AT 103 First Exam Flashcards
Failure of early aircraft was primarily due to a:
lack of power source that could sustain flight
Failed engines had these characteristics:
poor efficiency, lack of dependability, high cost, excessive weight, low power produced
Challenges to aviation include wanting engines with:
high power-to-weight ratios, efficiency, reliability, and environmentally friendly aspects
Who built the first flight simulator
Edwin Link
In 1860 the first practical gas engine was built by _____ and these 400 engines powered _______
Jean Lenoir (France), lathes and printing presses
!! First four stroke engine was built in 1876 by ___ !!
August Otto and Eugen Langen
First gasoline engine was built in 1885 by ____ and operated on the four stroke principle
Gottlieb Daimler (similar one by Karl Benz)
First successful aircraft engine was built in 1903 by _____ and was ____ cooled with ____ cylinders
Charles Taylor, water (cooled), four (cylinders)
First flight of jet engine power on an aircraft was in _____ and an example is ______
1939, Heinkel HeS 3B or Heinkel He 178
First turbojet was built by _____ and was manufactured by _____
Sir Frank Whittle (W1 Engine), General Electric Company
Some challenges of gas-turbine engines include:
performance, sound levels, fuel efficiency, maintenance ease, dependability, and reliability
What engine is this: crankshaft is held stationary while cylinders rotate around with the prop
rotary type radial
Disadvantages of the rotary type radial include
torque and gyro effect making the aircraft difficult to control and the usage of castor oil
What engine is this: cylinders are arranged in a row parallel to crankshaft. Cylinders are above or below the crankshaft.
In-line engine
Characteristics of in-line engines include:
usage in low and medium horsepower applications, small frontal area for low drag and streamlining, harder to cool the bigger they get
What engine is this: cylinders are in two rows forming the letter V
V-type
Pros of radial engines
lowest weight to horsepower ratio of all reciprocating engines
Cons of radial engines
large frontal area, cooling problems, hard to see over
Multiple-Row Radial Engine facts:
largest and most powerful reciprocating engine, can produce 3,500 hp or 4,300 hp with two turbo and one super charger
what was the multiple row radial engine replaced by and why
gas-turbine engines, more lightweight and powerful, fewer moving parts, and TBO increased
Opposed and flat type engine characteristics:
100-400hp, cylinders and crankshaft horizontal, low weight to hp ratio, streamlined flat shape, reasonably free from vibration
Engine designation: L
left hand rotation
Engine designation: T
turbocharged
Engine designation: i
fuel injected (remember lack of I normally means carborated)
Engine designation: G
geared
Engine designation: S
supercharged
Engine designation: O
opposed cylinders
Engine designation: R
radial engine
Engine designation: ###s
volume displaced to nearest 5 in^3
Why is excessive heat bad for reciprocating engines
adversely affects behavior of combustion of air fuel charge, weakens/shortens life of engine parts, impairs lubrication
Air cooling advantages
weighs less (no radiator, no connecting hoses/lines, no coolant liquid), less affected by cold weather, less vulnerable to gunfire
air cooling disadvantages
requires forward movement for ram air to sufficiently cool engine
How does liquid cooling work?
coolant circulates through engine areas requiring heat removal and transfers heat to liquid
liquid goes to radiator and cools
coolant circulates back through engine
relief valve prevents excessive pressure
What is the common liquid for coolant
ethylene glycol mixed with water
crankcase characteristics
foundation of engine
must support self
enclosure for lubricating oil
mounting to aircraft and mounting to cylinders
needs strength and rigidity
What type of crankcase? Two matching, reinforced aluminum-alloy castings divided vertically at centerline and fastened with studs and nuts
opposed-engine
What type of crankcase? Multiple sections (3-7): front, main power, fuel induction and distribution, accessory
radial engine
What type of crankcase? Four main sections: front, power, fuel induction and distribution, accessory. Sections may be cast together
In-Line and V Type Engines
Purpose of aircraft bearings
produces minimum friction, max wear resistance
Good bearing characteristics:
material strong enough to withstand pressure, permit movement with minimum wear and friction, be held with very tight tolerances, quiet and efficient operation while not sacrificing freedom of motion
Name the bearing: low power engines, radial loads, can be used for thrust when flanges added
Used for: connecting rods, crankshaft, camshaft
Made of: silver, lead, bronze
Plain bearing
Name the bearing: high power application, tapered rollers can withstand radial and thrust loads
roller bearing
What does the crankshaft do?
