1、Introduction to Aircraft Design,Chapter 7 Whats 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 ai

2、rcraft 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.,2020/7/1,2,隱身技術(shù),7.1 Avionics Systems,Modern efficient, reliable avionics have dramatically s

3、implified 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

4、 and attack targets at heights of 30m and speeds approaching the speed of sound. Fig. 7.2 and 7.3.,2020/7/1,3,隱身技術(shù),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. T

5、he most common communication system in use today is VHF, large a/c are usually equipped with HF, some are fitted with UHF systems. VHF (100150MHz) radio waves follow approximately straight lines. The range of contact is determined by the heights of the transmitting and receiving antennas.,2020/7/1,4

6、,隱身技術(shù),7.1.1 Communication,Typical ranges are 200 miles (320km) at 20 000ft (6000m) . UHF systems are similar to VHF but operate in the 200400MHz band. HF (230MHz) communication system is used for long range communication, which operates essentially in the same way as VHF systems. Communications over

7、 long distances are possible with HF radio because of ionospheric reflection.,2020/7/1,5,隱身技術(shù),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

8、 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-ba

9、sed or airborne radars.,2020/7/1,6,隱身技術(shù),7.1.2 Navigation systems,The knowledge of aircraft position has always been important in flying and initially involved visual fixes made in good visibility, with the aid of a compass. This method is still used by some light aircraft pilots, but increasing soph

10、isticated navigation systems have been developed.,2020/7/1,7,隱身技術(shù),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-direc

11、tional 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 .,2020/7/1,8,隱身技術(shù),7.1.2.2 VHF omnidirectional range (VOR) system,The VOR is an electronic naviga

12、tion system. The all-directional range station provides the pilot with courses from any point within its service range. It produces 360 usable radials or courses, any one of which is a radio path connected to the station. The radials can be considered as lines that extend from the transmitter antenn

13、a. It operates in VHF band and the range is up to 130 n mile at 12 000ft with an accuracy of 1 .,2020/7/1,9,隱身技術(shù),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

14、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.,2020/7/1,10,隱身技

15、術(shù),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 o

16、f energy strike the Earths 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.,2020/7/1,11,隱身技術(shù),7.1.2.5 Long ran

17、ge navigation (LORAN) and Omega,LORAN has been a major navigation system which utilizes the hyperbolic principle. Position is fixed by using several ground stations to produce intersecting hyperbolic systems whose intersections describe unique points. Fig. 7.4 The ranges is up to 2 500 n mile where

18、the signal reflected from the ionosphere. A more modern system is Omega, which uses eight ground stations world-wide and uses VLF transmitters.,2020/7/1,12,隱身技術(shù),7.1.2.6 Global positioning by satellite (GPS),This I is a relatively recent system which is being increasingly used by civil and military a

19、/c. It takes position fixes from signals from a global array of geo-stationary satellites. It is phenomenally accurate, light-weight and relatively cheap. Accuracies to tens of meters may be achieved.,2020/7/1,13,隱身技術(shù),7.1.2.7 Inertial navigation,INS measures inertial forces, or the effects of accele

20、rations, with accelerometers mounted on a stabilized platform. Corrections have to be made for the effects of the Earths rotation, and Coriolis and centrifugal forces. Accelerations are resolved into north-south and east-west components and then integrated successively to provide, at any time during

21、 the flight, instantaneous speed and accumulated distance from take-off.,2020/7/1,14,隱身技術(shù),7.1.2.8 Area navigation,In an area navigation (RNav) system, bearing and distance, position or velocity information from such aids as VOR is processed in a computer. This produces steering information between w

22、aypoints (geographical positions where heading changes are made). Autopilot coupling and flight-director outputs are common in such systems, and they may be electronic data display and a moving-map image.,2020/7/1,15,隱身技術(shù),7.1.3 Radar system,Radar is a device used to see certain objects in darkness,

23、fog, or storms, as well as in clear weather. In addition to the appearance of these objects on the radar scope, the range and relative position are also indicated. Radar is an electronic system using a pulse transmission of radio energy to receive a reflected signal from a target. A radar system con

24、sists of a transceiver and synchronizer, an antenna installed in the nose of the a/c.,2020/7/1,16,隱身技術(shù),7.1.3.1 Weather radar,In the operation of a typical weather radar system, the transmitter feeds short pulses of radio-frequency energy through a waveguide to the dish antenna in the nose of the a/c

25、. Part of the transmitted energy is reflected from objects in the path of the beam and is received by the antenna. Most weather radars have alternative modes to provide simple ground-mapping information.,2020/7/1,17,隱身技術(shù),7.1.3.2 Attack radar,Attack radar operates in a similar manner to the weather r

26、adar described above. The main difference is that attack systems use more power and are used to detect small fast-moving targets than weather formations. Most systems are also used to guide semi-active radar homing missiles and must be designed to be resistant to enemy jamming.,2020/7/1,18,隱身技術(shù),7.1.

