Aircraft Propulsion Systems (Piston Engine) Reviewer
Heat Engine - Converts chemical energy (fuel) into heat energy. Heat energy is then converted into mechanical energy.
Reciprocating Engine - a type of heat engine that derives its name from the back-and-forth, or reciprocating movement of its pistons. It is this
reciprocating motion that produces the mechanical energy needed to accomplish work.
Primary Engine Requirements:
1. Lightweight – powerplant weight must be kept as low as possible to provide greater weight for useful load and provide a margin of
safety.
2. Reliability – a powerplant is reliable when it can be depended upon to do what it is intended for it to do by the manufacturer.
3. Durability – this is the measure of the engine life, while maintaining the desired reliability.
4. Compactness – it is necessary to affect proper streamlining and balance of the airplane, and in single engine airplane, the shape and size
of the engine affects the visibility of the pilot.
5. Flexibility – the ability of the engine to run smoothly and perform in the desired manner at all speeds from idling to full power output
and through all variations of atmospheric conditions. The ability to operate efficiently regardless of the conditions.
6. Weight per horsepower – the ratio of the weight of the engine to the horsepower it can produce. This is the factor that engine
manufacturers consider the most. The engine must produce a large amount of power but must also be light in construction.
7. Specific power output – the amount of power produced in a given amount of fuel.
8. Fuel economy – it is a factor of the fuel characteristics, fuel must be more resistant to detonation, to allow an increase in engine
compression ratio.
9. Balance – if the powerplant is free from vibration, it is said to be balance.
10. Reasonable cost – the first cost must be low enough to meet the competition in the market and be accepted by the airframe
manufacturer.
11. Economy of operation – it must have a reasonable cost of operation, it must be such that it will make profit for the operator.
Classification/Types of Reciprocating Engine:
1. Radial Engine – can be Single row, Double row and multiple row or corncob. Consists
of a row, or rows of cylinders arranged radially about a central crankcase. Has the
greatest drag of all types, lowest weight per horsepower ratio, and some problems in
cooling. Radial engines helped revolutionize aviation with their high power and
dependability. Most widely used engines ever built.
Single-row radial engine - has an odd number of cylinders attached radially to a
crankcase. A typical configuration consists of five to nine cylinders evenly spaced on
the same circular plane with all pistons connected to a single crankshaft.
Multiple-row radial engines consisted of two single row engines in line with each other
connected to a single crankshaft. This type of engine is sometimes referred to as a double-row radial engine and typically has a total of 14 or 18
cylinders.
2. In-Line Engines - An in-line engine generally has an even number of cylinders that are aligned in a
single row parallel with the crankshaft. This engine can be either liquid-cooled or air cooled and the
pistons can be located either upright above the crankshaft or inverted below the crankshaft
In-line Engines Advantages:

Small frontal area and, therefore, allows for better streamlining. Least drag.

When mounted with the cylinders inverted, the crankshaft is higher off the ground. The higher
crankshaft allowed greater propeller ground clearance which, in turn, permitted the use of
shorter landing gear.
In-Line Engines Disadvantages:

Have relatively low power-to-weight ratios.

The rearmost cylinders of an air-cooled in-line engine receive relatively little cooling air, so inline engines were typically limited to only four or six cylinders.

With these limitations, most in-line engine designs were confined to low- and medium-horsepower engines used in light aircraft.
3. V-type Engines - the cylinders of a V-type engine are arranged around a single crankshaft in two inline banks that are 45, 60, or 90 degrees apart. Capable of producing more horsepower than an inline engine. The cylinders on a V-type engine could be above the crankshaft or below it, in which case
the engine is referred to as an inverted V-type engine. Most V-type engines had 8 or 12 cylinders and
were either liquid-cooled or air cooled.
4. Opposed Engines - opposed-type engines are the most popular reciprocating engines used on light
aircraft. A typical opposed engine can produce as little as 36 horsepower to as much as 400 horsepower.
Always have an even number of cylinders, and a cylinder on one side of a crankcase "opposes" a cylinder
on the other side. While some opposed engines are liquid-cooled, the majority are air cooled. Have high
power-to-weight ratios because they have a comparatively small, lightweight crankcase. Opposed engines
typically vibrate less than other engines because an opposed engine's power impulses tend to cancel
each other. Most efficient, dependable, and economical type available for light aircraft.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Engine Components:
1. Crankcase - The foundation of a reciprocating engine. It contains the engine's internal parts and
provides a mounting surface for the engine cylinders and external accessories. It is the housing that
encloses the various mechanisms surrounding the crankshaft. The crankcase provides a tight enclosure
for the lubricating oil as well as a means of attaching a complete engine to an airframe. Most aircraft
crankcases are made of cast aluminum alloys.
General Functions of the Crankcase:
1. The crankcase must support itself
2. It contains the bearings in which the crankshaft revolves
3. It provides a tight enclosure for the lubricating oil
4. It supports various internal and external mechanisms of the powerplant to the airplane
5. It provides support for the attachment of the cylinders
6. By the reason of its strength and rigidity, it prevents the misalignment of the crankshaft and it bearings.
Types of Engine Crankcases:

In Line and V type crankcase

Opposed engine crankcase

Radial engine crankcase
In Line and V type Engine Crankcase

Usually has four major sections:

Front or Nose section - directly behind the propeller in most tractor type airplanes. Its function is to house the propeller shaft, the
propeller thrust bearing, the propeller reduction gear train, and sometimes a mounting pad for the propeller governor.

Main or Power section - where the cylinders are normally mounted

Fuel induction and Distribution section - normally located next to the main or power section this section houses the diffuser vanes
and supports the internal blower impeller. Contains the induction manifold.

Accessory section - It contains the accessory drive gear train has mounting pads for the fuel pump, coolant pump, vacuum pump,
oil pump, magnetos, tachometer generator
Opposed Engine Crankcase - A typical horizontally opposed engine crankcase consists of two halves of cast aluminum alloy that are manufactured
either with sand castings or by using permanent molds.
Radial Engine Crankcase - radial engine crankcases are divided into distinct sections.
Four Main Sections of Radial Engine Crankcase:

nose section

power section

supercharger section

accessory section
Nose Section - mounted at the front of a radial engine crankcase and
bolts directly to the power section. The nose section usually houses
and supports a propeller governor drive shaft, the propeller shaft, a
cam ring, and a propeller reduction gear assembly if required. In
addition, many nose sections have mounting points for magnetos
and other engine accessories.
Main or Power Section - represents the section of the crankcase where the reciprocating motion of the pistons is converted to the rotary motion of
the crankshaft. Supports crankshaft bearings, contains cylinder pads where cylinders are mounted.
Diffuser/Blower Section/Supercharger Section - located directly behind the power section and is generally made of cast aluminum alloy or
magnesium. As its name implies, this section houses the supercharger and its related components. Also called “fuel induction and distribution
section”. Provides housing for attachments of induction pipes, manifold pressure lines.
Accessory Section - A typical accessory section houses gear trains containing both spur- and bevel-type gears that drive various engine components
and accessories. Has mounting pads for fuel pump, oil pump, tachometer generators etc.
2. Cylinder - provides a combustion chamber where the burning and expansion of gases takes place to produce
power. Considered as the powerhouse of the engine, where the chemical energy of the fuel is converted to
mechanical energy. A cylinder houses the piston and connecting rod assembly as well as the valves and spark
plugs. The two parts are cylinder head and the cylinder barrel.
Cylinder Barrel - The most commonly used material is a high-strength steel alloy such as chromiummolybdenum steel (SAE 4130 or 4140), or nickel chromium molybdenum steel. The exterior of a cylinder barrel
consists of several thin cooling fins that are machined into the exterior cylinder wall. The inside of a cylinder is
called cylinder bore.
Choke Bore Cylinder – cylinder with bores that are machined with a slight taper. In other words, the
diameter of the top portion of the barrel is slightly smaller than the diameter at the cylinder skirt. This is
designed to compensate for the uneven expansion caused by the higher operating temperatures and larger
mass near the cylinder head.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Principal Requirements of a Cylinder Assembly Design:

Strength to withstand internal pressures developed during operation.

Light weight

heat conducting properties to obtain efficient cooling

a design which is easy and inexpensive to manufacture, inspection, and maintenance
Cylinder Heads - acts as a lid on the cylinder barrel to provide an enclosed chamber for combustion. Cylinder heads contain intake and exhaust
valves, ports, spark plugs, valve actuating mechanisms, and also serve to conduct heat away from the cylinder barrels. Air-cooled cylinder heads are
generally made of either forged or die-cast aluminum alloy.
Inner Shapes of Cylinder Heads:

Flat

Semispherical - has proved to be the most satisfactory because it is stronger and provides for more rapid and thorough scavenging of
exhaust gases.

Peaked
Cylinder Numbering:

Regardless of how an engine is mounted in an aircraft, the propeller shaft end is always referred to as the front of an engine, and the
accessory end is always the rear of an engine.

