avionics notes

5/15/2018 Avionics Notes

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BE - VII SEMESTER - AE 1401 AVIONICSUNIT-I

INTRODUCTION TO AVIONICSAn overview on AVIONICS -

Combination of aviation and electronics Avionics system or avionic sub system dependent on electronics Avionics industry - now a multibillion dollar industry world wide Avionics equipment on modem military or civil aircraft can account for around 30% of

the total cost of the aircraft 40% of in the case of a maritime patrol/anti -submarineaircraft or helicopter Over 75% of the total cost in the case of an airborne early warningaircraft such as an AWACS

NEED FOR AVIONICS or Avionics systems are essential To enable the flight crew to carry out the aircraft mission safely and efficiently Mission is carrying the passengers to their destination (civil airliner) Intercepting a hostile aircraft, attaching a ground target, reconnaissance or maritime

patrol.MAJOR DRIVER IN THE DEVELOPMENT

To meet the mission requirements with the minimum flight crew (namely the first pilot andthe second pilot)

Economic benefits like Saving of crew salaries Expenses and training costs Reduction in weigh -more passengers or longer range on less fuel

IN THE MILITARY CASE A single seat fighter or strike (attack) aircraft is lighter Costs less than an equivalent two seat version Elimination of the second crew member (navigator/observer/crew member) Reduction in training costs

OTHER VERY IMPORTANT DRIVERS FOR AVIONICS SYSTEMS ARE Increased safety Air traffic control requirements All weather operation Reduction in fuel consumption


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Improved aircraft performance and control and handling and reduction in maintenancecosts

In the military case, the avionics systems are also being driven by a continuing increasein the threats posed by the defensive and offensive capabilities of potential aggressors

CORE AVIONICS SYSTEM

_ , _ . - - -

I n e f t l i c a lSensors

ExtarnOl l1 Wor l !dSensors

InfraRMSenSQfS

Figure 1 Core Avionics SystemSystems Which Interface Directly with the Pilot:These comprise displays, communications, data entry and control and flight control.Display:

The Display Systems provide the visual interface between the pilot and the air- craftsystems and comprise head up displays (HUDs), helmet mounted displays (HMDs) and headdown displays (HDDs). Most combat aircraft are now equipped with a HUD. A small butgrowing number of civil aircraft have HUDs installed. The HMD is also an essential system


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in modem combat aircraft and helicopters. The prime advantages of the HUD and HMD arethat they project the display information into the pilot's field of view so that the pilot can behead up and can concentrate on the outside world.

The HUD now provides the primary display for presenting the essential flightinformation to the pilot and in military aircraft has transformed weapon aiming accuracy. TheHUD can also display a forward looking infrared (FUR) video picture one to one with theoutside world from a fixed FLIR imaging sensor installed in the aircraft. The infrared picturemerges naturally with the visual scene enabling operations to be carried out at night or inconditions of poor visibility due to haze or clouds. The HMD enables the pilot to be presentedwith information while looking in any direction, as opposed to the limited forward field ofview of the HUD. An essential element in the overall HMD system is the Helmet Trackersystem to derive the direction of the pilot's sight line relative to the aircraft axes.

This enables the pilot to designate a target to the aircraft's missiles. It also enables thepilot to be cued to look in the direction of a threat(s) detected by the aircraft's Defensive Aidssystem. The HMD can also form part of an indirect viewing system by driving a gimbaledinfrared imaging sensor to follow the pilot's line of sight. Image intensification devices canalso be integrated into the HMD. These provide a complementary night vision capabilityenabling the aircraft (or helicopter) to operate at night or in poor visibility.

Colour head down displays have revolutionized the civil flight-deck with multi-function displays eliminating the inflexible and cluttered characteristics of 1970s generationflight-decks with their numerous dial type instrument displays dedicated to displaying onespecific quantity only.

