WELCOME TO AT 262 !
BASIC AIRCRAFT POWERPLANT SCIENCE
Introduction:
Professor Michael Leasure
Handout Syllabus and review
Review class and lab schedule
Sign-in sheet explanation (Lab and Lecture)
Outline of lab project content
Lab tour
O-290 Lycoming
Lab#1 …………………………...…Engine Familiarization
Lab#2…………………...……Engine Parts Familiarization
Lab#3…………Horsepower Computations and Dyno Run
Lab#4………………………...Test Cell Dynamometer Run
Lab#5………………………………....100 Hour Inspection
Lab#6……………………………...….Ignition Lead Repair
Lab#7………………………………..…..Valve Adjustment
Lab#8……………………………….Troubleshooting Runs
Lab#9……………………………….…Turbocharging Run
262 Unit #1
Reciprocating Engine Description
• Intermittent combustion
• Piston travels up and down
in cylinder (reciprocates)
• Ignition of fuel/air is timed
to piston position
• Burning fuel/air increases
pressure in the cylinder and
drives the piston downward,
performing work
Reciprocating Engine Operating Principles
• Internal combustion
• The ignition of the fuel/air
occurs inside a cylinder or
combustion chamber
• An example of external
combustion would be a
steam engine
• All internal combustion
engines have the following
sequence of events in
common:
Reciprocating Engine Operating Principles
• Intake - fuel and air are
taken into the combustion
chamber
• Compression - fuel and air
are compressed
• Ignition - mixture is ignited
• Power - gases burn and
expand
• Exhaust - burnt gases are
expelled to clear
combustion chamber
Reciprocating Engine Operation
•
Otto Cycle, Single Cylinder, Animation
Two Stroke Reciprocating Engines
• All events must occur in one revolution of the
crankshaft (2 strokes)
• Most commonly used in ultralight, experimental,
and development aircraft engines
• The crankcase is used as a manifold for the fuel/air
mixture
• Intake and exhaust valves are not used. Ports in the
cylinder opening and closing perform the valve
function
• 2 strokes are less efficient and more difficult to
lubricate, however, they are simpler and often
lighter than 4 stroke engines
Two Stroke Reciprocating Engines
A. Crankcase intake/ Cylinder Compression
B. Ignition/ Power/ Crankcase pressure
C. Cylinder Intake/ Cylinder Exhaust
Two Stroke Reciprocating Engines
4 Stroke Reciprocating Engine
• Otto cycle is the term used to describe events
• Two revolutions of the crankshaft are required to
complete one cycle (4 strokes)
• Intake and exhaust valves are used to control the
fuel/air mixture
• Ignition is timed to piston position by number of
degrees before top center on the compression
stroke
• Valve overlap is defined as the number of degrees
that both valves open
4 Stroke Reciprocating Engine
INTAKE
COMPRESSION
POWER
EXHAUST
4 Stroke Reciprocating Engine
• Terms:
•
TDC - Top Dead Center (top of piston travel)
•
BDC - Bottom Dead Center
•
BTC - Before Top Center
•
ATC - After Top Center
•
BBC - Before Bottom Center
•
ABC - After Bottom Center
•
IO - Intake Opens
•
IC - Intake Closes
•
EO - Exhaust Opens
•
EC - Exhaust Closes
Valve Timing Diagram
Formulas and Calculations for Engines
•
Cubic Inch Displacement
• CID = 3.14 x radius of cylinder squared x stroke
• Answer x number of cylinders is total CID
• Example: bore = 5”
stroke = 6”
number of cylinders = 4
total CID = 471 cubic inches
• More cubic inches creates more power
• A “square” engine (bore=stroke) is considered to
be the most efficient
Formulas and Calculations for Engines
Formulas and Calculations for Engines
•
Compression Ratio
• Volume in the cylinder at the bottom of its travel as
compared to the top
• Expressed as a ratio 10:1, 7:1, etc……..
