15.1 Fundamentals Flashcards
What is the definition of energy?
Something that gives a body the capacity to do work.
What is the unit of measurement for both ‘Work Done’ and Energy?
Joules (J)
What is the definition of Potential Energy?
The stored energy of a body at rest.
What are the 3 ways in which Potential Energy is generated?
- Due to a body’s position (height).
- Due to a body’s distortion (springs/Elastic tension).
- Due to a chemical action (batteries).
Potential Energy equation?
PE = mgh (mass x gravity x height)
What is the definiton of Kinetic Energy?
The energy of a body in motion, converting it’s PE into work done.
Kinetic Energy Equation?
KE = ½mV² (0.5 x mass x Velocity²)
What is Newton’s first law?
Law of Inertia. (A body in motion stays in motion….).
What is Newton’s second law?
Law of Motion. (Force = Mass x Acceleration).
Applies to GTE as Thrust is proportional to mass of airflow multiplied by acceleration of airflow.
What is Newton’s third law?
Law of Action and Reaction. (Every action has an equal and opposite reaction…)
(Turbojet Engines)
What’s the Brayton Cycle in 4 simple stages?
Suck, Squeeze, Bang, Blow.
How do the 4 stages of the Brayton Cycle correlate to the stages of a GTE?
Intake = Suck.
Compressor = Squeeze.
Expansion/Combustion Chamber = Bang.
Exhaust = Blow.
What happens to the pressure and volume of air, in the compressor?
Air pressure increases greatly.
Air volume decreases.
What happens to the pressure and volume of air, in the combustion chamber?
Air pressure remains constant.
Air volume increases as it expands.
What happens to the pressure and volume of air, in the exhaust section?
Air pressure continues to decrease.
Air volume continues to expand.
It reaches the point of ‘final high velocity’ = Thrust.
What are the 4 ideal changes of state?
Isobaric.
Isochoric.
Isothermal.
Isoentropic.
Isobaric definition?
p = Constant
Isochoric definition?
v = constant
Isothermal definition?
t = constant
Isoentropic definition?
Heat is neither added nor rejected. (Adiabatic System).
Q = O
What type of heating is used in the combustion chamber?
Isobaric heating. (Heat is added to the air, as fuel is burned at a constant pressure)
Unit of measurement for Thrust?
lbs
Formula for Work?
Work = Force x Distance (Joules or Nm)
Formula for Power?
Power (Nm/s) = (Force x Distance) / Time
(Work over time)
Definition of Velocity?
Speed with a direction, a ‘vector quantity’.
Definition of Acceleration?
Rate of change of Velocity.
Formula for Acceleration?
Accel (m/s)² = Change in velocity / time
What is the basic operation of a Turbojet engine?
A turbine driven compressor draws the air in and compresses it, which enters the combustion chamber and is mixed with injected fuel. Explosion expands air and is exhausted via exhaust nozzles/jet.
What are the advantages of a Turbojet?
- Simple design.
- Very high speeds.
- Takes up little space.
What are the disadvantages of a Turbojet?
- High fuel consumption.
- Loud.
- Poor slow speed performance.
- Limited range and endurance.
What’s the difference between a twin-spool and triple-spool Turbofan engine?
The triple-spool engine adds an additonal turbine and compressor pair, as the ‘Intermediate Pressure’ (IP) section.
Twin-spool has just two turbine and compressor pairs, as the Low Pressure and High Pressure sections.
What % of Thurst does the fan generate in a Turbofan engine?
Approx. 80%
Advantanges of a Turbofan engine?
- Fuel efficient.
- Less noisy.
- Streamlined appearance.
Disadvantages of a Turbofan engine?
- Heavy.
- Larger frontal area.
- Inefficient at very high altitudes.
How does a turboprop engine operate compared to other engine types?
Operates in the same principles as a turbojet engine, but produce shaft horsepower to drive a propeller.
What key mechanical parts are additional to a turboprop engine?
They have additional turbines, a power shaft, and a reduction gearbox.
Advantages of a Turboprop?
- Very fuel efficient.
- Most efficient at mid-range speeds (250-400knts).
- Most efficient at mid-range altitudes (18000-30000ft).
Disadvantages of a Turboprop?
- Limited airspeed.
- Gearing systems are heavy, and can fail.
What is the definition of a Turboshaft engine?
A gas turbine engine that delivers power through a shaft to operate something OTHER than a propeller.
Where are turboshaft engines used?
As helicopter engines, and APUs.
How do Turboshaft engines operate compared to other engine-types?
The same principles as a turbojet, but with an additional power section.
How is the power turbine within a turboshaft engine usually described?
As a ‘Free Power Turbine’.
It’s not mechanically linked, and is only linked by the stream of hot gasses.
What is the purpose of having a Free Power Turbine?
Allows its speed to be optimised for the machinery that it will energise. It does this without the need for a reduction gearbox.
Advantages of a Turboshaft engine, compared to piston?
- Much higher power to weight ratio than piston engines.
- Typically smaller than piston engines.
What are the two disadvantages of a Turboshaft engine? (one of these is the same as turboprops).
- Loud.
- Complex gear systems, they can fail.
Which area of a GTE forms the cold section?
From the inlet, to the compressors and diffusers.
Which area of a GTE forms the hot section?
From the combustion chambers to the exhaust.
What is the greatest influencing factor for design?
The type of compressor that will be used.
What are the advantages of Modular Construction, for the engine manafacturer?
- Rotating parts can be pre-balanced.
- Fewer spare engines needed in stock.
- More flexibility with changing engine parts.
- Modules are easily stored and transported.
What are the advantages of Modular Construction, for the engine operator?
- Modules easily removed/replaced with minimal disturbance to other components.
- No re-balancing required after module changes.
- Modules can be replaced in-situ.
- Less need for spares.
- Easily transported.
What can a module replacement be classed as?
A ‘Minor Repair’ and thus can be carried out in an MRO, instead of sending the engine away for Overhaul.
Where is Aluminium Alloy used?
- Gearbox housings.
- Fan stator casings.
- Low loaded module parts.
Where are composites used?
- Fan blades.
- Fan case.
Where are Ceramics used?
- Combustion chamber coastings.
- High pressure turbine.
Where are Steel Alloys used?
- N1 shaft.
- Engine bearings.
- Main structural frames.
Where are Cobalt-base alloys used?
- High heat resistance areas.
- 1st stage High Pressure turbine stators.
Where are Titanium alloys used?
- Fan.
- LP compressor.
- Front stages of HP compressor.
(Titanium has the same strength as steel, for half the weight).
Where are Nickel-based alloys used?
- High centrifugal loads at high temps.
- HP compressor.
- Combustion section.
- HP and LP turbines.