The multi-function colour displays provide the primary flight displays (PFDs) ofheight, airspeed, Mach number, vertical speed, artificial horizon, pitch angle, bank angle andheading, and velocity vector. They provide the navigation displays, or horizontal situationindicator (HSI) displays, which show the aircraft position and track relative to the destinationor waypoints together with the navigational information and distance and time to go. Theweather radar display can also be super- imposed on the HSI display. Engine data arepresented on multi-function colour displays so that the health of the engines can easily bemonitored and divergences from the norm highlighted. The aircraft systems, for example,electrical power supply system, hydraulic power supply system, cabin pressurization systemand fuel management system, can be shown in easy to understand line diagram format on themulti-function displays. The multi-function displays can also be reconfigured in the event of afailure in a particular display.

Communications System:The Communications Systems play a vital role; the need for reliable two way

communication between the ground bases and the aircraft or between aircraft is self-evidentand is essential for air traffic control. Radio transmitter and receiver equipment was in fact thefirst avionic system to be installed in an aircraft and goes back as far as 1909 (MarconiCompany). The communications radio suite on modem aircraft is a very comprehensive oneand covers several operating frequency bands. Long range communication is provided by high


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frequency (HF) radios operating in the band 2-30 MHz Near to medium range communicationis provided in civil aircraft by very high frequency (VHF) radios operating in the band 30-100MHz, and in military aircraft by ultra-high frequency (UHF) radio operating in the band 250-400 MHz (VHF and UHF are line of sight propagation systems.) Equipment is usually atduplex level of redundancy; the VHF radios are generally at triplex level on a modem airliner.Satellite communications (SAT COM) systems are also installed in many modem aircraft andthese are able to provide very reliable worldwide communication.

Data Entry and Control System:The Data Entry and Control Systems are essential for the crew to interact with the

avionic systems. Such systems range from keyboards and touch panels to the use of directvoice input (DVI) control, exploiting speech recognition technology, and voice warningsystems exploiting speech synthesizers.

Flight Control System:The Flight Control Systems exploit electronic system technology in two areas, namely

auto-stabilization (or stability augmentation) systems and FBW flight control systems. Mostswept wing jet aircraft exhibit a lightly damped short period oscillatory motion about the yawand roll axes at certain height and speed conditions, known as 'Dutch roll', and require at least ayaw auto-stabilizer system to damp and suppress this motion; a roll auto-stabilizer system mayalso be required. The short period motion about the pitch axis can also be insufficiently dampedand a pitch auto-stabilizer system is necessary. Most combat aircraft and many civil aircraft infact require three axis auto-stabilization systems to achieve acceptable control and handlingcharacteristics across the flight envelope.

FBW flight control enables a lighter, higher performance aircraft to be producedcompared with an equivalent conventional design by allowing the aircraft to be designed witha reduced or even negative natural aerodynamic stability. It does this by providing continuousautomatic stabilization of the aircraft by computer control of the control surfaces fromappropriate motion sensors. The system can be designed to give the pilot a maneuver commandcontrol which provides excellent control and handling characteristics across the flightenvelope. 'Care free maneuvering' characteristics can also be achieved by automaticallylimiting the pilot's commands ac- cording to the aircraft's state. A very high integrity, failuresurvival system is of course essential for FBW flight control.Aircraft State Sensor SystemsThese comprise the air data systems and the inertial sensor systems.

Air Data System:The Air Data Systems provide accurate information on the air data quantities that is the

altitude, calibrated airspeed, vertical speed, true airspeed, Mach number and airstream


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incidence angle. This information is essential for the control and navigation of the aircraft. Theair data computing system computes these quantities from the outputs of very accurate sensorswhich measure the static pressure, total pressure and the outside air temperature. The air-stream incidence angle is derived from air-stream incidence sensors.

Inertial Sensor System:The Inertial Sensor Systems provide the information on aircraft attitude and the

direction in which it is heading which is essential information for the pilot in executing amaneuver or flying in conditions of poor visibility, flying in clouds or at night. Accurateattitude and heading information are also required by a number of avionic sub-systems whichare essential for the aircraft's mission - for example, the autopilot and the navigation systemand weapon aiming in the case of a military aircraft.

