MILPORT - APR 1
MILPORT - Aircraft Performance
MILPORT - Aircraft Performance
Set of flashcards Details
| Flashcards | 57 |
|---|---|
| Language | English |
| Category | Traffic |
| Level | Other |
| Created / Updated | 12.09.2016 / 16.01.2023 |
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Name 3 types of engines.
TURBO JET
TURBO FAN
TURBO PROP
Tuorbojets consist of which 5 components?
air inlet
air compressor
combustion chamber
gas turbine
nozzle
How does a turbojet engine work?
Compressor compresses air into the combustion chamber, there it is heated and expanded by the fuel combustion and expands out through the turbine into the nozzle, where it gets accelerated to high speed to provide propulsion.
What's the turbine doing?
driving the air compressor
Name 2 disadvantages of a turbojet engine.
inefficient (if flown below about Mach 2) and very noisy
Turbojets are still very common in ....... due to their ....., ..... and .....
medium range cruise missiles
high exhaust speed, low frontal area, relative simplicity
What are the stators doing?
air inlet: guiding the airlow of the compressed gases
The air intake (or inlet) is designed to be as efficient as possible at ..... ?
recovering the ram pressure of the air stream tube approaching the intake
What does the compressor do?
rotates at very high speed, adding energy to the airflow and at the same time squeezing (compressing) it into smaller space
-> pressure and temperature of the air rise
What is bleed air extracted for from the compressor in most turbojet aircraft? (3)
- air conditioning/pressurization
- engine inlet anti-icing
- turbine cooling
Name 4 types of compressor used in turbojets and gas turbines.
- axial
- centrifugal
- axial-centrifugal
- double-centrifugal
After leaving the compressor section, the compressed air enters the ...... ?
combustion chamber
Combustion chamber: as the mixture burns its temperature ..... dramatically, but the perssure actually ..... a few percent.
increases / decreases
Turbine: some shaft power is extracted for what reason?
to drive accessories like fuel, oil and hydraulic pump
In a turbojet almost ... (how much) of all the power generated by burning fuel is used by the compressor to compress the air for the engine?
2/3 --> inefficient
A turbofan engine provides propulsion using a combination of what?
ducted fan
jet exhaust nozzle
The rather (slower/higher?) bypass airflow produces thrust more ..... than the (high/low?)-speed air from the core, and this reduces ..... ?
slower bypass airflow
efficiently
high-speed air
specific fuel consumption
Explain the general principle of a turbofan engine?
Ducted fan, driven by a low-pressure compressor, ducts part of the airstream to bypass the engine, and part of the airstream through the core where it provides oxygen to burn fuel to create power.
What's the advantage of turbofan engines?
much lower net exhaust speed -> more efficient at subsonic speeds and relatively quiet
Explain the 2-spool arrangement.
compression system split in two,
Low Pressure (LP) compressor, driven by a LP turbine, supercharges the High Pressure (HP) compressor.
Each compressor is mounted on a separate (co-axial) shaft, driven by its own turbine.
In a turbofan, the LP compressor is often called a ..... ?
fan
What's the difference between fans in civil-aviation and most military-aviation engines?
civil-aviation: usually single fan stage
military: multi-stage fan
What's the advantage uf ducted fans?
Fan blades must operate at subsonic inlet velocities to be efficient, ducted fans allow efficient operation at higher vehicle speeds.
Ducted fans operate best from about ..... to ..... km/h?
400 to 2000 km/h
What kind of fan belongs normally to a high specific thrust/low bypass ration?
multi-stage fan (developing a high pressure ratio -> high exhaust velocity)
What are Variable Inlet Guide Vanes for?
low-bypass ratio: to direct air onto first rotor stage -> improves fan surge margin
Most jet fighters have what kind of engines (regarding ratio)?
low/medium bypass turbofans with mixed exhaust, afterburner and variable area final
Name some modern low-bypass military turbofans. (3)
- Pratt & Whitney F119
- Eurojet EJ200
- General Electric F110 F414
Low specific thrust is achieved by replacing ..... ?
... the multi-stage fan with a single stage unit.
Where are high-bypass and low-bypass turbofans used? What's the difference?
high-bypass -> civil aviation (quieter and lower specific fuel consumption)
low-bypass -> military (except transport aircraft)
What is "compressor surge"?
Instability resulting from stalling of compressor aero foils
(high overall pressure ratio -> more difficult to throttle compression system)
How can compressor stall be avoided?
by progressively:
- opening interstage / intercompressor blow-off valves (inefficient) and/or
- closing variable stators within compressor
Name one example of a single shaft turbofan driven aircraft?
Mirage fighter -> SNECMA M53
What means "boosted" two spool?
overall pressure ratio is increased by adding an Intermediate Pressure (IP) Compressor between the fan and HP compressor, to supercharge or "boost" the latter
Who uses a three spool configuration (IP compressor mounted on seperate shaft)?
Rolly-Royce
What's the featured called, used to allow LP turbine and fan to operate at their optimum speeds?
reduction gearbox / geared fan
Modern military aircraft are usually ..... ? (type of spool system)
Basic Two Spool
High Pressure Turbine: what's used by military, what by civil?
civil: high efficiency, 2-stage HP turbine (or IP)
military: single stage HP turbine
Low Pressure Turbine: what's used by military, what by civil?
civil: multi-stage LP turbine
military: one or two LP turbine stages (due to much lower bypass ratio)
What's the engine of the F/A-18 Hornets?
General Electric: F404
