Turbine Engines
- Why turbine over reciprocating
o 25% moving parts
o Constant smooth power
o Less vibration
o Higher operating speeds
o Lighter weight vs reciprocating
o Higher altitudes
- Physics review
o Force- push or pull acting on body
o Acceleration- rate of change in velocity
o Work- body moves over a distance because a force was applied to it
o Power- rate at which work is accomplished
o Metric- a lot like electricity don’t get confused. Power in measured in watts and kilowatts
o Energy
§ Potential energy
· Result of position, stored energy
§ Kinetic energy
· Is the result of motion
o Speed- the distance a body travels per unit of time
o Velocity- is the rate of movement in a specific direction
o Mass- measurement of matter in mass
o Momentum- mass multiplied by velocity
o Newton’s laws
§ 1st: object at rest remain at rest
§ 2nd: acceleration is directly proportional
§ 3rd: for every action there ia equal and opposite reaction
- Factors affecting thrust
o Temp of air entering compressor
o Pressure of air entering compressor
o Humidity of air entering compressor
o Aircraft speed v1
o Engine speed rpm
o Compressor air bleeds
o Temperature of air in turbine
o Formula- thrust available = airflow mass
o How to increase thrust – increase velocity of airflow or airmass. Problem with higher velocity and kinetic energy the more wasted energy
o Increasing mass of airflow
§ Increase the size of intake
§ Increase velocity of incoming air
§ Increase the density of the air
o Temperature
o Pressure
- Operating Speed
o Larger the engine the slower rotational speeds
o Relative speed of interior blades vs exterior blades
o Thrust production is not as direct as reciprocating engines
§ Drop in 1% speed could cause a 5% drop in thrust
§ Speed seldom drops below 85% in flight
o Spool up and down time significantly higher than reciprocating engine
- Compressor air bleeds
o This air taken off compressor of engine to run diff equip
o Mainly for pressurization or heating of aircraft
- Temperature of air entering turbine
o Excess temps can cause damage to engine
o Need to monitor temp to make sure turbine doesn’t overheat
o If overheating engine will need to be inspected by a mechanic
- Types of jet engines
o Four main types
§ Turbojet
§ Turboprop
§ Turbofan
§ Turboshaft
o Which type to use
§ Ac below 250
· Reciprocating engine
o Lower initial cost
o Lower operating cost
· Speed between 250-450
o Turboprop
o Better power to weight ratio
§ Speeds near 450
· Turbojet
· Newer turbofan
§ Helicopters
· Turboshaft engines
· How the transfer of power goes to the rotor
o Turbojet engines
§ Uses heat energy to produce rotating mechanical energy
§ Few moving parts
§ Simple in design
§ Thrust is the air leaving the rear engine
§ Cycle of ject engine
· Intake, compression, combustion, exhaust
· Smoot uninterrupted power
· Always working
o Turboprop engines
§ Jet engine drives a propellor
§ Propeller creates 75% or more of thrust
§ Exhaust creates 5 to 25 percent
o Turbofan engines
§ Modification to turbojet
§ Produces more power while reducing noise
§ Initial compression fan that begins compression earlier
§ Some air moved by initial fan actually bypasses combustion and is used for thrust
o Turboshaft
§ Used in helicopters
§ Much like a turboprop engine
§ Jet engine is geared down to provide rotation to rotor
o Turbine Engine Components
§ Air inlet
§ Compression
§ Combustion section
§ Turbine
§ Exhaust
§ Accessory section
§ Support systems
o Air inlet duct
§ Needs smoothly bring air to the compressor
§ Design considers
· Air density
· Airspeed
· Rotational speed
o Compressors
§ 2 mian functions
· Compress air
· Provide bleed air to run aircraft systems
o Bleed air
§ Can be pulled off various compression stages
§ Used for:
· Cabin pressurization
· Cabin heating
· Auxiliary drive nuts
· Deicing and anti-icing
· Pneumatic engine starting
· Gyro operation
§ 2 main types of compressors
· Centrifugal flow
o Air that enters engine is turned 90 degrees and accelerated
o This acceleration then begins to compress the air in the engine
· Axial flow
§ Parts of Centrifugal flow compressor
· Impeller
· Diffusor
· Compressor manifold
§ Impeller
· What compresses the air
· Changes air direction by 90 degrees
· Accelerates air outwards
· Many different designs
§ Diffuser
· 2 purposes
o Direct air from impeller to manifold
o Slows velocity of air
· Why slow velocity
o Slower velocity means higher pressure
o Slower velocity will not blow out flame in combustion chamber
§ Manifold
· Takes air from diffuser and moves it to combustion chamber
· Each outlet feeds one combustion chamber
· Evenly divides air to all chambers
· Changes airflow from outward to axial flow
§ Advantages
· High pressure rise
· Did in one stage
· Good efficiency over wide range
· Low weight
· Low cost
· Low starting power
· Less fod damage
§ Disadvantages
· Large frontal area increases drag
· Multiple stages not as practical because of energy loss