The attitude and heading information is provided by the inertial sensor system(s). Thesecomprise a set of gyros and accelerometers which measure the aircraft's angular and linearmotion about the aircraft axes, together with a computing system which derives the aircraft'sattitude and heading from the gyro and accelerometer outputs. Modem attitude and headingreference systems (AHRS) use a strapped down (or body mounted) configuration of gyros andaccelerometers as opposed to the earlier gimballed systems.

The use of very high accuracy gyros and accelerometers to measure the aircraft's motionenables an inertial navigation system (INS) to be mechanized which provides very accurateattitude and heading information together with the aircraft's velocity and position data (groundspeed, track angle and latitude/longitude co-ordinates). The INS in conjunction with the air datasystem also provides the aircraft velocity vector information. The INS is thus a very importantaircraft state sensor system - it is also completely self-contained and does not require any accessto the outside world.Navigation Systems

Accurate navigation information, that is the aircraft's position, ground speed and trackangle (direction of motion of the aircraft relative to true North) is clearly essential for theaircraft's mission, whether civil or military. Navigation systems can be divided into deadreckoning (DR) systems and position fixing systems; both types are required in the aircraft.

Dead Reckoning Navigation System:The Dead Reckoning Navigation Systems derive the vehicle's present position by

estimating the distance travelled from a known position from knowledge of the speed anddirection of motion of the vehicle. They have the major advantages of being completely self-contained and independent of external systems. The main types of DR navigation systems usedin aircraft are:

(a) Inertial navigation systems. The most accurate and widely used systems.


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(b) Doppler/heading reference systems. These are widely used in helicopters.(c) Air data/heading reference systems these systems are mainly used as a reversionary

navigation system being of lower accuracy than (a) or (b).A characteristic of all DR navigation systems is that the position error builds up with

time and it is, therefore, necessary to correct the DR position error and update the system fromposition fixes derived from a suitable position fixing system.Position Fixing Systems:

The Position Fixing Systems used are now mainly radio navigation systems based onsatellite or ground based transmitters. A suitable receiver in the aircraft with a supportingcomputer is then used to derive the aircraft's position from the signals received from thetransmitters.

The prime position fixing system is without doubt GPS (global positioning system). Thisis a satellite navigation system of outstanding accuracy which has provided a revolutionaryadvance in navigation capability since the system started to come into full operation in 1989.

There are also radio navigation aids such as VORIDME and TACAN which provide therange and bearing (Rl8 ) of the aircraft from ground beacon transmitters located to providecoverage of the main air routes.

Approach guidance to the airfield/airport in conditions of poor visibility is provided bythe ILS (instrument landing system), or by the later MLS (microwave landing system).

A full navigation suite on an aircraft is hence a very comprehensive one and can includeINS, GPS, VORIDME, ILS, MLS. Many of these systems are at duplex level and some may beat triplex level.Outside World Sensor Systems

These systems, which comprise both radar and infrared sensor, systems enable allweather and night time operation and transform the operational capability of the aircraft (orhelicopter).

A very brief description of the roles of these systems is given below. The Radar Systemsinstalled in civil airliners and many general aviation aircraft aircraft provide weather warning.The radar looks ahead of the aircraft and is optimized to detect water droplets and providewarning of storms, cloud turbulence and severe precipitation so that the aircraft can altercourse and avoid such conditions, if possible. It should be noted that in severe turbulence, theviolence of the vertical gusts can subject the aircraft structure to very high loads and stresses.These radars can also generally operate in ground mapping and terrain avoidance modes.

Modem fighter aircraft generally have a ground attack role as well as the pnme


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interception role and carry very sophisticated multi -mode radars to enable them to fulfill thesedual roles. In the airborne interception (AI) mode, the radar must be able to detect aircraft up to100 miles away and track while scanning and keeping tabs on several aircraft simultaneously(typically at least 12 aircraft). The radar must also have a 'look down' capability and be able totrack low flying aircraft below it.

