Welcome to

PILOT TRAINING SCHOOL.

 PTS/PL 011
Piston Engines
 Learning –Teaching methods

1. Lecture -Discussion
2.Group work
3.Individual reading assignment
4.Video Analysis
Assessment Methods

1. Written Test
2. Group project presentations
3. Individual assignment presentation
Objective
 At the end of this course you will be able to:
 Describe the principles of operation of internal
combustion engines.
 Describe the operating principles of piston engines.
 Describe the purpose of the different piston engine
components.
 Explain reciprocating engine fuel metering system and
associated components.
 Describe the difference between petrol and diesel
engines.
• Describe the operation of the different types of
carburetors and fuel injection systems
 Objective cont….

 Describe the different methods of piston engine

cooling mechanisms.
 Describe piston engine cooling system and
components
 Describe the operation of piston engine lubrication
system
 Describe piston engine ignition system systems
 Describe the principles of operations of propellers
 Explain the principles of operations of constant speed
propellers
 Describe propeller control levers ,degraded modes of
operation ,indication and warning
 References

• Private pilot Hand Book(Jeppesen)

• Aircraft Powerplant, Bent/McKinley
• FAA-H-8083-75:Pilots Handbook Aeronautical
Knowledge.
Introduction

• Aircraft:
 require thrust to produce enough speed for the wings to
provide lift or enough thrust to overcome the weight of the
aircraft for vertical takeoff.
 For an aircraft to remain in level flight, thrust must be
provided that is equal to and in the opposite direction of
the aircraft drag.
 This thrust, or propulsive force, is provided by a suitable
type of aircraft heat engine.

06/08/2024 8
Introduction Cont’d

Powerplant:
The complete installation of an aircraft
engine, propeller and all the accessories needed
for its proper operation.

06/08/2024 9
Cont’d

 What is your expectation from piston

Engine?
 Have you seen ever how the piston Engine
works?
 General / History.
 Early powered flight was thwarted by the lack of a suitable
Engine to provide necessary power
 In 1876 Beau De Rochas Developed the engine where the
combustion process takes place in side the engine.
Dr. Otto and Langen engines - 1876
 Four stroke engine – Otto cycle engine Two stroke engine –later
Daimler – 1885
 1st successful gasoline engine on four stroke five event cycle.
General- Types of internal -combustion engines:basic principles,
definitions

Prime movers

Heat engine Nature as source of

power
Internal
External
combustion
combustion
Hydraulic turbine
Gasoline engine
Steam engine
Gas engine Windmill

Steam turbine Diesel engine Solar engine

Gas turbine
Cont…

• First powered flight – December 17,1903

Engine used
• Built by Wright brothers and Charles Taylor
 Water cooled
 4 cylinders
 12 hp.
 80 lb.
 Mechanically operated exhaust valves and
automatically operated intake valves
 High tension magneto
Engine

• Definition
 Is a machine in which power is applied to do work
by the conversion of various forms of energy into
mechanical force or motion.
 A device for converting a source of energy to
useful work
Types of Power Plants
• Piston engine
• Reciprocating motion of pistons.
• Jet engine
 Derives its thrust from the reaction to the ejection of combustion products.
• Rocket engine
• Not intake of any outside substance (Atmospheric air.)
Principles of Operation.
Principle of Operation

• Energy :- Capacity of doing work

 Kinetic energy
 Potential energy
 Heat energy
 Mechanical energy
 Chemical energy
 Electrical energy …
Types of Internal combustion Engine

1. Compression Ignition engines (Diesels)

2. Two stroke and four stroke spark ignition
engines
3. Wankel Rotary engines
Terminologies used to understand piston engine operation

 Top Dead Center(TDC):- the position of the piston

at the highest point in the cylinder
 Bottom Dead Center(BDC):- the position of the
piston at the lowest point in the cylinder
 Stroke:-the distance between TDC and BDC
 Swept volume:-the cylinder volume contained
between TDC and BDC
 Clearance volume:- the cylinder volume contained
between TDC and top of the cylinder.
Terminologies used to understand …. Cont’d
Cont’d
 Revolutions per minute( RPM) per(RPM)
 (abbreviated rpm, RPM, rev/min, r/min) is a measure of the
frequency of rotation, specifically the number of
rotations around a fixed axis in one minute. It is used as a measure
of rotational speed of a mechanical component.

 Torque, moment, or moment of force is the tendency of a force to

rotate an object about an axis, fulcrum, or pivot. Torque is a measure
of how much force acting on an object causes that object to rotate.

