Engines Flashcards

1
Q

What is thermodynamics?

A

Thermodynamics is the study of heat / pressure and the behaviour of gasses with different heat / pressure variations.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is Bernoulli’s theorem?

A

Bernoulli’s theorem is that in the steady flow of an ideal fluid, the sum of the pressure and kinetic energy remains constant.

Pressure + KE = Constant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain a venturi?

A

A venturi (convergent / divergent duct) shows the practical application of Bernoulli’s theorem.

Converging:

Static Pressure - Decreasing

Dynamic Pressure - Increasing

Temperature - Decreasing

Velocity - Increasing

Diverging:

Static Pressure - Increasing

Dynamic Pressure - Decreasing

Temperature - Increasing

Velocity - Decreasing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the combustion cycle of an aeropiston engine?

A

WORKS ON CONSTANT VOLUME

Induction

Compression

Expansion

Exhaust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the compression ratio in a piston engine?

A

Compression Ratio = Total volume / Clearence volume

The ratio of the total cylinder volume with the piston at BDC and the volume remaining at the end of the compression stroke with the piston at TDC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What produces the ignition in a piston engine?

A

Magnetos are used in a piston engine to supply the high tenstion voltage neccessary to create an electric spark at the spark plug.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does blue / black / white exhaust smoke indicate from a piston engine?

A

Blue - engine is burning oil (indicative of wear on the piston ring).

Black - Engine is running too rich and carbon build up is caused in the cylinder where not all of the fuel can be burnt.

White - Often indicates a high water content in the combustion chamber which is exhausted as white steam.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is engine torque?

A

Torque is a force that causes rotation (eg of the crankshaft) and is measured in pounds per inch.

Torque = Force x Distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is a “normally aspirated engine”?

A

A normally asperated engine is an engine which does not have a turbocharger or a supercharger and uses the normal atmospheric air density. Therefore the power output it is restricted by the cylinder capacity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the disadvantages to a piston engine? (3)

A

Lack of power output, especially with increased altitude

Lower airspeed due to propellor RPM limitiations

Mechanical inneficiency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a supercharged piston engine?

A

A supercharger simply increases the air delivered to the engine cylinder above its normal aspirated capacity by compressing the intake air. This requires more fuel to be delivered at the carbouretta and produces a greater power output, allowing greater efficiency of the engine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is the piston engine output increased to compensate for low atmospheric pressure? (2)

A

Superchargers artificailly increase the manifold pressure to compensate for low atmospheric pressure either:

to increase the engine power output for take off / climb (ground boost).

OR

to increase the engines performance at higher altitudes by maintaining MSL pressure (altitude boost).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What regulates the supercharger to deliver a constant MAP?

A

Turbo - Absolute Pressure Controller (APC) uses an aneroid capsule that is sensitive to the compressor outlet pressure which changes the position of the wastegate with use of oil within the engine.

Supercharger - An Auto Boost Controller (ABC) is designed to maintain a given pressure at altitude. At low altitudes, in order to avoide detonation and engine stress due to excessively high combustion pressure, the throttle valve is only partially open. As the aircraft climbs, this valve is increasingly opened.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is engine power monitored? (2)

A

MAP / Boost

On an ISA day, the MAP will read 29.92 inHg or Zero boost.

The gauge reading before ngine start is known as static boost.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What advantages does an aircraft gain from a propellor? (4)

A

Slipstream creates more lift over the wing

Increased fin / rudder effectiveness

Slipstream suppresses the stall speed of the aircraft

Quicker “low speed” recovery with propellow and piston engine aircraft

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the main disadvantage of a propellor?

A

It is restricted by its RPM limitations which are due to compressability when the blade becomes sonic.

Therefore it is restricted by:

its lower TAS and shorter range.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What produces the thrust on a propellor driven aircraft? (2)

A

This is an example of Newtons Third Law: “The application of a force will cause an equal and opposite reaction”.

The power output of the engine which drives the prop shaft, combined with the blade angle of attack produces the thrust of a propellow driven aircraft.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is a propellor blade twisted?

A

The propellor blade is twisted in order to maintain a constant agle of attack.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you define propellor efficiency?

A

Prop Efficiency = Prop thrust (air mass x velocity) / Engine BHP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the disadvantages of a fix pitch propellor?

A

It can only be efficient for one predetermined RPM, at one stage of the flight. This is because as TAS increases the AoA on the propellor blade becomes smaller and causes a reduced angle of attack. Therefore the propellor blade needs to be coarsened with an increase of TAS.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is a variable pitch propellor and why is it used?