In the ground attack or mapping mode, the radar system is able to generate a map typedisplay from the radar returns from the ground, enabling specific terrain features to be identifiedfor position fixing and target acquisition.Infrared Sensor Systems:

The Infrared Sensor Systems have the major advantage of being entirely passivesystems. Infrared (IR) sensor systems can be used to provide a video picture of the thermalimage scene of the outside world either using a fixed FUR sensor, or alternatively, a gimballedIR imaging sensor. The thermal image picture at night looks very like the visual picture indaytime, but highlights heat sources, such as vehicle engines, enabling real targets to bediscriminated from camouflaged decoys. An IR system can also be used in a search and trackmode; the passive detection and tracking of targets from their IR emissions is of highoperational value as it confers an all important element of surprise.

FUR systems can also be installed in civil aircraft to provide enhanced vision in poorvisibility conditions in conjunction with a HUD.Task Automation Systems

These comprise the systems which reduce the crew workload and enable minimum crewoperation by automating and managing as many tasks as appropriate so that the crew role is asupervisory management one. The tasks and roles of these are very briefly summarized below.Navigation Management:

Navigation Management comprises the operation of all the radio navigation aid systemsand the combination of the data from all the navigation sources, such as GPS and the INSsystems, to provide the best possible estimate of the aircraft position, ground speed and track.The system then derives the steering commands for the autopilot so that the aircraftautomatically follows the planned navigation route, including any changes in heading asparticular waypoints are reached along the route to the destination. It should be noted that thisfunction is carried out by the flight management system (FMS) (if installed).Autopilots and Flight Management System:

The Autopilots and Flight Management Systems have been grouped together. Becauseof the very close degree of integration between these systems on modem civil aircraft. It shouldbe noted, however, that the Autopilot is a 'standalone' system and not all aircraft are equipped


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with an FMS.The autopilot relieves the pilot of the need to fly the aircraft continually with the

consequent tedium and fatigue and so enables the pilot to concentrate on other tasks associatedwith the mission. Apart from basic modes, such as height hold and heading hold, a suitablydesigned high integrity autopilot system can also provide a very precise control of the aircraftflight path for such applications as automatic landing in poor or even zero visibility conditions.In military applications, the autopilot system in conjunction with a suitable guidance systemcan provide automatic terrain following, or terrain avoidance. This enables the aircraft to flyautomatically at high speed at very low altitudes (100 to 200 ft.) so that the aircraft can takeadvantage of terrain screening and stay below the radar horizon of enemy radars.

Sophisticated FMS have come into wide scale use on civil aircraft since the early 1980sand have enabled two crew operations of the largest, long range civil jet airliners. The taskscarried out by the FMS include:

Flight planning. Navigation management. Engine control to maintain the planned speed or Mach number. Control of the aircraft flight path to follow the optimized planned route. Control of the vertical flight profile. Ensuring the aircraft is at the planned 3D position at the planned time slot; often

referred to as 4D navigation. This is very important for air traffic control. Flight envelope monitoring. Minimizing fuel consumption.

Engine Control and Management System:The Engine Control and Management Systems carry out the task of control and the

efficient management and monitoring of the engines. The electronic equipment involved in amodem jet engine is very considerable: it forms an integral part of the engine and is essentialfor its operation. In many cases some of the engine control electronics is physically mountedon the engine. Many modem jet engines have a full authority digital engine control system(FADEC). This automatically controls the flow of fuel to the engine combustion chambers bythe fuel control unit so as to provide a closed-loop control of engine thrust in response to thethrottle command. The control system ensures the engine limits in terms of temperatures,engine speeds and accelerations are not exceeded and the engine responds in an optimummanner to the throttle command. The system has what is known as full authority in terms of thecontrol it can exercise on the engine and a high integrity failure survival control system isessential. Otherwise a failure in the system could seriously damage the engine and hazard thesafety of the aircraft. A FADEC engine control system is thus similar in many ways to a FBWflight control system.

