Lectures 12-16 Flashcards
What are the four principal parts of the induction system?
Air scoop
Air filter
Alternate air valve
Carburetor air heater
What is the air scoop?
Opening on the front of the aircraft that faces into the airstream
Receives ram air
What do air filters do?
Where are they located?
Blocks dirt, abrasive particles, sand, and larger foreign materials
Reduces air pressure to the carburetor
Installed at or near the air scoop
What are wetted type mesh filters? How do they catch particles?
Mat or metal filaments encased in a frame and dipped into oil
Oil film catches and holds dust and sand particles
How do dry paper filters catch particles?
Air passes through pleated paper element
Replaced on a time-in-service basis
What are polyurethane foam filters?
Polyurethane foam and a wetting agent
Newer type of air filter
What is the purpose of the alternate air valve?
Allow air to flow to the engine if the air filter is clogged
Serve as carburetor heat
How is the alternate air valve controlled?
From the cockpit or automatic
When is the alternate air valve used?
While flying through heavy rain and weather
When the air filter is clogged
How is the carburetor heat valve controlled?
Carburetor heat control in the cockpit
When should the carburetor heat valve not be used?
During high-power operation
What does the carburetor heat valve do?
Close the main air duct and open the duct to the heater muff
What is the heater muff?
A pipe around a section of the exhaust
It allows air to flow around the exhaust pipe and heat the air
(exhaust pipe is hot so it heats the air)
What are intake manifolds?
Individual pipes that lead the air fuel mixture to each cylinder
Why would the intake manifolds travel through the oil sump?
Slight cooling of the oil
Slight heating of the air fuel mixture to aid in vaporization of the fuel
What causes induction system icing?
Depends on atmospheric temperature, humidity, and operating conditions of the engine
Flying through:
Clouds
Fog
Rain
Sleet
Snow
High moisture clear air
What is induction system icing?
Ice cuts off air fuel charge or varies the fuel ratio
Where can induction system icing happen?
Anywhere from the air scoop to the intake port of the cylinder
How can you detect induction system icing?
Reducing the engine power while maintaining the same throttle position
Aircraft operating in icing conditions should be equipped with a _____ gage which reads temperature of the air
as it enters the _____.
carburetor air temperature (CAT)
carburetor
If carburetor air temperature (CAT) is below _____ and experiencing engine loss of power, it is assumed that _____ exists. _____ should be applied
32°F
icing
Carburetor heat
What do exhaust systems do?
Remove the toxic and hot exhaust gases of combustion from the engine safely and effectively
What can poor maintenance of the exhaust system cause?
Nacelle fire
Toxic gases entering the cockpit and cabin
Damage to parts and structure in nacelle
Poor engine performance
List some characteristics of early exhaust systems
Short steel stacks were attached to the exhaust ports
Noisy
Permitted exhaust gases to flow into open cockpits
How did pilots troubleshoot engines with early exhaust systems?
Looking at the exhaust flame color in the steel stacks at night
As exhaust systems developed, what was heat collected for?
Cabin heating
Carburetor anti-icing
Windshield defrosting
What do modern aircraft exhaust systems include?
Exhaust Manifolds
Heat Exchangers
Mufflers
Turbochargers
Augmenters
What types of alloys are used for manufacturing modern exhaust systems?
Heat and corrosion resistant alloys
What characteristics must gasoline possess to make it suitable for aviation fuel?
High heat value (high energy)
Ability to evaporate when exposed to air
Ability to evaporate at ordinary temperatures
High volatility (evaporate quickly)
What can happen with fuel that is too volatile?
Too high volatility will form bubbles in the fuel lines causing “vapor locks”
Fuel must not be too volatile because it forms excessive vapors in the system
In leaded gas, _____ remains as a residue in the cylinders. This residue can be prevented by adding a _____ compound to the lead forming _____.
lead oxide
bromine
lead bromide
_____ is now added to leaded fuel to further reduce deposits in the cylinders which converts lead into _____.
Tricresyl Phosphate (TCP)
lead phosphate
What are the two main types of leaded AVGAS and what color designates each type? Which type is most commonly used?
