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AMT 115
A/C POWERPLANT 1
MODULE 1
MODULE 1:
● HISTORY AND PROGRESS OF INTERNAL
COMBUSTION ENGINE
● ENGINE CYCLE AND STROKE
INTRODUCTION/OVERVIEW:
The lack of efficient and practical powerplants has
limited aircraft development throughout history. For
example,in 1483 Leonardo daVinci conceived a flying
machine he called the aerial screw. However, without
a powerplant,the aerial screw was never developed. In
fact , the first patent for a heat engine was taken out in
1791 by JohnBarber. Unfortunately, Barber's engine
was neither efficient nor practical. In 1860, Etienne
Lenoir of France built the first practical piston engine.
Lenoir's engine, which employed a battery ignition
system and used natural gas for fue l, operated
industrial machinery such as lathes. The next major
breakthrough in piston engine development came in
1876 when Dr. August Otto developed the four-stroke,
five-event cycle. The Otto cycle is still used in most
modern reciprocating aircraft engines.
LEARNING OUTCOMES:
After completing this module, the students are expected
to develop an understanding about the history and
progression of internal combustion engines.
TIME ALLOTMENT : 1 Week
INSTRUCTIONAL DELIVERIES/LEARNING
ACTIVITIES/PRACTICE ACTIVITIES AND EXERCISES
TASK 1 : (ASYNCHRONOUS) READING NOTES WITH GUIDED
QUESTION IN GOOGLE CLASSROOM
EXERCISES PROVIDED IN GOOGLE CLASSROOM
WATCH THE YOUTUBE VIDEO: https://youtu.be/U5SAttn-e4E
https://www.youtube.com/watch?v=Pu7g3uIG6Zo
: (SYNCHRONOUS) EXPLAINING OF THE TOPIC IN
GOOGLE MEET.
ASSESSMENT : QUIZ # 1 - GOOGLE CLASSROOM
process takes place inside the engine. Aircraft engines come in many
different types, such as gas turbine based, reciprocating piston, rotary, two
or four cycle, spark ignition, diesel, and air or water cooled. Reciprocating
and gas turbine engines also have subdivisions based on the type of
cylinder arrangement (piston) and speed range (gas turbine).
Many types of reciprocating engines have been designed. However,
manufacturers have developed some designs that are used more
commonly than others and are, therefore, recognized as conventional.
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 air-cooled
engines, this heat transfer is direct from the cylinders to the air. Therefore,
it is necessary to provide thin metal fins on the cylinders of an air-cooled
engine in order to have increased surface for sufficient heat transfer. Most
reciprocating aircraft engines are air cooled although a few high powered
engines use an efficient liquid-cooling system. In liquid-cooled engines, the
heat is transferred from the cylinders to the coolant, which is then sent
through tubing and cooled within a radiator placed in the airstream. The
coolant radiator must be large enough to cool the liquid efficiently. The
main problem with liquid cooling is the added weight of coolant, heat
exchanger (radiator), and tubing to connect the components. Liquid cooled
engines do allow high power to be obtained from the engine safely.
Inline Engines
An inline engine generally has an even number of cylinders, although some
three-cylinder engines have been constructed. This engine may be either
liquid cooled or air cooled and has only one crank shaft, which is located
either above or below the cylinders. If the engine is designed to operate
with the cylinders below the crankshaft, it is called an inverted engine.
The inline engine has a small frontal area and is better adapted to
streamlining. When mounted with the cylinders in an inverted position, it
offers the added advantages of a shorter landing gear and greater pilot
visibility. With increase in engine size, the air cooled, inline type offers
additional problems to provide proper cooling; therefore, this type of engine
is confined to low- and medium-horsepower engines used in very old light
aircraft.
Opposed or O-Type Engines
The opposed-type engine has two banks of cylinders directly opposite each
other with a crankshaft in the center Figure 1. The pistons of both cylinder
banks are connected to the single crankshaft. Although the engine can be
either liquid cooled or air cooled, the air-cooled version is used
predominantly in aviation. It is generally mounted with the cylinders in a
horizontal position. The opposed-type engine has a low
weight-to-horsepower ratio, and its narrow silhouette makes it ideal for
horizontal installation on the aircraft wings (twin engine applications).
Another advantage is its low vibration characteristics.
Figure 2. Radial engine
[Figure 3] One type of radial engine has four rows of cylinders with seven
cylinders in each row for a total of 28 cylinders. Radial engines are still
used in some older cargo planes, war birds, and crop spray planes.