A

A variable pitch propellor uses and oil / spring medium in order to change the ptich angle of the propello from fine to course pitch (known as the RPM). A constant speed unit govner (which uses flyweights and centripetal force) adjusts the angle of the blade in order to keep the RPM at a constant speed. This increases the speed range of the aircraft and maximises the efficiency of the aircraft.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Is there a critical engine on a propellor aircraft?

A

Unless engines are counter rotating (Seneca V). The critical engine is the one that determines the critical control speeds of the aircraft and has the largest yawing moment in the event of an engine failure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why is the number 1 engine the critcal engine on a multiengine propellor aircraft? (2)

A

Slipstream effect:

Because engine number 1 creates a slip stream force on the fin; this helps to counteract the yawing moment from number 2 engine should it fail. However, should engine number 1 fail the the slipstream from engine number 2 will produce a sideways force that will aggrevate the yawing moment, which will result in a more critcal situation. This would mean that a higher speed would be required in order to increase the effectiveness of the rudder, determining engine number 1 as the dritical engine.

Asymmetric blade effect:

As the downgoing blade produces more thrust that the ugoing blade, this increases or decreases the thrust moment arm. The engine that creases the largest moment arm will be the critical engine as it creates the largest amount of yaw.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How do propellers generate noise?

A

Noise from propellors is generated from the sheer that is different between the propellers faster displaced air and the air that is surrounding it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How is propeller noise controlled or reduced? (2)

A

Using more blades which reduces that sheer between the air displaced by the propeller and the ambient air

Reduced thrust take-offs

26
Q

What is the theory behind a jet turbine?

A

Newton’s third law:

“Each action will create and opposite and equal reaction”

Such as letting go of a balloon.

A jet turbing produces thrust in a similar way to a propeller / piston engine. It works by propelling the aircraft forward as a result of moving a large quantity of air rearwards.

Thrust = Air mass x Velocity

27
Q

What is specific fuel consumption (SFC)?

A

SFC = Quantity fuel / Thrust

28
Q

What is the combustion cycle of a jet engine?

A

WORKS ON CONSTANT PRESSURE

Induction

Compression

Expansion

Exhaustion

29
Q

Why was the jet turbine engine invented?

A

Frank Whittle, a man in the RAF who was originally from coventry was obsessed with finding a new method of propulsion in order to gain higher speeds and altitude. Initially, finded by himself was told his idea would never work. The war then led to money being invested into this and a new metal was created that could withstand the higher temperaturs of the jet engine.

30
Q

Describe how a triple spool high bypass turbine engine works?

A

A triple spool turbine such as Rolls Royce RB211 consists of 3 compressors:

Low stage: N1 (or fan)

Intermediate stage: N2

High stage: N3

As fuel is added to the combustion chamber the turbine for the N1 stage turns the fan. This type of engine has a high bipass ratio (5:1) and the fan actually produces around 75% of the engines total thrust. The air travelling through the N1 and N2 compressors become very compressed of which 1/3 is used for combustion and 2/3 is used for interncal cooling.

31
Q

Advantages of a turbo fan engine?

A

The N1 fan can be build to its optimum efficiency, taking into account the size of the chord as it is not connected to any other compressor.

In fact, all of the compressors can work more efficiently because because they have their own separate turbine powering them.

Easier to start as only one spool needs to be turned by the starter.

Smaller engine size

Better propulsive efficiency

Better SFC (SFC = Fuel / Thrust)

Reduction in engine noise

Contamination is centrapetally bypassed around the core of the engine reducing it’s affect

32
Q

What is a fuel injection system and what is its advantages / disadvantages?

A

A fuel injection system delivers metered fuel directly to the induction manifold and then into the combustion chamber without the use of a carburetor.

Advantages

Freedom from carburetor icing

Good fuel distribution

Doesn’t mind steep maneouvres

Disadvantages

Vapour lock

Very fine fuel lines are more suseptable to contamination

33
Q

What are thrust reversers and how do they work? (3)

A

Reverse thrust on jet engines reverse the airflow forward and create a braking action. They are all typically operated by hydraulic or pneumatic actuators and redirect the gas flow.

There are 3 different types of reverse thrusters:

Clam shell doors: The use of cascade vanes which are revealed when operated.

Bucket doors: The rear of the exhaust pipe is shaped like 2 halves of a bucket and they swing open and reverse the thrust.

Blockers doors (high bypass engines only): These block the cold bypass air and redirect them via cascade vanes.

34
Q

What is maximum continuous thrust?

A

Simply a thrust setting that is designed for maximum continuous use, espressed as N1 or EPR.

35
Q

What is the compression ratio of an engine?

A

This is the ratio of the air pressure between the inlet and the outlet parts of either an individual compressor or the complet section of the engine.

For example:

First compressor stage:

Inlet: 15 psi

Outlet: 60 psi = 4:1

Second compressor stage:

Inlet: 60 psi

Outlet: 180 psi = 3:1

Total compression ratio:

12:1

36
Q

Why is a fan engine flat rated?

A

In order to give increased engine life and reduced overhaul costs as well as fuel savings and, under certain circumstances, it may be possible to increase the maximum takeoff weight for a specific runway by using a reduced thrust profile.

37
Q

When and where is a jet bypass engine at its most efficient, and why? (3)

A

At high altitudes and high RPM speeds.

As altitude increases the air density is reduced and consequently the thrust requirements are lower because the thrust must only be equal to the drag.

Best engine SFC (SFC= fuel quanity / thrust) which indicates the best endurance speed (Vmd).

NB: This gives a higher TAS for an IAS providing an increased range.

38
Q

Explain the jet engine’s thrust to thrust lever position?

A

The thrust lever produces more engine thrust from its movement towards the top of its range than its bottom.

39
Q

What are the main engine instruments? (7)

A

Engine Pressure Ratio (EPR)

N1 - Fan or low stage comp RPM

Exhaust Gas Temperature (EGT)

N2 - Intermediate stage comp RPM

Fuel Flow

Oil temp gauge

Vibration meter

40
Q

What is Engine Pressure Ratio (EPR)?

A

On a fan engine, a ratio of turbine discharge / fan outlet pressure to compressor inlet pressure.

41
Q

What is EGT and why is it important?

A

One of the main weaknesses in a jet engine is the temperature of the turbines. Should the maximum temperatures be exceeded then it could damage the engine, especially the turbines as well as shorted the life of the engine.

42
Q

Wet start: Causes, indications and actions?

A

A wet start is when the starter moter engages but does not ignite the fuel in the combustion chamber. This is usually caused by an ignition problem.

Indications: EGT does not rise and RMP stabilises at the starter maximum.

Actions: Close the throttle supply as soon as the wet start is identified. Then motor over the engine for approximately 60 seconds in order to blow out the fuel.

43
Q

Hung start: Causes, indications and actions?

A

A hung start is when an engine starts but does not reach self sustaining RPM.

The cause is often a lack of airflow to support combustion caused by: High altitude / Hot conditions/ Inefficient compression / low starter RPM

Indication: High EGT / Low RPM below self sustaining speed

Action: Close start lever / Motor engine for around 60 seconds

44
Q

Hot start: Causes, indications and actions?

A

A hot started is when an engine reaches self sustaining speed but the combustion is unstable and the EGT rises rapidly.

Causes: Overfuelling (throttle open) / Air intake/Exhaust blocked / Tail wind (causing compressor to run backwards) / seized engine (ice)

Indications: High EGT / Unstable combustion

Action: Close fuel lever and wait for RPM to reduce. Motor over engine for around 60 seconds

45
Q

What is reduced thrust take off? What are the benefits? (2)

A

Reduced thrust take off uses the aircrafts actual take off weight, which is a reduced thrust value from the maximum take off thrust value, with an assumed temperature that achieves the aircraft’s one engine inoperative performance requirements.

The main benefits of this are to protect against the engine life / improve engine reliability

AND

To reduce noise generated by the aircraft

46
Q

Can a maximum weight aircraft use a reduced thrust take off technique?

A

Yes, as long as TOR in not limiting because you can trade lower thrust setting for longer TOR.

47
Q

What are the limitations of a reduced thrust take off?

A

Main restrictions

TORA

Net take off flight path (engine out obstacle clearence)

Max OAT limitation

If not restricted by the above:

Reduced assumed temp (flex) not set below a set amount (engine specific)

Cannot be less than max continuous thrust (at final takeoff path)

Cannot be below actual OAT

48
Q

When can you NOT use reduce take off thrust?

A

Contaminated runway / Icy or slippery

Reverse thrust inop

no antiskid

Increased V2 procedure used to improve obstacle limited take off weight

49
Q

What happens to engine pressure ratio (EPR) during the take off roll?

Prior to openning throttle levers?

Initially openning throttle leavers?

Steady increase?

Takeoff power?