 Thrust specific fuel consumption (TSFC) or sometimes

simply specific fuel consumption, SFC, is an engineering term that is
used to describe the fuel efficiency of an engine design with respect to
thrust output.
Cont’d
 Mechanical efficiency measures the effectiveness of a
machine in transforming the energy and power that is input
to the device into an output force and movement .
 Thermal power station. ... A thermal power station is
a power plant in which heat energy is converted to
electric power
 Volumetric efficiency in internal combustion engine
engineering is defined as the ratio of the mass density of
the air-fuel mixture drawn into the cylinder at atmospheric
pressure (during the intake stroke) to the mass density of
the same volume of air in the intake manifold
Cont’d

• Thermodynamics
 First Law:- heat and mechanical energies
are mutually convertible

 Second Law:-Heat cannot be transferred

from a region of lower temperature to a
region of higher temperature without an
expenditure of energy from external source.
Principle of Operation

• Power
• Rate of doing work
• 1hp = 550ft.lb/s
= 33,000ft.lb/m
= 746 watt
Principle of operation
 By inducing a mixture of air and fuel in to
the cylinder
 Then compressed by a piston
 The mixture is ignited and
 The rapid rise in temperature causes the
pressure in the cylinder to rise
Cont’d

 Itpushes piston down the cylinder

 The linear motion is converted to mechanical
rotation by connecting road and crank shaft.
 The burnt gas then exhausted from the
cylinder
 The engine converts heat energy in to
mechanical energy.
Two Stroke Engine
 Completes all five events in two strokes of the piston
• Advantages
 Mechanically simpler
 Light in weight
• Disadvantages
 Less power
 Cooling problem
 Lubrication problem
 Used on ultralight Aircraft
TWO STROKE CYCLE ENGINE.
Four Stroke-Cycle Engine
 Completes all the five events in four strokes of the
piston
• Advantages
• No power loss
• Less cooling problem
• No lubrication problem
 Disadvantage
• Long power gap
Four Stroke Five Event Cycle Engine
Four Stroke-Cycle…Con’t
1
Diesel Engine

 With out electrical ignition

 Air alone is compressed
 High compression ratio
 Fuel injection system
Engine : Design, operation , components and
Materials
 Engine Construction
• Crank case
 Usually made in two halves to make installation
and removal easier
 It houses the main bearings for the crankshaft,
 Supports the cylinders
 Provides mounting faces and spigots
 Generally made of light alloy
 Forms sealed chamber for lubricating oil
 7Provided with means of attaching engine to the
airframe.
Crankshaft

 Converts reciprocating or linear motion

of piston to rotary motion.
 Journals the main part of the shaft are
supported by the main bearings in the
crank casing.
 Connected to piston by connecting rods
 Accurately balanced to minimize
vibration.
Crankshaft (Cranked shaft)
 Connecting Rod

 Transmits the force of combustion to crank

shaft
 Convert linear motion of piston to rotary motion
of crank shaft
 Made of H section high tensile steel to
combine lightness with strength necessary to
withstand tensile and compressive loads.
 The rod is connected to the shaft by the big
end of the Rod.
Cont’d
Piston
• Generally made of Aluminum alloy
• Forms sliding plug
• Bosses are formed to house the
‘Gudgeon pin’ which fastens the rod with
small end.
• Circumferential grooves are machined in
the piston to bear piston rings.
Piston Cont’d
Engine construction
Types of piston rings

 Compression Rings;- upper portion of

the piston
 Scarper rings or Oil control rings:-
lower part of the piston
 The rings are made of special grade of
cast Iron and
 The rings are sprung against cylinder
walls
Types of piston rings Cont’d
Cylinder Block
Cylinder Head

 Made of Aluminum Alloy to improve heat

dissipation
 Accommodates Valves, Valve guide,
sparking plug
Cylinder Head Cont’d
Valve operating Gear

 Consistsof Camshaft driven from

crankshaft in halve crankshaft speeds.
(Why?)
Valve operating Gear Cont’d
Engine layout
Engine layout Cont’d

• Inline Engine:-
• Liquid or air cooled
•Many inline types have inverted cylinders
so that crank shaft is on top and piston
below
• Give more ground clearance
Engine layout Cont’d
Engine layout Cont’d

• V-engine arrangement
• Used for larger more powerful engines
• 8-12 cylinders
• Easily be streamlined to reduce drag
• Liquid cooled
• Increased weight and complexity
Engine layout Cont’d
Engine layout Cont’d

• Radial Engine:-
• Gave large frontal area to aircraft
 Short in length
 Although Drag was increased the Engines were
light rigid and produced high power.
 By placing further rows of cylinders behind the first
produced Double and triple Bank Radials.
 The Ultimate in piston engine Design
 Up to 27 cylinders are arranged to power large
military and civil airliners during 1940-50
• Air cooled
Engine layout Cont’d
Cylinder Barrel Or Block

• Made of Alloy steel

 Resists combustion pressure and
provides working surface for piston
 30% of heat generated is transferred to
cylinder.
 Can be cooled either by liquid or air
 Sump
 Casing attached to the base of crank
case.
 Collects lubricating oil after it has passed
through engine.
 Some times used as reservoir.
Accessory Housing(Wheel case)

• Oil pumps
• Fuel pumps
• Superchargers and
• Magneto ignition systems
Cont’d
Cont’d
 Some engines may contain gear box fitted between
crankshaft and propeller shaft it is called reduction
Gearbox.
 Two types of Reduction Gearing are Spur Gear and
Planetary Gears.
FUEL
Fuels
 Blend of Hydrogen and carbon
 Jet and diesel fuels are also derived from
oil.
 The process of extracting is called
cracking.
 Aircraft Piston engines use Gasoline fuel
called Avgas.
 Equipment used to dispense the fuel is
color coded.
Types, grades, characteristics, limitations