Although many of these engines still exist, their use is limited. The
single-row, nine-cylinder radial engine is of relatively simple construction,
having a one-piece nose and a two-section main crankcase. The larger
twin-row engines are of slightly more complex construction than the single
row engines. For example, the crankcase of the Wright R-3350 engine is
composed of the crankcase front section, four crankcase main sections
(front main, front center, rear center, and rear main), rear cam and tappet
housing, supercharger front housing, supercharger rear housing, and
supercharger rear housing cover. Pratt and Whitney engines of comparable
size incorporate the same basic sections, although the construction and the
nomenclature differ considerably.
Figure 3. Double row radials
Design and Construction The basic major components of a reciprocating engine are the crankcase, cylinders, pistons, connecting rods, valves, valve-operating mechanism, and crankshaft. In the head of each cylinder are the valves and spark plugs. One of the valves is in a passage leading from the induction system; the other is in a passage leading to the exhaust system. Inside each cylinder is a movable piston connected to a crankshaft by a connecting rod. Figure 1 illustrates the basic parts of a reciprocating engine.
aluminum alloy is generally used for crankcase construction because it is light and strong. The crankcase is subjected to many variations of mechanical loads and other forces. Since the cylinders are fastened to the crankcase, the tremendous forces placed on the cylinder tend to pull the cylinder off the crankcase. The unbalanced centrifugal and inertia forces of the crankshaft acting through the main bearings subject the crankcase to bending moments which change continuously in direction and magnitude. The crankcase must have sufficient stiffness to withstand these bending moments without major deflections. [Figure 2] Figure 2. The crankcase If the engine is equipped with a propeller reduction gear, the front or drive end is subjected to additional forces. In addition to the thrust forces developed by the propeller under high power output, there are severe centrifugal and gyroscopic forces applied to the crankcase due to sudden changes in the direction of flight, such as those occurring during maneuvers of the airplane. Gyroscopic forces are particularly severe when a heavy propeller is installed. To absorb centrifugal loads, a large centrifugal bearing is used in the nose section. The shape of the nose or front of the crankcase section varies considerably. In general, it is either tapered or round. Depending upon the type of reciprocating engine, the nose or front area of the crankcase varies somewhat. If the propeller is driven directly by the crankshaft, less area is needed for this component of the engine. The crankcases used on engines having opposed or inline cylinder arrangements vary in form for the different types of engines, but in general they are approximately cylindrical. One or more sides are surfaced to serve as a base to which the cylinders are attached by means of cap screws, bolts, or studs. These accurately machined surfaces are frequently referred to
as cylinder pads. If the propeller is driven by reduction gearing (gears that slow down the speed of the propeller less than the engine), more area is required to house the reduction gears. A tapered nose section is used quite frequently on direct-drive, low-powered engines, because extra space is not required to house the propeller reduction gears. Crankcase nose sections are usually cast of either aluminum alloy or magnesium. The crankcase nose section on engines that develop from 1,000 to 2,500 hp is usually larger to house reduction gears and sometimes ribbed to get as much strength as possible. The governor is used to control propeller speed and blade angle. The mounting of the propeller governor varies. On some engines, it is located on the rear section, although this complicates the installation, especially if the propeller is operated or controlled by oil pressure, because of the distance between the governor and propeller. Where hydraulically operated propellers are used, it is good practice to mount the governor on the nose section as close to the propeller as possible to reduce the length of the oil passages. The governor is then driven either from gear teeth on the periphery of the bell gear or by some other suitable means. This basic arrangement is also used for turboprops. On some of the larger radial engines, a small chamber is located on the bottom of the nose section to collect the oil. This is called the nose section oil sump. Since the nose section transmits many varied forces to the main crankcase or power section, it must be secured properly to transmit the loads efficiently. The machined surfaces on which the cylinders are mounted are called cylinder pads. They are provided with a suitable means of retaining or fastening the cylinders to the crankcase. The general practice in securing the cylinder flange to the pad is to mount studs in threaded holes in the crankcase. The inner portion of the cylinder pads are sometimes chamfered or tapered to permit the installation of a large rubber O-ring around the cylinder skirt, which effectively seals the joint between the cylinder and the crankcase pads against oil leakage. Because oil is thrown about the crankcase, especially on inverted inline and radial-type engines, the cylinder skirts extend a considerable distance into the crankcase sections to reduce the flow of oil into the inverted cylinders. The piston and ring assemblies must be arranged so that they throw out the oil splashed directly into them. Mounting lugs are spaced about the periphery of the rear of the crankcase or the diffuser section of a radial engine. These are used to attach the engine assembly to the
Gear trains, containing both spur- and bevel-type gears, are used in the different types of engines for driving engine components and accessories. Spur-type gears are generally used to drive the heavier loaded accessories or those requiring the least play or backlash in the gear train. Bevel gears permit angular location of short stub shafts leading to the various accessory mounting pads. On opposed, reciprocating engines, the accessory gear trains are usually simple arrangements. Many of these engines use simple gear trains to drive the engine’s accessories at the proper speeds
