Test 2 Flashcards
Purpose of the lubrication system
Supply oil to the engine at the correct
- Pressure
- Volume
- Location
The oil tank must…
hold adequate amounts of oil
Oil Capacity
- Capacity should be sufficient to supply engine
- Multi-engine planes require independent oil systems for each engine
Plumbing for lubrication system
- If subjected to vibration, its made w/a synthetic hose
- If not subjected to vibration, its made out of aluminum alloy
- Hoses should be fire resistant
Temperature regulation
- Oil coolers regulate the temp of the flowing oil
- It is regulated by a thermostat valve
Oil pressure relief valve
- Controls and limits the lubricating oil pressure
- Prevents damage to the lubrication system
- Ensures lubrication in case of a system failure
Engine Oil Filters
Full Flow Type
- Filters ALL contaminants in the oil
- Oil is filtered before passing through bearings
Bypass type
- Filters only about 10% of contaminants
- Oil is NOT filtered before passing through bearings
Strainer type
- A tubular screen
- Designed to collapse when clogged
Disposable Filter cartridge
- Filter canister is reused while the filter element is
replaced
Spin on filter
- Incorporates wrench pad, steel case, cellulosic paper,
and a mounting plate
- Full flow type
Cuno Oil filter
- A series of laminated plates or disks
- Contaminants are trapped on the outer diameter of
the plates
- The spacing of the plates determines the size of the
particles let through
Oil Pressure Gauge
- Measures from no pressure to above max pressure
- They are usually a bourdon tube type
Oil Temperature Gauge
- Sensors are usually at the oil inlet line or on the oil filter
housing
Oil Pressure pump types
- Gear
- Vane
Capacity of oil pump > than engine requires
Scavenge Pump
- Usually used for a dry-sump lubrication system
- > capacity than pressure pumps
Air scoop
Air scoop
- Opening facing airstream
- Receives RAM air
Air filter
Air filter
- Wetted Mesh Filters
- Mat or metal filaments dipped in oil so it catches
particles
- Dry paper filters
- Air passes through a pleated layer of paper elements
- Replaced on a time-in-service basis
- Polyurethane foam filters
- Polyurethane foam and a wetting agent
- Newer type of air filter
Alternate air valve
Alternate air valve
- Allows air to flow to the engine if the air filter is clogged
- Can be manually controlled
- Is unfiltered air
Carburetor Heat Valve
- Valve closes main air duct and opens duct to the heater muff
- The heater muff is a shroud around the exhaust
- It helps heat the air
- Don’t use it during high-power operations
Intake Manifolds
- For opposed engine types
- Individual pipes leading to each cylinder
- Brings the fuel-air mixture to the cylinders through the pipes
Induction system icing
- May cut off fuel-air charge or vary fuel-air ration
- Icing is classified into three types
- Impact Ice
- Fuel evaporation ice
- Throttle ice
- Uses Bernoulli’s principle
- Between 40-70 F is where carb ice occurs
Exhaust systems
- Safely removes the products of combustion from the engine
- Exhaust gases are very toxic and hot
- Heat collected from the exhaust is employed for
- Cabin heating
- Carburetor anti-icing
- Windshield defrosting
Poor maintenance may lead to…
- Toxic gases getting into the cabin
- Poor engine performance
- Damage to parts/structures
- Nacelle fire
Carburetion
- Provides a combustible mixture of fuel and air necessary for the engine to operate
- Carburetor plays a part in
- Engine performance
- Engine mechanical life
- General efficiency of the aircraft
Gasoline
Gasoline does not burn in liquid state, but when mixed with oxygen it becomes flammable
Slide 8
picture of carburetor
Fuel pump
takes fuel from fuel tank and brings it to the carburetor
Fuel Strainer
strains fuel of any unwanted components
Float chamber
Holds liquid fuel
Fuel metering needle
Helps control amount of fuel in chamber
- Like a toilet
Main metering system
Controls the fuel feed in the upper half of the engine
3 Units:
- Main metering jet
- Main discharge nozzle
- Passage leading to idling system
3 functions:
- Proportion the A/F mixture
- Decreases the pressure at the discharge nozzle
- Control the airflow at full throttle
Idling System
- At idling, the airflow through the venturi is too low to draw
sufficient fuel from the discharge nozzle - In order to keep the engine operating at idle speed, an idling
system w/ an outlet at the throttle valve is added - Delivers fuel only when the throttle valve is nearly closed
- Needle valve type adjustment is provided to set idle fuel flow to
the correct air-fuel ratio
Carb Icing
If the up draft air is moisture laden, then it can freeze because as the air pressure decreases, the temp can decrease and create ice
Carb heat is not a preventative measure
If using carb heat the entire time, the engine will run worse
What are you doing when you move the throttle?
