FUNDAMENTALS Flashcards
What is acceleration due to gravity?
9.8 metres per second.
How does a gas turbine, turbo fan and turbo prop engine produce thrust?
Accelerating ambient air.
What is the single purpose of a turbojet engines?
Producing high velocity gases.
On turbo jet aircraft what is all gas energy that isn’t used to drive the compressor and accessories converted into?
Thrust.
What aircraft speeds are turbojet aircraft developed for?
High aircraft speeds
What are 2 disadvantages of turbojet aircraft?
They are very loud and inefficient.
How do turboprop aircraft engines produce thrust?
Small acceleration of a large quantity of air.
Where can the turboprop propeller be driven from?
Directly from the compressor shaft or by a free turbine and a long centre drive shaft
What is required to reduce the high gas turbine engine rotation speeds that can be managed by the propeller?
Reduction gearbox.
Turboprop engines convert gas energy into torque. The are very efficient, but what does the propeller not permit?
High aircraft speeds.
What spool are turbofan engines?
Twin or triple
Normally, what do turbofan engines have to reduce the speed of the fan?
Nothing, the fan does not have a reduction gear box.
What is the total thrust of turbo fan engines?
The sum of the thrust developed by the core engine and fan.
What is weight measured in?
Newton’s.
What is the formula for work?
Force x distance
What is the formula for power?
Work / Time
What is energy?
Capacity of a body to perform work.
What can mechanical energy be divided into?
Potential energy (energy virtue by position) Kinetic energy (energy virtue by movement)
What type of engine is more fuel efficient?
Piston type
What are disadvantages of the piston engine (only used on small aircraft)?
Performance decrease at higher altitudes
Ratio of weight and power decreases with size.
What are the 4 types of gas turbine engine?
Turboprop
Turbo fan
Turbojet
APU
What was the first gas turbine engine?
Turbojet
Why are turbojet engines extremely loud?
High exhaust gas velocities.
Require too much fuel
What force do engines create which moves the aircraft?
Propulsion.
What is an engine which uses jet propulsion called?
A reaction engine.
Uses Newton’s law of motion
What is the principle of jet propulsion?
A force is always created when a body of mass is accelerated.
What must be done to accelerate the air?
Air pressure increase.
Mechanically with compressor, or thermally by increasing volume of air
What is the formula for kinetic energy?
KE = 1/2 mV squared
What is Newton’s first law called?
Law of inertia.
What is the formula for force?
Mass x acceleration
How much of the total thrust does the fan produce in a turbo fan engine?
80% dependent on the bypass
On a modern turbo fan engine, what are the typical bypass ratios?
Between 4:1 and 9:1
What are Most turbofan engines usually?
Short ducted.
Long ducted
Combined with separate exhausts
What is the advantage of propfan engines to high bypass engines?
Have a higher bypass ration 90:1
Use 20% less fuel
Why are propfan engines not used on modern jet aircraft?
Due to mounting difficulties
What is a non-modular engine design?
An engine built in one whole unit.
What is an advantage of a Non-modular engine design?
Saved weight and was fully functional
Where are non-modular engine designs commonly used?
Some APU’s and older aircraft.
Take the whole engine off to gain access to some places
What are most modern jet aircraft engine constructions?
Modular design.
What are modular design engines further developed into?
Major engine modules and sub-modules.
What type of maintenance is a module replacement on modular design engines?
Minor maintenance - can be done by maintenance organisation
What are the Advantages to the manufacturer in modular design?
- rotating parts pre balanced
- less spare engines needed
- more flexibility when changes to an individual part
What are the advantages to an operator with modular engines?
- modules replaced without major disturbance
- no rebalance when models changed
- module can be replaced while engine remains on aircraft
Where is aluminium alloy used in engines?
Gearbox housing, fan stator casings and other LOW LOADED parts of the fan module.
Where are ceramic casings used in engines?
Combustor and high pressure turbine
Where are steel alloys used in engines?
N1 drive shaft, engine bearings and structural frames.
Where are cobalt parts used on engines?
Stator or the first part of the HP turbine.
Heat resistant
Where are titanium based alloys used in engines?
Fan, LP compressor, and front stages of the HP compressor
Strong as steel but half as heavy
Where are nickel based alloy used on engines?
HP compressor, combustion section, HP/LP turbines.
High centrifugal loads and high temps
What is Newton’s third law referred to?
The law of action and reaction.
Every action has equal and opposite reaction
What is the Brayton cycle?
Pressure energy increased
Addition of heat energy
Conversion to kinetic energy
What’s the cycle of a four stroke piston engine?
Induction
Compression
Combustion
Exhaust
In what engine are the four stage cycle intermittent (one after the other) ?
Piston.
Gas is simultaneously
What does a simultaneous (gas turbine) four process do?
More fuel burnt quicker producing greater power.
What is the process of heating at constant pressure (isobaric heating)?
Pressure of air not rising during combustion but volume increasing.
(Gas turbine engine)
What conditions are there in isobaric heating?
No peak or fluctuating pressures
What do the peak pressures make it necessary for piston engine to employ?
Cylinders of heavy construction and high octane fuels.
What type octane fuels do gas turbine engines use?
Low octane fuels.
