Highlights from Notes Flashcards
A relatively ____ mass of air is given a relatively ______ acceleration to the rear by a propeller
A relatively ____ mass of air is given a ____ acceleration to the rear by a ‘jet’ engine of some kind
Reactive force is termed Thrust
A relatively large mass of air is given a relatively small acceleration to the rear by a propeller
A relatively small mass of air is given a large acceleration to the rear by a ‘jet’ engine of some kind
Gas Turbine Engine = The constant _______ cycle
Piston Engine = The constant ______ cycle
Gas Turbine Engine = The constant Pressure cycle
Piston Engine = The constant Volume cycle
A turbojet engine consists of what components? (5)
which are cold vs hot section
Cold Section = Air intake, compressor
Hot Section = Combustor, Turbine, Exhaust
A turbojet engine has no _______
bypass air
A turbofan engine has ______
bypass air
Propeller
- Helicopters, as the main power plants; and
- Auxillary Power Units (APU’s) in transport aircraft
A uniform and steady airflow is necessary to avoid ______ ____ and excessive ____ ___ ______ At the turbine
A uniform and steady airflow is necessary to avoid compressor stall and excessive internal engine temperature at the turbine
____ intakes are used in low speed installations such as helicopters
Bellmouth
Nose cowl anti-icing systems are ______ from each other
independent
The primary pupose of a compressor is to _______ the pressure of the mass of air entering the engine inlet and discharge it to the diffuser and then the combustion section at the correct ______, ______ and ______
The primary pupose of a compressor is to increase the pressure of the mass of air entering the engine inlet and discharge it to the diffuser and then the combustion section at the correct temperature , pressure and velocity
The secondary pupose of the compressor section is to supply Engine Service Bleed Air to ____ ____ ___ ____, to pressurise _____ ____, and to supply _____ ____ ___ ___ ___ and fuel system _____ for ___ ___
Another secondary pupose is to extract air for aircraft services. This is called ______ _____ ____ ____
The secondary pupose of the compressor section is to supply Engine Service Bleed Air to cool hot section parts, to pressurise Bearing seals, and to supply heated air inlet anti icing and fuel system heat for de-icing
Another secondary purpose is to extract air for aircraft services. This is called Customer Service Bleed Air
What is the ‘vaneless space’ in the centrifugal compressor?
It is the space that exists between the impeller vane tips and the diffuser.
What are the 5 main advantages of a centrifugal compressor?
- High pressure rise per stage. Up to 10:1 and 15:1 in a dual stage
- Good efficiency over a wide rotational speed range
- Simplicity of manufacture and low cost compared to axial engines
- Low weight
- Low starting power requirements
Why is it called an Axial Flow Compressor?
The axial compressor is so named because airflow and compression occur in parallel to the rotational axis of the compressor
A complete compressor stage is defined as …
A complete compressor stage is defined as a row of rotor blades followed by a row of stator blades
The rotor shaft, between driving turbine and driven compressor, it commonly consists of a two piece unit, the items being flange bolted together.
The shaft is supported by, and rotates in, ____, ____ and _____ bearings
The rotor shaft, between driving turbine and driven compressor, it commonly consists of a two piece unit, the items being flange bolted together.
The shaft is supported by, and rotates in, front, centre and rear bearings
Rotor blades are manufactured from ______, _____ or ______
Rotor blades are manufactured from aluminium alloy, steel or titanium
Stator vanes are _____ (divergent / convergent)
Stator vanes are divergent
Midspan shroud is formed about ____% up the blade length
60%
Compressor Surge is
reversal of airflow at the high-pressure end, often leading to complete airflow breakdown, sometimes so severe as to cause a loud bang as air is spat out of the front of the compressor
A mild compressor stall is usually called a ‘‘________’’
Not usually harmful to the engine and often correct themselves
Transient stall
A severe stall is called a _______.
This can significantly decay engine performance causing loss of power or even engine failure
Hung stall
Compressor stalls usually occur from one of the following 4 problems:
- Turbulent or disrupted airflow to the engine inlet
- Excessive fuel flow caused by abrupt engine acceleration
- Contaminated or damaged compressor
- Damaged turbine components, causing loss of power to the compressor
Bleed valves prevent problems by bleeding off excess airflow.
Just as the engine reaches idle speed, they _____
close
Define Primary Airflow
Secondary Airflow
Tertiary Airflow
Primary Airflow - Primary air is that portion of the air, which mixes with the fuel for combustion purposes
Secondary Airflow - Secondary air is that part of the air, which is metered into the combustion chamber to complete combustion.
Tertiary Airflow - Acts as a cooling agent. This air takes no part in combustion.
How many igniters are usually found in Two combustor cans in a multiple chamber system?
Two igniters are used usually in two combustor cans
The turbine blades and disks are made from super alloys, usually ______ based.
Nickel
Where are Impulse Turbine blades usually found?
In pneumatic air starters
To prevent overheating of the turbine disk by combustor exhaust gases, the disks are ____ cooled with airflow from the ______
air
compressor
By what method are turbine blades attached?
'’Fir Tree’’ method
-retained by locking plates
Turbine blade material includes:
Nimonic Alloys, Nickel based alloys are always used
How are turbine blades manufactured and what is their future>
- Nimonic alloys, nickel based alloys
- Single crystal construction
Future is reinforced ceramics
The greatest reduction in noise levels is achieved by the ___________
high by-pass ratio Turbo fan engine
What is reverse pitch?
Thrust reverser equivalent for prop aircraft
'’A negative angle of attack of the propeller blade to the relative airflow’’
A system of _____ ______-_________ keeps the crew or ground operator fully informed as to thrust reverser position via warning lights on the flight-deck
proximity micro-switches
Compare the viscosity of oil needed for:
Modern Gas turbine engines
Turbo-prop engines
Modern Gas turbine engines = low viscosity synthetic oils
Turbo-prop engines = slightly higher viscosity synthetic oils
Which has a lower freezing point and thus is used by most commercial airlines?
Jet A1 or Jet A
Jet A1 has a lower freezing point than Jet A
