飞机设计导论(第七章)

Introduction to Aircraft Design
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2012年7月17日星期二
7.1 Avionics Systems


Modern efficient, reliable avionics have dramatically simplified the flight operation and have eliminated to need of crew members such as navigator, wireless operator and flight engineer. The growth in the capabilities of military avionics has been even more dramatic and make it possible for pilot of single-seat aircraft to navigate, communicate, detect and attack targets at heights of 30m and speeds approaching the speed of sound. Fig. 7.2 and 7.3.
IntroduБайду номын сангаасtion to Aircraft Design
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2012年7月17日星期二
7.1.1 Communication



Typical ranges are 200 miles (320km) at 20 000ft (6000m) . UHF systems are similar to VHF but operate in the 200~400MHz band. HF (2~30MHz) communication system is used for long range communication, which operates essentially in the same way as VHF systems. Communications over long distances are possible with HF radio because of ionospheric reflection.
Introduction to Aircraft Design
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2012年7月17日星期二
7.1.2.1 Automatic direction finding (ADF)



The aerial is directional and the signal becomes weaker or stronger as the radio is rotated about a vertical axis. On a/c, loop aerials are rotated in the direction of a ground-based non-directional beacons (NDBs). The radio magnetic indicator gives the magnetic bearing of the NDBs which will give information to locate the a/c on a map. Max. range is 10-150 n mile with a typical accuracy of ±4 °.
Introduction to Aircraft Design
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2012年7月17日星期二
7.1.1 Communication




Air traffic controllers need to know the position of all a/c within their control areas. Ground-based radar systems detect all a/c but some system is required to identify them. Civil a/c carry equipments called ATC transponders which receive pulses from the ground radar sets. The transponder the transmits a sequence of pulses which identifies the a/c and gives its height to the controller. IFF (identification friend or foe) for military a/c responds to signals from either ground-based or airborne radars.
Introduction to Aircraft Design
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2012年7月17日星期二
7.1.2.3 Distance measuring equipment (DME)




This is a interrogation and response system, where the a/c equipment sends a VHF signal to a ground station which then responds to the a/c. The DME receiver computes the time delay and calculates the distance from the beacon. Its distance is similar to that of VOR, with an accuracy of ±0.5 n mile. TACAN (tactical air navigation) is used for military a/c, which combines features of both VOR and DME and gives range and bearing.
Introduction to Aircraft Design
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2012年7月17日星期二
7.1.1 Communication



Airborne communications systems vary considerably in size, weight, range, power requirements, quality of operation, and cost, depending upon the desired operation. The most common communication system in use today is VHF, large a/c are usually equipped with HF, some are fitted with UHF systems. VHF (100~150MHz) radio waves follow approximately straight lines. The range of contact is determined by the heights of the transmitting and receiving antennas.
Introduction to Aircraft Design
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2012年7月17日星期二
7.1.2.4 Doppler navigation



This is a medium to long-range self-contained system. A typical system accuracy might be 1% in distance and heading, which would be serious at long ranges unless corrected by other systems. The Doppler radar emits narrow beams of energy at on frequency, and these waves of energy strike the Earth’s surface and are reflected. The earth-returned energy is intercepted by the receiver and compared with the outgoing transmitter energy. The difference, due to Doppler effect, is used to develop ground speed and wind drift angle information.
Introduction to
Aircraft Design
Chapter 7 What’s under the skin? Avionics, flight control and weapon systems
7.1 Avionics Systems



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 new aircraft can be attributed to avionics. There is a bewildering range of avionics systems, each of which usually requires the use of many acronyms. Fig. 7.1 shows an avionics fit for a small executive aircraft.