Piston engine powerplant

MACHINE and ENGINE

MACHINE
:
Is a set of mechanism that joints and work together which convert
input energy into useful output energy.

ENGINE :
Is a machine which convert heat energy from combustion process
of fuel and air mixture into useful output energy.
Note
:
The output energy normally is mechanical energy of the rotor
shaft.

The aircraft powerplant
 The airplane engine and
propeller, often referred to
as the aircraft powerplant,
work in combination
engine and propeller to
produce thrust. The
powerplant propels the
airplane and drives the
various systems that
support the operation of
an airplane.

INTERNAL COMBUSTION ENGINE
 is an engine which
combustion process and
power developed inside
in the engine

EXTERNAL COMBUSTION ENGINE
 is an engine which
combustion process and
power developed in
different engine

Reciprocating engines
 Most small airplanes are designed with reciprocating
engines. The name is derived from the back-and-forth, or
reciprocating, movement of the pistons. It is this motion
that produces the mechanical energy needed to
accomplish work. Two common means of classifying
reciprocating engines are:
 By cylinder arrangement with respect to the crankshaft—
radial, in-line, v-type or opposed.
 By the method of cooling—liquid or air-cooled.

 RADIAL ENGINE
 Radial engines were widely used
during World War II, and many
are still in service today. With
these engines, a row or rows of
cylinders are arranged in a
circular pattern around the
crankcase. The main advantage
of a radial engine is the favorable
power-to-weight ratio

 IN-LINE ENGINE
 In-line engines have a
comparatively small frontal area,
but their power-to-weight ratios
are relatively low. In addition, the
rearmost cylinders of an aircooled, in-line engine receive
very little cooling air, so these
engines are normally limited to
four or six cylinders.

 V-TYPE ENGINE
 V-type engines provide more
horsepower than in-line
engines and still retain a
small frontal area. Further
improvements in engine
design led to the
development of the
horizontally-opposed engine.

 OPPOSED ENGINE
 Opposed-type engines are the most
popular reciprocating engines used on
small airplanes. Opposed-type engines
have high power-to-weight ratios
because they have a comparatively small,
lightweight crankcase. In addition, the
compact cylinder arrangement reduces
the engine’s frontal area and allows a
streamlined installation that minimizes
aerodynamic drag.

 The main parts of a reciprocating
engine are:
 Cylinders
 Crankcase
 Housing

The intake/exhaust valves spark plugs,
and pistons are located in the
cylinders. The crankshaft and
connecting rods are located in the
crankcase. The magnetos are normally
located on the engine accessory
housing.

 Reciprocating engine
use four stroke cycle :





Intake
Compression
Power
Exhaust

Combustion
 Combustion
 During normal combustion, the
fuel/air mixture burns in a very
controlled and predictable
manner.
 Detonation is an uncontrolled,
explosive ignition of the fuel/air
mixture within the cylinder’s
combustion chamber.

Combustion

Some common operational causes of detonation :
1. Using a lower fuel grade than that specified by the aircraft
manufacturer.
2. Operating with extremely high manifold pressures in conjunction
with low r.p.m.
3. Operating the engine at high power settings with an excessively lean
mixture.
4. Detonation also can be caused by extended ground operations, or
steep climbs where cylinder cooling is reduced.

Propeller
 The propeller is a rotating airfoil. It provides the necessary
thrust to pull, or in some cases push, the airplane through
the air.

 The engine power is used to rotate the propeller, which in
turn generates thrust very similar to the manner in which a
wing produces lift. The amount of thrust produced
depends on the shape of the airfoil, the angle of attack of
the propeller blade, and the r.p.m. of the engine. The
propeller itself is twisted so the blade angle changes from
hub to tip. The greatest angle of incidence, or the highest
pitch, is at the hub while the smallest pitch is at the tip.

Propeller

Figure 3: Changes in propeller blade angle from hub to tip.

Propeller
 The reason for the twist is to produce uniform lift from the hub
to the tip. As the blade rotates, there is a difference in the actual
speed of the various portions of the blade. The tip of the blade
travels faster than that part near the hub, because the tip travels
a greater distance than the hub in the same length of time.
 Changing the angle of incidence (pitch) from the hub to the tip
to correspond with the speed produces uniform lift throughout
the length of the blade. If the propeller blade was designed with
the same angle of incidence throughout its entire length, it
would be inefficient, because as airspeed increases in flight, the
portion near the hub would have a negative angle of attack
while the blade tip would be stalled.