 Ithas to fulfill the requirement of Directorate

of Engine Research and
Development(DERD)
 The specification number is DERD-2485
• Grade 80:- low lead content, used for
low compression engines.
• Grade 100:- high lead content used
for high compression engines.
• Grade 100LL:- compromises the two,
medium lead.
Grades

 Some Aviation Authority permit Car petrol for

some Aircraft. These are called MOGAS(Motor
Gasoline)
Characteristics

 Calorific Value
 Volatility
 High Volatility
• Stability:- instability should be prevented by
oxidation inhibitors
• Sulphur Content:- it is necessary to minimize
sulphur content to a minimum. In aviation fuels
the max percentage of sulphur permitted is
0.001%
Combustion Process
• It is a controlled rate of burning
• Not explosion
 Gasoline Vapor(84.2% of Carbon and 15.8%
Hydrogen by weight) is combined with Air(78%
Nitrogen,21% oxygen and 1% other gases)
 When combustion is done H combines with O to form
water vapor and C with O form Carbon dioxide. Other
gases will play no part in combustion but expands as
they are heated.
Flame Rate

 In normal combustion flame rate is 60-80

ft/sec giving a steady and smooth temp.
 Max pressure is generated after
combustion has been completed and the
crank angle of 8-10 degrees ATDC
 Should a max pressure occurs at or
before it the engine will tend to run
backward.
 Pre-ignition and Detonation in an Engine.

Pre-ignition
 Is caused when there is a hot spot in the engine that ignites the fuel -
air mixture before the spark plug fires.
• Rough running
• Running on and
• Causes loss of power
• By avoiding over heating it can be prevented

Detonation
 Detonation is the spontaneous combustion of the End-
gas(remaining fuel/air mixture)in the chamber.
• Detonation occurs when fuel in the cylinders explodes instead of
burning smoothly.
• It always occurs after normal combustion is initiated by the spark plug
Detonation or knocking

 Detonation occurs after ignition and is unstable

combustion
Normal Combustion.

NORNORMAL COMBUSTIONMAL
COMBUSTION
Detonation.

DETONATDETONATIONION
Detonation Cont’d
 Effects of Detonation

 The explosion of end gas will burn piston crown and

eventually to collapse.
 Overheating of combustion chamber may occur.
 This may cause valves to split and distort and
possibly burn the sparking plug electrode.
 Rise of pressure also cause vibration which applies
shock loads to the engine components.
 Because of high pressure piston has to overcome
high pressure and power has lost.
Effects of Detonation Cont’d
Causes of Detonation

• Incorrect mixture strength

• High charge Temp
• Incorrect ignition timing
• Cooling
• Cylinder head design
• Use of incorrect fuel
Recognition of Detonation

 Itis spontaneous combustion and

recognized by its knocking sound or
pinking
 Much damage may be done under high
power circumstances especially in aircraft
 Fuel Quality Control
 One of the easiest way of controlling detonation is by
controlling fuel quality.
 There are two chemically pure fuels
 Iso-Octane:- good combustion property, little
tendency to detonate, ignited at very high
temperature, given a rating of 100
 Normal-Heptane:- detonates very rapidly and given
rating 0
Octane rating of 95 means 95% of iso-octane and
5% of iso-heptane, therefore octane rating is anti-
knock value
Fuel Additives

 Detonation can be Avoided by adding small

amount of additives in the fuel.
 The principal one be Tetra-Ethyl Lead(TEL)
 Ethyl Di Bromide is also added to fuel
 Iso-Octane number no longer works but
performance Index works
Advantage of High Octane Anti Detonation Ratings

 Increased compression Ratios, Increase

Thermal efficiency, better fuel
consumption, increased power
 Increased Induction pressure and greatly
increased power by using Superchargers.
Thermal Efficiency

 Less than 30% of fuel energy is converted to

useful work at the propeller shaft
 If fuel is very volatile excessive loss occur in
the fuel tank
 Fuel tend to boil and vaporize at the inlet side
of pump causing cavitations and vapor locks to
form.
 Carburetor Icing may occur at certain
condition.
 Engine Fuel Pumps
 Supplies more fuel than is required by engine and
recirculation path is provided.
 Two pumps are arranged in parallel, Mechanical and
Electrical.
 When Mechanical pump is not operating fuel under
positive pressure can bypass the mechanical pump,
allowing electrical pump to be used for engine priming
and starting and in an emergency.
• The two types of Engine Fuel pumps are:-
 Gear type
 Vane type
Carburetor/Injection system
 Carburetor
Purpose
 Meters the amount of air entering in to cylinder
and adds required amount of fuel under all
operating conditions.
 For aircraft required amount of fuel is added
regardless of Attitude and Altitude.
 Injector can be installed instead of carburetor
in some engines
 Injection Manifold- metal tube connects
carburetor/injector with cylinder.
Carburetors
Basic Requirement of Carburetor