Other very important engine avionic systems include engine health monitoring systemswhich measure, process and record a very wide range of parameters associated with the


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performance and health of the engines. These give early warning of engine performancedeterioration, excessive wear, fatigue damage, high vibration levels, excessive temperaturelevels, etc.House Keeping Management:

House Keeping Management is the term used to cover the automation of thebackground tasks which are essential for the aircraft's safe and efficient operation. Such tasksinclude:

Fuel management. This embraces fuel flow and fuel quantity measurement and controlof fuel transfer from the appropriate fuel tanks to minimize changes in the aircraft trim. Electrical power supply system management. Hydraulic power supply system management. Cabin/cockpit pressurization systems. Environmental control system. Warning systems. Maintenance and monitoring systems. These comprise monitoring and record- ingsystems which are integrated into an on-board maintenance computer sys- tern. Thisprovides the information to enable speedy diagnosis and rectification of equipment andsystem failures by pin-pointing faulty units and providing all the information, such as partnumbers, etc., for replacement units down to module level in some cases.

ILLITIES OF AVIONICSDigital avionics are rife with ilities and it is helpful to examine them early since they

serve as valuable yardsticks by which to access a design. The importance of ilities depends onthe system design and its application.Major 'ilities of Avionics System Capability Reliability Maintainability Certificability Survivability(military) Availability Susceptibility vulnerability Life cycle cost(military) or cost of ownership (civil) Technical riskCapability:

- How capable is avionics system?can they do the job and even more?


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- Designer to maxmuze the capability of the system within the constraints that areimposed.

Reliability:- Designer strives to make systems as reliable as possible.- High reliability less maintenance costs.- If less reliable customer will not buy it and in terms of civil airlines the certificatingagencies will not certify it.

Maintainability:Closely related to reliabilitySystem must need preventive or corrective maintenance.System can be maintained through built in testing, automated troubleshooting and easyaccess to hardware.

Availability:Combination of reliability and maintainability

- Trade of between reliability and maintainability to optimize availability.- Availability translates into sorties for military aircraft and into revenue flights for civil

aircrafts.Certificability:- Major area of concern for avionics in civil airlines.

Certification conducted by the regulatory agencies based on detailed, expert examinationof all facets of aircraft design and operation.

- The avionics architecture should be straight forward and easily understandable.- There should be no sneak circuits and non obvious modes of operation.- Avionics certification focus on three analyses: preliminary hazard, fault tree, and FMEA.

Survivability:- It is a function of susceptibility and vulnerability.

Susceptibility: measure of probability that an aircraft will be hit by a given threat.- Vulnerability: measure of the probability that damage will occur if there is a hit by thethreat

Life cycle cost (LCC)or Cost of ownership:- It deals with economic measures need for evaluating avionics architecture.- It includes costs of varied items as spares acquisition, transportation, storage and training

(crew and Maintenance personnel's), hardware development and test, depreciation andinterest.

Risk:- Amount of failures and drawbacks in the design and implementation.

Overcome by using the latest technology and fail proof technique to overcome bothdevelopmental and long term technological risks.

Functional IntegrationAs avionics systems have evolved, particularly over the past two or three decades, the level

of functional integration has increased dramatically. The nature of this increase and theaccompanying increase in complexity is portrayed in Figure

In the early stages, the major avionics subsystems such as radar, communications,navigation and identification (CNI), displays, weapons and the platform vehicle could b


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considered as discrete subsystems, the function of which could be easily understood. Theperformance requirements could be relatively easily specified and captured, and, although therewere information interchanges between them, each could stand alone and the boundaries of eachsubsystem was 'hard' in the sense that it was unlikely to be affected by the performance of aneighbouring subsystem.

As time progressed, the functionality of each subsystem increased and some boundariesblurred and functions began to overlap. Also, the number of subsystems began to increase owingto the imposition of more complex mission requirements and because of the technologydevelopments that furnished new sensors. Improved data processing and higher bandwidth databuses also contributed to providing much higher data processing capabilities and the means toallow the whole system to become more integrated.

