Powerplant

Aircraft require thrust to produce enough speed for the wings to

provide lift or enough thrust to overcome the weight of the aircraft

for vertical takeoff. This thrust, or propulsive force, is provided by a

suitable type of aircraft heat engine. All heat engines have in common

the ability to convert heat energy into mechanical energy by the flow

of some fluid mass (generally air) through the engine.

➢ THRUST – DRAG

➢ LIFT – WEIGHT

AIRCRAFT ENGINE

often referred to as an aero engine, is the power component of an

aircraft propulsion system.

➢ Piston Engines

➢ Gas Turbine Engines

AIRCRAFT PISTON ENGINE

also commonly referred to as a reciprocating engine, is an internal

combustion engine that uses one or more reciprocating pistons to

convert pressure into a rotational motion.

GAS TURBINE

also called a combustion turbine, is a type of continuous and internal

combustion engine. The main elements common to all gas turbine

engines are: an upstream rotating gas compressor a combustor a

downstream turbine on the same shaft as the compressor.

DIFFERENCE BETWEEN PISTON AND GAS TURBINE ENGINE

Piston, or reciprocating engines convert pressure into rotating motion

using pistons, while a gas turbine engine, or a combustion turbine,

uses the pressure from the exploding fuel to turn a turbine and

produce thrust. The piston engine focuses on creating rotational

motion while the turbine engine creates linear motion through thrust.

1829 - F.D. Artingstall

constructed a full-scale steam-powered ornithopter,

1848 – John Stringfellow

achieved the first powered flight using an unmanned 10 ft wingspan

steam-powered monoplane.

Russian Alexandr Mozhaysky (1884), Englishman Hiram Maxim

(1894), and Frenchman Clément Ader (1890)

Each jumped full-scale steam-powered machines off the ground for

short distances, although none of these craft was capable of sustained

or controlled flight.

1896 – Samuel P. Langley

achieved the first sustained flights when he launched two of his

relatively large steam-powered model aircraft.

1860 - Étienne Lenoir of Belgium

built the first internal-combustion engine, fueled with illuminating gas.

1876 - Nikolaus A. Otto of Germany

took the next step, producing a four-stroke engine burning liquid fuel.

1885 - Gottlieb Daimler of Germany

pioneered the development of lightweight high-speed gasoline engine.

1888 - Gottlieb Daimler persuaded Karl Woelfert,

a Lutheran minister who longed to fly, to equip an experimental airship

with a single-cylinder gasoline engine that developed all of eight

horsepower.

The Wright Brothers

Known for Inventing, building, and flying the world’s first successful

motor-operated airplane, the “Wright Flyer”

The early experiments of Orville and Wilbur Wright employed a

horizontally arranged inline 4-cylinder, four cycle engine designed by

Wright employee and mechanic Charles Taylor. This engine,

which powered the “Wright Flyer” on 17 December 1903 when Orville

flew those immortal 12 seconds over Kitty Hawk, North Carolina.

1913 - Igor Sikorsky

developed the first four engine aircraft that could carry 13 passengers.

It would eventually create 600 hp and be used as a bomber in World

War I.

1919 – Superchargers

which increased the pressure of the air entering the engine cylinders,

first showed up in 1919 and greatly increased performance at higher

altitudes. These were both mechanical and turbo powered.

(1925-1926)

Introduction of lightweight, air- cooled radial engines. The

introduction of a new generation of lightweight, air-cooled radial

engines revolutionizes aeronautics, making bigger, faster planes

possible.

The creation of the National Advisory Committee for Aeronautics

(NACA) a joint government I multi-company promoted the sharing of

information between the America’s best engine designers, engineers,

and industrial manufacturing talents. National Advisory Committee for

Aeronautics (NACA) the predecessor to today’s National Aeronautics

and Space Administration (NASA).

Reciprocating engines may be classified according to the cylinder

arrangement (in line, V- type, radial, and opposed) or according to the

method of cooling (liquid cooled or air cooled). Actually, all piston

engines are cooled by transferring excess heat to the surrounding air.

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 liquidcooled or air cooled and the pistons can be located either upright

above the crankshaft or inverted below the crankshaft.

Disadvantage of In-line engines

relatively low power-to-weight ratio.

receive relatively little cooling air

V-TYPE ENGINE

are arranged around a single crankshaft in two in-line banks that are

45, 60, or 90 degrees apart. 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.

RADIAL ENGINE

consists of a row, or rows of cylinders arranged radially about a central

crankcase.

Two Types of Radial Engines

Rotary-type Radial engines

the cylinders of a rotary type radial engine are mounted radially

around a small crankcase and rotate with the propeller, while

the crankshaft remains stationary.

Static-type Radial engines

the crankcase remains stationary and the crankshaft rotates to

turn the propeller.

Types of Static-type Radial engines

Single-row radial engines

Double-row radial engines

Multiple-row radial engines

Disadvantage of Rotary-type Radial engines

Carburetion

Lubrication

Torque

Exhaust System

OPPOSED ENGINE

always have an even number of cylinders, with each cylinder on

one side of the crankcase “opposing” a cylinder on the other

side. While some opposed engines are liquid-cooled, the

majority are air cooled. Opposed engines are typically mounted

in a horizontal position when installed on fixed-wing aircraft,

but can be mounted vertically to power helicopters.

Advantage of Opposed-type engines

good power-to-weight ratio

relatively small frontal area.

less vibration than other engine types

ENGINE COMPONENTS

➢ Crankcase

➢ Crankshaft

➢ Connecting Rods

➢ Cylinders

➢ Pistons Valves

➢ Valve operating mechanism

CRANKCASE

It is the foundation of a reciprocating engine which contains the

engine’s internal parts and provides a mounting surface for the engine

cylinders and external accessories.

OPPOSED ENGINE CRANKCASE

Consists of two halves of cast aluminum alloy that are manufactured

either with sand casting or by using permanent molds.

Cylinder Pads – a surface where a cylinder is mounted to crankcase.

Transverse webs – it supports the crankshaft and are cast directly into

a crankcase parallel to the cases longitudinal axis.

Camshaft bosses – it supports the camshaft which is part of the valve

operating mechanism

RADIAL ENGINE CRANKCASE

It is divided into distinct number of sections can be as few of as three

or as many as seven depending on the size and type of engine.

Nose section – it is mounted at the front of a radial engine crankcase

and bolts directly to the power section, usually houses and supports a

propeller governor drive shaft, propeller shaft, cam ring, and a

propeller reduction gear assembly if required.

Power section – the section of the crankcase where the reciprocating

motion of the pistons is converted to the rotary motion of the

crankshaft.

Supercharger section – is located directly behind the power section

and is used to compressed air and distributes it to the cylinder.

Accessory section – it provides a means for mounting accessories such

as magnetos, carburetors, pumps, starters, and generators.

CRANKSHAFT

Its purpose is to transform the reciprocating motion of the pistons and

connecting rods into rotary motion to turn a propeller

Crankshaft Basic Components

Main Journals – represent the centerline of a crankshaft and support

the crankshaft as it rotates in the main bearing. Crankpin – serve as

attachment points for the connecting rods. Crank cheeks – are used to

connect the crankpin to the crankshaft.

Types of Crankshafts

Single-Throw Crankshaft – consists of a single crankpin with two main

journals that support the crankshaft in the crankcase.

Two-Throw Crankshaft – are typically set 180 degrees from each other

and may consist of either one or three pieces.

Four-Throw Crankshaft – the two throws are arranged 180 degrees

apart from the other two throws.

Six-Throws Crankshaft – is forged as one piece and consists of four

main bearings and six throws that are 60 degrees apart.

BEARINGS

It is surface which supports and reduces friction between two moving

parts.

Types of Bearings

Plain Bearings

This type of bearing is generally used for crankshaft main bearings,

cam ring, and camshaft bearings, connecting rod end bearing and

accessory shaft bearings.

Ball Bearings

This type of bearing consists of grooved inner and outer races, one or

more sets of polished steel balls, and a bearing retainer.

➢ Magneto

➢ Alternator

➢ Turbocharger

➢ Pumps

Roller Bearings

This type of bearing is similar in construction to ball bearings except

that polished steel are used instead of balls.

CONNECTING ROD

It is the link which transmits the force exerted on a piston to a

crankshaft.

Three Types of Connecting Rod

Plain Connecting Rod

Plain connecting rods are used in opposed and in-line engines.

Master and Articulated Rod Assembly

This type of connecting rod is commonly used in radial engines.

Master Rod – the only connecting rod in a radial engine whose big end

passes around the crankshaft.

Articulated Connecting Rod – a link rod which connects the pistons in

a radial engine to the master rod.

Knuckle Pin – it is used to hinge the articulated rod to the master rod.

Fork-and-Blade Rod Assembly

This rod is used primarily in V-type engines and consists of fork

connecting rod and blade connecting rod.

PISTONS

A movable plug inside the cylinder of a reciprocating engine that

moves up and down.

Two Primary Functions of Piston

➢ draw fuel and air into the cylinder, compress the gases, and

purge burned exhaust gases from the cylinder.

➢ transmit the force produced by combustion to the crankshaft.

Parts of the Piston

Piston Ring Grooves – are cut into a pistons outside surface to hold a

set of piston rings.

Ring Land – the portion of the piston between the ring grooves. Piston

Head – the piston’s top surface and is directly exposed to heat or

combustion.

Piston Pin Boss – is an enlarged area inside the piston that provides

additional bearing area for a piston pin.

Piston Pin – the hardened and polished steel pin used to connect the

piston of a reciprocating engine to the connecting rod.

Piston Skirt – the piston base is extended to help align the piston in a

cylinder.

Cam Ground Piston

an aircraft engine piston ground in such a way that its diameter

parallel to the wrist pin boss is less than its diameter perpendicular to

the boss.

The Crown

is the top surface (closest to the cylinder head) of the piston which is

subjected to tremendous forces and heat during normal engine

operation.

The Ring lands

Are the reliefs cut into the side profile of the piston where the piston

rings sit.

Ring Groove

is a recessed area located around the perimeter of the piston that is

used to retain a piston ring.

Skirt

of a piston is the portion of the piston closest to the crankshaft that

helps align the piston as it moves in the cylinder bore.

Wrist pin boss

is a bore that connects the small end of the connecting rod to the

piston by a wrist pin.

Piston Head Design

➢ Flat head

➢ Recessed head

➢ Concave head

➢ Dome head

PISTON RINGS

Metal rings usually made of cast iron, that fit into grooves

around the outside of a reciprocating engine piston.

➢ prevent leakage of gas pressure from the combustion

chamber.

➢ transfer heat from the piston to the cylinder walls.

➢ reduce oil seepage into the combustion chamber

Piston Ring Gap

the point where a piston ring is split.

(Butt Joint, Angle Joint, Step Joint)

Piston Ring Gap Measuring

Blow-by

the loss of pressure in the engine cylinder caused by leakage

past of the piston ring

Two Main Types of Piston Rings

Compression Rings

The top rings used on reciprocating engine piston to seal the

piston in the cylinder so the upward moving piston can

compress the air in the cylinder. Prevent the gas from escaping

past the piston during engine operation and are placed in the

grooves immediately below the piston head.

Oil Rings

Controls the amount of oil that is applied to the cylinder walls as

well as prevent oil from entering the combustion chamber.

Two Types of Oil Rings

Oil Control ring – are placed in the grooves immediately below

the compression rings and regulates the thickness of oil film on

the cylinder wall.

Oil Scraper Ring – is used to regulate the amount of oil that

passes between the piston skirt and the cylinder wall

CYLINDERS

Provides the combustion chamber where the burning and

expansion of gases takes place to produce power.

➢ strong to withstand pressure

➢ lightweight

➢ good heat-conducting properties

➢ easy and inexpensive to manufacture.

Parts of Air-cooled Engine Cylinder

Cylinder Barrel

the high strength steel tube in which the piston moves up and

down in reciprocating engine.

Cylinder Skirt

the portion of the cylinder of an aircraft engine that protrudes

into the crankcase.

Cylinder Mounting Flange

it is used to attach the cylinder to crankcase.

Cooling Fins

thin ribs that extend outward from a surface to carry heat from

the surface into the air flowing through the fins

Cylinder Bore

the inside diameter of the cylinder barrel.

Choke Bore Cylinder

the diameter of the top portion of the barrel is slightly smaller

than the diameter at the cylinder skirt.

Cylinder Wall

shiny, well-polished inside surface of the cylinder barrel

Two common Methods used to provide a hard wearing surface

on cylinder walls

NITRIDING

is a form of case hardening that changes the surface strength

by infusing the metal with hardening agent.

Cylinder Honing

the surface is roughened in specified crosshatch pattern to

make it hold lubricating oil.

CHROME PLATING

refers to a method of hardening a cylinder by applying a thin

coating of chromium to inside of cylinder barrels.

Electroplating

it is the process used to chrome plate a cylinder bore.

Chrome Channeling

reverse current is applied causes microscopic cracks to retain oil

on the cylinder wall.

CYLINDER HEAD

acts as a lid on cylinder barrel to provide an enclosed chamber

for combustion.

Spark plug inserts

a threaded bronze or steel bushing screwed and shrunk into an

opening in the cast aluminum cylinder head of an engine.

Intake port

passage of fuel/air mixture to the cylinder when the intake valve

is open during intake stroke.

Exhaust port

passage of the burn gases of the cylinder when exhaust valve is

open during exhaust stroke.

Valve Guide

prevents the poppet valve from getting off axis during popping

motion.

Rocker Arm

absorb the lifting force of the push rod to open the poppet valve

and close when the lifting force is relieved.

Rocker Arm Bosses

support and give strength to the rocker shaft and hold in place

during operation.

Rocker Arm Pin

act as pivot for rocking arm action of a rocker arm.

Valve Seat Insert Ring

contact with the valve face to ensure no leakage of compress air

in the time of power pressure during power stroke and

compression stroke.

Priming Line

passage in injected raw fuel directed in the cylinder for an easy

engine start.

VALVES

It regulates the flow of gases into and out of a cylinder by

opening and closing at the appropriate time.

Intake Valve

controls the amount of fuel/air mixture that enters a cylinder

through the intake port.

Exhaust Valve

allows the exhaust gases to exit from the cylinder through the

exhaust port.

Poppet Valve

a t-shaped valve with a circular head

Types of Poppet Valve

Flat head valve

has a flat head and is typically used only on intake valve in

aircraft engines.

Semi-tulip valve

has slightly concave area on its head.

Tulip valve

has a deep wide indented area on its head.

Mushroom valve

have convex head and are not commonly found on aircraft

engines.

Basic Components of Poppet Valve

Valve face

the portion of the poppet valve that forms a seal with the valve

seat in an aircraft engine cylinder.

Valve stem

the portion of a poppet valve that rides in valve guide in the

cylinder head of a reciprocating engine.

Valve neck

it joins the valve stem to the valve head.

Valve head

the part of a vertically opening valve that is lifted off the valve

aperture to open the valve.

Valve Seating Components

Valve Springs

helically wound steel wire springs used to close the poppet

valves in the cylinders of an aircraft reciprocating engine.

Valve Spring Retainer

it is installed on the top of the valve springs used to hold the

spring.

Split Valve Key

it is used to lock the valve spring retainer to the valve stem.

Valve Float

occurs when the frequency of a valve spring begins to vibrate at

its resonance frequency

VALVE OPERATING MECHANISM

Camshaft

a straight, gear driven shaft that contains lobes used to operate

the intake and exhaust valves.

Cam Ring

a ring or plate with lobes ground around its periphery.

Cam Lobe

an eccentric used to change rotary motion in to linear motion

Valve Lifter

the component in the valve train of a reciprocating engine that

rides on the lobes of the camshaft or cam ring and pushes

against the push rod.

Solid Lifter

consist of a solid metal cylinder that transmits the lifting force

from the camshaft to the pushrod.

Hydraulic Lifter

it uses oil pressure to cushion the impact of the cam lobe

striking the lifter and removes any play within the valve

operating mechanism.

Push Rod

the component in a reciprocating engine which transmits the

movement of the cam to the rocker arm to open the valves of a

reciprocating engine

Valve clearance

describes the clearance, or space, between the tip of the valve

stem and the rocker arm face.

PROPELLER SHAFTS

All aircraft reciprocating engines are equipped with a propeller shaft.

As an aviation technician you must be familiar with the various types

of propeller shafts including the tapered, splined, and flanged.

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.

Splined propeller shafts

Increases in engine power demanded a stronger method of attaching

propellers. A spline is a rectangular groove that is machined into the

propeller shaft. Most high powered radial engines

Flanged propeller shafts

a flat flange is forged directly onto the end of a crankshaft and a

propeller is bolted to the flange. Most modern horizontally opposed

aircraft engines.

ENGINE IDENTIFICATION

an engine identification code consists of a letter or series of letters

followed by a number and model designation.

1 - Horizontally opposed engine

R - Radial engine

2 - 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 major parts of a reciprocating engine are the crankcase,

cylinders, pistons, connecting rods, valves, valve- operating

mechanism, and crankshaft .

• The cylinder barrel of a reciprocating engine is made of a

steel alloy forging with its inner surface hardened to resist

wear. One method used to harden cylinders is nitriding. In the

nitriding process, the cylinder is heated and exposed to

ammonia or cyanide gas.

• When operating properly, an engine equipped with hydraulic

lifters will have a valve clearance of zero.

• The stems of some valves have a narrow groove cut in them

just below the lock ring groove that allows for the installation

of safety circlets or spring rings. The circlets are designed to

prevent the valves from falling into the combustion chamber

should the valve tip break during engine operation.

• Each valve on a reciprocating engine is closed by two or three

helical coiled springs. If only a single spring were used to

close a valve, the spring would vibrate or surge at certain

speeds. However, with multiple springs, each spring vibrates

at a different engine speed resulting in rapid dampening of all

spring surge vibrations.

• Plain bearings used in aircraft engines are usually made of

nonferrous metals, such as silver, bronze, aluminum, and

various alloys of copper, tin, or lead. If this type of material is

found in the oil sump of an engine and on the surface of the

oil filter, it is an indication that the bearings may be

experiencing abnormal wear.