Aircraft Engines

Question 1

What is the 4 stroke engine 5 event cycle?

Answer 1

Induction, Compression, Power, Exhaust
(Ignition)
SUCK, SQUEEZE, BANG, BLOW !

Question 2

What is a carburettor?

Answer 2

The CARBURETOR is a device which provides a
suitable mixture of fuel and air to the cylinder
for ignition.
Air flowing through the carburetor draws fuel
from a reservoir through a ‘VENTURI’ tube.
1: The air accelerates through the Venturi
2: There is a drop in air pressure; (Benoulli’s principle)
3: This causes fuel to be drawn through the main jet
where it mixes with air in the Venturi.
The fuel/air mixture is then fed to each cylinder in turn.

Question 3

What are the problems with the Venturi?

Answer 3

• Prone to Carb Icing
  - Pressure drop = temp drop
  fuel burn - latent heat from air reduces temp further = Double Cooling.
  So more water vapour = greater icing

Question 4

How to avoid carb icing?

Answer 4

Fly above/below where moisture present;
Carb heating;
Fuel injection carburettors

Question 5

What is Feathering?

Answer 5

Adjustment of Variable Pitch Propeller by rotating it parallel to airflow
(reduce drag) if Engine fails

Question 6

What are the advantages of Piston Engined propeller a/c? A:

Answer 6

• Simpler design = reduced manufacture & maintenance costs;
• More efficient at low speed and low altitude
• Faster initial acceleration than jet engines
• Immediate reaction to pilot input
• Propwash over wings generate lift at low speeds = reduced t/o run & aids controllability
• Air cooled

Question 7

DISADVANTADGES of piston engine and propellers

Answer 7

Power output limited
Propeller performance limited
- Propellor blade Tips can become supersonic and this decreases their aerodynamic efficiency and noise increases.

Question 8

What is Blade pitch?

Answer 8

Blade pitch is defined as the angle made by the chord of the blade and its plane of rotation.
When the angle is great, the propeller is said to have a COARSE pitch.

Question 9

What is coarse pitch? And when is it used?

Answer 9

For speed at cruising altitude, a COARSE pitch is best.

Question 10

What is Fine pitch? And when is it used?

Answer 10

Used for Take off and climb

Question 11

What is standard pitch?

Answer 11

Prioritising efficiency over a range of power settings.

Usually fixed props

Question 12

What is variable pitch propellor?

Answer 12

Enables the pilot to change the pitch of the propeller to suit differing requirements

(Constant speed propellor)

Question 13

What can you do with variable pitch propellor?

Answer 13

Can be rotated to be parallel to airflow to reduce drag if the engine fails, or is deliberately shut down. This is known as FEATHERING

Reverse pitch angle
This reverses the direction of thrust and it is used to reduce the landing run and to
save wear on tyres and brakes.

Question 14

What are the Main differences in thrust between a jet and a propellor?

Answer 14

A jet engine accelerates a small volume of air by a large amount

A propeller accelerates a large volume of air by a small amount

Question 15

What is Newton’s second law?

Answer 15

Force (F) = Mass (M) x Acceleration (A)

Question 16

What are the principles of jet propulsion?

Answer 16

Intake - Compression - Combustion - Turbine - Exhaust

Suck, Squeeze, Bang, Blow

Air is sucked in and compressed between 3 – 40 times its original pressure.

Question 17

The basic parts of the jet engine are:

Answer 17

AIR INTAKE
COMPRESSOR STAGE/S
COMBUSTION CHAMBER/S
TURBINE STAGE/S – drives the compressor
EXHAUST

Question 18

Types of jet engines

Answer 18

Turbojet
Low Bypass Turbofan
High Bypass Turbofan
Turboprop
Ramjet
Scramjet
Turboshaft (Helicopters)

Question 19

Two types of jet engine compressor?

Answer 19

Centrifugal Flow Compressor - 90’ to the airflow
Axial flow compressor – same direction as airflow
- needs more compression stages

Question 20

What is a Turbo bypass engine?

Answer 20

Bypass engines use a fan to draw air both through, and around a core.

Developed in order to increase fuel efficiency
and to reduce noise,

Question 21

Advantages of turbofan engines?

Answer 21

• Efficient –power derived from 2 sources, core & fan;
• Significantly more power than piston engines (80 000 lbs thrust);
• Higher speed achievable;
• Afterburner can be used for additional thrust.

Question 22

DISADVANTADGES of turbofan engines?

Answer 22

• Complex design & manufacture results in high cost.
• Response to pilot input slow – ‘spool up’ time required to generate power.

Question 23

What is a turbo prop engine?

Answer 23

A turboprop engine is a jet engine, which drives a propeller.

The turbine at the back is turned by the hot gases and this turns a shaft that drives the propeller via a gearbox

Question 24

Benefit of a turbo prop?

Answer 24

Compared with a turbojet engine, the
turboprop has better propulsion
efficiency at flight speeds up to around
500 MPH.

Question 25

ADVANTADGES of turbo props

Answer 25

• Propeller has a higher efficiency than jet exhaust
  In dense air, i.e. lower levels, a
• Can operate from shorter runways than jets;
• Propeller can be ‘feathered’ to minimize drag in
  the event of engine failure,
• Mechanical reliability improves due to relatively few
  moving parts;
• Light weight.

Question 26

DISADVANTADGES of Turbo prop

Answer 26

• Propellers lose efficiency at high altitudes;
• Vibration and noise levels can cause passenger
  discomfort;
• Lower cruising levels can be susceptible to icing
  and turbulence;
• Lower cruising speeds can cause sequencing
  problems for ATC when mixed with jet
  operations.