27、3.3 Terrain-following radar,Military ground-based radars give good information about attacking aircraft. The curvature of Earth and hills leave a blind-spot at very low altitude. Attack a/c exploit this loophole and attack at extremely low level at high speed. An independent high-power system is use

28、d which detects ground obstacles and feeds control signals into the flight control system. It requires only a narrow beam width.,2020/7/1,19,隱身技術(shù),7.1.3.4 Airborne early-warning radar,This is a system designed to overcome the low-level blind-spot of ground-based radars. In this system powerful radar

29、sets are flown in long-endurance aircraft. The altitude of the aircraft is such that the range of the radar is much greater than with ground-based systems and even low-flying aircraft can be detected at greater distance.,2020/7/1,20,隱身技術(shù),7.1.4 Other avionic systems,Autopilot: Automatically control a

30、n a/c to a pre-set flight pattern. Instrument landing systems: ILS. More recent developments have led to the more accurate microwave landing system (MLS). Laser rangers and target markers: weapon aiming, missile or bomb flies along the laser beam to the target. Forward looking infra-red (FLIR): dete

31、cts heat producing target. An infra-red seeking missile can be directed onto the target.,2020/7/1,21,隱身技術(shù),7.1.4 Other avionic systems,Low-light television (LLTV): This is an optical system in which targets can be seen in clear air at night. This is done by using image intensifiers attached to a TV c

32、amera to produce a day-bright picture of the ground. Electronic counter-measure (ECM): these are systems which either generate fake signals to confuse enemy radar systems or produce a high-powered blanket signal to jam enemy reception.,2020/7/1,22,隱身技術(shù),7.2 Flight control system,The control system co

33、nsists of 4 basic elements, pilot or autopilot, linkage, actuators and control device itself. The autopilot computes the motion of the vehicle with the aid of accelerometers and gyros, and stabilizes it on a given flight path until it is overridden by a guidance command. The control actuators conver

34、t the signal from the autopilot into a motive force which is used to actuate the control device.,2020/7/1,23,隱身技術(shù),7.2 Flight control system,The control system must provide sufficient force for the vehicle to maneuver in a sufficient short time. Large a/c may have a flight g capability of 2.5, interc

35、eptor 9g, anti-aircraft missile 15g. This maneuverability is a function of wing lift. The rate at which the control system can cause the vehicle to achieve the required g is a function of its aerodynamics, structural design and control device.,2020/7/1,24,隱身技術(shù),7.2.1 Conventional trailing-edge flying

36、 control surfaces,Fig. 7.5 gives an illustration of the position of flying controls on an a/c. They are categorized into three groups. Primary group: includes ailerons, elevators and rudder. These surfaces are used for moving the a/c about its three axes. The ailerons and elevators are generally ope

37、rated from the cockpit by a control stick or by a wheel and yoke assembly. The rudder is operated by foot pedals.,2020/7/1,25,隱身技術(shù),7.2.1 Conventional trailing-edge flying control surfaces,Secondary group: includes trim and spring tabs. Trim tabs are used to trim-out any unbalanced condition and oper

38、ated by an independent control. Spring tabs are used to reduce pilot effort in moving the primary control surfaces. Auxiliary group: wing flaps, spoilers, speed brakes, and slats. On some a/c, spoilers are long narrow surfaces hinged at their leading edge to the upper surface of the wing. In the ret

39、racted position, the spoiler is flush with the wing skin. In the raised position, wing lift is greatly reduced.,2020/7/1,26,隱身技術(shù),7.2.2 All-moving tailplanes or foreplanes,Some a/c use a movable horizontal surface called an all-moving tail. This serves the same purpose as the tail plane and elevator