 Control air/ fuel ratios in response to throttle Setting

 It must function at all conditions of flight altitudes and
temperatures in the operating range.
 It must provide for ease of starting and may
incorporate a means of shutting off the fuel to stop
engine.
Carburetor cont…
• Carburetor employs two basic principles
 U tube
 Venturi
Components of the Carburetor are:-
• Main metering
• Idling
• Accelerating
• Mixture control
• Power enrichment
• Idle cutoff.
THE VENTURI
Simple Float type carburetor
FLOAT OPERATION
The Diffuser

 A device to prevent a mixture from becoming rich with

increasing RPM.
Slow running system
Air Bleed Diffuser
Mixture control
 Enables the pilot to improve fuel/air mixture for air
density variations.
 Works either by varying fuel or air going to the main
metering system.
 is used to stop engine by employing “fuel cut-off”
• There are two types of manual mixture controls
1. Needle type mixture control
2. Air bleed mixture control.
Engine controls.
Mixture control needle type
Air bleed Mixture control
Power enrichment /Economizer system
• Is essentially a valve which is closed at low
engine and cruising speeds but is opened at
high speeds to provide an enriched mixture to
reduce burning temperature and prevent
detonation.

1. Needle valve enrichment

2. Back suction economizer
Needle Valve Economizer jet
Back Suction Economizer
Accelerator Pump

 When throttle valve opens instantaneously air

flow responds immediately but fuel flow
responds slowly
 Temporary weakening of the mixture occurs
causing a flat spot(loss of power)
 Accelerator pump injecting fuel in to the
induction system reduced this effect when the
throttle opens quickly.
Accelerator Pump
Injection: design, operation, degraded modes of
operation, indications and warnings.
Fuel Injection system.

1.Direct injection system

2.Continous flow injection system
Fuel Injection
Direct Injection system
Fuel Injection.
Indirect fuel injection
• Low pressure
• Continuous flow type
• Advantages
• Low operating pressure
• Freedom from icing problem
• Components of the system are
• Fuel pump, fuel/air mixture control, fuel manifold/
distribution valves and discharge nozzles for each
cylinder.
Indirect Fuel Injection
Cont’d

 In addition, normal throttle valve controls

air flow to the engine and pressure gauge
is installed in it
 Fuel Air control Unit
• Mounted on the intake manifold and contains three control
elements.
1. The air throttle Assembly(throttle valve)
2. The throttle metering valve(metering fuel valve)
3. Mixture control Valve
• Fuel control unit attached to air throttle assembly and
controls fuel flow to the Engine by means of two valves.
1. Metering Fuel Valve:- connected to the air control and
controls fuel flow to manifold
2. Mixture Control Valve:-connected to pilots mixture control
levers and bleeds off fuel pressure applied to the metering
valve
Fuel manifold Valve

 Located on the engine crankcase and is the

central point for distributing metered fuel to the
engine
 When the engine is stopped all the valves are
closed no fuel can flow to engine.
 When engine starts fuel pressure start building
and the valves start to open
Discharge Nozzle

• Located in each cylinder head

• Out let directed in to inlet port.
•Calibrated in several ranges and fitted to
individual engines as a set.
•Each nozzle in a set having the same
calibration.
Engine Icing
 Atmospheric conditions specially high humidity(more
than 50% of relative humidity) and temperature
ranging from -7degrees centigrade to as high as 30
degrees centigrade may cause icing in any piston
engine.
Types of Ice
 Impact Ice:- forms on air filters and bends in the induction
system
 Refrigeration Ice (carburetor icing):-forms in float type
carburetor as a result of low pressure during vaporizing
 Fuel icing:- caused by moisture in the fuel coming out of
suspension and being frozen by the low temperature
Action To be Taken when Engine Icing Is Suspected!

 Carburetor heat control should be selected fully Hot and left in

the hot position till icing is removed
 This may take 1 minute or more depending on severity
 Partial heat should not be used unless the aircraft is fully
equipped with carburetor temperature.
 Icing should likely occur during reduced power flight.
 When icing condition exists select full hot air to get benefit of
hot air before power reduces.
 It is necessary to increase power periodically to a cruising
setting at intervals of between 500-1000ft during descent
 Carburetor icing can occur at taxiing during idle power use
Hot air to ensure that there is no ice.
• Never use Hot air during take off.
Engine Considerations
• Using carburetor hot air
• Reduces power by 15%
• Cause richer mixture can cause rough running
•Heat should not be applied at power setting more than
80% as it has a danger of detonation
•Continuous use of hot air should be avoided as it
causes change in mixture and increase of engine temp.
•Do not use carburetor heat once clear of icing but
check periodically.
Fuel Injected Engines
 Does not have a problem of ice formation in the
venture but other parts of the engine may accumulate
ice and reduce power.
 Fuel icing may gather at the bends, impact icing may
form at the impact sensing tubes, or on the air filters,
Operational Procedures

• Ground Operation
• Take Off
• Climb
• Flight operations
• Descents
• Approach and Landing
• Caution
Cooling Systems
 Reasons for cooling