When referring to either the right or left side of an engine, always assume you are viewing the engine from the rear, or accessory end

Crankshaft rotation is also referenced from the rear of an engine and is specified as either clockwise or counterclockwise.
Cylinder Numbering for Radial Engines:


Single-row radial engine cylinders are numbered consecutively starting
with the top cylinder and progressing clockwise as viewed from the rear
of the engine.
However, on double-row radial engines, all odd-numbered cylinders are
in the rear row, and all even numbered cylinders are in the front row.
Cylinder Numbering for In Line and V Engines:
The left and right side are determined by looking toward the propeller from the
accessory end. Cylinder number one on an in-line engine is the cylinder nearest the accessory
end, and the numbers progress toward the propeller.
Cylinders on a V-engine are numbered in the same way, but you identify the left and right banks
by looking from the accessory end toward the propeller, regardless of the way the engine is
installed in the aircraft.
3. Spark Plugs - an electrical device that fits into the cylinder head and ignites air fuel mixtures.
4. Pistons - a cylindrical plunger that moves up and down, back and forth within a cylinder. Pistons perform two primary functions; first, they draw
fuel and air into a cylinder, compress the gases, and purge burned exhaust gases from the cylinder; second, they transmit the force produced by
combustion to the crankshaft. Usually made of aluminum alloy AMS 4140 for forged pistons Alcoa 132 alloy for cast pistons.
Parts of a Piston:
1. Piston Head - The piston's top surface is called the piston head and is directly exposed to the
heat of combustion.
2. Ring Grooves - cut into a piston's outside surface to hold a set of piston rings. As many as six
ring grooves may be machined around a piston.
3. Ring Land - The portion of the piston between the ring grooves.
4. Piston pin boss - is an enlarged area inside the piston that provides additional bearing area for
a piston pin which passes through the piston pin boss to attach the piston to a connecting rod.
5. Piston skirt - To help align a piston in a cylinder, the piston base is extended to form the piston
skirt.
Piston Head Designs:
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Cam-Ground Piston - A cam ground piston is machined with a slightly oval shape. That is, the diameter of the piston
parallel to the piston boss is slightly less than the diameter perpendicular to the piston boss. All pistons expand as
they heat up. However, due to the added mass at the piston boss, most pistons expand more along the piston boss
than perpendicular to the piston boss. This uneven expansion can cause a piston to take on an oblong, or oval shape,
at normal engine operating temperatures, resulting in uneven piston and cylinder wear. One way to compensate
for this is with a cam ground piston.
Piston Rings - fit into the piston grooves but spring out to press against the cylinder
walls.
Purposes of Piston Rings:
1. They prevent leakage of gas pressure from the combustion chamber,
2. reduce oil seepage into the combustion chamber,
3. Transfer heat from the piston to the cylinder walls.
Piston Ring Joints
 Butt
 Step
 Angle
Types of Piston Rings:
1. Compression rings - prevent gas from escaping past the piston during engine operation and are placed
in the ring grooves immediately below the piston head. Most aircraft engines typically use two or
three compression rings on each piston. The cross section of a compression ring can be rectangular,
wedge shaped, or tapered.
2.
Oil rings - control the amount of oil that is applied to the cylinder walls as well as prevent oil from
entering the combustion chamber. The two types of oil rings that are found on most engines are oil
control rings and oil scraper rings.
Oil Control Rings - are placed in the grooves immediately below the compression rings. The primary
purpose of oil control rings is to regulate the thickness of the oil film on the cylinder wall.
Oil Scraper Rings - used to regulate the amount of oil that passes between the piston skirt and the cylinder
wall. Sometimes called an oil wiper ring, usually has a beveled face and is installed in a ring groove at the
bottom of the piston skirt.
Piston Pin - A piston pin joins the piston to the connecting rod. Piston pins are sometimes called wrist pins.
Piston Pin Classifications:
1. Stationary - are held tightly in place by a setscrew that prevents movement.
2. Semi-floating - retained stationary in the connecting rod by a set clamp that engages a slot in the pin. Allows little movement.
3. Full-floating - free to rotate in both the connecting rod and the piston, and are used in most modern aircraft engines.
5. Connecting Rods - the link which transmits the force exerted on a piston to a crankshaft. Most
connecting rods are made of a durable steel alloy; however, aluminum can be used with low
horsepower engines. One end of a connecting rod connects to the crankshaft and is called the crankpin
end the other end connects to the piston and is called the piston end.
Types of Connecting Rods:
1. Plain Type Connecting Rods - used in opposed and in-line engines.
2. Master and Articulated Rods - commonly used in radial engines. With this type of assembly, one
piston in each row of cylinders is connected to the crankshaft by a master rod. The remaining pistons
are connected to the master rod by articulated rods. Therefore, in a nine cylinder engine there is one master rod and eight articulating rods, while a
double row 18 cylinder engine has two master rods and 16 articulating rods.
3. Fork and Blade - used primarily in V-type engines and consists of a fork connecting rod and a blade connecting rod.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
6. Valves - regulate the flow of gases into and out of a cylinder by opening and closing at predetermined times in the combustion process. Each
cylinder has at least one intake valve and one exhaust valve.
Intake valve - controls the amount of fuel/air mixture that enters a cylinder through the intake port. Intake valves operate at lower temperatures
than exhaust valves are typically made of chrome, nickel, or tungsten steel.
Exhaust valve allows the exhaust gases to exit the cylinder through the exhaust port. Exhaust valves must endure much higher temperatures. They
are usually made of more heat resistant metals such as inconel, silicon-chromium or cobalt-chromium alloys. To help dissipate heat better, some
exhaust valve stems are hollowed out and then partially filled with metallic sodium. When installed in an operating engine, the sodium melts when
the valve stem reaches approximately 208 degrees Fahrenheit. The melted sodium circulates naturally due to the up and down motion of the valve
and helps carry heat from the valve head into the stem where it is dissipated through the cylinder head.
The most common type of valve used in aircraft engines is the poppet valve which gets its name from the popping action of the valve.
Head Profiles of aircraft engine valves:
Flat-head valve - has a flat head and is typically used only as an intake valve in aircraft engines.
Semi-tulip valve - has a slightly concave area on its head
Tulip - has a deep, wide indented area on its head.
Mushroom valves - have convex heads and are not commonly found on aircraft engines.
Basic Components of a Poppet Valve:
1. Valve face - is that portion of the valve that creates a seal at the intake and exhaust ports. A
valve face is typically ground to an angle of between 30 and 60 degrees to form a seal against
the valve seat when the valve is closed.
2. Valve Seat - a circular ring of hardened metal that provides a uniform sealing surface for the
valve face.
3. Valve stem - acts as a pilot to keep the valve head properly aligned as it moves back and forth.
4. Valve Neck - Most valve stems are surface hardened to resist wear and are joined to the valve
head at the valve neck.
Split key or keeper key - acts as a lock ring to keep the valve spring retaining washers in place and
hold the valve in the cylinder head.
Safety circlet or spring ring - prevents the valve from falling into the cylinder in the event the valve
tip breaks off.
Valve Seating Components:
1. Valve Face - portion of the valve that creates a seal at the intake and exhaust ports.
2. Valve Seat - a circular ring of hardened metal that provides a uniform sealing surface for the valve
face.
3. Valve Guide - is a cylindrical sleeve that provides support to the valve stem and keeps the valve face
aligned with the valve seat.
4. Valve Springs - are helical-coiled springs that are installed in the cylinder head and provide the force
that holds the valve face firmly against the valve seat.
5. Valve Spring Retainer – holds the valve springs in place.
Valve float/Valve Surge - occurs when the frequency of a valve spring begins to vibrate at its resonant
frequency. When this occurs, the spring loses its ability to hold the valve closed. By installing two or more
springs of different sizes, it is nearly impossible for both springs to vibrate at the same time, leaving one
spring free to close the valve.
Valve Operating Mechanisms - open each valve at the correct time, hold it open for a certain period, and then close the valve. Consists of
Camshaft, valve lifter or tappet, push rod, and rocker arm.
The valve operating mechanism
in a typical horizontally opposed engine:
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Camshaft – a device for actuating the valve lifting mechanism. Typically used in opposed engines, camshaft consists of a
round shaft with a series of cams, or lobes, that transform the circular motion of the crankshaft to the linear motion needed
to actuate a valve. The camshaft is driven by a gear that mates with another gear attached to the crankshaft.
Cam ring - in place of a camshaft, a radial engine uses one or two cam rings, depending on the number of cylinder rows. A
circular piece of steel with a series of raised cam lobes on its outer edge. A cam ring for a typical seven cylinder engine has
three or four lobes while a cam ring in a nine cylinder engine has four or five lobes. Each lobe is constructed with a cam ramp
on each side of a lobe. This ramp reduces the initial shock of an abruptly rising lobe. The smooth area between the lobes is
called the cam track.
Valve lifter or tappet – a mechanism to transmit the force of the cam to the push rod. Most opposed engines use
hydraulic lifters. Hydraulic lifters differ from solid lifters in that a hydraulic lifter uses oil pressure to cushion the impact
of the cam lobe striking the lifter and removes any play within the valve operating mechanism.
Cam Ring Rotation Speed:
Push Rod – a steel or aluminum alloy rod or tube situated between the valve lifter and the rocker arm to transmit the motion of the valve lifter.
Rocker Arm – a pivoting lever located in the cylinder head that changes the lifting movement of the push rod into the downward motion needed
to open a valve. The entire rocker arm pivots on a shaft that is suspended between two rocker arm bosses that are cast into the cylinder head.
Valve clearance describes the clearance, or space, between the tip of the valve stem and the rocker arm face. It is either cold or hot or running
clearance. a cold clearance is set when the engine is cold and, due to the expansion properties, is typically less than the hot or running clearance,
which is set when the engine is hot.
7. Crankshafts - the backbone of a reciprocating engine. Its main purpose is to transform
the reciprocating motion of the pistons and connecting rods into rotary motion to turn
a propeller. A typical crankshaft has one or more cranks, or throws, located at specified
points along its length. Generally made of chromium-nickel molybdenum steel.
Parts of a Crankshaft
1. Main Bearing Journal/Main Journal - - represent the centreline of a crankshaft
and support the crankshaft as it rotates in the main bearings. Center of rotation
of the crankshaft. All crankshafts require at least two main journals to support the crankshaft, absorb the operational loads, and transmit
stress from the crankshaft to the crankcase.
2. Crankpin - or connecting-rod bearing journals or throws, serve as attachment points for the connecting rods. To reduce total crankshaft
weight, crankpins are usually hollow. This hollow construction also provides a passage for lubricating oil. In addition, a hollow crankpin serves
as a collection chamber for sludge, dirt, carbon deposits, and other foreign material. This is called sludge chamber
3. Crank cheek or crank arm - required to connect the crankpin to the crankshaft.
4. Counterweights and dampers - helps balance the crankshaft. Its function is to relieve the whip and vibration caused by rotation of the
crankshaft.
Crankshaft Balance
1. Statically Balance - when the weight of an entire crankshaft assembly is balanced around its axis of rotation.
2. Dynamically Balance - refers to balancing the centrifugal forces created by a rotating crankshaft and the impact forces created by an
engine's power impulses. The most common means of dynamically balancing a crankshaft is through the use of dynamic dampers.
Dynamic Dampers - a weight which is fastened to a crankshaft's crank cheek assembly in such a way that it is free to move back and forth in a small
arc.
Crankshaft Types:
1. Single Throw or 360 degree - used on single-row radial engines. As its name implies, a single-throw crankshaft consists of a single crankpin
with two main journals that support the crankshaft in the crankcase. A single-throw crankshaft may be constructed out of either one or two
pieces.
2. Two Throw - Used on Twin-row radial engines, one throw for each bank of cylinders. The throws on a two-throw crankshaft are typically set
180 degrees from each other and may consist of either one or three pieces.
3. Four Throw - used on four cylinder opposed engines and four cylinder in-line engines.
4. Six Throw - Used on six cylinder opposed and in-line engines and 12 cylinder V-type engines.
8. Bearings - any surface which supports and reduces friction between two moving parts. A part in which a journal, pivot, shaft turns or revolves.
Typical areas where bearings are used in an aircraft engine include the main journals, crankpins, connecting rod ends, and accessory drive shafts.
There are two ways in which bearing surfaces move in relation to each other. One is by the sliding movement of one metal against another, and the
second is for one surface to roll over another.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Types of Bearings:
1. Plain Bearing - generally used for crankshaft main bearings, cam ring and camshaft bearings, connecting rod end bearings,
and accessory drive shaft bearings. These bearings are typically subject to radial loads only. Plain bearings are usually made
of nonferrous metals such as silver, bronze, babbit, tin, or lead.
2.
Ball Bearing - consists of grooved inner and outer races, one or more sets of polished steel balls, and a bearing retainer.
The balls of a ball bearing are held in place and kept evenly spaced by the bearing retainer, while the inner and outer
bearing races provide a smooth surface for the balls to roll over. Ball bearings have the least amount of rolling friction.
Ball bearings are well suited to withstand thrust loads
3.
Roller Bearing - similar in construction to ball bearings except that polished steel rollers are used instead of balls. The
rollers provide a greater contact area and a corresponding increase in rolling friction over that of a ball bearing. Has two types
namely: straight roller bearings which suitable when the bearing is subjected to radial loads only such as crankshafts main
bearings, and tapered roller bearings that allow the bearing to withstand both radial and thrust loads.
9. Propeller Reduction Gears - permits a propeller to turn slower than the engine. This allows an engine to turn at a relatively fast
speed and a propeller to turn at a more efficient slower speed. Reduction gear systems currently used on aircraft engines utilize spur gears, planetary
gears, or a combination of the two.
Spur gears - have their teeth cut straight across their circumference and can be either external or
internal. The simplest type of reduction gearing consists of two external tooth spur gears, one small
gear on an engine crankshaft and one larger gear on the propeller shaft.
Planetary reduction gear - In a planetary gear system, the propeller shaft is attached to a housing
which contains several small gears called planetary gears. The planetary gears rotate between a sun
gear and a ring or bell gear. The crankshaft drives either the sun gear or ring gear, depending on the
individual installation.
10. Propeller Shafts – has three types namely: Tapered Propeller Shafts, Splined Propeller Shafts, Flanged Propeller Shafts
Tapered Propeller Shafts - were used on most of the early, low-powered engines. On a tapered propeller
shaft, the shaft tapers, or gets smaller in diameter, as you move out toward the end of the shaft. The end of
the shaft is threaded to receive a propeller retaining nut.
Splined propeller shafts - Increases in engine power demanded a stronger method of attaching propellers.
Therefore, most high powered radial engines use splined propeller shafts. A spline is a rectangular groove that
is machined into the propeller shaft.
Flanged Propeller Shafts - Most modern horizontally opposed aircraft engines use a flanged propeller shaft. With
this type of propeller shaft, a flat flange is forged directly onto the end of a crankshaft and a propeller is bolted to the
flange.
Engine Identification:
The first letters indicate an engine's cylinder arrangement and basic configuration. A list of the letters used include:
O - Horizontally opposed engine
R - Radial engine
1 - In-line engine
V - V-type engine
T - Turbo charged
I - Fuel injected
S - Supercharged
G - Geared nose section (propeller reduction gearing)
L - Left-hand rotation (for multi-engine
installations) H - Horizontal mounting (for helicopters)
V - Vertical mounting (for helicopters)
A - Modified for aerobatics
The numbers in an engine identification code indicate an engine's piston displacement in cubic inches. For example, an 0-320 indicates a
horizontally opposed engine with a displacement of 320 cubic inches. Some engine identification codes include a letter designation after the
displacement to indicate a model change or modification to a basic engine.
Engine Identification Examples:
LIO – 360 – C