40、combined. As this is a larger control surface than the elevator, it has a more powerful effect. The fore plane of an a/c with canard configuration can be used for pitch control. Canard arrangements generally exhibit more stability and control problems than do conventional layout. All-moving tail pla

41、nes can be used as tailerons.,2020/7/1,27,隱身技術(shù),7.2.3 Reaction devices,There are various ways of producing control forces by reaction means. For example moving fins in a rocket exhaust or the nozzle may be moved in some way, so that changes in thrust direction are obtained. Reaction controls are esse

42、ntial on very high flying vehicles where the air density is too low to enable sufficient aerodynamic force to be developed. Reaction controls are also used in vertical take-off and landing a/c such as the Harrier.,2020/7/1,28,隱身技術(shù),7.2.4 Linkage between pilot and control surfaces,The flying control l

43、inkage once consisted of a simple arrangement of levers and wires (Fig. 7.6). The situation in a modern high speed a/c is very different. The control system is often reduced to a signaling device with artificial feedback on control forces to give the pilot some idea of the loads being imposed on the

44、 aircraft. Since a control failure can not be tolerated, multiplexed system is required as in F-16 fighter.,2020/7/1,29,隱身技術(shù),7.2.4 Linkage between pilot and control surfaces,Advances in computational power have led to the development of active control which have applications as MLC(機(jī)動(dòng)載荷控制), GLA(陣風(fēng)載荷

45、減緩), and Relaxed static stability: RSS is used to reduce the tail plane size below that required for natural stability. This has the effect of increasing manoeuvrability, and reducing the mass and drag of the tail plane or fore plane. Stability is reduced and may indeed be negative. The active contr

46、ol system has to sense any impending destabilizing event and then rapidly send a correcting signal to the surfaces. It usual to have 34 electrical signaling systems. Fiber-optical signaling is being developed as an alternative.,2020/7/1,30,隱身技術(shù),7.3 Weapon systems,Guns: Aircraft cannon are effective

47、in attack against all types of vehicles, field guns, aircraft on the ground, moving troops and ship superstructures. Their ranges are about 8001000 m air-to-air and 2000 m air-to-ground. Smaller caliber machine guns have even less range and their use is limited to armed light aircraft and helicopter

48、s. There are 2 categories of aircraft cannon.,2020/7/1,31,隱身技術(shù),7.3.1 Guns,Gas-operated revolver: uses a single barrel combined with a 4 or 5 chamber rotary revolver, very much like the cowboys 6-shooter. The operation of the gun is powered by the gas discharged during the firing of the 1st round. Se

49、e Fig. 7.7 and table 7.1 for the performances. Rotary Gatling type: the caliber from 7.62 mm through the popular 20 mm Vulcan cannon to the powerful 30 mm GAU-8 (Fig. 7.8) fitted to the A-10. This type gun has a varying number of identical barrels ranging between 3 and 7. External power is required

50、to rotate the barrel cluster, and rotate a cam to feed and fire the ammunition. External power may be electric, hydraulic or pneumatic.,2020/7/1,32,隱身技術(shù),7.3.2 Bombs,They are the primary weapons for stationary targets, for the destruction of runways, oil dumps and other installations. Conventional fr

51、ee-fall bombs: high explosive charge, or nuclear or chemical warhead. Retarded bombs: the bomb is fitted with a retarder tail to slow the bomb down and steepen its trajectory. Cluster bombs: comprises a large number of small bomblets, each of them has its own sensor and fusing device. For both hard

52、and soft targets. Laser-guided bombs: a ground or airborne target designator homes the bomb onto the target.,2020/7/1,33,隱身技術(shù),7.3.3 Rockets,Rockets provide greater hitting power than guns and when used in a dive attack, are highly lethal and economic relative to guided missiles. A typical modern 6-r

53、ound pod is shown in Fig. 7.9. This uses large unguided 135 mm rockets with a typical range of 3 km. Smaller 68 or 57 mm rockets are available in pods containing 18 or more rounds. These unguided rockets have a shorter range and must be used in situations where there is little opposition, or heavy a

54、/c losses will follow.,2020/7/1,34,隱身技術(shù),7.3.4 Guided missiles,Missile guidance surface-to-surface and air-to-surface: the simplest type of guidance system is that of using a predetermined magnetic heading to keep the missile on the desired course. Other guidance systems used are similar to those of manned a/c, radio navigation a