100 - green
100LL (low lead) - blue
Grade 80 & 87 is red
Most commonly used is 100LL
What type of AVGAS did Professor Z help develop?
UL94 (unleaded)
Sold at over 200 airports
Why is AVGAS dyed?
Indicate presence of lead
Easy identification
What color of shirt is associated with the fuel handler?
Why?
What is the nickname for them?
Purple
Fuel being used was purple (AVGAS 115), purple shirts hid splashes
Grapes
List some negatives of lead
No known safe levels of human lead exposure
Harmful to developmental growth in children
Does not decay
How can lead exposure occur?
Airborne lead emissions impacting neighboring communities
Past emissions deposited to soil and other surfaces
Occupational lead exposures for airport workers, including inhalation, ingestion, and dermal absorption
Why are leaded AVGAS emissions worse than automotive emissions?
AVGAS have a smaller particle size
Lead gets into the lungs easier
What location in the US has the worst amount of lead deposits? Who comes in second?
Daytona beach due to the Daytona 500 and airports
Purdue
If leaded fuel is bad, why do we still use it?
Aircraft engines are designed to operate with specific fuel octane ratings or performance numbers
The _____ octane rating or performance number is more critical than the _____.
minimum
maximum
Too high or too low of an _____ may cause engine damage or failure.
octane rating
Using fuel with _____ of an octane rating leads to detonation and can damage pistons and cylinders.
Using fuel with _____ of an octane rating leads to slower burning and can cause engine power loss.
too low
too high
Gasoline specifications change _____ and _____. The auto gas you buy during the _____ months most likely _____ meet auto gas STC regulations.
geographically
with the seasons
winter
does not
Why is auto gas not acceptable or safe for aircraft applications?
Acceptable high vapor pressures in automobiles are not safe for aircraft applications
Regular auto gas is not designed for safety of flight
What are some impurities that aviation fuel must be free of?
Water
Dirt
Microorganisms
Acid
Alkali
Sulfur
Gum Contents
Why is sulfur bad in aviation fuel?
It is corrosive on many metals
What can having gum contents in aviation fuel cause?
Valves to stick
Clog fuel metering jets
Cause restrictions within the fuel system
Why is water in an aircraft fuel system a serious problem?
Small amounts don’t have much effect on performance
Large amounts will stop the flow of fuel and cause engine failure
At high altitude, fuel cools below freezing point, the water then forms ice crystals
Ice crystals block off the fuel system and shut off the flow of fuel
What are the two principal sections of a fuel system?
Aircraft fuel system
Engine fuel system
List some parts of the aircraft fuel system
Tanks
Electric boost pump
Tank strainer
Fuel control or selector valves
Fuel flow and pressure gages
Fuel drain valves
What does the engine fuel system include and where does it begin?
Fuel control units in the carburetor or fuel metering device
Begins from engine driven pump
List some requirements of fuel systems
Capable of delivering continuous flow of clean fuel under positive pressure from fuel tank to the engine
Under all conditions of engine power, altitude, attitude, and approved flight maneuvers
Boost pump available for starting, takeoff, landing, and high altitudes
Fuel Systems must provide valves to shut off fuel. Valve must be accessible to the pilot
Fuel lines should:
Be sufficient to carry maximum required fuel flow under all conditions
Have no sharp bends or rapid rises, and be kept away from hot parts of the engine
Fuel tanks should:
Have drains and sumps to remove water and dirt from the bottom of the tank
Withstand all loads they may be subjected to during operation
Provide baffles if a shift in fuel position will cause a change in aircraft balance
_____ must be sufficient to substitute engine driven pump when it fails
Boost pump
_____ aircraft engines are supplied from its own tank, lines, and fuel pump. In an emergency, it can _____ fuel from tank to tank or it can run _____ from one tank.