 It was stated that only 30% of heat energy is converted to

mechanical energy at best.
 70% is wasted
 40 % of it is exhausted.
 Some A/C recover this energy to drive turbine
• *Remaining 32% raises the temperature of engine and
if not controlled leads to Structural failure of engine component
 Over temp of oil leads to breakdown of its lubricating property
• Pre ignition may happen
Cont’d
 Problems occur due to low temperature
 High values of thermal efficiency require engine to operate at
high temperature
 Low temperature increase the internal friction of lubricant-low
viscosity
 The ability of liquid fuel to change its state to gas is reduced-
which affects fuel mixture and combustion.
 To operate efficiently engine must operate at highest
Temperature consistent with safe operation.
 Allowances for ambient and internal temperature require
cooling system to control and maintain this temperature.
Liquid and air cooled systems

• Two types of cooling systems used

 Liquid cooled:-use water and glycol(anti
freeze) to dissipate heat from engine areas
through passages then the liquid pass through
air cooled Radiator.
 Air cooled:- uses the cooling air from the
propeller slipstream and the aircraft’s forward
speed.
Liquid Cooled system
Cooling System Radiator.
Air cooled system
Air Cooling System Cont’d
Air cooled system

• **The main factors governing efficiency

of air cooled system are
 Air temperature
 Speed of airflow
 Cooling fins
 Baffles
 Engine construction
 Cowlings, cowl flaps and Gills
Cylinder Head temperature gauge

•Used to monitor engine temperature

•If one sensor is used it is installed in hottest
cylinder
• Other wise thermocouple is used.
Operational Procedures
 Forward speed is needed to cool air cooled engine this is not
always happens, e.g. During climbing
 Therefore climbing at best speed Vy is needed.
 During Descend engine may be over cooled.
 Sudden change may produce what is called Thermal shock.
 This can cause components to fracture.
• The pilot should control this by cowl flaps
 High Power Ground operations should be limited
 Prior to shutdown engine should run at idle power for short
period of time.
Lubrication system.
Lubricants: characteristics,limitations.
 When moving parts in contact there is resistance to their
movement, this is called Friction.
 Friction increases as load, temperature and speed increases.
 Movement also produces wear.
 Both friction and wear can be reduced by inserting some
material which is less resistant to movement.
 This materials are called Lubricant.
 The oil can be forced “pressure Lubrication” or components
can be splash lubricated.
Lubrication systems Cont’d

 Primary purpose of Lubricating system is to

reduce friction and wear.
• It has a number of secondary purposes.
 Cooling
 Cleaning
 Corrosion protecting
 Indicating Medium
Wet and Dry sump lubricating System
• Wet Sump
• Most light, non aerobatic aircraft use this
• The oil is stored in the bottom of engine
• This simplifies construction but has a no. of
disadvantages
• Lubrication difficulty during maneuvering
• Temp of oil is difficult to control as it is near engine
• The oil becomes easily oxidized and contaminated
• Oil supply is limited by sump capacity
 Dry Sump
 Overcome the above problem by storing oil in
remotely mounted Tank.
 Principle of oil supply is the same for both
methods
 Pressure pump circulates oil through the
engine
 In dry sump scavenge pumps return the oil to
the tank
Design, operation, indications and warnings

• Oil Tank(Dry sump)

• Oil filters
• Pressure and Scavenge Pumps
• Oil cooler(Radiator)
• Oil pressure and temp gauge
• Necessary interconnecting lines
Dry Sump Lubrication
Oil tank
 Made of sheet metal, possibly Baffled and strengthened
internally because of Oil surging during maneuvering
 Placed above oil pump to give gravity feed.
 Reservoir to store oil enough for engine
 Also has air space used
 Increased oil return when engine starts
 For expansion of oil
 Frothing due to aeration
 Displacement of oil from variable pitch propeller and other
automatic devices.
Component cont’d
 Hot pot: To reduce time taken to raise temp of
oil when engine starts in cold by restricting oil
flow to engine.
 Suction Filter:- Remove large particles before it
enters the pressure pump.
Pressure Pump
• Actual oil pressure depends on
• Speed of the Pump
• Oil temperature
• Resistance offered by the components
Cont’d

• Check Valve(non return Valve,):- hold back oil

•Pressure Filter:-used to remove very small
particles before oil passes to the bearing surface.

•Scavenge pump:-returns the oil back to pressure

pump.

