UNIT 4AIRCRAFT SECONDARY POWER SOURCES

AIMS OF THE UNIT:- to describe the construction of secondarypower sources

- to describe the characteristics of secondarypower sources

- to describe the operating principles of secondarypower

sources
-to speak about the ways in which emergency poweris

supplied to naval aircraft

- to understand the grammar point ‘ Conditional mood’

TASKS

1 Do your best to answer the brainstorming questions. 2 Read the text for general understanding.

3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian

equivalents of the words.

5 Write sentences with the new vocabulary. 6 Do the given exercisesfor better remembering the tеxt.7 Study grammar point ‘First conditional ` do the tasks.

8 Speak on the topic. Given schemes will help you to remember and understand the

topic. 9 Find more information about the topic. Do some research, create slideshow or a

project work and present them.

 

Brainstorming questions

 

 

1 What do secondary power sources include?

2 What are the operating principles of secondarypower sources?

 

Secondary power sourcesinclude electronic power supplies, and emergency/backup power sources such asemergency generators, batteries, and external powersupplies. Many of the electrical and electronic systems in naval aircraft require precise voltages to operate;therefore, each of these systems has its own powersupply. These power supplies come in many differentshapes, sizes, and designs, but all operate basically thesame way.

In high performance aircraft, avionics systemshelp the pilot communicate, navigate, or fire missiles. Othersystems, such as radar and autopilot (AFCS), ease thepilot’s workload. Each of these systems requiresprecision voltage inputs for proper operation. Normally, each avionics system has its own powersupply. The power supply requirements are for a 120-/208-volt, three-phase,four-wire, 400-Hz electrical power input. The autotransformers have taps from each transformerwinding at the proper position to produce the requiredvoltage. Under fairly constant load conditions, nofurther voltage regulation is necessary.

Full-wave rectifiers produce dc voltages. Each pair of rectifiers (either CR7 and CR10 or CR8 and CR9) conducts during alternate half cycles of the acinput from the secondary coil of step-down transformerT7. The unfiltered dc provides power to operate lightsand relays for internal operation of the system and feedsa filter network. Also, filtered dc supplies transistorbias to the electronic amplifiers in the autopilot system.The circuit develops precisiondc voltages. Diode CR1 is a Zener diode that develops aconstant dc voltage at the input of amplifier A1,regardless of input voltage fluctuations. If the dc inputvoltage at the top of R1 increases, CR1 will conductharder; the excess voltage drops across R1. If thevoltage decreases, CR1 conducts less; less voltagedrops across R1. This maintains the voltage at theanode of CR1 at a constant, precision potential.If no current flows through R2, the same potentialpresent at the input of amplifier A1 and on the anode ofCR1 is the same. Feedback voltage through resistors R3and R4 control the gain of amplifier A1. If thecombined resistance values of R3 and R4 are the sameas the resistance of R2, the potential of the outputvoltage and the anode of CR1 are the same. Variable resistor R4 provides fine-tuning of the output voltage tothe desired level. Isolation amplifier A1 prevents changes in the load current from being felt at the Zenerdiode.

Naval aircraft have backup (emergency) electricalpower if primary sources of electrical power fail. The various ways of supplying this emergency power are aircraft storage batteries, auxiliary power units, and hydraulic motor driven generators.