Unit 1: Introduction

Question 1

how can propulsion systems be classfied?

Answer 1

The way they produce thrust:
- By a jet of energy / plasma
- Powered by a propeller fan or rotor.

Question 2

What are the other possible propulsion energy sources, apart from chemical?

Answer 2

Solar, Nuclear and Electromagnetic

Question 3

What are the type of aerospace engines?

Answer 3

Piston engine, Gas turbine, Ramjet (all airbreathers).
Rocket (Non-airbreather).

Question 4

What is an airbreather type of engine?

Answer 4

The process of using the air around as an oxidiser for the combustion process and as a working fluid producing power/thrust.

Question 5

What is the power to weight ratio?

Answer 5

ratio of power output to total propulsion system weight.

Question 6

Why did gas turbine take over piston engine?

Answer 6

As flight speed increased towards supersonic.
- Piston engine limitation due to it complexity, lack of power and excessive weight, so gas turbine were favoured.

Question 7

What are the main components of a gas turbine engine and used in what type of engines?

Answer 7

The main components are the compressor, combustor and turbine.
Then some sort of exhaust.
Common is turbojet, turbofan, turboprop and turboshaft.

Question 8

What components are included in a turbojet, apart form the main gas turbine components?

Answer 8

Apart from the main 4 component, a turbojet also includes an inlet and nozzle.

Question 9

What components are included in a turbofan, apart form the main gas turbine components?

Answer 9

Apart from the main 4 component, a turbojet also includes an inlet, fan and nozzle.

Question 10

How does a turbofan work?

Answer 10

It accelerates a larger mass of air flow to a lower velocity, for a higher propulsive efficiency. It has a larger frontal area than turbojet and hence more drag and weight.

Question 11

How does a turboprop and turboshaft work?

Answer 11

Using the main components of a gas turbine.
The expansion of gas through the turbine supply energy required to turn propellers.

Turboshaft - used to supply power to VTOL, helicopters.

Question 12

What are the advantages and disadvantage of turboprops?

Answer 12

Good performance for lower speed and short take-off.

Loses aerodynamic efficiency when reaching higher speeds, due to compressibility effect on propellers.

Turbofan have better aerodynamic performance at high subsonic speed.

Question 13

How does a ramjet work?

Answer 13

Ramjet components: inlet, combustion zone and nozzle.
(no compressor or turbine).

Air enters inlet where it is compressed then enters the combustion zone where it is mixed with fuel and burned. Hot gases are expelled to produce thust.

The higher the velocity on air entering, the higher pressure rise -> therefore operates better in supersonic velocities.

Question 14

How does a gas turbine work?

Answer 14

• In the compressor section, pressure and temperature increase as a result of work
  being done on the air. The temperature of the gas is further increased by burning in
  the combustor.
• In the turbine section, energy in removed from the gas stream and
  converted to shaft power to turn the compressor. The energy is removed by an
  expansion process which results in a decrease of temperature and pressure.
• In the
  nozzle, the gas stream is further expanded to produce a high exit kinetic energy.
• All sections of the engine must operate in such a way as to efficiently produce
  maximum thrust for minimum weight