Evolution of avionics

Many thousands of years back homosapiens lived in jungles. They were primarily food gatherers. They wandered around for food, shelter and protection from nature. They just had the basic instincts of animals like eating, sleeping, protecting from dangers and reproduction.

During the process of evolution there came a stage when he could think. This is the time he realised that he need not wander around for food, shelter, protection and reproduction. He could sow seeds at one place, produce his own food, build a dwelling place to protect himself and his people from nature, animals and other threats, choose his life mate and live at one place,

reproduce, rear the off springs etc.

During this time he also questioned himself about flying in the air like a bird and swimming in side the water like a fish. He did many types of attempts to fly in the air like a bird.

On December 17, 1903, the first successfully piloted, power-driven heavier-than-

air machine viz “Flyer” was flown four times by the Wright brothers. Their longest flight lasted for 59 seconds and covered 852 feet. This aircraft had three instruments on board: a stopwatch to time the length of flights, a "Veedor" engine-revolutions counter to measure engine rpm and an anemometer to measure the distance.

More and more man flew the aircraft, he realised that there are many parameters of aircraft he wanted to know, he realised that he has to monitor and control so that he can fly to the destination without any accident.

Initially his aim was to just fly. Later he aimed at reaching a known destination. During this process he realised that navigation is important. He

had to know the places in between. When he flew low he could see the land. When he flew high he could not see the land. So, navigation was difficult. Also a number of times the engines malfunctioned. The airframe structure developed many defects due to Foreign Object Damages (FOD) and stresses due to aerodynaics, loads carried and temperature. He did not know at what altitude, speed,

elevation or roll he is flying. At the time of landing, altitude became a critical parameter for him to be known. He also faced lots of problems during nights with respect to navigation and landing. Bad weather and poor visibility added problems. Rains, dangerous clouds, lightening and all such natural hazards added additional problems. When more aircraft flew in the air,

collision avoidance was a challenge for him.

All these problems made him to realise that he needed to know many parameters. He also realised that for measuring the parameters he had to place many sensors at different places outside and inside the aircraft and engines.

Initially the sensors he used were mechanical in nature. For e.g for altitude

measurement he used the technique of measuring the outside pressure. He knew that the pressure varies as the altitude changes. So, by placing a pitot tube which projected outside to the front he measured the dynamic pressure. The static pressure was measured by tapping the air pressure on the airframe skin by making holes on the airframe. The air pressure trapped was transmitted to the gauges in

cockpit through metallic and rubber tubes. So, the transmission system was also mechanical. The gauges were bellow guages with metal tubes which expanded and moved the needle on the graduated scale as per the changes in the pressure. So, the indication system was also mechanical.

So, in the first stage the sensors, transmission system and the indication…

all three were mechanical in nature. As years progressed we realised that Barometric Pressure measured this way is the most reliable method of measuring the altitude and it is still used on board all types of aircraft. But using mechanical systems for measuring, transmitting and indicating all types of physical parameters on engines and airframe was not possible. So, many parameters could not be

measure by him e.g fuel flow rate, oil (used for cooling the engines) temperature, engine vibration etc.

When the transducer technology developed we had primary and secondary transducers. With these some of the physical parameters could be sensed and converted in to electrical signals. Some of the physical parameters e.g oscillatory movement could be converted to another

physical parameter which could be converted into electrial signal. So, the sensors converted a physical parameter into an electrical signal. The sensors became electrical devices.

When the physical parameter was converted into electrical signal the transmission system became electrical wires. This lead to replacement of indicating devices from mechanical to

electro mechanical i.e moving coil gauges.

So, the second stage of development had electrical sensors, electrical transmission system and electromechanical indication system.

During this stage, the transmission system involved many electronic units like pre amplifiers, power amplifiers, filters etc which were referred to as

Signal Conditioning equipment. Initially they contained tube devices and subsequently when solid state electronics came into existence, they were replaced by semiconductor components.

When analog signals were converted into digital signals the wires got changed to bus. Only the power supply high currents from generators to the consumers were carried by wires. As

technology developed further, optical fibre cables became part of the transmission system.

When electromagnetic waves were invented they also entered the aircraft and transformed the avionics with RF devices for generation, transmission and reception of EM waves. Magnetron and TWTs were used on board aircraft. Rigid and Flexible waveguides were used for transmission of EM

waves inside the aircraft from one device to the other.

Different types of antennae were fitted on the airframe outside for the transmission and reception of EM waves. Visual navigation changed to Dead Reconing. With introduction of Radars onboard the aircraft got their eyes to see the front and all around by few hundred kilometers. They also helped to establish the weather around (weather

radars) to a distance of several hundread kilometers. Weapon aiming radars and fire control radars were used to search, track, aim and fire the weapons towards the targets accuratly.

This helped the pilot to fly the aeroplane to farther distances and also use it for several other roles like transportation of goods, people and animals, carry troops from one place to the other, especially to high

altitudes, jungles, deserts etc. Aircraft were used for military purposes. They were also used at sea to detect surface targets and sub surface targets and destroy them with bombs. When the weapons technology developed they also carried missiles and torpedoes.

This type of long range flying far away from mother base necessitated development of communication equipment

which used EM waves. They transmitted and received the EM waves, converted them into audio signals for hearing. Increased use of aircraft for military purposes also brought in a wide range of tactical and warfare electrical, electronic, magnetic and optical equipment on board.

So, invention of semiconductor devices and EM waves lead to a major

change in the avoinics on board.

The indicating and control equipment in the cockpit and else where in the aircraft also improved as the technology developed.

Invention of mono chrome Cathode Ray Tube (CRT) resulted in replacement of moving coil gauges in some applications. E.g CRTs were used to display targets as bright spots in radars. CRTs

helped to display multiple parameters in one display. This also reduced number of gauges in the cockpit and associated hardware inside the aircraft.

Subsequently when colour CRTs were developed, it could indicate warning signs with red and related colours, distinguishing of target based on threat levels could be possible, weather displays gave better appreciation of environment

to the pilot with different colours for different types of clouds / densities.

Development of LCD displays reduced the size of the displays, occupied less space, multiple functions could be displayed, a large number of parameters could be displayed, pictures for better appreciation of targets and tactical scenario could be displayed.

Introduction of computers, micro controllers, software driven systems, embedded systems etc increased redundancy, reliability, modes of operation, capabilities of systems and reduced the errors of aircrew in carrying out the missions.

Modular design, software driven non destructive real time testing methods while the system is performing its core tasks etc resulted in easy maintenance, less

maintenance, less spares for repairs, increased reliability, airworthiness and role worthiness.

All these developments also lead to electronic warfare technology where in ESM, ECM and ECCM techniques with associated hardware and software through Electronic Reconnaisance Systems could be used.

So, the modern aircraft of today is a highly complicated engineering marvel, a flying high tech factory with all scientific developments and technologies incorporated onboard.

Possible Questions

1. Describe how the avionics evolved over a period of time.

2. List various technological developments that lead to evolution of avionics.

3. What caused evolution of avionics… technological developments or needs of human beings in exploitation of aircraft?