• Higher compression ratios produce more power
• Compression ratio is limited by fuel octane and
engine strength
• The higher the compression ratio, the more apt the
engine is to detonate or “knock”
Formulas and Calculations for Engines
BDC
TDC
Compression Ratio
Horsepower
• Work accomplished over time
Horsepower
• Brake horsepower is used to compare aircraft
engines and is the power measured at the propellor
shaft using a dynamometer (Prony brake)
Horsepower
Dynamometer in Test Cell (Purdue)
Horsepower
Dynamometer at G&N Engines Inc.
Small Engine Dynamometer
Horsepower
•
•
•
•
•
BHP = F x L x 2 x 3.14 x RPM
33,000
F = force produced by the lever arm
L = length of lever arm
RPM = speed of engine measured at the crankshaft
• Indicated horsepower is the total power produced
in the cylinders and it includes both brake
horsepower and friction horsepower
Volumetric Efficiency
• VE is the ratio of the amount of air the engine
takes into the cylinder to the total displacement of
the cylinder
• The ratio will always be less than 100% in engines
that are not supercharged due to bends and
restrictions in the induction system
• VE = volume of fuel/air charge
•
piston displacement
• The fewer bends and restrictions in the induction
system, the higher the VE
Volumetric Efficiency
Factors Affecting Engine Performance
• Detonation
The explosion of the fuel/air mixture instead of
a steady burning at approximately 35 ft/sec
• This explosion causes an abrupt rise in cylinder
temperatures and pressures that may cause engine
damage (knock)
• Detonation may be caused by several factors:
low octane fuel
high cylinder temperatures
high prop load (cylinder pressure)
lean mixture
high compression ratios
etc………..
Factors Affecting Engine Performance
• Preignition
The ignition of the fuel/air mixture before the
properly timed spark occurs (ping)
• Preignition may be caused by several factors:
hot spots on the cylinder wall
improper spark plug heat range
carbon glowing hot in the combustion area
• Preignition causes the temperature and pressure in
the combustion chamber to rise and may lead
quickly to detonation
Factors Affecting Engine Performance
• Prevention of detonation and preignition
–
–
–
–
use fuel with the proper octane rating
use correct spark plug
operate engine according to pilot’s operating handbook
do not lean the mixture during high power operations
Engine Descriptions and Classifications
• Cylinder arrangement is one method of identifying
engines
• Typical arrangements include:
inline (upright and inverted)
“V” (upright and inverted)
Opposed
Radial (including multiple rows of cylinders)
• Prefix letters (GTSIO - 520)
L - left hand rotation
V - vertical crankshaft helicopter
H - horizontal crankshaft helicopter
A - aerobatic
Engine Descriptions and Classifications
• Prefix letters
T - turbocharged
I - fuel injected
G - gear reduced prop drive
S - supercharged
O - opposed
R - radial
• The numbers are the cubic inch displacement
• Colors are Lycoming gray/blue or Continental gold
• Suffix letters vary by manufacturer and model and
must be deciphered by reference to the service
manual
Engine Descriptions and Classifications
INLINE INVERTED
Engine Descriptions and Classifications
RADIAL
Engine Descriptions and Classifications
OPPOSED
Engine Descriptions and Classifications
“V”
Engine Operation
• A checklist from the pilot’s operating handbook
should be used for start, run, and shutdown
procedures
• The checklist will contain any precautions or
procedures that are specific to the engine
• Controls are required by regulation to be legibly
marked as to type and direction of action, such as:
MIXTURE
PULL LEAN
CARB HEAT
PULL HOT
Engine Operation
• Typical checklist for starting
•
•
•
•
•
•
•
•
•
•
•
Inspect engine exterior
Check oil level
Drain fuel filter
Fuel valve “ON”
Mixture “RICH”
Throttle open 1/4”
Magneto switch to “BOTH”
Carburetor heat “COLD”
Engage starter
Check oil pressure
Run at 1000 RPM to warm