A

Prior to openning the throttle leavers the Compressor inlet (P2) and Exhaust pressure (P7) will read almost the same and therefore EPR will be 1.0 / 1.05.

When throttle leavers are initially openned P2 will have a slightly higher pressure than P7 as when a greater mass of air is taken into the engine it takes time to reach P7. This will mean a reading of for example 0.89.

Then as the aircraft starts to accellerate down the runway, the RPM increases and the EPR reading increases. A steadyincrease will be around 1.25.

Take off power will be around 2.0.

50
Q

Why does EPR need to be set before 40 - 80 KIAS?

A

So that the pilot is not chasing the needles on take off roll.

To ensure that adequate aircraft acceleration so that the performance calculated V1 and Vr are achieve by the TORR.

51
Q

What is an engine windmilling start?

A

An engine windmilling start is a start that is completed without the use of a starter motor and done when there is enough airflow passing through the compressor and turning it over which produces enough charge to the combustion chamber where fuel and ignition is added and a stable start is formed.

52
Q

What are engine relight boundaries and what is their purpose? (2)

A

Engine relight boundaries are subdivisions of the flight envelope which ensures that there will be sufficient air turning over the compressor in order to restart the engine in flight.

Usually there will be 2 sections; windmilling and starter assist.

53
Q

What is jet turbine upset and how do you identify it? (3)

A

A jet turbine upset is when disturbed or turbulent airflow will cause the airflow over the fan blades to break up and cause a compressor stall. This is because its designed to operate in a clean uniform airflow pattern within attitude limitations.

It can be identified by:

  • Increase of TGT
  • Engine vibrations
  • RPM fluctuations
54
Q

What is a surge in a jet engine (1), what causes it (2), what indicates it (2) and what is the required action (1)?

A

A surge is a reversal of airflow through an engine where the high pressure air in the combustion chamber is expelled forward accompanied by a loud bang!

Causes:

All of the compressor stages have stalled

An excessive fuel flow, requiring a greater pressure in order to maintain equilibrium which is higher than the blades can handle

Indicators:

A total loss of thrust

A large increase in TGT

Neccessary action:

Close throttle smoothly and slowly

55
Q

Why are bleed valves fitted to gas turbine engines (5)?

A

Bleed valves are usualy fitted to a jet engine in order to provide:

Bleed air for air conditioning packs

Heating

Engine cooling (especially turbines and combustion chamber)

Cooling of engine driven systems (gearbox etc)

To regulated different pressures between different engine sections.

56
Q

Why do jet engines have auto igniters and how do they work?

A

This is a feature on some aircraft and is typically activated by the aircraft stall warning system which automatically selects auto ignition.

57
Q

What is fadec?

A

FADEC is Full Authority Digital Engine Control and is a system that automatically controls engine functions such as start procedures, engine monitoring, ignition systems and power levels required.

58
Q

What jet fuels are used commonly for civil jet aircraft? (3)

A

Jet A1 (AVTUR): -50’C Waxing point

Jet A: -40’C Waxing point (usually only available in USA)

Jet B (AVTAG): -60’C Waxing point but low flash point so not usually used in civilian aircraft (can replace jet 1).

59
Q

How does a jet engine generate noise?

A

The faster moving air from the jet exhaust creates a sheer between that and the surrounding ambient air.

60
Q

How does a jet engine control noise or reduce it? (3)

A

High bypass engines reduce the sheer effect with the bypass air

Reduced thrust take off

Maximum angle of climb after take off to get above any noise sensitive areas

61
Q

Is there a critical engine on a jet aircraft?

A

On a twin engine jet aircraftt with symetrically postioned engines that have opposing revolution then no.

Obviously wind can take an effect but this is an environmental effect and is not considered when calculating speeds for critical engine.

A governor engine can however be a “master” engine that sets the speed for the other but is not to be confused with a critcal engine.

62
Q

Describe a typical aircraft fire detection and protection system? (1 type, 2 sub sypes)

A

The main type of detectoin system is a firewire system.

There are two main types of this system: one has a negative coefficient of resistsance and the other has a high coefficient of capacitance with an increase in temperature.

Usually there are two loops and both of them need to detect a fire to give a warning.

In the even of a fire, a claxham horn will sound and a visual warning will be displayed. Usually there are a minimum of 2 fire extinguishers that are able to be fired in to each engine.

The APU will automatically shut down if a fire is detected, or high oil pressure, overspeed but can manually be shut down. I usually only has 1 fire extinguisher bottle.