transforms reciprocating motion of piston to rotary motion and turns propellor
What does the main journal do?
serves to keep crankshaft alignment
what does the crankpin do
when forced applied to pin other than direction parallel to crankshaft, it will rotate the crankshaft
why are crankpins usually hollow?
reduces weight
passage for oil
collects carbon deposits, sludge, other stuff
Crank Cheek / Arm characteristics
oil passages drilled through
connects crank pin to main journal
has counterweights for static balance
What do dynamic dampers do
relieve whip and vibration
overcome forces generated by power impulses causing deflection of crankshaft
Name the shaft: end has milled slot for key
treaded forward end of shaft receices propeller retaining nut
caused propellors to spin off
used on small motors now
tapered shaft
Name the shaft: high power uses
rectangular groves on shaft and in engine
one grove blocked by screw to ensure position
spline
Name the shaft: bolts need to be tightened in sequence
has short stub forward of it that secures prop
much flatter than other types
what the pipers have
flange
connecting rod characteristics
steel alloy or aluminum for low power
H or I cross sectional
end of connecting rod connecting to crankshaft:
large end (crankpin end)
end of connecting rod connecting to piston pin
small end (piston-pin end)
At each stroke connecting rods will:
stop, change direction, start
Name the connecting rod:
common in lin line and opposed engines
small end is bronze serving as bearing
large end has cap with two piece bearing
plain rod
name the connecting rod: used for V type
split on large end
other rod fits between split on large end
fork and blade rod
name the rod: used in radial engines
subject to a lot of stresses
design to highest quality
alloy-steel forging and heat treated
master and articulated rod
what does the master rod do
provides attachment points for articulated rods on large end
Articulated rods:
attached to paster by steel knuckle pins
lock plate on each side to prevent lateral movement
!! What does the connecting rod do? !!
Connects piston to crank shaft
How does the master and articulated rod work?
piston to articulated rod, articulated rod to master rod, master rod to crankshaft
!! What is the purpose of the piston rings? !!
create seal against cylinder wall
(think of syringe stopper)
Why is the process with piston rings so precise
there needs to be a gap clearance for heat expansion
excessive clearance allows rings to cock in grooves
what happens if a piston ring cocks in the groove
leads to considerable wear and possible failure
why are piston ring joints staggered?
prevents flow of gasses from combustion chamber into crank case
what do piston rings do
seal to hold pressures in combustion chamber
prevents excessive oil from entering combustion chamber
conducts heat from piston to cylinder walls
What happens when a piston ring is worn or defective
loss of compression
excessive oil consumption
excessive oil discharge from crankcase breather
excessive blue smoke from exhaust
What do piston pins do
attatch piston to connecting rod
Why are piston pin retainers made out of soft material
allows contact to cylinder without damage
prevents pin from slamming into sidewall
unaligned engine will shave off pieces
What is blowby?
flow of gases from combustion chamber into crankcase (This is bad!)
What does the oil ring do and where is it located
controls thickness of oil film on cylinder walls
prevents oil from passing into combustion chamber
located below the compression rings
Cylinder Assembly Requirements
strength to withstand internal pressures
light weight
heat conducting properties
how should cylinder assemblies be designed
for inexpensive manufacturing, inspecting, and maintenance
Why are cylinder barrel surfaces carefully controlled
too smooth: will not be able to hold oil
too rough: causes excessive wear to piston rings and cylinder wall
What does it mean if a cylinder barrel is chokebored
bore nearest the head is smaller for heat expansion
not a perfect cylinder shape until heated
!! Does the intake or exhaust valve have cooling fins and why? !!