•Should be greater than pressure pump.(25%-50%)

greater than oil pump.
Oil cooler

 Consists of matrix or tube block which spreads

the oil in thin film and subjects it to cooling air
 When starting the engine from cold to force the
oil through thin holes of cooler will be very
difficult. To prevent this the cooler Anti surge
fitted to by pass the matrix when the engine is
cold.
Cont’d

• The temperature of the oil depends on

 The amount of heat generated by the
engine
 The temperature of cooling air
 The rate at which air flows through the
cooler
Lubrication Monitoring Instrument
• Temperature:- measured at the outlet of pressure
pump
 Most aircraft use electrical sensors to measure
temp, and 85 degree Celsius would be considered
normal
• Oil pressure: measured at the outlet of pressure
pump the amount of pressure depends on the
capacity of pump.(50-100 psi being typical value.)
• Oil quantity:- if oil quantity is not displayed some
means is used to measure oil quantity.
Viscosity

 Measure of fluid’s internal friction or resistance

to flow.
 Thin films have low viscosity and thick films
have higher viscosity
 It changes with change in temp.
 The oil viscosity remain in certain limit when
the engine temp varies from cold to hot, this
range is called Viscosity Index.
Viscosity Index Numbering
• Two standards are used to measure viscosity
• Society of American Engineers(SAE)
• Saybolt universal(SU)
• Both systems use numbers to indicate index.
• The lower the viscosity system the thinner the oil.
 Types of Oil
 Mineral based oils are used in aircraft engine
 If no additives are there it is called straight oil
 To meet certain requirement to the engine certain additives are
added to the oil. These are Anti oxidants, detergents, and
oiliness agents. These oils are called Compound Oils.
 Two oils are identified by numbering system; for straight oils
only numbers are needed, but for compound oils letters are
added before numbers. The numbers depend on the
manufacturer. e.g AD80 indicated Ashless Dispersant (specific
cleaning agent and viscosity of 80)
Types of oils
Operational Considerations
 On radial and inverted engines the pilots knowledge of
lubrication system required even before engine starts.
 Engine suffers from Hydraulicing where oil accumulates in
lower cylinders b/n piston and cylinder head. As oil is
incompressible it may damage the engine. prior to starting
these engines should be pulled through the cycle by using
propellers to ensure no hydraulic lock has occurred.(confirm
Magnetos are off before turning)
 At starting oil viscosity is high and pressure may be raised
this is considered normal as it falls to normal. Oil temp and
pressure should be within specified range.
Cont’d
 Coring:- occurs at the starting of engine in very cold weather.
The temp raise is high but only locally. To avoid this closing
flaps is used to distribute heat to entire engine.

 Oil consumption:- if engine consumes oil beyond its limit

there is wear of parts in the engine.

 For dry sump oil can be checked immediately after engine

shut down, but it takes 15-20 minutes to check oil level for wet
sump.
IGINITION Circuits
Design, operation
 All aero engines are equipped with dual ignition systems(two
electrically independent ignition systems)

 Each engine cylinder has two sparking plugs fed by two

separate magnetos.

 This reduces the risk of engine failure due to ignition

system and increases engine power by facilitating combustion.
Magnetos
 Self contained engine driven electrical generators.

 Produce Extra High Tension(EHT) electrical sparks

at the sparking plugs in the correct firing sequence
for ignition of petrol and air mixture.

 Combines permanent magnet generator and step

up transformer in order to generate EHT voltage to
breakdown the gap between the sparking plug
electrodes.
Magneto circuit
Distributor
 Distributes EHT voltage to the sparking plug in the
correct firing sequence.
Capacitor
 To prevent burning or arcing across the contact breaker and
assist in creating EHT voltage in secondary coil by causing
rapid change of flux (magnetic field) in the primary coil.
Ignition switch

 Provide complete control of engine magneto

circuit. Magnetos become inoperative by
Earthing the primary circuit
Magneto Checks

 Dead cut check:- check during engine running

to check weather both magnetos are
working(L,R, BOTH).
 This check is not normally done due to
damaging the exhaust manifold
 Single ignition check:- to ensure that ignition
system is functioning satisfactory
Mixture
Definition, characteristic, mixtures
control Instruments, associated
control levers, Indications
The practical Mixture ratio
 In practice mixing and distribution are less than
perfect and this produces some regions being richer
and other regions being weaker than the optimum
mixture.
 Slightly rich mixture does not have much effect on
power
 Weak mixture however rapidly reduces power since
all the oxygen is still consumed.
 It is quite common to run engine at 12.5:1 to ensure
that no cylinder is left running at severely reduced
power from unduly weak
The practical Mixture …Cont’d

• Black smoke from the exhaust may indicate a rich mixture

or worn piston rings.
• A rich mixture is necessary at slow running. as necessary
when needed
• Excessive cylinder head temperatures could be caused by
prolonged use of a weak mixture, especially at high
altitude.
Mixture Cont’d
• The chemically correct ratio
 Although air/fuel mixtures can burn in ratio from
8:1(rich) to 20:1(weak) the complete combustion
occurs at a mixture of 15:1 by weight
 This is Chemically Correct ratio(all of oxygen in the
fuel combines with hydrogen and carbon)
 The chemically correct ratio does not give best
result, because temperature can be very high and
power can be lost through detonation.
Problems Caused By Weak Mixtures
 Slow running and Starting
 At start engine temperature is cold and fuel
is not vaporized. Therefore rich mixture of
fuel is required to produce more heat.
 To obtain efficient scavenging of the burnt
gas and to give impetus to the incoming
charge.
 At lower speed the exhaust gas is sucked by
the exhaust valve and dilutes.
 To maintain smooth running at low speed
rich mixture is needed.
Take Off Power