Propeller
 Fixed-pitch propeller
 The pitch of this propeller is set by the manufacturer,
and cannot be changed. With this type of propeller,
the best efficiency is achieved only at a given
combination of airspeed and RPM.

Propeller
 Adjustable-pitch propeller
 The pitch of this propeller can be changed. Some
older adjustable-pitch propellers could only be
adjusted on the ground, most modern adjustablepitch propellers are designed so that you can change
the propeller pitch in flight.

Propeller
 THE TACHOMETER
 A tachometer is calibrated in hundreds of r.p.m., and gives a
direct indication of the engine and propeller r.p.m. The
instrument is color-coded, with a green arc denoting the
maximum continuous operating r.p.m.
 The revolutions per minute are regulated by the throttle, which
controls the fuel/air flow to the engine.

Propeller
 THE TACHOMETER

 The propeller is usually mounted
on a shaft, which may be an
extension of the engine
crankshaft. In this case, the r.p.m.
of the propeller would be the
same as the crankshaft r.p.m.
 On some engines, the propeller is
mounted on a shaft geared to the
engine crankshaft. In this type,
the r.p.m. of the propeller is
different than that of the engine.
In a fixed-pitch propeller, the
tachometer is the indicator of
engine power.

Propeller
 THE TACHOMETER

 When operating altitude increases, the tachometer may not show
correct power output of the engine. For example, 2,300 r.p.m. at
5,000 feet produce less horsepower than 2,300 r.p.m. at sea level.
 The reason for this is that power output depends on air density.
Air density decreases as altitude increases.
 Therefore, a decrease in air density (higher density altitude)
decreases the power output of the engine. As altitude changes,
the position of the throttle must be changed to maintain the
same r.p.m. As altitude is increased, the throttle must be opened
further to indicate the same r.p.m. as at a lower altitude.

Carburetor systems
 Carburetor is a device to blends air and fuel for an
internal combustion engine.

Carburetor systems
 In the operation of the float-type carburetor system,
the outside air first flows through an air filter, usually
located at an air intake in the front part of the engine
cowling. This filtered air flows into the carburetor and
through a venturi, a narrow throat in the carburetor.
 When the air flows through the venturi, a lowpressure area is created, which forces the fuel to flow
through a main fuel jet located at the throat. The fuel
then flows into the airstream, where it is mixed with
the flowing air.

Carburetor systems
 The fuel/air mixture is then drawn through the intake manifold
and into the combustion chambers, where it is ignited. The
“float-type carburetor” acquires its name from a float, which
rests on fuel within the float chamber. A needle attached to the
float opens and closes an opening at the bottom of the
carburetor bowl.
 This meters the correct amount of fuel into the carburetor,
depending upon the position of the float, which is controlled by
the level of fuel in the float chamber. When the level of the fuel
forces the float to rise, the needle valve closes the fuel opening
and shuts off the fuel flow to the carburetor. The needle valve
opens again when the engine requires additional fuel.

 The flow of the fuel/air mixture to the combustion chambers is
regulated by the throttle valve, which is controlled by the
throttle in the cockpit.

Mixture control
 To maintain the correct fuel/air mixture, you must lean the
mixture using the mixture control. Leaning the mixture
decreases fuel flow, which compensates for the decreased air
density at high altitude.
 Carburetors are normally calibrated at sea-level pressure, where
the correct fuel-to-air mixture ratio is established with the
mixture control set in the FULL RICH position. However, as
altitude increases, the density of air entering the carburetor
decreases, while the density of the fuel remains the same.

Carburetor icing
 One disadvantage of the
float-type carburetor is its
icing tendency.
 The reduced air pressure and
the vaporization of fuel,
contributes to the
temperature drop. It make ice
formation possible . If enough
ice builds up, the fuel/air
mixture will be restricted and
reduces power.

Carburetor icing
 Carburetor ice is most
likely to occur when
temperatures are below
70°F (21°C) and the relative
humidity is above 80
percent.
 However, due to the
sudden cooling that takes
place in the carburetor,
because the temperature
drop can be as much as 60
to 70°F.

Carburetor heat
 Carburetor heat is an anti-icing system that preheats
the air before it reaches the carburetor.

 Carburetor heat is intended to keep the fuel/air
mixture above the freezing temperature to PREVENT
the formation of carburetor ice.
 Carburetor heat can be used to melt ice that has
already formed in the carburetor provided that the
accumulation is not too great. The emphasis,
however, is on using carburetor heat as a preventative
measure.

Carburetor heat
 The use of carburetor heat causes a decrease in
engine power, sometimes up to 15 percent, because
the heated air is less dense than the outside air that
had been entering the engine. This enriches the
mixture.
 When ice is present in an airplane with a fixed-pitch
propeller and carburetor heat is being used, there is a
decrease in r.p.m., followed by a gradual increase in
r.p.m. as the ice melts. The engine also should run
more smoothly after the ice has been removed

Ignition system
 The ignition system
provides the spark that
ignites the fuel/air
mixture in the cylinders
and is made up of
magnetos, spark plugs,
high-tension leads, and
the ignition switch.

Ignition system
 Most standard
certificated airplanes
incorporate a dual
ignition system with two
individual magnetos,
separate sets of wires,
and spark plugs to
increase reliability of the
ignition system.

Ignition system
 The operation of the
magneto is controlled in
the cockpit by the ignition
switch. The switch has five
positions:
 OFF
 R—Right
 L—Left
 BOTH
 START

Fuel systems
 The fuel system is designed to provide an uninterrupted
flow of clean fuel from the fuel tanks to the engine. The
fuel must be available to the engine under all conditions of
engine power, altitude, attitude, and during all approved
flight maneuvers. Two common classifications apply to
fuel systems in small airplanes - gravity-feed and fuelpump systems.

Fuel systems

 The gravity-feed system utilizes
the force of gravity to transfer the
fuel from the tanks to the engine for example, on high-wing
airplanes where the fuel tanks are
installed in the wings.

Fuel systems
 Airplanes with fuel pump systems
have two fuel pumps. The main
pump system is engine driven, and
an electrically driven auxiliary
pump is provided for use in engine
starting and in the event the
engine pump fails. The auxiliary
pump, also known as a boost
pump, provides added reliability to
the fuel system. The electrically
driven auxiliary pump is controlled
by a switch in the cockpit.

Fuel systems
 FUEL TANKS
Normally located inside the wings of an airplane, have a filler opening on
top of the wing through which they can be filled. Fuel tanks also include
an overflow drain that may stand alone or be collocated with the fuel
tank vent. This allows fuel to expand with increases in temperature
without damage to the tank itself. If the tanks have been filled on a hot
day, it is not unusual to see fuel coming from the overflow drain.
 FUEL DRAIN
Fuel samples should be drained and checked visually for water and
contaminants. Water in the sump is hazardous because in cold weather
the water can freeze and block fuel lines. In warm weather, it can flow
into the carburetor and stop the engine. If water is present in the sump,
it is likely there is more water in the fuel tanks, and you should continue
to drain them until there is no evidence of water

Fuel systems
 Fuel primer
 The primer is used to draw fuel
from the tanks to vaporize it
directly into the cylinders prior
to starting the engine.
 This is particularly helpful during
cold weather, when engines are
hard to start because there is
not enough heat available to
vaporize the fuel in the
carburetor.
 It is important to lock the primer
in place when it is not in use.

Fuel systems
 Fuel Selector
 The fuel selector valve allows
selection of fuel from various
tanks. Our A/C have valve
contains three positions: LEFT,
RIGHT and OFF. Selecting the
LEFT or RIGHT position allows
fuel to feed only from that tank.

Fuel systems
 Fuel gauges
 The fuel quantity gauges
indicate the amount of fuel
measured by a sensing unit in
each fuel tank and is displayed in
gallons or pounds.

Engine cooling systems
 The burning fuel within the cylinders produces intense heat, most of
which is expelled through the exhaust system. Much of the
remaining heat, however, must be removed.
 Otherwise, the extremely high engine temperatures can lead to loss
of power, excessive oil consumption, detonation, and serious engine
damage.
 Oil system is vital to internal cooling of the engine, and additional
method of cooling is necessary for the engine’s external surface.


The engine oil system performs several important functions:
• Lubrication of the engine’s moving parts
• Cooling of the engine by reducing friction
• Removing heat from the cylinders
• Providing a seal between the cylinder walls and pistons
• Carrying away contaminants

 Air cooling is accomplished by
air flowing into the engine
compartment through
openings in front of the engine
cowling. Baffles route this air
over fins attached to the engine
cylinders, and other parts of the
engine, where the air absorbs
the engine heat. Expulsion of
the hot air takes place through
one or more openings in the
lower, aft portion of the engine
cowling.

CONCLUSION
 REVIEW

 KEY POINT :









Reciprocating Engine
Four Strokes
Propeller
Carburetor Icing
Ignition
Magneto
Fuel
Engine Cooling

Piston engine powerplant

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