You control the amount of air that goes into the induction system
Acceleration System
- Airflow suddenly increases when the throttle is suddenly pushed
- Fuel flow does not accelerate proportional to the airflow increase
- Fuel lags behind and may cause the engine to run lean which
could cause it to stop working - The acceleration system discharges extra fuel into the carburetor
when the throttle is suddenly opened
How do you engage the acceleration system?
You engage the acceleration system by pushing the throttle fully forward
Economizer (AKA power enrichment system)
- A valve that is closed at the low engine and a cruising speed
Mixture Control System
- Prevents mixture from becoming too rich at high altitudes
- Economize on fuel during engine operation in the low power
range
Idle Cutoff
- Stops the flow of fuel from the discharge nozzle
- Used to stop the engine
- Engine ignition switch is turned off after the engine is first
stopped by means of moving the mixture control to the idle
cutoff position - Ensures all fuel in cylinders is used
Disadvantage of Float Carburetors
- The fuel flow disturbances in aircraft maneuvers may interfere
with the functions of the float mechanism
Fuel Injected Carburetor
- Discharges fuel into the airstream at or near the carburetor (throttle body)
Fuel Injection System
- Discharges fuel into the intake port of each cylinder
Advantages of Fuel Injection System
- Freedom from carb icing
- More uniform delivery of fuel-air mixture to each cylinder
- Improved control of fuel-air ration
- Instant accel. after idling
- Increased engine fuel efficiency and power
Carburetor vs Fuel Injected
Carburetor - fuel meets air in the throat/carburetor
Fuel Injected - fuel is mixed immediately before entering the cylinders or in the cylinder
Bendix (servo)
The heart of a fuel injection system
- Designed to meter fuel in direct ratio to the volume of air being
consumed
Carburetor vs Servo
- Carburetors is a mixing device
- A servo is a metering device
What are the air and fuel separated by in the servo?
2 diaphragms
Impact tubes
- Hangs out into the airstream
- It fills w/ air (looks like a straw) and pushes against the air diaphragm
Unmetered vs Metered
- Coming into the servo is unmetered fuel pressure
- Coming out of the servo is metered fuel pressure
Metered
fuel measured to correct ratio
Idle valve
- At idle, low airflow is not sufficient to accurately control the fuel
flow - Idle valve meters fuel accurately at idle speed
- Is externally adjusted
- Adjusts where ball-valve returns too
Manual Mixture Control
- Used by a pilot to reduce the metering size
- Can lean or enrich fuel
- Allows for shutting off fuel of fuel flow to the engine at the engine shutdown
Manual Mixture Control
- Used by pilot to reduce metering size
Flow dividers
- These are either a single-four way fitting or a tee that divides the flow into two paths
- 2 primary functions
- Ensures equal distribution of metered fuel to the nozzles
- Provide isolation of each nozzle for clean engine shutdown
Fuel Nozzles
- Nozzles are of air-bleed type
- Fuel is discharged inside the nozzle body into a chamber
Spark Plugs
- Produces a spark so that it can ignite the fuel air mixture
- Has three parts
- The electrodes
- Has a positive and negative so spark jumps between - Ceramic Insulator
- Inside to shield electrodes from outer shell - Outer shell
- How the spark plug connects to other things
- Prevents electrical interference
- The electrodes
Resistor-Type Spark Plugs
- Designed to reduce the burning and erosion of electrodes in engines having shielded harness
- Energy it can discharge is considerably greater than necessary to ignite fuel air mixture
- It can prolong a spark plug life
Massive Electrode Type
- Electrodes consist of a copper core
Unshielded spark plugs
Used in light aircrafts
Fine wire type
- similar construction to massive electrode type
- Electrodes are made of platinum and iridium
- Plat. and Irid. ensure max conductivity and min wear
4 ways to sort Spark Plugs
- Shielded vs Unshielded
- Resistor vs no resistor
- Fine wires vs massive
- Spark plug reach (distance from shell gasket seat to end of shell threads)
How many spark plugs do we have in a cylinder?
Two. One on bottom and one on top
Heat rating Range of spark plugs
26-50 - indicates coldest to hottest heat range
#76-99 - indicates special application aviation plugs
Gap and Electrode Style
E = two prong
N = four prong
P = Platinum fine wire
B = Two prong massive
R = Push wire
Magneto Ignition
- Superior to battery ignition
- Produces a hotter spark at high engine speeds
- Self-contained unit
- Not dependent on any external source of electrical energy
Magneto Classification
- Low tension magnetos
- High tension magnetos (most common)
- Rotating magnet magnetos (most common)
- Inductor rotor magnetos
- Single magnetos
- Double magnetos (usually bad bc there is only one shaft)
- Flange mounted magnetos
- Base mounted magnetos (majority of modern magnetos)
What happens when you turn magnetos off
It diverts the charge through a “p” wire which grounds out the charge
Higher the Octane…
The slower the fuel burns
What does lead do to the flame front?