engine that has left hand rotation,

is fuel injected and

horizontally opposed,

displaces 360 cubic inches, and

C model
GTSIO-520-F

geared,

turbo-supercharged,

fuel injected,

horizontally opposed,

displaces 520 cubic inches, and

is an F model.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Engine Controls
1. Throttle – controls the engine power
2. Propeller Control – for constant speed and controllable pitch propeller
3. Mixture Control – used to adjust fuel air mixture with settings, full rich, lean, idle cut off
4. Carburator air heater – operate the gate valve in the air induction system to provide either cold air or hot air for carburator. Heated air is
required when in danger of icing.
5. Miscellaneous Engine Controls – includes cowl flaps, oil coolers, superchargers etc.
Reciprocating Engine Theory of Operation:
The Four Stroke Five Event Engine Cycle:

Strokes
1. Intake - During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture.

2.
Compression - As the piston rises the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives
the piston upward, compressing the fuel/air mixture.
3.
Power - At the top of the compression stroke the spark plug fires, igniting the compressed fuel. As the fuel burns it expands,
converting the heat produced by the combustion into mechanical energy, driving the piston downward. Both Valves remain closed.
4.
Exhaust - At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the
piston drives the exhausted fuel out of the cylinder.
Events
1.
2.
3.
4.
5.
Intake
Compression
Ignition
Power or Expansion
Exhaust or Scavenging
The Two Stroke Cycle Engine - The two-stroke cycle is similar to the four-stroke cycle in that the same five events occur
in each operating cycle. However, the five events occur in two piston strokes rather than four strokes. This means that
one cycle is completed in one crankshaft revolution.
Two Stroke, Three events cycle:
Stroke
Intake, Compression
Power, exhaust stroke
Events
Compression
Ignition and Power
Exhaust and Intake
Two Stroke Cycle Operation:
As a two-stroke cycle begins, the piston moves up and two events occur simultaneously. The piston compresses the fuel/air charge in the cylinder
and creates an area of low pressure within the crankcase. This low pressure pulls fuel and air into the crankcase through a check valve. Once the
piston is a few degrees before top dead center, ignition occurs and the fuel/air mixture begins to burn. As the piston passes top dead center the
pressure from the expanding gases begin to force the piston downward on the power stroke. This downward stroke also compresses the fuel/air
charge in the crankcase. As the piston approaches the bottom of the power stroke, the exhaust port is uncovered and spent gases are purged from
the cylinder. A split second later, the piston uncovers the intake port and allows the pressurized fuel/air charge in the crankcase to enter the cylinder.
The cycle then repeats itself as the piston compresses the fuel/air charge in the cylinder and draws a fresh fuel/air charge into the crankcase.
Two Stroke Advantages:

Requires fewer moving parts to accomplish the same amount of output as four stroke engines.

Cheaper to maintain than four stroke engines.

Smaller and simple in construction than four stroke engines.
Two Stroke Disadvantages:

Less fuel efficient than four stroke.

Quicker wear of the engine’s moving parts.

More polluting than four stroke engines since oil is burnt with the fuel and air mixture.
The Diesel Engine/Compression Ignition Engine - A diesel engine is an internal combustion engine which operates using the diesel cycle named after
Dr. Rudolph Diesel. Diesel engines have the highest rate of energy to fuel (kwh/lbs) compared to any internal or external combustion engine. The
defining feature of the diesel engine is the use of compression ignition to burn the fuel, which is injected into the combustion chamber during the
final stage of compression
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
The Four Stroke of Diesel Engine:
1. Suction stroke: Pure air gets sucked in by the piston sliding downward.
2. Compression stroke: The piston compresses the air above and uses thereby work, performed by the crankshaft.
3. Power stroke: In the upper dead-center, the air is max. Compressed: Pressure and Temperature are very high. Now the black injection
pump injects heavy fuel in the hot air. By the high temperature the fuel gets ignited immediately (auto ignition). The piston gets pressed
downward and performs work to the crankshaft.
4. Expulsion stroke: The burned exhaust gases are ejected out of the cylinder through a second valve by the piston sliding upward again.
Engine Geometry Terminologies:
Cycle – series of events returning to its original state. One cycle includes the intake, compression, ignition,
power, and exhaust events.
Engine Cycle – series of events that an internal combustion engine undergoes while it is operating and
delivering power. There are two revolutions of the crankshaft for each cycle of the engine.
Top Dead Center (TDC) – the position of the piston inside the cylinder when it reaches the top most of its
travel.
Bottom Dead Center (BDC) – the position of the piston inside the cylinder when it reaches the bottom most
of its travel.
Stroke (S) – the total distance that the piston travels from the top dead center to the bottom dead center.
Bore – the inside diameter of the cylinder
Piston displacement or volume displacement (VD) – the volume being travelled by the piston as it moves
from the TDC to the BDC. The product of the area of the piston, length of the stroke, and the number of
cylinders.
Clearance volume (Vc) – the volume within the cylinder when the piston is at the TDC.
Total volume (VT) – the overall or total volume within the cylinder.
Valve timing is the term used to describe the point at which the intake and exhaust valves begin to open and close during the four-stroke cycle. The
number of crankshaft degrees that the intake valve opens before the piston reaches top dead center is called valve lead. The number of degrees the
exhaust valve remains open past top dead center is called valve lag. The combination of valve lead and lag is called valve overlap and represents the
number of degrees that both the intake and exhaust valves are unseated.
Purposes of Valve Overlap:
1. To allow the fuel/air charge to enter the cylinder as early as possible to increase engine efficiency and aid in cylinder cooling.
2. To provide more complete exhaust gas scavenging.
Firing Order - An engine's firing order represents the sequence in which the ignition event occurs in different cylinders. Each engine is designed
with a specific firing order to maintain balance and reduce vibration.
Single Row Radial Engines Firing Order - On all single-row radial engines, the odd numbered cylinders fire in succession first, followed by the even
cylinders. Therefore, the firing order on a seven cylinder radial engine is 1-3-5-7-2-4-6 while the firing order on a nine cylinder radial engine is 1-35-7-9-2-4-6-8.
Double Row Radial Engines Firing Order - A double-row radial engine is essentially two single-row radial engines that share a common crankshaft.
Like the single-row radial, the power pulses must occur between alternate cylinders in each row, in sequence. In other words, two cylinders in the
same row can never fire in succession. In addition, to balance the power pulses between the two rows, when a cylinder fires in one row, its opposite
cylinder must fire in the second row.
For example, consider a 14 cylinder double-row radial engine, consisting of two rows of seven cylinders each. All the odd numbered cylinders are in
the rear row while all the even numbered cylinders are in the front row. Therefore, if the number 1 cylinder fires in the back row, the cylinder opposite
the number 1 cylinder in the front row must fire. In a 14 cylinder double-row engine, the number 10 cylinder is opposite the number 1 cylinder. The
power pulses then go back and forth between rows in alternating cylinders to obtain a firing order of 1-10-5-14-9-4-13-8-3-12-7-2-11-6
Piston Displacement/Volume Displacement - defined as the volume of air displaced by a piston as it moves from bottom center to top center. To
determine a piston's displacement, you must multiply the area of a piston head by the length of the piston stroke. Expressed in cubic inches of
volume. The total piston displacement of an engine is the total volume displaced by all the pistons during one revolution of the crankshaft. It equals
the number of cylinders in the engine multiplied by the piston displacement of one piston. All other factors remain equal, the greater the total
piston displacement, the greater the maximum horsepower that an engine can develop
Formula for Piston Displacement:
Piston Displacement = Area of piston x L
where:
Area of the Piston
=
d
4
2
L = lenght of stroke
where:
d = diameter of the piston head/bore
Total Piston Displacement = Area of the piston x L x n
where: n = number of cylinders
Square Engine - The Bore and Stroke are equal. It provides the best and efficient engine performance
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Engine Power Calculations:
Indicated Horsepower (IHP) - is the total power actually developed in an engine's cylinders without reference to friction losses within the engine. To
calculate indicated horsepower, the average effective pressure within the cylinders must be known. This average pressure is referred to as indicated
mean effective pressure
Where:
P = the Indicated Mean Effective Pressure, or IMEP inside the cylinder during a power stroke.
L = the length of the stroke in feet or fractions of a foot.
A = the area of the piston head in square inches.
N = the number of power strokes per minute for one cylinder. On a four-stroke engine, this is found by dividing the rpm by two.
K = the number of cylinders on the engine.
Problem:
Compute the indicated horsepower for a six-cylinder engine that has a bore of five inches, a stroke of five inches, and is turning at 2,750 rpm with a
measured IMEP of 125 psi per cylinder.
Answer: IHP = 255 hp
Friction Horsepower - The power required to overcome the friction and energy losses is known as friction horsepower.
Brake Horsepower - The actual amount of power delivered to the propeller shaft is called brake horsepower. One way to determine brake
horsepower is to subtract an engine's friction horsepower from its indicated horsepower.In practice, the measurement of an engine's brake
horsepower involves the measurement of a quantity known as torque, or twisting moment. Torque is a measure of load and is properly expressed
in pound-inches or pound-feet. 85 – 90% of the IHP.
Devices that measure Engine Torque:

