all the answers

Why is maximum reverse thrust capability always less than forward thrust capability?

Because of the engine's design limitations Signup and view all the answers

What can happen when operating in reverse at low ground speeds?

Re-ingestion of hot gases and compressor stalls Signup and view all the answers

What are the two main categories of thrust reversers?

Mechanical and aerodynamic blockage Signup and view all the answers

What is the mechanical blockage system also known as?

Clamshell thrust reverser Signup and view all the answers

What happens when reverse thrust is selected?

The doors rotate to uncover the ducts and close the normal gas stream exit Signup and view all the answers

What can be ingested into the engine when operating in reverse at low ground speeds?

Fine sand and other runway debris Signup and view all the answers

Study Notes

Thrust Reversers

Cascade vanes direct the gas stream forward to oppose the aircraft motion
Post-exit system is commonly known as a bucket type, hydraulically actuated and uses bucket-type doors to reverse the hot gas stream
Bucket system is used where reversal of the hot jet nozzle gas interferes with the aerodynamics of the fan section or causes hot gas re-ingestion into the engine inlet and prevents hot gases from coming into contact with the fuselage

Cold Stream Mechanical Blockage Type

Places a movable obstruction in the pre-exit fan airstream
Blocker doors open to redirect the fan airflow forwards, mechanically blocking the normal gas stream exit
Typically hydraulically operated

Aerodynamic Blockage

Modern aerodynamic thrust reverser system consists of a translating cowl, blocker doors, and cascade vanes that redirect the fan airflow to slow the aircraft
Some aircraft may use a combination of aerodynamic blockage and mechanical blockage type reversers

Jet Pipe

An extension of the exhaust section that directs exhaust gases safely from the exhaust cone to the exhaust or jet nozzle
Use of a jet pipe penalizes an engine's operating efficiency due to heat and duct friction losses

Exhaust Section Nozzles

Exhaust nozzle provides the exhaust gases with a final boost in velocity
Size of the nozzle must be carefully matched to the mass airflow of the engine

Divergent Nozzles

Used in helicopter tailpipes to nullify thrust produced, enhancing hover capabilities
Decreases the velocity of the exhaust gas and thereby reduces the thrust produced

Convergent/Divergent Nozzles

Accelerates the turbine exhaust gases to sonic (Mach 1) speed at the narrowest part of the duct
Accelerates the exhaust gases further in the nozzle's divergent portion, exiting the nozzle well above the speed of sound

Variable Geometry Nozzles

Necessary on engines that utilize an afterburner
Area of the exhaust nozzle must be increased when an afterburner is being used

Thrust Reverser Operation

Thrust reversal lever is locked until the main engine power lever is in the idle position and the undercarriage squat switch is closed
Initial movement of the reverser control lever locks the main throttle lever in the idle position and allows the reversers to unlock and deploy

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Description

This quiz covers the different types of thrust reversal systems used in aircraft engines, including cascade vanes and bucket type systems.

Aircraft Engine Thrust Reversal Systems