The lack of efficient and practical powerplants has limited aircraft development throughout history. For example, in 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 by John Barber. Unfortunately, Barbers engine was neither efficient nor practical. In , Etienne Lenoir of France built the first practical piston engine.
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The lack of efficient and practical powerplants has limited aircraft development throughout history. For example, in 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 by John Barber. Unfortunately, Barbers engine was neither efficient nor practical.
In , Etienne Lenoir of France built the first practical piston engine. Lenoirs engine, which employed a battery ignition system and used natural gas for fuel, operated industrial machinery such as lathes. The next major breakthrough in piston engine development came in when Dr.
August Otto developed the four-stroke, five-event cycle. The Otto cycle is still used in most modern reciprocating aircraft engines. Heat engines convert thermal energy into mechanical energy. A specific volume of air is compressed, and then heated through the combustion of a fuel.
In a reciprocating engine, the heated air expands, creating a force that moves a piston and in turn, the piston rod, crankshaft, and propeller or rotor. Reciprocating engines derive their name from the back-and-forth or reciprocating movement of their pistons. It is the downward motion of pistons, caused by expanding gases, which generates the mechanical energy needed to accomplish work. Many types of reciprocating engines have been designed for aircraft since the Wright brothers made aviation history using a four-cylinder in-line engine.
Reciprocating engines are commonly classified by cylinder arrangement radial, in-line, V-type, or opposed and by fuel type gasoline or diesel.
The two basic types of radial engines are the rotary-type and the static-type. During World War I, rotary-type radial engines were used extensively because of their high power-to-weight ratio.
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. Some of the more popular rotary-type engines were the Bentley, the Gnome, and the LeRhone. On rotary-type radial engines, the propeller and cylinders are bolted to the crankcase and rotate around a stationary crankshaft.
The large rotating mass of cylinders produced a significant amount of torque, which made aircraft control difficult. This factor, coupled with complications in carburetion, lubrication, and the exhaust system, limited the development of the rotary-type radial engine.
In the late s, the Wright Aeronautical Corporation, in cooperation with the U. Navy, developed a series of five-, seven-, and nine-cylinder static-type radial engines. These engines were much more reliable than previous designs. Using these engines, Charles Lindbergh and other aviation pioneers completed long distance flights, which demonstrated to the world that the airplane was a practical means of transportation.
The most significant difference between the rotary and the static radial engine is that with the static engine, the crankcase remains stationary and the crankshaft rotates to turn the propeller. Static radial engines have as few as three cylinders and as many as The higher horsepower engines proved most useful.
Static radial engines also possessed a high power-to-weight ratio and powered many military and civilian transport aircraft. Radial engines helped revolutionize aviation with their high power and dependability. Single-row radial engines typically have an odd number of cylinders arranged around a crankcase.
A typical configuration consists of five to nine evenly spaced cylinders with all pistons connected to a single crankshaft. To increase engine power while maintaining a reasonably-sized frontal area, multiple-row radial engines were developed.
These engines contain two or more rows of cylinders connected to a single crankshaft. The double-row radial engine typically has 14 or 18 cylinders. To improve cooling of a multiple-row radial engine, the rows are staggered to increase the amount of airflow past each cylinder. The largest, mass-produced, multiple-row radial engine was the Pratt and Whitney R, which consisted of 28 cylinders arranged in four staggered rows of seven cylinders each.
The R developed a maximum 3, horsepower, making it the most powerful production radial engine ever used. The Pratt and Whitney R engine was the largest practical radial engine used in aviation.
Development and advancement in turbojet and turboprop engines eclipsed the performance of large multiple-row radial engines.
The pistons are either upright above or inverted below the crankshaft. This engine can be either liquid-cooled or air-cooled. The Austro Engine company manufactures inline diesel-powered aircraft engines. In-line engines have a comparatively small frontal area, which enables them to be enclosed by streamlined nacelles or cowlings.
Because of this, in-line engines were popular among early racing aircraft. A benefit of an inverted in-line engine is that the crankshaft is higher off the ground. The higher crankshaft allowed greater propeller ground clearance, permitting the use of shorter landing gear. Historically, in-line engines were used on tail-wheel aircraft; they enabled manufacturers to use shorter main gear, which increased forward visibility while taxiing. In-line engines have two primary disadvantages.
They have relatively low power-toweight ratios and, because the rearmost cylinders of an air-cooled in-line engine receive relatively little cooling air, in-line engines are typically liquid-cooled or are limited to only four or six cylinders. As a result, most in-line engine designs are confined to low- and medium-horsepower engines used in light aircraft. In , Thielert Aircraft Engines now Centurion Aircraft Engines began delivering new, certified kerosene-powered, in-line reciprocating engines for light aircraft.
In , Austro Engine certified a similar engine. Two rows of cylinders, called banks, are oriented 45, 60, or 90 degrees apart from a single crankshaft. Two banks of cylinders typically produce more horsepower than an in-line engine.
Because the cylinder banks share a single crankcase and a single crankshaft, V-type engines have a reasonable power-to-weight ratio with a small frontal area. The pistons can be located either above the crankshaft or below the crankshaft. Most V-type engines had 8 or 12 cylinders. Vtype engines can be either liquid- or air-cooled. V engines developed during World War II achieved some of the highest horsepower ratings of any reciprocating engine. Today, V-type engines are typically found on classic military and experimental racing aircraft.
V-type engines provide an excellent combination of weight and power with a small frontal area. Opposed-type engines are the most common reciprocating engines currently used on light aircraft. Opposed engines can be designed to produce as little as 36 horsepower or as much as horsepower. Opposed engines always have an even number of cylinders, with each cylinder on one side of a crankcase opposing a cylinder on the other side.
The majority of opposed engines are air-cooled and horizontally mounted when installed on fixed-wing aircraft, but they can be mounted vertically in helicopters. Opposed engines have a relatively small, lightweight crankcase that contributes to a high power-to-weight ratio. The compact cylinder arrangement provides a comparatively small frontal area, which enables the engine to be enclosed by streamlined nacelles or cowlings. With opposing cylinders, power impulses tend to cancel each other out, resulting in less vibration than other engine types.
A horizontally opposed engine combines a good power-to-weight ratio with a relatively small frontal area. This style of engine powers most light aircraft in service today. Wankel engines have a good power-to-weight ratio, and their compact design can be enclosed by streamlined nacelles or cowlings. Instead of using a crankshaft, connecting rods, pistons, cylinders, and conventional valve train, the Wankel engine uses an eccentric shaft and triangular rotor turning in an oblong combustion chamber.
This reduction in moving parts contributes to increased reliability. Early designs had problems associated with sealing the combustion chamber, which affected efficiency and engine life. A Wankel engine uses an eccentric shaft to turn a triangular rotor in an oblong combustion chamber. As an aviation maintenance technician, you must be familiar with an engines components in order to understand its operating principles.
Furthermore, your understanding of an engines basic construction enhances your ability to perform routine maintenance operations. The basic parts of a reciprocating engine include the crankcase, cylinders, pistons, connecting rods, valves, valve-operating mechanism, and crankshaft. The valves, pistons, and spark plugs are located in the cylinder assembly, while the valve operating mechanism, crankshaft, and connecting rods are located in the crankcase.
The piston compresses the fuel mixture and transmits power to the crankshaft through the connecting rods. For all of the reciprocating engine types discussed, the horizontally opposed and statictype radial designs represent the majority of reciprocating engines in service today.
Because of this, the discussion on engine components centers on these types. The use of diesel fuel in reciprocating engines designed for aircraft is increasing.
For a discussion of components specific to diesel engines, see Chapter 1, Section C. It contains the engines internal parts and provides attach points for the cylinders, external accessories, and airframe installation.
Additionally, the crankcase provides a tight enclosure for the lubricating oil. Due to great internal and external forces; crankcases must be extremely rigid and strong. A crankcase is subjected to dynamic bending moments that change continuously in direction and magnitude. For example, combustion exerts tremendous forces to the pistons and the propeller exerts unbalanced centrifugal and inertial forces. To remain functional, a crankcase must be capable of absorbing these forces while maintaining its structural integrity.
Today, most crankcases consist of at least two pieces; however, some crankcases are cast as one piece, and some consist of up to five pieces. To provide the necessary strength and rigidity while reducing weight, most aircraft crankcases are made of cast aluminum alloys.
A typical horizontally-opposed engine crankcase consists of two pieces of cast aluminum alloy manufactured in sand castings or permanent molds. Crankcases manufactured by the permanent mold process, or permamold, as it is called by some manufacturers, are denser than those made by sand-casting. Greater density permits molded crankcases to have relatively thinner walls than similar sand-cast crankcases.
[PDF Download] A & P Technician Powerplant Textbook [PDF] Full Ebook
Color illustrations, charts and diagrams, end of section quizzes and summary checklists make tough concepts easier to grasp. ISBN Not only does it provide the fundamentals for the student studying to become a certificated aviation maintenance technician, but it also serves as an excellent resource for the experienced maintenance professional. It includes a wealth of colored illustrations and examples to help maximize the most from your study efforts. Each section includes comprehensive exercises that check the understanding of the material. The textbook introduces the fundamental concepts, terms and procedures that are the foundation of the more complex material that will be encountered in later maintenance training. New Features include: A comprehensive glossary Summary checklists after each chapter New color images and graphics Key terms End of chapter questions Subjects include: Reciprocating engine operation, instruments, maintenance and overhaul Turbine engine operation, instruments, maintenance and overhaul Induction systems Exhaust systems Fuel and Fuel-metering systems Ignition and electrical systems Motors and generators Lubrication systems Cooling systems Engine fire protection Propeller systems Powerplant and propeller inspections Troubleshooting
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