It slows the flame front which increases octane
Fuel grades and their colors
- 80/87 = Red
- 100LL = Blue (Aviation)
- 100/130 = Green
- 115 = Purple
- Jet = Clear
- Unleaded = Clear
*** Purpose of a Fuel system
- Get clean, water-free fuel through the system
How much fuel must a fuel system supply to the engine?
For gravity fed fuel tanks (high wing aircraft), they must provide 150% of the fuel needed.
For pressure fuel tanks (low wing aircraft), they must supply 125% of required fuel.
Fuel system must also be able to shut off
Vapor Lock
- when an air bubble forms in the fuel line
- Could be ice as well
- To prevent vapor lock, make sure there aren’t any sharp bends in the
piping
Fuel bladders must be filled w/ fuel to prevent shriveling or shrinking
Methods for Producing Thrust
Aerodynamic action
- Utilizes propellers
- Lift produced along a horizontal plane
- Large mass of air through small change in velocity
Jet reaction
- Mass of air heated inside the engine
- Jot air is discharged at high velocities through a shaped nozzle
- Mass of air and amount of air accelerated determines thrust
- Small mass of air w/ large change in velocity
Brayton Cycle
- Same events, but different locations
- Intake, compression, combustion, exhaust
- Events all happen continuously but at different places
Similarities and differences between the Brayton and Otto cycle
Similarity - have the same cycles
Differences:
- Otto - all events happen in the same place and are one after another
- Entire cylinder is built for every stroke
- Brayton - events all happen in different places and are continuous
- Back is built for flame and front is not
Convergent Duct (subsonic airflow)
______
————–
————–
______
Velocity increases, pressure decreases, temp decreases
Divergent Duct (subsonic airflow)
_______
———-
———-
_______
Velocity decreases, pressure increases, temp increases
What does a compressor do
It increases air velocity not pressure
Divergent vs Convergent (supersonic airflow)
Essentially the roles switch
Convergent - velocity decreases, pressure and density increase
Divergent - velocity increases, pressure and density decrease
Combustion in turbine engines
- needs to happen at subsonic speeds
- air flows through a chocked nozzle to slow to subsonic speeds then combustion happens and it speeds up again and exits the system.
Type of turbine engines
Non-Air breathing engines (rockets)
- Carry all the needed oxygen within their fuel
- Generates heat by chemical reaction
Airbreathing reaction engines
- Turbojet
- Turboprop
- Turboshaft
- Turbofan
- Pulsejet
- Ramjet
Turbojet engines
- Takes air through air inlet
- Compresses air
- Mixed compressed air with fuel
- Air forced out through specially shaped nozzle
Has a cold and hot section
- Intake and compression happen in cold section
- Combustion and exhaust happen in hot section
All the air that is brought in is compressed and exhausted`
Turboprop
- Drives a propeller
- Two methods to drive a propeller
- Connecting prop to the compressor
- Connecting prop to a turbine separated from the core engine
Turboshaft
- Commonly used for helicopters
- More efficient at a constant rpm
- Most drives output shaft with multistage free turbine
- Reduction gearbox is remote from the engine
Turbofan (bypass)
- Increased propulsive efficiency
- Lower noise
- Lower fuel consumption
3 types:
- Low bypass = 2:1 air bypassed to air used
- High bypass = 4:1 air bypassed to air used
- Ultra high bypass = 30:1 air bypassed to air used
- More bypass air => quieter, more fuel efficient
- Fan can produce 30%-75% of the thrust
Unducted Fan (UHB)
- More similar to turboprop
- Drives multi-plane, contra-rotating, variable pitch propellers
Pulse Jet engines
Early air breathing reaction engines
Used in WWII for missles
Ramjet
- Simplest form of air breathing engines
- Requires near supersonic speed to operate
Thrust
- Change in momentum experienced by air flowing through the engine
- Momentum of the fluid
- The forces caused by the difference in pressure across the exhaust nozzle multiplied by the area of the nozzle
- Always measured in pounds
Two Types of Thrust
Net Thrust
- Thrust produced by the engine while in flight
Gross Thrust
- Thrust produced by the engine while static and not moving
Thrust Indication
Smaller Jet engines
- Compressor speed in % RPM
Larger Engines
- Engine Pressure Ratio (EPR)
- Ratio of the turbine discharge total pressure to the compressor inlet
total pressure
Ways to increase thrust
Afterburners
- Fuel is sprayed into hot exhaust gases which adds extra combustion
and produces more thrust