 In full power mixture is further enriched to

10:1.
 Apart from cooling effect the excess fuel
is wasted due to insufficient oxygen
available for it to burn completely.
Climbing Power

 When higher power is required for climbing the

mixture is enriched to about 11:1
 The extra fuel in vaporizing cools the mixture
and reduces tendency to detonate.
Cruise power
 Onlymoderate power is required and this
should be produced with the minimum
expenditure fuel to achieve economy
 Exhaust Gas Temperature Gauge
 Consists of thermocouple fitted in to the
exhaust pipe
 More heat means more power
 Thermocouple produces voltage directly
proportional to temperature
 The mixture control should always be moved
slowly
AIRCRAFT PROPELLERS.
Aircraft propellers.
Propellers Definitions, general
 The aircraft propeller consists of two or more blades and a central
hub to which the blades are attached.
 Each blade of an aircraft propeller is essentially a rotating wing.
 As a result of their construction, the propeller blades are like airfoils
and produce forces that create the thrust to pull, or push, the aircraft
through the air.
 The engine furnishes the power needed to rotate the propeller blades
 Propellers Definations, general
 A means of converting engine power in to propulsive
force
 Rotating propeller results in rearward acceleration of
mass of air, the reaction to this rearward acceleration
of a mass of air, is a forward force on the propeller
blade is called thrust.
 Fixed pitch propeller :-propellers whose blade angle
can not be changed after they are manufactured.
 Used on older single engine aircraft.
How A Propeller produces thrust?
 In accordance with Newton’s third law of
motion.

 The propeller accelerates a large mass of air

to the rear of the airplane.

 As a result, the airplane is pulled or pushed in

the direction opposite to which the air is
accelerated, i.e. the airplane moves forward.
Propeller operation.

I. Propeller pitch:
Is the distance that a propeller will move
forward in one revolution.
 Geometric pitch: Is the theoretical distance
that an a/c will move forward in one revolution of
the propeller.
 Effective pitch: Is the forward distance that an
a/c actually moves in one revolution.
 Slip= Geometric pitch - Effective pitch.
Indicates the loss of propeller efficiency.

Note:- EFFECTIVE PITCH = (0 – 90% OF GEOMETRIC PITCH)

Propeller Tips
Cont’d

Flight

path

AIRFLOW [kgs-
VELOCITY
CHANGE Air Flow
[ ms-1 ] ]
1
PROPELLER OPERATION./ AERODYNAMICS OF A
PROPELLER.
Propeller operation Cont’d.

Path of a propeller blade element through the air.

Propeller operation Cont’d.

Slip= Geometric pitch - Effective pitch.

Blade Geometry

 A propeller consists of two or more

aerodynamically shaped blades Attached to a
central Hub.
 As the air flows past the propeller, the pressure on one side is
less than that on the other
Blade or Pitch angle.
 The angle between the chord line of a propeller blade and the plane
of rotation.
Constant-speed propeller: design, operation, system components

 A variable pitch propeller allows the blade angle to vary in

flight in order to fully utilize Engine power.
• The original variable pitch propeller had two settings
1. Fine pitch for take off and climb
2. Course pitch to enabling full engine speed for use in cruise
 The introduction of an engine driven governor enables the
blade angle to alter Automatically defining it as a constant
speed
 The pitch setting varies automatically to maintain a
preselected rotational speed.
 As a result engine and propeller both operate at their
maximum efficiency.
Governor

• It has two names

• Constant speed unit(CSU) for piston Engine.
• Propeller control Unit(PCU) for a turbo prop.
Constant speed Propeller blade positions
Cont’d
• Feathered :- when blade chord line is parallel to the airflow there fore preventing
windmill

• Course pitch:-the maximum cruising pitch in normal operation

• Flight fine pitch:-the minimum pitch obtainable in flight

• Ground Fine Pitch:-minimum torque position for ground operation and referred to
as superfine pitch

• Reverse Pitch:-aerodynamic brake position used for braking and ground

maneuvering

• Alpha Range:-the flight operating range from fine pitch to course pitch.

• Beta range:-ground operating range from fine pitch to reverse pitch, hydro-
mechanically controlled by flight deck lever.
PROPELLER AT LOW BLADE ANGLE.
PROPELLER AT HIGH BLADE ANGLE.
PROPELLER AT ITS MAXIMUM BLADE ANGLE. /FEATHERD POSITION/
Single Acting propeller
Low Pitch stop or centrifugal Latch
Cont’d
 It is important not to shut down the engine from High
RPM, otherwise the latches do not engage and the
propeller feathers.
 Take care in flight to prevent the RPM from Falling
such as engine failure below a pre determined figure
usually from 800-1000 RPM as the latches engage
and prevent feathering
Constant speed Unit
 CSU
 Consists centrifugal flyweights, a control valve, a
control spring(speeder spring), a non return
valve, and an oil pump to boost an engine oil
pressure for propeller control mechanism
operation.
CSU
Cont’d
Single Acting Propeller Feathering
Single Acting Propeller Un-Feathering
Propeller Control Unit
Double acting Propeller
Double acting Propeller Feathering
Pitch stops