Multiengine
transfer
two engines
Gravity fed systems
Fuel is delivered to the engine solely by gravity
Must have tanks placed high enough from the carburetor to provide 150% of required fuel flow pressure (takeoff)
Supply fuel to one engine from one tank or multiple smaller interconnected tanks to ensure equal fuel feed
No boost pump because fuel is always under positive pressure to carburetor
Fuel quantity gage shows pilot the quantity of fuel in the tanks at all times
Pressure systems
Must be capable of 125% of the actual takeoff fuel flow of the engine
When fuel tanks cannot be placed the required distance above the carburetors or a greater pressure is required for operation
Fuel boost pumps and engine driven fuel pumps are used
Fuel boost pumps are located at the bottom of the fuel tank and are usually submerged in the fuel
Engine driven fuel pump is in series with the boost pump
List some differences between gravity fed and pressure systems
Gravity fed systems have the option to take fuel from both tanks while pressure systems need tanks to be switched manually every 30 minutes
Pressure systems have a boost pump while gravity fed systems do not
Gravity fed systems must provide 150% of required fuel flow pressure while pressure systems must be capable of 125% of the actual takeoff fuel flow of the engine
What do strainers and filters do?
Remove dirt particles from the fuel
Where are main strainers located?
The lowest point in the fuel system
Why is there an air gap in the spark plug?
Allows the high voltage of the ignition system to produce a spark
How is heat energy produced using a spark plug and magneto?
Electric energy of the high-voltage current produced by the magneto converts to heat energy
Why do we need heat energy?
It is required to ignite the air fuel mixture in the cylinders
What are the three major parts of a spark plug?
Electrodes
Ceramic insulator
Metal shell
Describe resistor-type spark plugs
Designed to reduce the burning and erosion of electrodes in engines having shielded harness
The energy it can discharge is considerably greater than necessary to ignite the air fuel mixture
It can be reduced by means of a resistor to prolong spark plug life
Describe massive electrode type spark plugs
Named because of the size of the center and ground electrodes
Electrodes consist of a copper core
Two prong “E” ground electrodes
Describe fine wire type spark plugs
Similar construction to the massive electrode type
Electrodes are made of platinum and iridium to ensure maximum conductivity and minimum wear
What is spark plug reach?
The linear distance from the shell gasket seat to the end of the shell threads
What determines the reach of the spark plug?
The cylinder-head design
Why must electrodes be positioned at a satisfactory reach?
For proper ignition in the combustion chamber
What are the two classifications of spark plug shell threads?
Long reach
Short reach
What is the heat range of spark plugs?
The ability of the spark plugs to transfer heat from the firing end of the spark plug to the cylinder head
If an engine typically runs _____, a relatively _____ spark plug is required.
If an engine typically runs _____, a relatively _____ spark plug is required.
hot
cold
cold
hot
If a hot spark plug is installed in a _____ engine, spark plug tip will _____ and cause _____.
If a cold spark plug is installed in a _____ engine, spark plug tip will collect _____.
hot
overheat
pre-ignition
cold
unburned carbon
What must you do if you drop a spark plug?
Throw it away, the ceramic insulator is most likely broken
Why is magneto ignition a better choice than battery ignition?
Superior to battery ignition
Produces a hotter spark at high engine speeds
Self contained unit
Not dependent on any eternal source of electric energy
What is the most common magneto classification?
High tension magnetos
Rotating magnet magnetos
Single magnetos
Base mounted magnetos
Describe low tension magnetos
Delivers current at a low voltage
By rotation of an armature wound with only one coil in the field of a permanent magnet
Its low voltage must be transformed to a high voltage by a transformer at or near the spark plug
Describe high tension magnetos
Delivers high voltage to the spark plug
Has both a primary winding and a secondary winding
The low voltage generated in the primary winding induces a high voltage current in the secondary winding when the primary circuit is broken
How are single type magnetos used for a reciprocating engine?
Two single type magnetos are usually used on reciprocating engines
Describe dual type magnetos
Essentially two magnetos having one rotating magnet and driveshaft common to both
Contains two sets of breaker points
Describe flange mounted magnetos
Attached to the engine by means of a flange on the end of the magneto
Mounting holes are not circular but slots that permit slight adjustment
Describe base mounted magnetos
Attached to the engine by means of brackets securing the base
Studs pass through holes in the brackets and are secured by tapped holes in the engine
How often are magnetos inspected?
Inspected after every 100 hours of operation or during the annual inspection
In depth inspection required after 500 hours
What should a carburetor do concerning the air fuel mixture?
Provide combustible mixture of air and fuel necessary for the engine to operate
Deliver an accurately metered air fuel mixture
Provide for automatic or manual mixture correction under changing conditions
How should a carburetor be constructed?
Sturdy to provide durability and resistance to the effects of vibration
Carburetors play an extremely important part in:
Engine performance
Engine mechanical life
General efficiency of the aircraft
Why must fuel be fixed with air instead of just using fuel?
Liquid fuels will not burn in the liquid state
They must be vaporized and combined with the correct amounts of oxygen to form a combustible mixture
What happens when there is just enough, too little, or too much oxygen in the fuel air mixture?
Just enough oxygen: the fuel will burn completely
Not quite enough oxygen: combustion will occur but will not be complete
Too much oxygen: the mixture will not burn
List the essential parts of a float type carburetor
Float mechanism
Float chamber
Strainer
Main metering system
Idling system
Economizer system
Accelerating system
Mixture control system
What does the float mechanism do?
Control the level of fuel in the float chamber
How does the float mechanism control the fuel level?
The float is attached to a lever which pivots to engage the float needle valve
When float rises, the needle valve closes and stops the flow of fuel into the chamber
Fuel level must be maintained slightly below the discharge nozzle outlet holes to:
Provide the correct amount of fuel flow
Prevent leakage of fuel from the nozzle when engine is not running
What is the fuel strainer?
Filters fuel before it enters the carburetor
A fine wire mesh that will intercept any dirt particles that can clog the needle valve or metering jets
What does the main metering system control?
The fuel feed in the upper half of the engine speed range
Cruising and full throttle operations
What three units make up the main metering system?
Main metering jet
Main discharge nozzle
Passage leading to the idling system
What are the three functions of the main metering system?
Proportion the A/F mixture
Decrease the pressure at the discharge nozzle
Control the airflow at full throttle
Explain the idling system
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 with an outlet at the throttle valve is added
Delivers fuel only when throttle valve is nearly closed
Needle valve type adjustment is provided to set idle fuel flow to the correct air fuel ratio
When is the accelerating system used?
When throttle of the engine is suddenly opened
Explain what happens when the accelerating system is used
An additional quantity of fuel discharges into the carburetor airstream when throttle is opened suddenly
Causes a temporary enrichment of the mixture and provides a smooth acceleration of the engine
What can happen when the throttle is opened too quick?
Airflow suddenly increases
Fuel flow does not accelerate in proportion to the airflow increase
Fuel lags behind, causing a temporary lean mixture and may cause the engine to miss or backfire
Why are carburetors equipped with an accelerating system?
To prevent too lean of a mixture from entering the engine
What does the accelerating system look like in the carburetor?
How does the throttle affect this system?
A sleeve-type piston pump
Operated by the throttle
When the throttle is closed, the pump cylinder fills with fuel
If the throttle is opened quickly, the piston is forced down pushing fuel to flow through into the main fuel passage
If the throttle is opened slowly, fuel pressure is not enough to overcome the spring that holds the valve closed
What is the economizer system?
A valve that is closed at low engine and cruising speeds
Opens at high speeds to provide an enriched mixture to reduce burning temperatures an prevent detonation
The system supplies and regulates additional fuel required for all speeds above the cruising range
What are the functions of the mixture control system?
Prevent mixture from becoming too rich at high altitudes
Economize on fuel during engine operation in the low power range
What is 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 mixture control to idle cutoff position
Helps ensure all the fuel within the cylinders are used
What are disadvantages of float type carburetors?
The fuel flow disturbances in aircraft maneuvers may interfere with the functions of the float mechanism
Results in erratic fuel delivery and sometimes causing engine failure
During icing conditions, the discharge of fuel into the airstream ahead of the throttle causes a drop of temperature and results in ice forming at the throttle valve (carb ice)