Dynamometer

Prony Brake Dynamometer

Electric or Hydraulic Dynamometer

Torquemeter
Computations of Engine Power using Prony Brake Dynamometer:

As the propeller shaft rotates, it tries to spin the brake which, in turn, applies
force to a scale.

If the resulting force registered on the scale is multiplied by the length of the
arm, the resulting product represents the torque exerted by the rotating shaft.
Problem:
Given:
Force on scales = 200 lb
Length of arm = 3.18 ft
RPM = 3000
Answer: BHP = 363 hp
IHP  BHP  FHP
Indicated Horsepower in terms of BHP and FHP:
Mean Effective Pressure - an average pressure inside the cylinders of an internal combustion engine based on some calculated or measured
horsepower. It increases as manifold pressure increases.
That portion of IMEP that produces brake horsepower is called brake mean effective pressure (BMEP).
The remaining pressure used to overcome internal friction is called friction mean effective pressure (FMEP).
Brake Mean Effective Pressure
33,000
BMEP  (bhp)
LANK
 792,000  bhp 


BMEP  
 disp  rpm 
Where: L = stroke, ft
A = area of bore, sq. in.
N = number of working strokes per minute
K = number of cylinders
- in a four stroke cycle engine, N = ½ rpm of the engine
 bhp 

BMEP  K 
rpm


AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
Where: disp. = engine displacement
Where: K = 792000/disp. or the K factor of the engine
PREPARED BY: ENGR IAN M. TALAG
Problems:
1. Given:
Bhp = 1000
Stroke = 6 in
Bore = 5.5 in
RPM = 3000
Number of cycles = 12
Answer: BMEP = 154.32 psi
2. If an R 1830 engine is turning at 2750 rpm and developing 1100 hp, what is the bmep?
Efficiency - The ratio of the input energy to the output energy, or the energy supplied to produce work and the actual energy being converted into
work.
Thermal Efficiency - An engine's thermal efficiency (TE) is a ratio of the amount of heat energy converted to useful work to the amount of heat energy
contained in the fuel used to support combustion. In other words, thermal efficiency is a measure of the inefficiencies experienced when converting
the heat energy in fuel to work. Thermal efficiency can be calculated using either brake or indicated horsepower. If brake horsepower is used, the
result is brake thermal efficiency (BTE), and if indicated horsepower is used, you get indicated thermal efficiency (ITE).
Brake Thermal Efficiency Formula:
BHPx 33,000
weightoffuelburned/ min xHeatValue( BTU ) x778
Indicated Thermal Efficiency Formula:
Note: Heat value in (BTU) = 1 pound of avgas contains 20,000 BTUs of heat energy
Problems:
1. Determine the brake thermal efficiency of a piston engine that produces 150 brake horsepower while burning 8 gallons of aviation gasoline per
hour.
2. An engine delivers 85 bhp for a period of 1 hour and during that time consumes 50 pounds of fuel. Assuming the fuel has a heat content of
18,800 BTU per pound, find the thermal efficiency of the engine.
Answer: BTE = 23 %
Volumetric Efficiency - Volumetric efficiency (VE) is the ratio of the volume of fuel and air an engine takes into its cylinders to the total piston
displacement. For example, if an engine draws in a volume of fuel and air that is exactly equal to the engine's total piston displacement, volumetric
efficiency would be 100 percent.
Mechanical Efficiency - the ratio of brake horsepower to indicated horsepower and represents the percentage of power developed in the cylinders
that reaches the propeller shaft. For example, if an engine develops 160 brake horsepower and 180 indicated horsepower, the ratio of brake
horsepower to indicated horsepower is 160:180, which represents a mechanical efficiency of 89 percent.
Mechanical Efficiency:
output BHP

input
IHP
Problems:
1. A four stroke cycle, 4 cylinder reciprocating engine with a speed of 1800 rpm has a stroke of 8.0 inches and a cylinder bore diameter of 6 inches.
The mean effective pressure inside the cylinder is 200 psi and the mechanical efficiency of the engine is 80 %. Determine:
a. Piston displacement
b. IHP
d. BHP
c. FHP
2. Compute the horsepower output of the following describe engine operating at 2000 rpm, bore 3.5 in., stroke 4.0 in., 6 cylinders, 140 psi bmep.
3. Compute the piston displacement of a radial engine having 9 cylinders, a bore of 5 in. and stroke of 5 in.
4. Compute the compression ratio of an engine which has a bore of 5 in. and a stroke of 5 in. when the volume at the combustion chamber is 16.36
cu.in. with the piston at TDC
5. Compute the bmep of an engine when the output is 450 hp, 2300 rpm, bore and stroke are each 5.5 in, and with 9 cylinders.
Manifold Pressure - the pressure of the fuel/air mixture in the intake manifold between the carburator or internal supercharger and the intake valve.
Changes in manifold air pressure affect the amount of power an engine can produce for a given rpm. Excessive pressures and temperatures shorten
engine life by overstressing cylinders, pistons, connecting rods, bearings, crankshaft journals, and valves. Continued operation past upper manifold
absolute pressure limits leads to worn engine parts, decreasing power output and lower efficiency, or worse, engine failure.
Detonation - the uncontrolled, explosive ignition of the fuel/air mixture in the cylinder. Detonation causes high cylinder temperatures and pressures
which lead to a rough running engine, overheating, and power loss. If detonation occurs in an engine, damage or even failure of pistons, cylinders,
or valves can happen. The high pressures and temperatures, combined with the high turbulence generated, cause a "hammering" or "scrubbing"
action on a cylinder and piston that can burn a hole completely through either of them in seconds. You can detect detonation as a "knock" in the
engine.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Causes of Detonation:

using a fuel grade lower than recommended

Allowing the engine to overheat.

Wrong ignition timing

fuel/air mixture too lean,

compression ratios of 12:1 or higher
Pre-ignition - takes place when the fuel/air mixture ignites too soon. It is caused by hot spots in a cylinder that ignite the fuel/air mixture before the
spark plugs fire. A hot spot can be caused by something as simple as a carbon particle, overheated valve edges, silica deposits on a spark plug, or a
red-hot spark plug electrode. Hot spots are caused by poor engine cooling, dirty intake air filters, or shutting down the engine at high rpm. When the
engine continues running after the ignition is turned off, preignition may be the cause.
Compression Ratio - defined as the ratio of cylinder volume with the piston at the bottom of its stroke to the volume with the piston at the top of its
stroke. For example, if there are 140 cubic inches of space in a cylinder when the piston is at bottom center and 20 cubic inches of space when the
piston is at top center, the compression ratio is 140 to 20. As a general rule, the higher the compression ratio, the greater an engine's power output.
Specific Fuel Consumption - the number of pounds of fuel burned per hour to produce one horsepower. For example, if an engine burns 12 gallons
per hour while producing 180 brake horsepower, the brake specific fuel consumption is .4 pounds per horsepower hour. Most modern aircraft
reciprocating engines have a brake specific fuel consumption (BSFC) that is between .4 and .5 pounds per horsepower hour.
Stoichiometric mixture - is a perfectly balanced fuel/air mixture of 15 parts of air to 1 part of fuel, by weight.
Best power mixture - develops maximum power at a particular rpm and is typically used during takeoff.
Best economy mixture - provides the best specific fuel consumption which results in an aircraft's maximum range and optimum fuel economy.
Take – Off Power Rating - determined by the maximum rpm and the manifold pressure at which the airplane may be operated during the process of
take-off. Time limitations of take-off power is 1 to 5 minutes
Rated Power - also called standard engine rating, the maximum horsepower output which can be obtained from an engine when it is operated at a
specified RPM and manifold pressure conditions, established as safe for continuous engine operations. Also called METO power or the Maximum
Except Take off Power.
Maximum Power - the greatest power output that the engine can develop at any time under any conditions. As manifold pressure increases, power
output of an engine increases. As rpm increases, power output of an engine increases.
Engine Distribution of Power:
Piston Engine Systems
INDUCTION SYSTEMS
Piston Engine Induction Systems
The primary purpose of an induction system in a reciprocating engine is to provide air in sufficient quantity to support normal combustion.
Classification of Reciprocating Engine Induction Systems:

