Practical Electricity for Aviation Maintenance Technicians

Dale Crane, Dennis Wilt

• Publisher: Aviation Supplies & Academics, Inc.
• Year: 2017
• ISBN:
  9781619543485
• Topic: Technologie et ingénierie
• Subtopic: Aviation

Practical Electricity for Aviation Maintenance Technicians is written as a classroom text for those preparing to enter the field of aviation maintenance, those seeking an introduction to electricity studies, as well as for experienced mechanics who want to increase their knowledge of electricity and electrical systems. Today's aircraft are loaded with electric motors, lights, instruments and heaters, and the avionics and electronic controls have made flight profitable, safe and efficient. This book provides a solid foundation for keeping up with this fast moving area of technology. After an introduction to the principles of electricity and discussion of DC and AC circuits, the reader is introduced to aircraft electrical circuit components and solid-state devices, followed by a discussion of the two major methods of producing electricity: chemical action, and magnetism. Basic electric motors and generators, aircraft electrical systems, electrical instrument systems, avionics systems, digital electronics, powerplant electrical systems, powerplant ignition systems, and electrical system installation are covered, and the book concludes with systematic troubleshooting methods for aircraft electrical systems. The information reflects both legacy aircraft fleets, and new technologies including glass cockpit components. Illustrated extensively throughout, each chapter concludes with review questions for classroom and self-study use; glossary and index included.

1

An Introduction to Electricity

rotary inverter. A self-contained motor-generator in which a DC motor drives an AC generator.

The progress made in aviation is closely related to the advancements made in electricity and its offshoot technology, electronics. For the first few decades of flight, an A & E (Airplane and Engine) mechanic needed to know little more about electricity than the way to coax a healthy spark from a magneto. Then, up through World War II, aircraft electrical systems consisted of no more than DC generators and batteries to operate the starters, lights, radios, and in some installations, retractable landing gear and flaps. Only a few of the largest aircraft had AC electricity, and this was only for special purposes and was usually produced by DC-powered rotary inverters.

Electronic communications and navigation have made flight so efficient that even small general aviation aircraft are equipped with electronic equipment that is far more sophisticated than that installed in transport aircraft immediately after World War II.

The proliferation of computerized monitoring systems and automatic controls in modern aircraft has made in-depth knowledge of electricity essential for the aviation maintenance technician of the twenty-first century.

avionics. The branch of technology that deals with the design, production, installation, use, and servicing of electronic equipment installed in an aircraft.

This text, Practical Electricity for Aviation Maintenance Technicians, is written to furnish background knowledge to allow you to better understand technical manuals and more advanced texts on specialized electrical and avionics equipment.

The History of Electricity

For years we did not know exactly what electricity was, but we were able to use it to do useful work. Within the past five decades, however, we have learned much more about electricity, and the more we learn about it, the more practical uses we find for it.

Centuries ago, it was discovered that when a piece of hardened tree rosin, called amber, was rubbed with sheep’s wool, the amber attracted tiny pieces of straw. But when the straw touched the amber, an invisible force pushed the straw away.

Because of these strange happenings, the theory was formulated that there was some kind of invisible fluid on the wool and the amber. The fluid was called “electrik,” after the Greek word for amber. There were thought to be two conditions: a lack of fluid and an excess of fluid. When an object having an excess of this invisible fluid was touched by an object having a lack of it, the electrik left one object and traveled to the other, often causing a spark as it went. When both objects had an excess of fluid, or when both had a lack of fluid, they would repel, or push away, from each other.

Lightning, the huge spark that jumps between clouds or from a cloud to the ground, seemed to prove this theory. And certain terms were developed to explain what was happening.

An object having an excess of electrik was said to be “positive,” and, in written explanations, a plus (+) sign was used to show this condition. The object having a lack of electrik was called “negative,” and this was shown by a minus (–) sign. When electrik passed from one object to another, it was said that “current” flowed between them.

This theory and its explanation worked quite well for years, even though no one knew exactly what it was that flowed or what caused the flow. Today, we know that this flow is made up of invisible particles of matter called electrons.

Knowing what it is that flows in an electrical device and understanding the way we can control this flow enables us to use this invisible force to accomplish almost unbelievable feats.

Atomic Makeup

chemical element. One of the fundamental building blocks of which all matter is made. There are just a few more than 100 different chemical elements. Some elements exist in nature by themselves, and others exist only in chemical compounds. Oxygen, carbon, gold, silver and hydrogen are examples of chemical elements.

atom. The smallest particle of a chemical element that can exist, either alone or in combination with other atoms.

chemical compound. A combination of two or more atoms of chemical elements that have joined together to form molecules.

molecule. The smallest particle of a substance that retains all the properties of the substance. A molecule is made up of one or more atoms.

proton. The positively charged particle in the nucleus of an atom.

neutron. The particle in the nucleus of an atom that has the same mass as a proton but no electrical charge.

The study of physics teaches that all matter is made up of slightly more than one hundred different chemical elements whose smallest particles are called atoms.

The nucleus, or center, of an atom is made up of positive electrical charges called protons, and neutrons, which have the same amount of mass as a proton, but with no electrical charge. Spinning around the nucleus in rings—or shells—are negatively charged particles called electrons. The mass of an electron is only about 1/1,846 that of a proton, but its negative electrical charge is exactly as strong as the positive charge of a proton.

Figure 1-1. Electrons circle the nucleus of an atom in shells, with all the electrons in each shell circling the nucleus the same ...