15.1 - Fundamentals

Question 1

Explain the difference between potential and kinetic energy.

Answer 1

Potential energy is energy that is stored and has the capacity to be converted into another form of energy and do work in the process. An accumulator is an example of potential energy.

Kinetic energy is energy that a body of mass possesses due to it’s motion. It is the work needed to accelerate a body of a given mass from rest to its current velocity.

Both are measured in Joules (J)

Question 2

State Newton’s Third Law.

Answer 2

To every action, there is an equal and oppostie reaction

Question 3

What is the “Brayton Cycle” also known as and name its four distinct phases.

Answer 3

The ‘’Brayton Cycle’’ is also known as the Constant Pressure Cycle

It’s four distinct phases are Intake, Compression, Combustion and Expansion

Question 4

Define Force and Work.

Answer 4

A force is the capacity to do work or can be defined as a vector quantity that tends to produce acceleration of a body in the direction of it’s application. Measured in Newtons (N)

Work is defined as a force acting on a body that causes it to move through a distance. Measured in Joules (J)

Question 5

What are the basic components of a gas turbine engine?

Answer 5

Air intake, compressor, combustor, turbine and exhaust pipe.

Question 6

Name the four types of gas turbine engines.

Answer 6

1. Turbojet Engines (no bypass)
2. Turbofan Engines (bypass)
3. Turboshaft Engines (turboprop with no propeller)
4. Turboprop (turboshaft with propeller)

Question 7

Describe briefly how a gas turbine engine works.

Answer 7

A gas turbine engine works according to the Brayton Cycle. Air (working medium) is taken in and compressed increasing it’s pressure, fuel is then added and ignited in the combustion stage which adds heat energy to the air, it then enters a turbine where it expands and does some work such as drive the compressor. The remaining energy is ejected out the exhaust and gives Thrust

Question 8

1. What is a “Free Turbine”?

Answer 8

A ‘’Free Turbine’’ contains no mechanical link from the propeller to the gas turbine engine allowing the propeller assembly to adopt its own optimum design speed while the engine adopts its own best design speed. The reduction gearbox is driven by a Free turbine stage at the rear of the engine core

Allows a propeller to be going at 2,000 RPM while core engine will go at 38,000 RPM

Question 9

Name three types of Turbofan engines.

Answer 9

1. Low by-pass engine (1:1),
2. Medium by-pass engine (2 or 3 :1)
3. High by-pass engine (>4:1)

Question 10

Name two applications of a Turboshaft engine.

Answer 10

1. Helicopters
2. APU’s

Question 11

What is potential energy (Give an example)?

Answer 11

Energy stored within a physical system. It has the potential to be converted into other forms of energy such as kinetic energy.

Example is an bike on a hill

Question 12

What are Newton’s 3 laws of motion?

Answer 12

1. An object at rest or in motion will remain at rest or in motion until acted upon by an external force
2. F = ma (relationship between Force, mass and accel)
3. For every action, there is an equal and opposite reaction

Question 13

What are the 4 phases of a working cycle of an engine?

Answer 13

1. Intake
2. Compression
3. Combustion
4. Expansion

Question 14

Constant pressure cycle and constant volume cycle describe what type of engines?

Answer 14

Constant pressure cycle = Gas turbine Engine

Constant volume cycle = Piston Engine

Question 15

Define force and state the formula for force?

Answer 15

The capacity to do work or A vector quantity that tends to produce acceleration of a body in the direction of it’s application

F = (mass)(acceleration)

Question 16

Define work and state the formula for work?

Answer 16

Mechanical work is present when a force acting on a body causes it to move through a distance

Work = (Force)(Distance)

Question 17

Define power and state the formula for power?

Answer 17

Power is the rate at which work is performed or energy is transmitted.

Power = Work / time

Question 18

What is the formula for force?

Answer 18

Force = (mass)(acceleration) …. 2nd law

or

Force = (Pressure)(Area)

Question 19

Define velocity?

Answer 19

Velocity is defined as the rate of change of position

Question 20

Differentiate between a turbojet and a turbofan engine?

Answer 20

In a turbojet engine, thrust is solely delivered from the reaction to the flow of hot gases out of the exhaust (jet) pipe. No bypass

In a turbofan engine, only a small proportion of the total airflow passes through the ‘‘core’’ engine. Some of the air is bypassed

Question 21

What are the two main parts of a spool?

Answer 21

A compressor being driven by a turbine is called a spool

Question 22

What are the advantages of a high bypass engine?

Answer 22

High by pass engine (>4:1)

1. Increased propulsive efficiency
2. Lower noise level
3. lower specific fuel consumption

They can combine the high thermal efficiency of a high pressure, high temperature core engine with the high, propeller like propulsive efficiency of a large fan

Question 23

What is specific fuel consumption?

Answer 23

The number of pounds of fuel burned per hour to produce one horsepower (one unit of thrust)