 To control propeller angle for ground and

flight operations.
 Ground pitch-stop:-
 Flight Pitch-stop
Automatic Feathering
Reduction Gearing Design
• Powerful aero engines needs a large propellers to
convert its power in to thrust
• Too large a diameter would bring the risk of sonic
compressibility and blade flutter if the propeller were
rotated too fast.
• In order to be able to use large diameter propeller the
engine turning at its maximum RPM cannot be
directly connected to the propeller, so the drive speed
must be reduced to a more suitable level by a
reduction gear placed in the driveline between engine
and prop shaft.
Reduction Gear types

Parallel spur gear

Epicyclical Reduction Gear
Propeller handling
 Propeller checks ensure the propeller governor and
operating Mechanism are functioning correctly
 The RPM lever is moved from MAX to MIN Observing
the drop in RPM.
 The RPM is returned to the MAX position ensuring
the restoration of the original figure.
 Carry out this three times to ensure that the propeller
operating mechanism is charged with low viscosity
hot oil there by preventing sluggish operation .
Engine performance and handling
• The weight of air/fuel determines the engine power
• Power output is a result of RPM and Manifold Pressure(MAP)
• Normally Aspirated engines take air not subjected to
supercharging
The effects of altitude on performance
• Pressure altitude
• Density altitude
• Critical altitude
Cont.
• Pressure Altitude:- the indicated Altitude when an altimeter is set to
29.92in Hg (1013 hpa in other part of the world). it is primarily used
in an aircraft performance calculations and in high altitude flight.
• Density Altitude:- Is formally defined as “pressure Altitude
corrected for non standard temperature variations.
• Critical Altitude:- The Maximum Altitude at which a turbocharged
reciprocating engine can deliver its rated horsepower.
Factors that Affect Engine performance

• Ram air pressure

• Humidity
• Carburetor air temperature
• Cruise control
Naturally/Normally/ aspirated engine.

 A reciprocating engine that depends upon atmospheric pressure

to force the fuel-air mixture into the cylinders. Naturally aspirated
engines are neither supercharged nor turbocharged.
• Waste gate.
A controllable butterfly valve in the exhaust pipe of a reciprocating
engine equipped with an exhaust-driven turbocharger.
Induction Systems.

Supercharging & Turbocharging

Turbocharger / Supercharger
 Piston engine produces max power when it “breathes” air at
sea-level pressure
 Because air pressure & density decrease with altitude, engine
becomes increasingly “breathless” as it climbs Power output
decreases.
 Turbochargers solve this problem, by compressing the thin air,
restoring its density, before engine inhales it.
Turbocharger vs Supercharger
 Supercharger is any device that pressurizes the air intake to
above atmospheric pressure
 Both superchargers and turbochargers do this;
 In fact, the term "turbocharger" is a shortened version of
"turbo-supercharger," its official name
• Difference is source of energy;
• Turbochargers are powered by the mass-flow of exhaust gases
driving a turbine.
• Superchargers are powered mechanically by belt or chain-drive
from engine's crankshaft.
Supercharging
 Internally driven compressor, powered by engine Compresses
fuel / air mixture
• Advantages
• Reliable, less expensive
• Disadvantages
• Heavy, takes power from engine.
Turbocharger / Supercharger
• Normally aspirated engine loses power as aircraft climbs,
because air density decreases as altitude increases
• High ambient air temperatures cause an engine to produce
less power
• Both the turbocharger and supercharger help to maintain sea
level pressure as altitude increases.
Turbocharging
• Turbocharging compresses air flowing into engine
• Engine can squeeze more air into a cylinder; more air, more
fuel can be added. Thus, more power from each explosion in
each cylinder
• Advantage: lightweight, does not take power from engine
• Disadvantage: very hot operating, expensive, maintenance
intensive.
Turbocharging
• In order to achieve this boost, the turbocharger uses exhaust
flow from the engine, to spin a turbine, which in turn spins an
air pump
Westgate
• Controls redirection of exhaust gases
• When open, the engine is not turbocharged
• When closed, the engine is turbocharged
Engine Handling.
 Pre-Start Inspection. Ensure the aircraft wheels are chocked, that
the propeller arc is clear of equipment and personnel, and that there
are no loose objects lying around which may be drawn into the
propeller.
 Follow the correct procedure to start the Engine.
 Follow the correct procedure after start and operating checks.
Cont..
• Basic procedures:-
 To increase power enrich mixture, increase rpm, advance throttle.
 To decrease power retard throttle, reduce rpm, adjust mixture.
 The life of a piston engine can be considerably lengthened if care is
taken in its operation and handling to ensure that stresses are kept as
low as possible. The engine is subject to two types of stress, thermal
and mechanical.
Cont..
 In order to ensure that engines can be operated safely throughout a
specified lifetime, manufacturers authorize a number of different
power ratings, some of these may be used continuously whilst others
are subject to time limit
• Typical power ratings are indicated below: