Lectures 2-11 Flashcards
Failure of early aircraft was primarily due to
Lack of power source that could sustain flight
What were some causes of failed engines?
Poor efficiency
Lack of dependability
High cost
Excessive weight
Low power produced
What did we want to design engines with?
High power-to-weight ratio
Efficient
Reliable
Environmentally friendly
Who built the first flight simulator?
Edwin Link
In 1860 the first practical gas engine was built by _____ and were built to operate _____.
Jean Lenoir of France
Lathes and printing presses
The first four stroke concept was built in 1876 by _____ and _____.
August Otto
Eugen Langen
The first gasoline engine was built in 1885 by _____ and operated with the _____. A similar engine was built by _____ in the same year.
Gottlieb Daimler
four stroke principle
Karl Benz of Germany
The first successful aircraft engine was built in 1903 by _____ and was _____ cooled, had _____ cylinders, produced _____ hp, and weighed _____.
Charles Taylor
water
4
12
180 lbs
The first flight of jet engine power aircraft was in _____ in _____. It was the _____ engine in the _____ aircraft.
1939
Germany
Heinkel HeS 3B Turbojet
Heinkel He 178
The first turbojet engine in England and the US was built by _____ and was manufactured by _____. The engine is known as the _____.
Sir Frank Whittle
General Electric Company
Whittle W1 Engine
What are some challenges of gas-turbine engines?
Performance
Sound levels
Fuel efficiency
Ease of maintenance
Dependability
Reliability
What are the cons of rotary type radial engines?
Torque and gyro effect make aircraft difficult to control
Castor oil was used as the engine lubricant, was nauseating to pilots
What is one advantage and one disadvantage of in-line engines?
Small frontal area allows streamlining and low drag nacelles
Harder to cool as they increase in size
What are the pro(s) and con(s) of radial engines?
Pro: lowest weight to horsepower ratio of all reciprocating engines
Cons: large frontal area creating drag, cooling problems
Describe an opposed engine
Most popular and most efficient for light aircraft
Cylinders and crankshaft horizontal
What are some pros of opposed engines?
Low weight-to-horsepower ratio
Easily streamlined
Reasonably free from vibration
Name cylinder (engine) arrangements
In-line
V Type
Double V or Fan Type
X Type
Opposed or Flat Type
Radial Single Row
Radial Double Row
Radial Multiple Row
Engine Designations:
L
T
I
G
S
O
R
V
470
L = Left-Hand Rotation
T = Turbocharged
I = Fuel Injected
G = Geared
S = Supercharged
O = Opposed Cylinders
R = Radial Engine
V = V-type engine
470 = Displacement to the nearest 5 in^3
Lack of “i” in engine designation means the engine is _____.
Carbureted
V and O together in engine designation means the engine is _____.
V-type
Why is excessive heat undesirable for reciprocating engines?
Negatively affects behavior of combustion of the air fuel charge
Weakens and shortens the life of engine parts
Impairs lubrication
What is air cooling?
Excessive heat generated by the engine is removed from the engine by the convection process
What help direct air flow around cylinders?
Baffles
What are the pro(s) for air cooling?
Weighs less (no radiator, no connecting hoses/lines, no coolant liquid)
Less affected by cold weather
Less vulnerable to gunfire
What are the con(s) for air cooling?
Requires forward movement for ram air to sufficiently cool engine
How does liquid cooling work?
Cooling liquid is circulated through the engine areas that require heat removal
Heat is transferred to the liquid
Heated liquid then passes through a heat exchanger (radiator) and cools down
The cooled liquid is then cycled back into the engine to repeat the cooling process
What is the most common liquid used for liquid cooling?
Ethylene glycol
Name some characteristics of the crankcase
The foundation of the engine
Must support itself
Contains bearings in which the crankshaft revolves
Enclosure for lubricating oil
Provides mounting to the aircraft
Provides mounting for cylinders
Needs Strength and rigidity to prevent misalignment
Describe an opposed-engine crankcase
Consists of two matching, reinforced aluminum-alloy castings
Castings are divided vertically at the centerline
Fastened together with studs and nuts
What are the sections of a crankcase
Consists of multiple sections (3-7)
The Front Section (Nose)
Main Power Section
Fuel Induction and Distribution Section
Accessory Section
What is the purpose of aircraft bearings?
Produce minimum friction and maximum wear resistance
What are some characteristics of good bearings?
