15.01 Fundamentals Flashcards
Figure of acceleration due to gravity
g = 9.8 m/s^2
Equation for work
Work (nm) = Force x Distance
SI unit is Joules.
Equation for Power
Power (Watt) = Work / Time
What can mechanical energy be divided into?
Potential energy and kinetic energy.
What is potential energy by definition?
The energy a body has by virtue of its position.
PE = mgh
What is kinetic energy by definition?
The energy a body has by virtue of its motion.
KE = 1/2mV^2
Newton’s First law?
Law of inertia = A body at rest remains at rest and a body in motion continues to move unless acted upon.
Newton’s second Law?
Law of motion.
Gas turbine engine.
Newton’s third law ?
Law of action/reaction = every action has an equal and opposite reaction.
Turbojet engine.
What is air referred to as?
A working fluid to provide thrust.
What is the Brayton cycle?
Induction,
Compression,
Combustion,
Exhaust.
In a piston engine, what word describes how the brayton cycle process occurs?
Intermittently
In a has turbine engine, what word describes how the brayton cycle occurs?
Simultaneously.
Advantages and disadvantages of a piston engine?
- More fuel efficient.
- Ideal for light aircraft.
- Performance decreases at higher altitudes.
- Weight to power ratio decreases with increased size.
Advantages of Gas Turbine engines?
- Operate at high altitudes.
- Easily provide thrust, torque, bleed air.
- Allow high speed flight.
What are the types of Gas turbine engines? (4)
- Turbofan. (high speed with good efficiency)
- Turbojet. (Very high speed but very loud and inefficient)
- Turboprop. (Good compromise for fuel efficiency and speed)
- APU. (Small engine to provide pneumatics and electric power)
What is the jet propulsion force?
The force that operates in the OPPOSITE direction to the flow of mass through the nozzle.
What is the name for an engine that uses the jet propulsion principle?
A reaction engine.
In what ways (methods) can air pressure be increased? (2)
- Mechanically with a compressor.
- Thermally by increasing the the volume of air, when a fuel/air mixture is burned.
A turbojet engine is designed for what single purpose?
Producing high velocity gases.
What is always required in turboprop engine?
A reduction gearbox.
How do turboprops produce their thrust?
Small acceleration of large air quantities, using a propeller.
Gas energy is converted into torque.
What does a turbofan engine combine?
The good efficiency and high thrust capability of turboprop engines, with the high speed and high altitude capability of the turbofan.
What are turbofan engines usually formed of? (Spool)
Twin or triple spools.
What do turbofan engines convert?
Hot gas energy from the core engine into thrust.
A large part of gas is converted into torque to drive the fan and compressors.
Total thrust of a turbofan engine?
Core engine thrust + Fan generated thrust.
What percentage of total turbofan thrust comes from the fan airflow?
More than 80%
What is the bypass ratio?
The ratio of air that passes through the fan duct compared with the air that passes though to core engine.
What is the bypass ratio on modern turbofan engines?
Between 4:1 and 9:1
What type of exhaust ducts (nozzles) are found on turbofan engines? (2)
- Short ducted (for most high bypass engines)
- Long ducted (combined or separate exhausts)
What are the advantages of an open rotor engine (propfan) ?
- Good speed.
- High altitude.
- Use up to 20% less fuel.
- Bypass ratio of up to 90:1.
Advantages and disadvantages of a non-modular engine? (are old engines and some APUs)
- Saved weight.
- Fulfilled main purpose.
- complicated.
- very hard for maintenance.
- parts matches individually.
Advantages of the modern modular engines ? (where engine is split up into major modules)
- Pre balanced.
- Flexibility with changes.
- Easily stored and transported.
- modules replaced/removed easily.
- no rebalancing required.
- modules replaced while engine is on aircraft.
- less need for spare parts.
What are the typical materials used on modern engines?
- Aluminium alloys.
- Ceramic material.
- Composite material.
- Cobalt base alloys.
- Nickel base alloys.
- CRES steel alloys.
- Titanium base alloys.
Where is aluminium alloy mainly used?
- Gearbox housings.
- Fan stator casings.
What are ceramic coatings used?
In the combustor and high pressure turbine.
Where are steel alloys usually found?
- N1 drive shaft.
- Engine bearings.
- Main structural frames (some engines)
Where are cobalt base alloys used?
In the stator of the first stage high pressure turbine.
Where are Titanium base alloys usually found?
- The fan.
- Low pressure compressor.
- Front stages of the the high pressure compressor.
Use of Nickel base alloys?
- High pressure compressor.
- Combustion section.
- High and Low pressure turbines.
