Avionics is one of the most rapidly developing fields of aircraft design. Its importance and range has increased over recent years and as much as 40% of the cost of a new aircraft can be attributed to avionics. There is a bewildering range of avionic systems, each of which usually requires the use of many acronyms.
Figure 7.1 shows an avionics fit for a medium-range airliner of the future. This aircraft is intended for flight with a crew of one or two pilots. If this aircraft had been in operation during the early post-war years, three additional crew-members would have been required, namely navigator, wireless operator and flight engineer. Modern efficient, reliable avionics have dramatically simplified these operations and have eliminated to need for these crew members.
The growth in the capabilities of military avionics has been even more dramatic and make it possible for pilots of single-seat aircraft to navigate, communicate, detect and attack targets at heights of 100 ft and speeds approaching the speed of sound. Figure 7.2 shows a schematic of such an avionic system whilst Fig. 7.3 shows the installation of components on the instrument panel.
Having looked at typical aircraft installations, the next stage is to examine the functions of various types of avionic systems in the following major groups: communications, navigation systems, radar systems and others.
Airborne communications systems vary considerably in size, weight, range, power requirements, quality of operation and cost, depending upon the desired operation.
The most common communications system in use today is the very high frequency (VHF) system. In addition to VHF equipment, large aircraft are usually equipped with high frequency (HF) communications systems and some are fitted with ultra high frequency (UHF) systems.
VHF airborne communication sets operate in the frequency range from 100 to 150 MHz. VHF receivers are manufactured that cover only the communications frequencies, or both communications and navigation frequencies. In general, the VHF radio waves follow approximately straight lines. Theoretically, the range of contact is the distance to the horizon and this distance is determined by the heights of the transmitting and receiving antennas. However, communication is sometimes possible many hundreds of miles beyond the assumed horizon range. Typical ranges are 200 miles at 20 000 ft. UHF systems are similar to VHF but operate in the 200–400 MHz band.