Exhaust

Question 1

What is the purpose of an exhaust?

Answer 1

Conduct gas flow away from the turbines and clear of the aircraft surface.

Question 2

What is the purpose of an exhaust in Turbojets, Turboprops and Turboshaft?

Answer 2

Turbojet: Produce thrust
Turboprop: Produce some thrust
Turboshaft: Acts as a diffuser

Question 3

What are the major components in an Exhaust?

Answer 3

Exhaust Unit:
- Tail cone
- Exhaust cone
- Exhaust fairing/strut

Exhaust Duct
Exhaust Nozzle

Question 4

What are exhaust components typically made from?

Answer 4

Nickel or titanium due to high temperatures

Question 5

What are the two ways that the heat from the exhaust is insulated from the aircraft structure

Answer 5

• Passing ventilating air
• Insulation blanket made up of a core of fibrous material wrapped in a dimpled stainless steel outer skin.

Question 6

How does the exhaust work on Turboshafts helicopters

Answer 6

The nozzle forms a divergent duct to diffuse air
- Does not increase thrust

Question 7

What are the two types of Turbofan exhausts?

Answer 7

Ducted and Unducted

Question 8

How does a ducted turbofan exhaust work?

Answer 8

Takes fan airflow and directs it to a common exhaust where the core flow and fan flow mix

Question 9

How does an unducted turbofan exhaust work?

Answer 9

Has two separate nozzles (one for core, one for fan).
- Both flow to ambient air through separate nozzles.
- Handles high amounts of airflow
- Converging nozzle exhaust produces 15-20% thrust

Question 10

In a turboprop, what is another word for exhaust duct?

Answer 10

Tailpipe

Question 11

What does a turboprop tailcone and struts do to the airflow?

Answer 11

Imparts an axial flow onto the air, straightening it.

Question 12

What percentage of thrust is produced from a turboprop exhaust?

Answer 12

10-15%

Question 13

On a turboprop, is the fwd section of the tailpipe connected to the exhaust?

Answer 13

No
- Fwd section is funnel shaped and surrounds the exhaust but DOES NOT CONTACT (Annular gap).

Question 14

Where is the rear section of the exhaust connected to on Turboprops?

Answer 14

Connected to the airframe by two support arms, one on each side.
- Support arms are connected to the wing in a way to compensate for heat expansion.

Question 15

What is the insulating blanked on a turboprop tailpipe made of?

Answer 15

Stainless steel on the outside and fiberglass on the inside
- Used when the exhaust is located some distance from an aircraft structure.

Question 16

What is Turbine Discharge Pressure?

Answer 16

Total pressure discharge in an LP turbine in a dual spool axial engine

Question 17

Where is the Turbine Discharge Pressure measured from in the exhaust?

Answer 17

Immediately aft of the turbine and fwd of the exhaust flange
- Pressure probes inserted.

Question 18

In large engines where its not practical to measure temperature at the turbine inlet, where is temperature measured?

Answer 18

EGT is measured on the turbine outlet

Question 19

What is the purpose of an Exhaust Cone (tailcone)

Answer 19

Form a divergent duct to reduce the velocity to Mach 0.5 and increase the pressure.

Question 20

What is the purpose of an Exhaust Duct?

Answer 20

The convergent duct is used to accelerate the gas to Mach 1 (Chocked Nozzle)
- Usually fixed geometry on subsonic aircraft

Question 21

When is a Convergent-Divergent (C-D) Nozzle used?

Answer 21

To help produce thrust when the exhaust velocity is higher than Mach 1.
- Best suited for supersonic aircraft due to higher pressure ratios in exhaust.

Question 22

What is the use of an afterburner limited by?

Answer 22

Fuel consumption

Question 23

What are some additional components that are needed to make an afterburner?

Answer 23

• Flame stabilizer
• Flame holder
• Fuel manifold
• Igniters
• VARIABLE AREA EXHAUST NOZZLE

Question 24

When energy and mass are added to fuel an afterburner, what must the exhaust nozzle do?

Answer 24

Widen to allow more fuel

Question 25

In a low bypass turbofan, what is the purpose of the fan air in an afterburner?

Answer 25

Provides more oxygen to the exhaust for burning.

Question 26

How is heat managed in an afterburner exhaust?

Answer 26

Using a special liner around the nozzle that is cooled with air
- Operates like a Single Can Combustion Chamber

Question 27

What is the purpose of Thrust Vectoring?

Answer 27

Directs thrust other than parallel to the longitudinal axis of the plane
- Used to change direction of the aircraft or VTOL
- Up to 20 degrees maneuverability

Question 28

How can Thrust Reversers be actuated?

Answer 28

Pneumatically or Hydraulically

Question 29

When are thrust reversers used?

Answer 29

On larger aircraft when braking cannot stop the aircraft alone

Question 30

What is the typical thrust production of a thrust reverser?

Answer 30

40-50% rearwards thrust

Question 31

What is the Braking force percentage of thrust reversers in normal runway conditions and icy/wet runway conditions?

Answer 31

• 20% in normal conditions
• 50% in wet or icy runways

Question 32

What are the two main types of thrust reversers?

Answer 32

• Mechanical blockage (clamshell or inverted cone) - Ducted turbofan
• Aerodynamic blockage (Cascades and blocker doors) - Modern

Question 33

What are the requirements when designing a thrust reverser?

Answer 33

• Light
• Strong
• Handle high temperatures
• Fail safe