Engines Flashcards
Bernoulli theorem
Total energy made of 3 forms (potential, pressure/temp and kinetic)
Pressure and kinetic energy proportional
Piston engine process
Induction, compression, combustion (expansion) and exhaust
What is the compression ratio
Ratio to BDC and TDC (total vol / clearance vol)
Different colour smoke meaning
Blue = oil burn in cylinders
Black = carbon granules
White = water content
What does a supercharger do
Delivers more air to the engine cylinder, meaning more fuel, meaning a greater power output
Advantages of propellers
-Extra wing lift due to prop
-slip stream suppresses stall speed (good low speed characteristics)
-slipstream makes fin/rudder more effective
Disadvantages of propeller
Lack of airspeed and range due to limited revolution speed to ensure blade doesn’t become sonic
What decides the prop force
Output of engine and blade angle
3 restrictions on propellers
- Blade length
- Chord size (aspect ratio, centrifugal turning moments)
- blade interference (too many)
Why do blades have washout (twisted)
To maintain blade AoA and prevent it becoming sonic
Three reasons for critical engines
Asymmetric blade affect due to downgoing blade travelling faster
C of G position and blade distance greater on one engine
Slip stream of props
What is specific fuel consumption
Fuel used per hour / thrust of engine
Combustion cycle of jet engine
Induction, compression, combustion, expansion, exhaust
Why were jet engines introduced
-to fly at higher speeds
-more simplistic and reliable
Describe the process of a gas turbine
-air enters and compressed
-ignited in combustion chamber to form more energy
-expansion and passes across turbine
-exhausted through nozzle