Normally Aspirated

Supercharged

Turbocharged
Four Major Components of an Induction System of a Normally Aspirated Engine:
1. Air Intake/Air Scoop - An air intake, sometimes referred to as an air scoop, is designed to direct outside air into a carburetor or other fuel
metering device.
2.
Induction Air Filter - filters are typically installed in air intake ducts to prevent dust, sand, abrasive materials, or other contaminants from
entering the engine.
3.
Fuel Delivery System - The fuel delivery system on a normally aspirated engine can be either a carburetor or a fuel injection system. The
purpose of a fuel delivery system is to meter the amount of fuel and air that is delivered to the cylinders.
4.
Induction Manifold - consists of ducting that goes from the fuel metering device to the individual cylinders.
On a typical horizontally opposed engine, the intake manifold is the connecting point of all the individual pipes which deliver air or fuel/air
mixture to the cylinders.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Distribution Impeller - In large radial engines, even distribution of the fuel/air mixture is difficult to achieve. Therefore, to help ensure equal
distribution, some radial engines utilize a distribution impeller which is attached directly to the rear of the crankshaft. As the fuel/air mixture goes
into the center of the distribution impeller, centrifugal force distributes the mixture to the cylinders.
Induction system icing - occurs when water freezes in an induction system and restricts airflow to the engine. Induction ice can form when an aircraft
is flying through clouds, fog, rain, sleet, snow, or even in clear air when the relative humidity is high. Induction icing is generally classified as one of
three types: fuel evaporation, throttle, and impact.
Fuel evaporation ice - sometimes referred to as carburetor ice, is a result of the temperature drop that occurs when fuel is vaporized.
Throttle ice - is formed on the rear side of the throttle, or butterfly valve when it is in a partially closed position. The reason for this is that, as air
flows across and around the throttle valve, a low pressure area is created on the downstream side. This has a cooling effect on the fuel/air mixture
which can cause moisture to accumulate and freeze on the backside of the butterfly valve.
Impact ice is caused by visible moisture striking an aircraft and then freezing. Impact ice can also collect at points in an induction system where the
airflow changes direction, or where dents and protrusions exist.
Icing Indications on an Engine:
1. Decrease in engine power output.
2. On an aircraft equipped with a fixed-pitch propeller, the decrease in engine power is indicated by a drop in rpm followed by engine
roughness.
3. If an aircraft has a constant-speed propeller, the first indication of induction ice is a decrease in manifold pressure with no change in engine
rpm.
Carburetor Heating System:
1. Heater Muff – a metal shroud that surrounds an exhaust pipe, which functions as an air-to-air heat exchanger that warms the intake air and then
directs it to a carburetor air box.
2. De Icing Fluid – uses a deicing fluid which is sprayed into the air stream ahead of the carburetor to eliminate induction ice. With this type of system,
alcohol is commonly used as a deicing fluid. A typical system includes an alcohol reservoir, an electric pump, a spray nozzle, and cockpit controls.
Carburetor air temperature gauge, or CAT gauge - help inform a pilot when the temperature at the carburetor can support the formation of ice.
Supercharger - basically an engine driven air pump that increases manifold pressure and forces the fuel/air
mixture into the cylinders. The higher the manifold pressure, the more dense the fuel/air mixture and the more
power an engine can produce. Superchargers can have one or more stages. One stage represents an increase in
pressure. Superchargers are generally classified as either single stage, two stage, or multi stage depending on the
number of times compression occurs.
Ground Boosted Supercharger - Where a supercharger is used to increase the engine power output at sea level,
rather than to maintain normal engine power output up to a high altitude, the engine is fitted with what is called
a Ground Boosted Supercharger.
Altitude Boosted Supercharger - Superchargers capable of maintaining sea level values of power up to high
altitudes are called Altitude Boosted Superchargers.
Sea level supercharger, or ground boost blower - An early version of a single stage, single speed supercharger.
With this type of supercharger, a single gear-driven impeller is used to increase the power produced by an engine
at all altitudes.
Single Stage Two Speed Supercharger - With this type of supercharger, a single impeller may be operated at two
speeds. At the low speed, the impeller gear ratio is approximately 8:1; however, at the high speed, the impeller
gear ratio is stepped up to 11:1. The low impeller speed is often referred to as the low blower setting while the
high impeller speed is called the high blower setting.
Turbocharger Systems - Turbochargers are powered by an engine's exhaust gases. In other words, turbocharger
recovers energy from hot exhaust gases that would otherwise be lost. Turbochargers can
be controlled to maintain an engine's rated sea-level horsepower from sea-level up to the
engine's critical altitude. A drawback of gear driven superchargers is that they use a large
amount of the engine's power output for the amount of power increase they produce.
This problem is avoided with a turbosupercharger, or turbocharger. One difference of
turbocharger to supercharger is that on turbocharger only air is compressed, while on
supercharger, the mixture of fuel and air are both compressed.
Critical Altitude - defined as the maximum altitude under standard atmospheric conditions that a turbocharged engine can produce its rated horsepower. In other words, when
a turbocharged engine reaches it critical altitude, power output begins to decrease like a
normally aspirated engine.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Components of a Turbocharger System:
1. Centrifugal compressor impeller
2. Radial turbine
3. Compressor and Turbine housings
Operation of Turbocharger Systems:
As exhaust gases spin the turbine, the impeller draws in air and compresses it. The
turbocharger compresses the intake air and then sends the air to the air metering section of
the fuel metering device. Once metered, the air is routed through the intake manifold to the
cylinder intake ports where it is mixed with a metered amount of fuel. In addition to the friction
caused by high rotation speeds, turbochargers are heated by the exhaust gases flowing through
the turbine, and the compression of intake air. Therefore, a continuous flow of engine oil must
be pumped through the bearing housing to cool and lubricate the bearings. Approximately four
to five gallons of oil per minute are pumped through a typical turbocharger bearing housing to
lubricate the bearings and take away heat. To control the amount of exhaust gases that flow
past a turbocharger turbine, a valve known as a waste gate is used. When a waste gate is fully
open, all of the exhaust gases bypass the turbocharger and pass out the exhaust stack.
However, when a waste gate is fully closed, all of the exhaust gases are routed through the
turbine before they exit through the exhaust. The position of a waste gate can be adjusted either manually or automatically.
Intercooler - a small heat exchanger that uses outside air to cool the hot compressed air before it enters the fuel metering device in turbocharger
system.
Overboosting - If all the exhaust gases were allowed to pass through the turbine of a turbocharger, excessive manifold pressures, or overboosting
would result.
Turbocharger Manual Control Systems:

Manual linkage between the engine throttle valve and the waste gate valve – as the throttle is advanced, since there is a linkage between
the throttle valve and waste gate valve, the waste gate will close.

Cockpit control for the waste gate – waste gate is operated using a cockpit control

Adjustable Waste Gate Restrictor - a screw type restrictor that functions as a waste gate valve. Can be adjusted while the aircraft is on the
ground. The amount the restrictor is threaded in or out of the exhaust pipe determines the amount of exhaust gas that is forced to flow
through the turbocharger.
Turbocharger Automatic Control Systems

Waste gate actuator - With a waste gate actuator, the waste gate is held open by spring pressure and is closed by oil pressure acting on a
piston. Oil pressure is supplied to the actuator from the engine's oil system.

Absolute pressure controller - APC consists of a bellows and a variable restrictor valve. The bellows senses the absolute pressure of the
air before it enters the fuel metering device. This pressure is commonly referred to as upper deck pressure. As the bellows expands and
contracts, it moves the variable restrictor valve to control the amount of oil that flows out of the waste gate actuator. With this
automatic control system, oil flows into the waste gate actuator through a capillary tube restrictor.

Pressure-ratio controller – installed in parallel with the absolute pressure controller. The purpose of a pressure-ratio controller is to
monitor both the ambient and upper deck pressures and prevent the turbocharger from boosting the upper deck pressure higher than
2.2 times the ambient pressure.

Rate-of-change controller - installed in parallel with the absolute pressure controller and pressure-ratio controller, and prevents the
upper deck pressure from increasing too rapidly.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Sea Level Boosted Engines - are engines that are equipped with the type of turbocharger systems that are designed to maintain sea level engine
performance from sea level up to their critical altitude.
Components of Sea Level Boosted Engines Turbocharger:

Exhaust By Pass Valve Assembly - functions in a manner similar to the waste gate actuator

Density Controller - regulates the bleed oil flow from the exhaust bypass valve assembly only during full throttle operation.

Differential Pressure Controller - When a sea level boosted engine is operated at less than full throttle, the differential pressure
controller regulates turbocharger output.
Sea Level Boosted Turbocharger System:
Bootstrapping - describes a condition that occurs when a turbocharger system senses small changes in temperature or rpm and continually
changes the turbocharger output in an attempt to establish equilibrium. occurs during part-throttle operation and is characterized by a
continual drift or transient increase in manifold pressure.
Overshoot - In this case, the turbocharger controllers cannot keep up with the throttle movement and the manifold pressure overshoots the
desired value requiring the operator to retard the throttle as appropriate.
Power Recovery Turbine System (PRT) - A turbo compound engine is a reciprocating engine in which
exhaust driven turbines are coupled to the engine crankshaft. This system is used to obtain additional
power.
EXHAUST SYSTEM
Types of Piston Engine Exhaust Systems:
1. short stack or open system
2. The collector system
Short Stack system - generally used on nonsupercharged engines and low powered engines where
noise level is not a factor. Consists of short sections of steel tubing welded to a flange and bolted to the cylinder exhaust port.
Collector System - used on most large nonsupercharged engines and on installations where it would improve nacelle streamlining or
provide easier maintenance in the nacelle area.
Types of Collector Systems

opposed type engine exhaust manifold

radial engine collector rings
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Opposed Engine Exhaust Manifold - A typical system consists of risers from each cylinder and an exhaust collector on each side of the engine.
Radial Engine Exhaust Collector Rings - Radial engines use an exhaust manifold made up of pieces of tubing that are fitted together with loose slip
joints.
Collector Rings
Risers
Muffler - receives the exhaust from the cylinders and passes it through a
series of baffles to break up the sound energy.
Heat Exchangers - a stainless steel shroud or shell can be placed around the muffler. This shroud brings in
unheated outside air into a space between the muffler and the shroud. Since the muffler is being heated by
the exhaust gases, the air in this space is heated. Then through heater hoses and ducting, the heated air can
be used as cabin heat, or for de-ice or anti-ice purposes.
Exhaust augmentors - use the velocity of the exiting exhaust gases to produce a venturi effect to draw more airflow over the engine. Since the
exhaust augmentor heats up similar to a muffler, a heat exchanger could be placed around the augmentor. This heated air could then be used for
cabin heat or for de-ice or anti-ice purposes.
FUEL SYSTEMS
Two Basic Sections of Fuel Systems:

Airframe section - consists of all fuel system components from the fuel tanks to the engine-driven fuel pump.

Powerplant section - consists of an engine-driven fuel pump, if installed, a fuel metering device, and any other fuel delivery
components on the engine.
Volatility - is a measure of a fuel's ability to change from a liquid into a vapor. Volatility is usually expressed in terms of Reid vapor pressure
which represents the air pressure above a liquid required to prevent vapors from escaping from the liquid at a given temperature. The vapor
pressure of 100LL aviation gasoline is approximately seven pounds per square inch at 100 degrees F.
Vapor Lock - The resulting partial or complete interruption of the fuel flow.
Three General Causes of Vapor Lock:
1. lowering of the pressure on the fuel,
2. high fuel temperatures, and
3. Excessive fuel turbulence.
Octane Rating System - The most common grading system used for this purpose is the octane rating system. The octane number assigned to a fuel
compares the anti-knock properties of that fuel to a mixture of iso-octane and normal heptane. For example, grade 80 fuel has the same antiknock properties as a mixture of 80 percent iso-octane and 20 percent heptane.The higher the number, the more resistant a fuel is to knocking.
Types of Reciprocating Engine Fuel System:
1. the Gravity-feed system
2. the Pressure-feed system
Gravity Feed Fuel System - the simplest form of aircraft fuel systems is the gravity-feed system used on many high-wing, single-engine aircraft.
Pressure Feed Fuel System - On low-wing aircraft, the fuel metering device is above the fuel tanks. Therefore, a fuel pump must be used to
pressure-feed fuel to the fuel metering device. High wing aircraft equipped with fuel-injection or pressure carburetors also require a fuel pump. In
addition, a backup, or auxiliary pump is installed in case the engine-driven pump should fail.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Gravity Feed Fuel System
Pressure Feed Fuel System
Fuel System Components:

multiple fuel tanks,

Lines

filtering units

Pumps

Gauges

a priming system

In addition, some systems will include central refueling provisions, fuel dump valves, and a means of transferring fuel.
Fuel Tanks - Fuel Tanks are made of 3003 and 5052 aluminum alloys and several composite type materials. All fuel tanks are required to have a sump
and drain installed at their lowest point. The sump provides a convenient location for water and sediment to settle, allowing it to be drained from
the system.
Lines and Fittings - In modern aircraft, flexible fuel lines are often constructed from synthetic materials such as neoprene or Teflon, with the line's
diameter being dependent upon the engine's fuel flow requirements.
Fuel Strainers - removes contaminants from the fuel by providing a low point in the system where water and solid contaminants can collect.
represents the lowest point in a fuel system and must be located between the fuel tank and either the fuel metering device or engine-driven
fuel pump.
Engine Driven Fuel Pumps - Engine-driven fuel pumps are the primary fuel pressure pumps in a
pressure-feed fuel system. The purpose of an engine-driven fuel pump is to deliver a continuous
supply of fuel at the proper pressure during engine operation. A positive-displacement pump is a
pump that delivers a specific quantity per revolution. One type of positive-displacement pump that
is widely used is the vane-type fuel pump.
Auxiliary Fuel Pumps/Boost Pump - maintain a positive fuel pressure on the inlet side of the enginedriven fuel pump.
Purposes of the Auxiliary Fuel Pumps:
1. Helps prevent pump cavitation and vapor lock by pressurizing the fuel in the lines.
2. Providing the required fuel pressure for starting and transferring fuel between tanks which enables a pilot to redistribute fuel weight in flight
and maintain aircraft stability.
3. serve as a backup source for fuel pressure to the engine if the engine-driven fuel pump becomes clogged or fails.
Hand Operated Pumps - Two hand-operated fuel pumps used in aircraft include the wobble pump and manual
primer. A typical wobble pump consists of a vane and drilled shaft assembly that is rotated by a pump handle.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Centrifugal Pumps - Centrifugal pumps may be either submerged in a fuel tank or attached to the outside of the tank. A centrifugal pump is driven
by an electric motor and uses a small impeller to build fuel pressure.
Pulsating Electric Pumps - another type of auxiliary fuel pump that is widely used in small, low-wing aircraft. A typical pulsating fuel pump
consists of a solenoid coil installed around a brass tube that connects a fuel inlet chamber with a fuel outlet chamber.
By Pass Valve - The purpose of these valves is to let fuel bypass the engine-driven pump during engine starting or in case the pump fails
Pulsating Electric Pump
Bypass Valve
Centrifugal Pump
FUEL METERING SYSTEMS
Fuel Metering System - controls the amount of fuel being delivered to the engine.
Types of Metering Devices:
1. Carburetor
 Float Type Carburetor
 Pressure Injection Carburetor
2. Fuel Injection Unit
 Continuous
 Direct Fuel Injection Systems
Air/Fuel Ratio or Mixture ratio - The proportion of fuel and air that enters an engine. For example, a mixture containing 12 pounds of air and 1 pound
of fuel is referred to as a ratio of 12 to 1 (12:1).
Stoichiometric Mixture - the perfect mixture for combustion of air and fuel which is 1 pound of air for .067 pounds of fuel, or a 15:1 ratio. With a
stoichiometric mixture, all the available fuel and oxygen are used for combustion. In addition, a stoichiometric mixture produces the highest
combustion temperatures because the greatest amount of heat is released from the mass of air/fuel charge.
Lean indicates that air has been added or fuel has been removed from a given mixture. As an example, a mixture ratio of 10:1 is leaner than a mixture
of 8:1.
Rich indicates that air has been removed or fuel has been added to a given mixture. In other words, a mixture ratio of 8:1 is richer than a mixture
ratio of 10:1.
Full rich describes the position of the mixture control which provides the maximum fuel flow from the fuel metering unit. This condition is achieved
by placing the mixture control in the full forward position and is normally used while operating an aircraft on the ground.
Leaning - accomplished by pulling the mixture control back and helps prevent an overly rich mixture from entering the engine and fouling the spark
plugs.
Idle-cutoff - describes the position of the mixture control which completely cuts off the flow of fuel to the engine. This condition is achieved by
placing the mixture control in the full out, or aft, position. The idle-cutoff position is always used to shut down an engine because it stops the flow of
fuel.
Rich best power - mixture ratios that provide the maximum rpm or manifold pressure for a given throttle position.
Lean best power – another mixture ratios that provide the maximum rpm or manifold pressure for a given throttle position which uses slightly less
fuel than a rich best power setting.
Best economy - describes the mixture ratio that will develop the greatest amount of engine power for the least amount of fuel flow.
Specific fuel consumption - the number of pounds of fuel burned per hour to produce one horsepower. For example, if an engine burns 12 gallons
per hour while producing 180 brake horsepower, specific fuel consumption (SFC) is .4 pounds per horsepower hour.
Backfiring - Results when the fuel/air mixture can become so lean, that it burns at an extremely slow rate. With a slow burning fuel/air mixture, it
is possible for the fuel/air charge to still be burning when the intake valve opens on the next cycle. In this case, when the fresh fuel/air charge
enters the cylinder, it is ignited before the intake valve closes and the engine backfires through the induction manifold.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
After firing - Results from an excessively rich fuel/air mixture. When an excessively rich fuel/air mixture is ignited, the lack of oxygen causes the
mixture to burn slowly. If the fuel/air mixture is not completely burned before the exhaust valve opens, it mixes with the air in the exhaust system
and continues to burn. This typically causes flames to appear as the unburned mixture exits the exhaust stacks.
Carburetors - mix fuel and air to establish an optimum fuel/air ratio.
Classifications of Carburetors:
1. Updraft Carburetor - the air flows upward through the carburetor barrel.
2. Downdraft Carburetor - the air flows downward through the carburetor barrel.
3. Side draft Carburetor – horizontal air entry
Carburetor Venturi Principles
All carburetors depend on the differential pressure created at the venturi throat to measure the
amount of air delivered to an engine and meter the proper amount of fuel. To control the volume of air that passes through a venturi, all carburetors
are equipped with a throttle valve. The throttle valve, sometimes referred to as a butterfly valve, consists of a flat, circular piece of metal that is
always installed between the venturi and the engine. The position of a throttle valve is controlled by a mechanical linkage that is connected to the
throttle lever in the cockpit. As the throttle lever is pushed forward, the throttle valve opens and engine power output increases. However, as the
throttle lever is pulled backward, the throttle valve closes and engine power decreases.
Carburetor Systems:
1. Main metering
2. Idling
3. Mixture control
4. Accelerating
5. Power enrichment or economizer
Types of Carburetors:
1. Float Type Carburetors
2. Pressure Injection Carburetors
Float Type Carburetors - is so named because it uses a float to regulate the amount of fuel that
enters a carburetor. In a float-type carburetor, fuel is stored in a float chamber. The amount of
fuel allowed to flow into a float chamber is controlled by a float-operated needle valve installed
in the fuel inlet.
Main Metering - The purpose of the main metering system is to supply the correct amount of
fuel to the engine at all speeds above idle. The main metering system is comprised of one or
more venturi tubes, a main metering jet and discharge nozzle, and a throttle valve. In some
carburetors, a single venturi is unable to create the pressure drop necessary to meter fuel. In
this case, a second boost venturi is installed inside, or just prior to, the primary venturi.
Principle of Operation:
The operation of the discharge nozzle is based
on the difference in pressure between the venturi and the
float chamber. For example, when no air flows through
the venturi, the pressure in the float chamber and venturi
are the same. However, once air starts flowing through
the venturi, the air pressure in the venturi decreases
below the air pressure in the float chamber. This pressure
differential, or metering force, forces fuel to flow through
the main metering jet and out the discharge nozzle into
the airstream.
Air Bleed - typically incorporated into the metering system, to decrease the surface tension of the
fuel. When an air bleed is installed in a carburetor, the low pressure at the discharge nozzle draws
fuel out of the float chamber and bleed air from behind the venturi. Ultimately, the bleed air and
fuel mix in the discharge nozzle, creating an emulsion, or mixture, which lowers the fuel's density and helps to break up its surface tension. By
disrupting this surface tension, the fuel discharges from the nozzle in a fine, uniform spray which promotes vaporization.
Idling System - When an engine is idling, the throttle valve is nearly closed. As a result, the air velocity through the venturi is greatly reduced which,
in turn, dramatically reduces the pressure differential between the venturi and float chamber. In fact, in some cases, the pressure differential may
be so low that a sufficient amount of fuel cannot be drawn from the main discharge nozzle. To correct this condition, a series of two or three small
passages are provided in the carburetor barrel near the edge of the throttle valve where a small amount of air can still flow.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Air Bleed System
Idling System
Mixture Controls:
1. Variable Orifice
2. Back Suction
Variable Orifice - the float chamber is vented to the atmosphere and a valve is installed in the float chamber that controls the size of the passage
between the float chamber to the main metering jet.
Back Suction - With a back suction mixture control system, low pressure is used to control the pressure differential between the venturi and the
float chamber. With this type of system, low pressure air is taken from the venturi and routed through a mixture control vent valve into the float
chamber.
Variable Orifice
Back Suction
Automatic Mixture Control - A few float-type carburetors utilize a mixture control system that automatically maintains the proper fuel/air mixture
during flight. With this type of system, as an aircraft ascends, the mixture is automatically leaned to provide the optimum fuel/air ratio. Likewise, as
the aircraft descends, the automatic mixture control enrichens the mixture.
Acceleration System - When the throttle of a carburetor is rapidly opened, the airflow through the carburetor increases before the discharge nozzle
has an opportunity to increase the amount of fuel flow. This delayed response creates a momentary leaning of the fuel/air mixture that can cause an
engine to initially stagger before accelerating. To prevent this, many carburetors are equipped with an acceleration system. An acceleration system
provides an immediate, but brief, increase in fuel flow in the throat of the carburetor to enrichen the mixture.
Acceleration Systems:
1. Acceleration well
2. Accelerator pump systems.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Acceleration Well - An acceleration well is basically an enlarged annular chamber that surrounds the main discharge nozzle at the main air bleed
junction. When the engine is running at a set speed, a charge of fuel is stored in the acceleration well. This way, when the throttle is rapidly advanced,
the excess fuel in the acceleration well is drawn out through the discharge nozzle so ample fuel is available to produce a rich mixture.
Accelerator Pump - an accelerator pump to provide a momentary rich mixture when the throttle is advanced rapidly.
Acceleration Well
Accelerator Pump
Power Enrichment/Economizer System – dissipates excess heat when engines are producing maximum amount of power by providing a rich
fuel/air mixture at high power settings. This way, the excess fuel in the mixture helps cool the cylinders.
Needle-type economizer system - uses an enrichment metering jet that operates in parallel with the main metering jet. With this type of system, a
needle valve is installed upstream of the enrichment jet and is operated by the throttle shaft.
Air Bleed Type economizer system - An air bleed economizer enrichens the fuel/air mixture at high power settings by controlling the size of the air
bleed opening.
Needle Type Economizer System
Air Bleed Type Economizer
System
Carburetor Limitations:
1. Float-type carburetors utilize relatively low operating pressures which can result in incomplete vaporization and inadequate fuel flow
from the discharge nozzle.
2. The float design does not respond well to sudden aircraft maneuvers and unusual aircraft attitudes.
3. tendency to accumulate ice
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Carburetor Icing:
1. Fuel evaporation ice - results from the temperature drop that occurs when fuel is vaporized in the venturi.
2. Throttle ice - is the term used to describe ice which forms on the rear side of the throttle valve when it is partially closed.
Pressure Injection Carburetors - pressure-injection carburetors do not utilize a float chamber to store fuel. Instead, fuel is delivered under pressure
by a fuel pump through the carburetor and out the discharge nozzle. Since fuel pressure is responsible for forcing fuel out of the discharge nozzle,
there is no need to place the discharge nozzle directly in a venturi.
A Typical Pressure Injection Carburetor
Carburetor
Fuel Injection Systems - differs from a carburetor in that, with fuel injection, fuel is injected either directly into each cylinder or into the intake port
just behind the intake valve.
Direct fuel injection system - When fuel is injected directly into the engine cylinders.
Continuous-flow fuel injection system - differs from a direct fuel injection system in that fuel is injected and mixed with air in each intake port just
behind the intake valve. In addition, fuel is continuously injected throughout the entire combustion cycle instead of only during the intake stroke.
PISTON ENGINE COOLING SYSTEMS
Effects of Excessive Heat:
1. Adversely affects the combustion of fuel and air charge.
2. Weakens and shortens life of engine parts
3. Impairs lubrication
Methods of Cooling:
1. Air Cooling
2. Liquid Cooling
Cooling Fins - are either cast or machined into the exterior surfaces of the cylinder barrels and heads. The fins provide a very large surface area for
transferring heat to the surrounding airflow.
Townend Ring or Speed Ring - To help reduce drag on aircraft equipped with radial engines, the Townend ring, or speed ring was developed. A
Townend ring is an airfoil shaped ring that is installed around the circumference of a radial engine. The airfoil shape produces an aerodynamic force
that smooths the airflow around the engine and improves the uniformity of air flowing around each cylinder.
Cooling Fins
Townend Ring/Speed Ring
NACA Cowling
NACA Cowling - Developed in the early 1930s. This streamlined cowling completely covers all portions of a radial engine and extends all the way
back to the fuselage.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Baffles and deflectors are basically sheet metal panels which block and redirect airflow
to provide effective cooling. Baffles and deflectors are installed between the cowling
and engine, as well as between the engine cylinders.
Cowl flaps - are hinged doors that are installed at the bottom rear of the cowling where
the cooling air exits. When the cowl flaps are open, a stronger low pressure area is
created in the lower cowl and more air is pulled through the cylinders. The position of
the cowl flaps is controlled from the cockpit and are typically operated manually,
electrically, or hydraulically.
Liquid Cooling

Liquid-cooled aircraft engines are constructed with a metal water jacket that surrounds the cylinders.

As coolant circulates in the water jacket, heat passes from the cylinder walls and heads to the coolant.

A coolant pump circulates the coolant in a pressurized loop from the water jacket to a radiator, where heat is transferred from the
coolant to the air.
A Typical Liquid Cooing System
PISTON ENGINE LUBRICATION SYSTEMS
Function of Lubricating Oils:
1. Reducing friction between moving parts
2. Removing a great deal of engine heat
3. creating a seal between moving parts
4. cushioning impact forces created by combustion
5. cleaning the engine
6. protecting against corrosion
Oil Properties:

Viscosity

Specific Gravity

Color

Cloud Point

Pour Point

Flash Point and Fire Point
Viscosity - a measure of an oil's resistance to flow. An oil that flows slowly is viscous, or has a high viscosity. On the other hand, oil that flows freely
has a low viscosity. Oil viscosity is measured using an instrument known as the Saybolt Universal Viscosimeter.
Viscosity Index or VI Number - The viscosity index is a standard used to identify an oil's rate of change in viscosity for a given change in temperature.
The index itself is based on a comparative analysis of the temperature-induced viscosity changes of two reference oils, arbitrarily chosen by the
American Society of Testing and Materials, or ASTM.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Specific gravity - is a comparison of the weight of an oil to the weight of an equal volume of distilled water at a specified temperature.
Oil color - is determined by the amount of light that passes through an oil sample in a glass container when placed in front of a light of known
intensity. The color test is conducted with a device known as an ASTM union colorimeter. The color is then compared to an ASTM color chart. A color
reference number of 1.00 on the chart is pure white, and a reference number of 8.00 is darker than claret red.
Cloud Point - the temperature at which paraffin wax and other solids normally held in a solution of oil begin to solidify and separate into tiny crystals.
At this temperature, the oil begins to lose clarity and appears cloudy or hazy.
Pour Point - represents the lowest temperature at which the oil can flow or be poured. Pour point is an oil property which determines a given oil's
ability to lubricate at low operating temperatures. As a general rule, the pour point of an oil should be within five degrees Fahrenheit of the average
ambient starting temperature to ensure oil circulation.
Flash Point and Fire Point - the temperature at which it begins to emit ignitable vapors. As temperature increases beyond the flash point, the oil's
fire point is reached and sufficient vapors are emitted to support a flame. An oil must be able to withstand the high temperatures encountered in an
operating engine without creating a fire hazard.
Carbon Residue Test - In the carbon residue test, a given amount of oil is placed in a stainless steel receptacle and heated to a controlled temperature
until it evaporates. The container is weighed before and after the test. The difference in weight is then divided by the weight of the original oil sample
to obtain the percentage of carbon, by weight, in the oil.
Ash Test - An ash test is an extension of a carbon residue test in that it requires the carbon residue to be burned until only ash remains. The amount
of ash remaining is then expressed as a percentage by weight of the carbon residue. New oil which leaves almost no ash is considered to be pure. On
the other hand, the ash left by used oil can be analyzed for iron and lead content. The amount of iron and lead found provide clues to the amount of
internal engine wear.
Engine Oil Grading System

Most commercial aviation oils are assigned numerical designations such as 80,100, or 120 that approximate an oil's viscosity.

