AGK Flashcards
What are the four stokes of the internal combustion engine?
1 Intake
2 Compression
3 Power
4 Exhaust
What is valve lead?
When the exhaust valve opens before bottom dead centre. (opens early)
What is valve lag?
Inlet valve closes after BDC
What is the firing interval for a 4 stroke engine?
720 divided by number of cylinders
Define volumetric efficiency?
What reduces VE?
The measure of success achieved drawing gas molecules into the cylinders
Hot days and dry altitudes
Reducing throttle from normal setting
RPM higher than normal setting
Why does detonation occur and how can it be managed?
Occurs due to increased temp and pressure of fuel to air mixture that causes instantaneous combustion burning when ignited. Caused by high power with inadequate cooling, high power with lean mixture, high manifold pressure wiht low rpm & use of incorrect fuel.
Cool engine by full rich mixture, reduce power and increase airspeed
What is pre ignition?
A hot spot/carbon deposit igniting charge and burn begins before spark plugs fire
Same solution as detonation
Compression ratio?
Clearance volume divided by swept volume divided by swept volume
What is the oil system responsible for?
Lubricate Cools Cleans Seals Protects
What is viscosity?
The oils resistance to flow.
High viscosity - thick and cold
Low viscosity - warm and runny
What is valve overlap?
TDC when inlet valve is opening & exhaust valve is closing
What is ashless dispersant oil and why is it used?
Synthetic oil which contains additives
- Prevents sludge bulid up
- Reduces engine wear
- Better compression seal around piston rings
- Reduces oil consumption
Straight Mineral Oil?
Contains no additives
- Used for run in periods on new engines
- Used to help piston rings, cylinder walls to wear
- Bedding in process (forms seal to prevent gas from leaking)
Oil Quantity characteristics
- less oil the temperature will rise
- fluctuations in oil pressure = low oil
- large or rapid loss may not be noticeable on temp gauge
What factors affect engine power output?
Manifold pressure
RPM
Semi Rigid rotor system?
Two main blades -Feather -Teater -Flap (underslung hub reduces mast bumping)
Fully articulated System
-Usually more than two blades
-Feathers
-Flaps
-leads (Hunts)
-Drags(lags)
(Prone to ground resonance)
Vertical Vibration?
Horizontal Imbalance?
Tail Rotor Imbalance
Blades out of track (Up & Down)Bounce in seat
Stick shake (Cyclic shake)
Felt through pedals (high frequency)
What is the difference between a de-icing system and a anti-icing system?
De-icing system is in flight or after it has formed ie inflatable
Anti icing - preventing ice from forming, covering blades etc
Define octane rating and how is it increased?
Fuels resistance to detonation
(Higher the rating higher resistance)
Adding lead and Bromine increases resistance
Name the four fuels and their colours
100LL - Blue (common piston fuel)
100/130 - Green (Rare piston fuel)
Mogas (80/87) - Red/Purple
AVTUR (Turbine) - Straw colour
What does the Stoichiometric mixture measure?
Ratio of fuel to air