Made of material strong enough to withstand pressure imposed on it
Permit the other surface to move with minimum wear and friction
Be held in position with very tight tolerances
Provide quiet and efficient operation while not sacrificing freedom of motion
What are thrust bearings?
In addition to reducing friction of moving parts they also take thrust loads and radial loads
What are plain bearings?
Used in low-power engines
Can be used as a thrust bearing when flanges added
Made out of softer metal
What are roller bearings?
Used in high-power applications
Tapered rollers can withstand both radial and thrust loads
Straight rollers are used for radial loads
What is the bearing race?
Channel where rollers travel
Rollers are situated between the inner and outer race
What are ball bearings?
Provides less friction than any other bearing types
Races have grooves in them to fit the curvature of the balls
Balls within the bearings are held in place by a ball retainer to maintain proper spacing between the balls
What does the crankshaft do?
Transform reciprocating motion of the piston to rotary
motion to turn the propeller
What is the crankshaft?
“Backbone” of an internal combustion engine
Subject to all the forces within the engine
May be one or more pieces
What are the parts of the crankshaft?
Prop shaft
Main Journal
Crankpin
Crank Cheek
Counterweights and Dampers
What does the main journal do?
Keep the crankshaft in alignment
Centerline in the crankshaft
What do crankpins do?
Crankpins are off center from the main journals
When a force is applied to the crankpin in any direction other than parallel, it will rotate the crankshaft
Why are crankpins hollow?
Reduces weight
Passage for lubricants
What does the crank cheek do?
Connects the crankpin to the main journal
Extends beyond the main journal to support counterweights
Oil passages are drilled through
What is the purpose of counterweights?
Provide static balance for the crankshaft
What is the purpose of dynamic dampers?
Relieve whip and vibration
Overcome forces generated by the pistons
Connecting rods connect the _____ (large end) to the _____ (small end)
Crankshaft/crankpin
Piston/piston pin
At each stroke connecting rods go through
Stop
Change of direction
Start
Describe a plain connecting rod
Small end has bronze bushing serving as bearing
Large end has end cap with a two piece bearing installed
The cap is secured on the end of the rod by bolts
Describe a fork and blade connecting rod
Used for V-type engines
Fork rod is split on the large end
Blade rod fits between the split large end of fork rod
Describe a master rod
Subject to a lot of stresses
Design and construction is to the highest quality
Provides attachment points for articulated rods
Describe an articulating rod
Attached to the master rod by steel knuckle pins
A lock plate on each side of the knuckle pin prevents its movement laterally
Why are piston rings split?
So they can be slipped over the outside of the piston into ring grooves
What is the purpose of gap clearance?
Allow for heat expansion during operation
What is blowby?
Flow of gases from the combustion chamber into the crankcase
What is blowby caused by?
Worn out piston rings or no staggering of the piston rings
How can blowby be detected?
Oil vapor, blue smoke, coming out of the exhaust
What is the function of a piston ring?
Provide seal against the cylinder wall to hold pressure in the combustion chamber
Prevent excessive oil from entering the combustion chamber
Conduct the heat from the piston to the cylinder walls
What happens when a piston ring is worn or defective?
Loss of compression
Excessive oil consumption
Excessively high oil discharge from the crankcase breather
Excessive blue smoke from exhaust during normal operation
What are the two types of piston rings?
Compression rings
Oil rings
What is the purpose of compression rings and where are they located?
Prevent gases from escaping past the piston during operation
Placed in the ring groove immediately below the piston head
Most engines have 2 or 3 per piston
What is the purpose of oil rings and where are they located?
Control the thickness of oil film on the cylinder walls
Prevent oil from passing into the combustion chamber
Placed in the ring groove immediately below the compression rings
Generally one per piston
What are the two types of oil rings?
Oil control rings
Oil wiper rings (Oil scraper rings)
What is the purpose of a piston pin?
To attach the piston to the connecting rod
What are the three types of piston pins?
Stationary
Semi-floating
Full-floating
How are stationary piston pins secured?
A set screw, not free to move in any direction
How are semi-floating piston pins secured?
A clamp screw
How are full-floating piston pins secured?
They aren’t secured, free to run or slide in the connecting rod and piston
What are piston pin retainers used for?
Inserted in the open ends of the piston pin
Soft material allows contact with cylinder walls without damage
Cylinder assembly requirements
Sufficient strength to withstand internal pressures
Light weight
Heat conducting properties for efficient cooling
Designed for inexpensive manufacturing, inspection, and maintenance
Why is surface roughness in the cylinder barrel controlled so much?
Too smooth – It will not hold sufficient oil for break-in period
Too rough – Excessive wear to piston rings and the cylinder wall
What is chokebored?
Bore nearest the head is made smaller to allow for heat expansion
At operating temperature, the bore will be straight
What does the cylinder head do?
Enclose the combustion chamber
Support rocker shafts
What does the cylinder head contain?
Intake valves
Exhaust valves
Valve guides
Valve seats
What is the shrink-fit method for joining the cylinder head to the barrel?
Barrel is dunked in liquid nitrogen
Cylinder head is heated up
Pieces are put together
Welded through heat differential
What is a valve?
Any device for regulating or determining the direction of flow of a liquid or gas by opening and closing a passage
Main purpose of valves is to open and close ports
Why are exhaust valves hollow?
To dissipate heat by filling them with metallic sodium
What is the purpose of a valve guide?
To support and guide the stems of the valves
What is the purpose of valve seats?
Create a metal on metal seal with the valve face, they are ground to the same angle as the face of the valve
What is the purpose of the valve spring?
Installed over the stem of each valve to close the valves
What are valve spring retainers?
“Seats” for the valve springs
What is the purpose of the valve operating mechanism?
To control the timing of the engine valves so that they open, stay open, and close at the correct time for the correct amount of time
What are the components of the valve mechanism
Cam
Valve lifter
Pushrod
Rocker arm
What does the cam do?
Actuates the valve lifting mechanism
What does the valve lifter do?
Transmits the force of the cam to the pushrod
What is the pushrod?
Rod between the valve lifter and the rocker arm that transmits the motion of the valve lifter
What does the rocker arm do?
One end presses on the stem of valve while the other end receives motion from pushrod
Heat engines utilize _____ to produce the power for _____.
heat energy
propulsion
What is energy?
The capacity for doing work
Energy cannot be _____ or _____
created
destroyed
Energy can be _____ from _____ to _____
transformed
one kind
another
What is kinetic energy?
Energy of motion
What is potential energy?
Energy of position or stored energy
What is Boyle’s Law?
Increasing the pressure on a volume of confined gas reduces its volume correspondingly (3 times more pressure decreases volume to 1/3)
What is Charles’ Law?
As the temperature of a gas increases, the volume remains the same
What is a cycle?
A complete sequence of events that return to the original state (the seasons)
What are the four strokes?
Suck, squeeze, bang, blow
Intake, compression, power, exhaust
What are the five events?
Intake, compression, ignition, combustion, exhaust
What is a stroke?
The distance the piston travels, TDC to BDC
What is TDC?
Top dead center
The top limit of the stroke
What is BDC?
Bottom dead center
The bottom limit of the stroke
Why is BDC and TDC important?
For setting timing and valve overlap of the engine
What is compression ratio?
The ratio of the volume of the space in the cylinder when the piston is at BDC to the volume when the piston is at TDC
When does ignition happen?
A few degrees before TDC
What keeps the engine running?
One cylinder is always in the power stroke, moving the crankshaft
What is valve overlap?
Intake valve opens before TDC
Exhaust valve closes after TDC
Why is there valve overlap?
Taking advantage of the inertia of outflowing exhaust gas to provide more complete scavenging and allow air fuel mixture to enter at the earliest possible moment
What determines valve overlap?
Position of cam lobes on the camshaft
Cons of two stroke engine
Less efficient
More difficult to lubricate
Harder to cool
Describe the process of a two stroke engine
Piston up: draws air fuel mixture into crankcase
Piston down: compresses mixture in crankcase, transfer port opens and compressed mixture enters the cylinder
Piston up: compresses mixture in combustion chamber, ignition of the mixture pushes the piston down, exhaust opens with transfer port
Who invented the rotary cycle engine and when?
Felix Wankel
1957
What is a disadvantage of rotary cycle engine?
Problems with internal seals
How many spark plugs are in a rotary cycle engine and how do they work?
Two individually firing spark plugs are used
One spark plug fires sooner (Leading and trailing spark plug)
How do “strokes” happen in a rotary cycle engine?
Intake, compression, power, and exhaust are completed three times per revolution
The rotor has three sides forming three combustion chambers
Each chamber is completing a different cycle simultaneously
What are some differences between two stroke and 4 stroke engines?
Half as many strokes
No valves, only ports
Moves down to compress
More robust
Oil is in the air fuel mixture
What are the pros of a diesel engine?
High compression ratio
No electric ignition
Fuel and oils are heavier and cheaper than gasoline
No need for spark
How is the intake of fuel air different in a diesel engine?
Fuel is injected under high pressure and atomized then injected into the cylinder while air comes in from the intake valve
What happens on the compression stroke of a diesel engine?
Air is compressed to an extent that the temperature is high enough to ignite the fuel without electric spark
What is the compression ratio for diesel engines?
As high as 14:1
What is the max compression ratio and most common ratio for gasoline engines?
11:1
7:1
Where can firing order of an engine be found?
Engine operators manual
Stamped into the crankcase
What is power and what does it depend on?
The rate of doing work
Force extended, distance the force moves, and time required to do the work
Who is James Watt?
Invented the term horsepower after finding that an English workhorse could work at the rate of 550 foot-pounds per second
What is piston displacement?
Multiplying the cylinder bore by the total distance that the piston moves during one stroke stated in cubic inches of volume
What is bore?
The diameter of the cylinder
What is total piston displacement?
The number of cylinders multiplied by the displacement of one piston
The _____ piston displacement, the ______ max _____ the engine can develop
Greater
Greater
Horsepower
What is a square engine?
Bore and stroke are the same distance (6in and 6in)
What is indicated horsepower?
Horsepower developed by the engine
What is brake horsepower?
Actual horsepower delivered to the propeller by the engine
85%-90% of indicated hp
What is friction horsepower?
The part of the total horsepower needed to overcome friction in the engine
How do you calculate brake horsepower?
bhp = ihp - fhp
How is takeoff power rating determined?
Max rpm and manifold pressure the engine can be operated at during takeoff, usually has a time limit
What is overspeed condition or Maximum Except Takeoff (METO) power?
About 10% over maximum allowance, the level above takeoff power, normally in twin engines
What is rated power or standard engine rating?
Max horsepower output for continuous operation
What is maximum power?
Greatest power output the engine can develop
What is critical altitude?
The highest altitude at which an engine will maintain a given horsepower output
What increases the critical altitude of engines?
Turbochargers or superchargers
What is Manifold Absolute Pressure (MAP)?
Absolute pressure of the air fuel mixture immediately before it enter the intake port
What are the risks of Manifold Absolute Pressure (MAP)?
Primary concern of high performance engines because they operate at close to max
Excessive or incorrect MAP leads to excessive cylinder pressure and temp
When operating under excessive cylinder pressure, components are overstressed
Excessive temp will cause detonation, pre-ignition, and loss of power
What is detonation?
When temperature and pressure of the compressed mixture reach levels to cause explosion instead of even burn
What is detonation caused by?
High inlet temperature
Insufficient octane rating
more octane=slow burn (prevent detonation)
less octane=fast burn (detonation)
Excessive engine load
Over advanced ignition timing
Excessive leaning of fuel-air mixture
Excessive compression ratio
What is preignition?
Hot spot in the engine ignites the air fuel mixture before the spark plug fires
What can cause preignition?
Hot spark plug electrodes
Carbon particles in the cylinder that reach burning temp
If compression ratio is higher than 10:1 then:
Pre-ignition or detonation may occur
Overheating
Loss of power
Cylinder pressure increases
What is maximum compression ratio limited by?
The type of fuel used
What factors affect performance?
Manifold Absolute Pressure
Detonation
Pre-ignition
Compression Ratio
Fuel-Air Ratio
What are the two base types of crude petroleum?
Naphthenic (found in Texas and California, 60mil years old)
Paraffinic (found in Pennsylvania region, 100mil years old)
What is lubricant?
Natural or artificial substance that have a greasy or oily property
Used to reduce friction between moving parts
List the pro(s) and con(s) of animal lubricants
Pro: highly stable at normal temperatures
Con: unsuitable for engines because fatty acids are produced at high temperatures
List the pro(s) and con(s) of vegetable lubricants
Pro: lower coefficient of friction than mineral oils
Cons: oxidizes when exposed to air, wears away steel rapidly
What did castor oil do to pilots?
Sprayed out of engine, causing use of goggles
Fumes caused nausea and diarrhea, causing use of scarf
List the pro(s) and con(s) of SOLID mineral lubricants
Pro: provide a slippery film that reduces friction
Con: does not dissipate heat enough for high-speed machines
List the pro(s) and con(s) of SEMI-SOLID mineral lubricants
Cons: extremely heavy, not suitable for circulating or continuous operating lubrication systems
List the pro(s) and con(s) of FLUID mineral lubricants
Pros: sprays easily, pumps easily, absorbs and dissipates heat quickly
What is the most common oil used in aviation?
Fluid mineral lubricants
List the pro(s) and con(s) of synthetic lubricants
Pro: tolerates high temps and does not evaporate or break down
Con: Fumes can cause harmful side effects such as Parkinson’s disease
List some important oil properties
Flash Point
Viscosity
Pour Point
Chemical Stability
Gravity
Color
Cloud Point
Carbon Residue
Ash Residue
Oxidation
Precipitation
Corrosion
Neutralization
Oiliness
What is gravity in relation to weight?
The weight of a measured volume of a product
What is viscosity?
Fluid friction of an oil
Resistance an oil offers to flowing
Oil must have chemical stability against
Oxidation
Thermal cracking
Coking (prevention against carbon deposits)
Oil must have physical stability against
Pressure
Temperature
What is sliding friction?
When one surface slides over another
No matter how smooth the surface is there is always sliding friction
What is rolling friction?
When a cylinder or sphere rolls over the surface of a plane object
Total friction by rolling contact is less than sliding contact
What is wiping friction?
Occurs between gear teeth
Continuously changes load and direction
Usually in extreme pressure
List some characteristics of aircraft oil
Viscosity
High antifriction characteristics
Maximum fluidity at low temperatures
Minimum changes in viscosity with changes in temperature
High anti-wear properties
Maximum cooling ability
Maximum resistance to oxidation
Noncorrosive
Name at least 3 functions of engine oil
Reduce friction between moving parts
Cools various parts of the engine
Seal combustion chamber by filling spaces between the cylinder walls and piston rings
Cleans the engine by carrying sludge and residue away from moving engine parts to oil filter
Prevent corrosion by protecting metal from corrosive agents
Serves as cushion between parts that sees impact loads
The purpose of a lubrication system is to supply oil at
Correct pressure
Correct volume
Correct location
(Correct time)
Why is oil capacity important?
The capacity must be sufficient to supply the engine
Fuel-Oil ratio should be around 30:1 by volume
Plumbing for oil systems must be _____. Protective _____ aids in protection in high temp areas.
fire-resistant
fire sleeve
What is the purpose of temperature regulation of oil?
Maintains a good temperature of the oil
Commonly includes oil coolers
How does a thermostat valve affect oil flow?
Oil flow through the oil cooler is controlled by a thermostat valve
Thermostat will open or close depending on oil temperature
What does the oil pressure relief valve do?
Control and limit the lubricating oil pressure
Prevent damage to the lubrication system
Ensure lubrication in case of a system failure
What are full-flow type engine oil filters?
Filters all circulated oil of contaminants before passing through bearing surfaces
If filter is clogged, a relief valve will open, allowing oil bypass
What are bypass type engine oil filters?
Filters about 10% of the oil through filtering element and returns oil to sump (where oil is contained, oil pan)
Oil passing through bearings are not filtered oil
What are strainer type engine oil filters?
A simple tubular screen
Designed to collapse when clogged or designed with relief valves that also open when clogged
What are spin-on type engine oil filters?
Newest style
Canister and filter element are one unit
Full-flow type
What are cuno type engine oil filters?
Series of laminated plates or disks
Contaminants are trapped on the outer diameter of the plates
The spacing of the plates determine the particle size that may pass through
What is oil inspection? Why is it important?
Excellent method for discovering internal engine damage
Filter screen and filter housing are examined for metal particles
If unusual metal particles or residues are found, engine should be taken out of service and inspected
What is oil analysis?
Determine the origin of the foreign particles discovered
Predict potential future failures
Oil samples are sent for analysis periodically or when metal particles are found in the filter elements
What does the oil pressure gage do?
Measures from no pressure up to above the maximum pressure
Where are oil temperature gages found?
The oil inlet line or on the oil filter housing
What are the two types of oil pressure pumps?
Gear Type
Vane Type