To further simplify the oil grading process, a system designed by the Society of Automotive Engineers (SAE) was designed. The SAE system
scale divides all oils into seven groups, ranging from SAE 10 to SAE 70.
Types of Oil
1. Straight Mineral Oils
2. Ashless Dispersant Oils
3. Multi-Viscosity Oils
4. Synthetic Oils
Straight Mineral Oil - MIL-L-6082E is a straight mineral oil that has no additives and, for many years, the principle type of oil used in aircraft.
Ash less Dispersant Oil - The most commonly used oil in reciprocating engines. Ashless-dispersant, or AD oil conforms to MIL-L-22851D.
Multi Viscosity Oils - differ from single viscosity oils in that they provide adequate lubrication over a wider temperature range. This allows multiviscosity oils to flow more quickly in cold weather and keep from thinning in hot weather. A typical multi-viscosity oil, such as SAE 15W50, can
generally be safely used over the combined temperature range of an SAE 15 and SAE 50 oil.
Synthetic Oils - have multi-viscosity properties due to their chemical composition and are similar to automotive grades SAE-5 to SAE-20. They are a
blend of chemical additives and certain diesters, which are synthesized extracts of mineral, vegetable, and animal oils. Synthetic oils have an
extremely low internal friction, they have a high resistance to thermal breakdown and oxidation. Synthetic oils are not compatible with, and cannot
be mixed with, mineral based oils. Tendency to blister or remove paint wherever it is spilled.
Extreme Pressure Lubricants - Extreme pressure (EP) lubricants, also known as hypoid lubricants, are specially formulated to provide protection
under high loads. A hypoid lubricant contains additives that bond to metal surfaces to reduce friction under high pressures or high rubbing velocities.
Ways of Distributing Oil:
1. Pressure Lubrication
2. Splash Lubrication
3. Spray Lubrication
4. Combination System
Pressure Lubrication - the primary type of lubrication used in reciprocating engines. All pressure lubrication systems rely on a pump to supply
pressurized oil to critical engine parts. In most cases, the pump used in a pressure system is a positive displacement, engine driven pump.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Splash Lubrication - produced by the movement of internal components which splash oil around. This method of
lubrication is very effective in engines where oil is stored in the crankcase. In this configuration, as a piston reaches the
bottom of a stroke, its associated crank throw partially submerges in oil and splashes it onto other components.
Spray Lubrication - uses the same pressurized oil in a pressure lubrication system; however, instead of routing the oil
to a component through an oil passage, the oil is sprayed on to a component through a nozzle. Engine components that
are lubricated by sprayed engine oil include some cylinder walls and camshaft lobes.
Combination System - a combination of pressure and splash lubrication.
Reciprocating Engine Lubrication System Classification:
1. Wet Sump System
2. Dry Sump System
A Splash Lubrication System
Wet Sump Lubrication System - With a wet-sump system, all the oil is carried in the engine crankcase,
much the way it is in a car. With this type of system, the oil is picked up by a pump and distributed
throughout the engine. Once the oil has circulated, it drains down into the sump where it is picked up
and recirculated.
Advantages of Wet Sump Lubrication System

Relative simplicity

Lightweight
Disadvantages of Wet Sump Lubrication System

Oil capacity is limited by the sump size

More difficult to cool the oil since it is contained within the engine which is a source of heat
Dry Sump Lubrication System - differ from wet-sump systems in that the oil is stored in a separate oil tank. This typically allows a larger quantity of
oil to be carried. This makes dry-sump systems well suited to large radial engines. In this type of system, an oil pump pulls the oil from the oil
tank and circulates it throughout the engine. Once circulated, the oil accumulates in the bottom of the crankcase where a scavenge pump picks
up the oil and pumps it back to the tank.
Lubrication System Components:
1. Oil Reservoir
2. Oil Pump
3. Oil Pressure Relief Valve
4. Oil Filter
5. Oil Cooler
6. Vent Lines
7. Pipings and Connections
NOTE: In addition, on engines that incorporate a dry-sump system, a
scavenge pump is required to move the oil back to the oil reservoir.
Oil Reservoir - An oil reservoir must be large enough to hold an adequate
supply of oil to lubricate an engine. The amount of oil that is considered
adequate is based on the maximum endurance of the airplane and the
maximum acceptable oil consumption rate plus a margin to ensure adequate
circulation, lubrication, and cooling.
FAR 23 Oil Reservoir Requirements:
1. All oil reservoirs must have an expansion space at least 10 percent
greater than the tank capacity, or 0.5 gallon, whichever is greater.
2. All oil filler caps or covers must be marked with the word "OIL" and the permissible oil designations, or reference to the Airplane Flight
Manual for permissible oil designations.
Scupper drain - The oil reservoirs installed in some dry-sump systems include a scupper drain. Is basically a drain that is built into the filler cap well
that catches overflow oil and drains it overboard when servicing the tank.
Bayonet gauge - Most aircraft oil systems are equipped with a dipstick-type quantity gauge, sometimes referred to as a bayonet gauge. However,
some large aircraft may be equipped with an oil quantity indicating system that shows the quantity of oil during flight.
Hopper, or temperature accelerating well - The purpose of a hopper is to partially isolate a portion of the oil
within the reservoir during start-up. By doing this, a smaller portion of the oil is circulated through the engine
during start-up allowing the engine to warm up faster.
A Hooper/Temperature Accelerating Well
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG
Oil Pumps
1. Gear Pump
2. Gerotor pump
A Gear Pump
A Gerotor Pump
Gear Pumps - The most common type of oil pump used in reciprocating engines. A typical gear-type pump consists of two meshed gears that rotate
inside a housing. Oil is picked up by the gears at the pump inlet and then becomes trapped between the teeth and the housing. As the gears
rotate, the trapped oil is released at the pump outlet.
Gerotor Pumps - A typical gerotor-type pump consists of an engine driven spur gear that rotates within a free spinning rotor housing. The
rotor and drive gear ride inside a housing that has two oblong openings. One opening is the oil inlet while the other is the oil outlet
Scavenge Pumps - In addition to a pressure pump, most dry-sump systems must utilize a scavenge pump to return oil to the oil reservoir. A
scavenge pump may be either a gear- or gerotor-type pump that is driven by the engine. As a rule, scavenge pumps have a capacity that is greater
than the pressure pump.
Pressure Relief Valve - To prevent excessive pressure from damaging an engine, a pressure relief
valve must be installed in the oil system. A typical pressure relief valve consists of a spring loaded
valve that is held in the closed position. In a typical system, the relief valve is installed between
the main supply pump and the internal oil system.
Compensated Oil Pressure Relief Valve - maintains a higher system pressure when the oil is
cold then, once the oil warms up, it automatically lowers pressure to the normal operating
range.
Oil Filters - The purpose of the filter is to remove solid particles that are suspended in the oil.
This filtration is required to protect the engine's moving parts from solid contaminants.
A Pressure Relief Valve
Oil Filters
Two Types of Filtration Systems:
1. Full Flow System
2. Bypass or Partial Flow System
Full Flow Filter System - In a full-flow filter system, all of the engine oil passes through a filter each time it circulates through an engine. To
accomplish this, the filter is installed in series with the oil pump between the pump and the engine bearings.
Bypass or Partial Flow Filter System - With a bypass, or partial flow system, the filter is installed in parallel with the engine bearings. In this type of
system, only about 10 percent of the oil is filtered each time the oil circulates through the system. However, over time, the entire oil supply will
pass through the filter.
A Full Flow Filtration System
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
A Bypass Filtration System
PREPARED BY: ENGR IAN M. TALAG
Oil Bypass Valve on Oil Filters - FAR requirements dictate that all oil filters be constructed and installed in a way that permits full oil flow even if the
filter becomes completely blocked. On a full-flow filter system some means of bypassing the filter must be provided. One way to meet this
requirement is to incorporate an oil bypass valve that automatically lets oil bypass the filter entirely once it becomes plugged.
Methods of Filtration:
1. depth filtration,
2. semi-depth filtration,
3. surface filtration,
4. edge filtration
Depth filters - consist of a matrix of fibers that are closely packed to a depth of about one inch. Oil flows through this mat and contaminants are
trapped in the fibers. Depth-type filters are very effective because the large number of filters used have the capacity to trap a large quantity of
contaminants.
Semi-depth filter - The type of filter used most often in today's general aviation aircraft is a disposable, semi-depth filter made of resin
impregnated fibers. These fibers are formed into a long sheet, folded into pleats, and assembled around a perforated sheet steel core. A typical
semi-depth filter mounts to the engine with a threaded fitting and, therefore, is often referred to as a spin-on filter.
A Semi Depth Filtration in a
Removable Can
Surface Filtration - Several aircraft engines are equipped with a standard woven wire-mesh oil screen, or strainer. This screen filter is useful for
trapping some of the larger contaminants that flow through the engine; however, it does little to catch the small contaminants.
Edge Filtration - Edge filters may be either the spiral-wound or Cuno type. A spiral-wound element consists of a long strip of wedge-shaped metal
that is wound into a tight spiral. The Cuno filter consists of a large number of thin metal disks that are stacked on a center shaft. Thin spacers,
which are attached to the filter housing, separate the disks so oil can pass between the disks.
Oil Coolers - Excess heat is removed by an oil cooler, or oil temperature regulator. An oil cooler is an oilto-air heat exchanger. When installed in a dry-sump system, the oil cooler is typically located between
the scavenge pump outlet and storage reservoir.
Surge Protection Valve - When cold oil becomes congealed in a dry-sump system, the scavenge pump can
build up a very high pressure in the oil return line. To prevent this high pressure from damaging the oil
cooler or hose connections, some oil coolers incorporate a surge protection valve. A typical surge
protection valve is installed at the oil cooler inlet and is normally held in the closed position by spring
pressure. However, if the oil within the cooler is severely congealed, oil pressure will build at the cooler
inlet and overcome the spring pressure acting on the surge valve.
Oil Dillution - On some large reciprocating engines that are operated in extremely cold temperatures, an oil dilution system may be installed. The
purpose of such a system is to dilute the oil with fuel within the engine to help prevent the oil from congealing when it is cold. With a typical oil
dilution system, fuel is injected into the oil pump before the engine is shut down. This distributes diluted oil throughout the lubrication system.
AIRCRAFT PROPULSION SYSTEMS (PISTON ENGINE)
PREPARED BY: ENGR IAN M. TALAG