Exhaust valve: air is significantly hotter exiting than entering
How does the shrink fit method work for joining the cylinder head to barrel
barrel goes into liquid nitrogen while the head is heated. They are then put together and essentially welded through that heat differential
What is a valve
any device that opens and closes ports
“any device for regulating the direction of flow of liquid or gas by opening and closing a passage”
what does the exhaust valve do
allows burned gasses to expel from cylinder
what does the intake valve do
allows fuel-air charge to enter cylinder
!! Exhaust valves are hollow and filled with _____ and why !!
sodium metal, it turns into liquid at high temperatures which helps dissipate heat through the valve stem
Why are there different shapes of valves
to account for different demands of combustion chambers
two key factors of the valve tip:
groove machined to receive split-ring stem keys
designed to prevent valves from falling into combustion chambers if tips fail
Intake valve low vs high power:
heads are flat for low power
tulip design for high power
Important characteristic of valve guides:
fine tune measured to the valve it is supporting
Important traits of the valve seat:
separate piece put into cylinder head that is very strong and designed to not wear out
hardened and reinforced to create metal-metal seal
what does the valve spring do
closes valves
(valves are in a default closed position)
What does the valve operating mechanism do:
controls timing of engine valves
(open at correct time, remain open for correct time, close at correct time)
what does the Cam do
it is the actuated valve lifting mechanism
what does the valve lifter do
transmits force of cam to pushrod
What is the pushrod
rod/tube between valve lifter and rocker arm
(transmits valve lifter motion)
How does the rocker arm work
One end presses on stem of valve while the other end receives motion from pushrod
Camshaft turns at the same speed as the:
crankshaft
Connected at rear of crankshaft
Order of cylinder assembly
cam -> valvelifter -> pushrod ->rockerarm-> stem valve
What is energy?
The capacity for doing work
What is Boyle’s law?
V1P1 = V2P2 or V1/V2 = P2/P1
What is Charle’s Law?
V1/T1 = V2/T2
What are the four strokes of an engine?
Suck, squeeze, bang, blow
or
intake, compression, power, exhaust
! What are the steps (events) of a four stroke engine !
Intake
compression
ignition
combustion
exhaust
What is a stroke?
Distance the piston travels
What is the top dead center TDC?
top limit of a stroke
what is the BDC?
bottom dead center
Why are the top and bottom limits important?
set timing and valve overlap of engine
What is the compression ratio
ratio of volume of space in cylinder when piston is at BDC to the volume when piston is at TDC
What is typically the max compression ratio for aviation?
9:1
What happens in the intake step?
air fuel mixture is drawn into cylinder
What happens in the compression step
air fuel mixture is compressed and ignition happens just before TDC
What happens in the power stroke?
heat and pressure from ignited air fuel mixture force piston down
! What keeps the engine running? !
one cylinder is constantly in the power stroke
What happens in the exhaust stroke
gasses in cylinder are forced out as piston moves back up
Why is there valve overlap?
takes advantage of the inertia of gas and provides optimization and efficiency
What determines valve overlap?
position of cam lobes on camshaft
Cons of two stroke engine
less efficient (loss when air fuel mixture mixes with exhaust)
loss of air fuel mixture through exhaust
more difficult to lubricate (also oil doesn’t burn)
harder to cool engine
How does two stroke work?
air is drawn into crankcase (below piston) while piston is compressed and igniting air
burnt fuel forces piston down, exposing exhaust valve and letting intake air back in
Rotary stroke engine characteristics
internal seal problems
use in lower hp
!! intake and exhaust ports eliminate need for valves !!
!! has two individually firing spark plugs !!
