15.01 Fundamentals

Question 1

Figure of acceleration due to gravity

Answer 1

g = 9.8 m/s^2

Question 2

Equation for work

Answer 2

Work (nm) = Force x Distance

SI unit is Joules.

Question 3

Equation for Power

Answer 3

Power (Watt) = Work / Time

Question 4

What can mechanical energy be divided into?

Answer 4

Potential energy and kinetic energy.

Question 5

What is potential energy by definition?

Answer 5

The energy a body has by virtue of its position.

PE = mgh

Question 6

What is kinetic energy by definition?

Answer 6

The energy a body has by virtue of its motion.

KE = 1/2mV^2

Question 7

Newton’s First law?

Answer 7

Law of inertia = A body at rest remains at rest and a body in motion continues to move unless acted upon.

Question 8

Newton’s second Law?

Answer 8

Law of motion.

Gas turbine engine.

Question 9

Newton’s third law ?

Answer 9

Law of action/reaction = every action has an equal and opposite reaction.

Turbojet engine.

Question 10

What is air referred to as?

Answer 10

A working fluid to provide thrust.

Question 11

What is the Brayton cycle?

Answer 11

Induction,
Compression,
Combustion,
Exhaust.

Question 12

In a piston engine, what word describes how the brayton cycle process occurs?

Answer 12

Intermittently

Question 13

In a has turbine engine, what word describes how the brayton cycle occurs?

Answer 13

Simultaneously.

Question 14

Advantages and disadvantages of a piston engine?

Answer 14

• More fuel efficient.
• Ideal for light aircraft.
• Performance decreases at higher altitudes.
• Weight to power ratio decreases with increased size.

Question 15

Advantages of Gas Turbine engines?

Answer 15

• Operate at high altitudes.
• Easily provide thrust, torque, bleed air.
• Allow high speed flight.

Question 16

What are the types of Gas turbine engines? (4)

Answer 16

• Turbofan. (high speed with good efficiency)
• Turbojet. (Very high speed but very loud and inefficient)
• Turboprop. (Good compromise for fuel efficiency and speed)
• APU. (Small engine to provide pneumatics and electric power)

Question 17

What is the jet propulsion force?

Answer 17

The force that operates in the OPPOSITE direction to the flow of mass through the nozzle.

Question 18

What is the name for an engine that uses the jet propulsion principle?

Answer 18

A reaction engine.

Question 19

In what ways (methods) can air pressure be increased? (2)

Answer 19

• Mechanically with a compressor.

- Thermally by increasing the the volume of air, when a fuel/air mixture is burned.

Question 20

A turbojet engine is designed for what single purpose?

Answer 20

Producing high velocity gases.

Question 21

What is always required in turboprop engine?

Answer 21

A reduction gearbox.

Question 22

How do turboprops produce their thrust?

Answer 22

Small acceleration of large air quantities, using a propeller.
Gas energy is converted into torque.

Question 23

What does a turbofan engine combine?

Answer 23

The good efficiency and high thrust capability of turboprop engines, with the high speed and high altitude capability of the turbofan.

Question 24

What are turbofan engines usually formed of? (Spool)

Answer 24

Twin or triple spools.

Question 25

What do turbofan engines convert?

Answer 25

Hot gas energy from the core engine into thrust. A large part of gas is converted into torque to drive the fan and compressors.

Question 26

Total thrust of a turbofan engine?

Answer 26

Core engine thrust + Fan generated thrust.

Question 27

What percentage of total turbofan thrust comes from the fan airflow?

Answer 27

More than 80%

Question 28

What is the bypass ratio?

Answer 28

The ratio of air that passes through the fan duct compared with the air that passes though to core engine.

Question 29

What is the bypass ratio on modern turbofan engines?

Answer 29

Between 4:1 and 9:1

Question 30

What type of exhaust ducts (nozzles) are found on turbofan engines? (2)

Answer 30

- Short ducted (for most high bypass engines) | - Long ducted (combined or separate exhausts)

Question 31

What are the advantages of an open rotor engine (propfan) ?

Answer 31

- Good speed. - High altitude. - Use up to 20% less fuel. - Bypass ratio of up to 90:1.

Question 32

Advantages and disadvantages of a non-modular engine? (are old engines and some APUs)

Answer 32

- Saved weight. - Fulfilled main purpose. - complicated. - very hard for maintenance. - parts matches individually.

Question 33

Advantages of the modern modular engines ? (where engine is split up into major modules)

Answer 33

- Pre balanced. - Flexibility with changes. - Easily stored and transported. - modules replaced/removed easily. - no rebalancing required. - modules replaced while engine is on aircraft. - less need for spare parts.

Question 34

What are the typical materials used on modern engines?

Answer 34

- Aluminium alloys. - Ceramic material. - Composite material. - Cobalt base alloys. - Nickel base alloys. - CRES steel alloys. - Titanium base alloys.

Question 35

Where is aluminium alloy mainly used?

Answer 35

- Gearbox housings. | - Fan stator casings.

Question 36

What are ceramic coatings used?

Answer 36

In the combustor and high pressure turbine.

Question 37

Where are steel alloys usually found?

Answer 37

- N1 drive shaft. - Engine bearings. - Main structural frames (some engines)

Question 38

Where are cobalt base alloys used?

Answer 38

In the stator of the first stage high pressure turbine.

Question 39

Where are Titanium base alloys usually found?

Answer 39

- The fan. - Low pressure compressor. - Front stages of the the high pressure compressor.

Question 40

Use of Nickel base alloys?

Answer 40

- High pressure compressor. - Combustion section. - High and Low pressure turbines.