Pros of Diesel engine
high compression ratio
no electric ignition
fuel and oils are heavier and cheaper than gasoline
no need for spark
How is fuel intake in diesel different from others
fuel is injected separate from air
- Where are the engine operator manuals for the archers?
in mike davis’s office across from maintenance binders
- how do you know engine firing order
stamped onto crankcase
What is power and what does it depend on
rate of doing work; force, distance, time
Greater piston displacement = greater or less horsepower
greater
HP rating on aircraft is indicated horsepower or brake horsepower
brake horsepower
What is indicated horsepower
the hp developed by engine
(total hp converted from heat energy to mechanical)
What is brake horsepower
actual horsepower delivered by engine to propeller
How is takeoff power rating determined
max rpm and manifold pressure that engine can be operated during takeoff
- what is the take off power limitation on an archer
2700 rpm (can’t find time limit if anyone finds that let me know)
What is critical altitude
highest altitude at which an engine will maintain a given hp output
! When do the spark plugs fire !
just before TCD to lead to an even burn of fuel mixture
What is pre-ignition !!
hot spot in engine ignites air fuel mixture before spark plug fires
What is detonation? !!
poor fuel air mixture detonating (but at the correct time)
What can affect brake horsepower?
manifold pressure
detonation
preignition
compression ratio
fuel-air ratio
two primary purposes of oil
lubrication
cooling
Why aren’t animal oils used in aviation
fatty acids get produced at high temperatures
Why aren’t vegetable oils used in aviation (nowadays)
wears away at steel
What oil is mainly used in aviation
Fluid mineral oil
What oil is used for gas-turbine engines
synthetic
What disease could synthetic oil cause
parkinson’s
What are some important oil properties
viscosity
flashpoint
chemical stability
gravity
color
carbon residue
oxidation
corrosion
neutralization
What is viscosity in relation to oil
fluid friction in oil
resistance an oil has to flowing
heavy oil = high viscosity = slow flowing
Oil for aircraft must have good chemical and physical stability. What factors do these include?
oxidation resistance
no thermal cracking
protection against coking (prevention against carbon deposits)
good under temperature and pressure
What is sliding friction
one surface sliding over another (straight up and down)
Explain rolling friction and how does it compare to sliding friction
cylinder or sphere rolls over surface of plane object
total rolling friction is lower than sliding
Where is wiping friction found
gear teeth
continuously changes load and direction
what are the characteristics of aircraft oil
Viscosity
High antifriction
Maximum fluidity at low temperatures
Minimum change in viscosity with temperature
High anti-wear
Max cooling ability
Max oxidation resistance
Noncorrosive
What are the functions of engine oil
Reduces friction between moving parts
cools by carrying away heat
seals chamber by filling gap between cylinder walls and piston ring
cleans engine
prevents corrosion
makes cushion between parts that see impact loads
!! Purpose of lubrication system is to supply oil at !!
correct pressure
correct volume
correct location
(correct time)
Key points of oil plumbing:
Should be fire resistant
No vibration = aluminum alloy
vibration = synthetic
What does the oil pressure relief valve do
controls and limits lubricating oil pressure
prevents damage to system
What are some oil properties
flash point
viscosity
pour point
chemical stability
physical stability
gravity
color
cloud point
carbon residue
ash residue
oxidation
precipitation
corrosion
neutralization
oiliness
When oil is in proper limits:
minimum coefficient of friciton
max adhesion to surface
good oiliness
adequate fill strength
Fuel flow type filter
filters all circulated oil of contaminants
all oil goes through before passing to surfaces
why is oil inspection beneficial
oil filter:
discovers internal engine damage
filter screen and housing examined for metal particles
Analysis:
determines origin of particles
predict future failures
oil pumps:
excess oil returned by relief valve to oil inlet
accommodates engine wear and growing clearances
What is a thrust bearing
bearings that in addition to reducing friction, take thrust and radial loads