Further technology developments added another spiral to this trend, resulting in greaterfunctionality, further increasing integration and with a blurring of functional boundaries assubsystems became able to share ever greater quantities of data. This evolution has been acontinual process, although it is portrayed in three stages in Figure for reasons of simplicity.The outcome of this evolution has been to increase: performance; sensor types;functionality; cost; integration; complexity; supportability (reuse); software programs in terms ofexecutable code; memory requirements; throughput; reliability; data handling; data links; andobsolescence.

The result has been to decrease: size; weight; power consumption; and technologywindows.


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Air Superiority

-,_- ._,_,_ - -_,_, _,_,-_._,_,_ - - - - _,_._-Role Description

The primary aim of this role is to deny to an enemy the airspace over the battlefield, thusallowing ground attack aircraft a free rein in destroying ground targets and assisting groundforces, secure in the knowledge that the airborne threat has been suppressed.The air superiority aircraft is typically designed to enable the pilot to respond rapidly to adeployment call, climb to intercept or loiter on combat air patrol (CAP) and then to engageenemy targets, preferably beyond visual range. The aircraft should also have the capability toengage in close combat, or dogfight; with other aircraft should this prove to be necessary. Forthis to be successful, an extremely agile machine is necessary with 'carefree handling' capability.

The systems must allow for accurate navigation, accurate identification of targets,prioritization of targets, accurate weapon aiming capability and the ability to join the tacticalcommunications network. A typical mission profile is shown in FigureKey Performance Characteristics

The air superiority aircraft is usually a highly maneuverable aircraft with a high Machnumber capability and rapid climb rate. Many fighters are equipped with afterburning to allowMach 2 capability, a power to weight ratio greater than 1, allowing acceleration in a climb, andthe ability to climb to beyond 60 000 ft. Some types are designed to operate from carriers andwill be equipped for catapult launch and for steep approaches and arrestor wire decelerations.

Many modem fighters are unstable and have full authority flight contro 1systems that aredesigned to allow the pilot to execute maneuvers to envelope limits without fear of losing controlor damaging the aircraft. This is known as 'carefree handling' capability.Crew Complement

Usually single pilot, but some types employ a pilot and a rear-seat air electronics officeror navigator depending on the role. Trainers or conversion aircraft will have two seats forinstructor and student.Systems Architecture

Typical air superiority platform architecture is shown in Figure


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Air Superiority - Aircraft TypesThe various types of air superiority aircraft are as follows:McDonnell Douglas F-4 Phantom;English Electric Lightning;Eurofighter Typhoon;Panavia Tornado F-3;Dassault Rafale;Dassault Mirage 2000;SAAB Gripen;F-lS;F-16;F-18;Mig-21 Fishbed;Mig-23 Flogger;F-117.

GROUND ATTACKRole Description

The ground attack role has been developed to assist the tactical situation on thebattlefield. The pilot must be able to identify the right target among the ground clutter andmultiplicity of targets and friendly units on the battlefield. The ability to designate targets bylaser has enabled precision bombing to be adopted by the use of laser-guided bombs or 'smart'bombs. The role must enable fixed targets such as buildings, radar installations and missile sites,as well as mobile targets such as tanks, guns, convoys, ships and troop formations, to bedetected, positively identified and engaged.

This role includes close air support (CAS), where support is given to ground forces, oftenunder their direction, where weapons will be deployed in close proximity to friendly forces.


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Key Performance CharacteristicsDepending on the target and the on-going military situation, the ground attack role may

be performed by either fixed-wing or rotary-wing aircraft. A fixed-wing aircraft usually needsvery fast, low-level performance with good ride qualities. It should also be reasonably agile toperform attack maneuvers and take evasive action. Rotary-wing aircraft benefit from extremelow-level nap of the earth penetration, and the ability to loiter in natural ground cover - poppingup when required to deliver a weapon.

-,----_._._._-_._._._-_._.-

System Architecture

Crew ComplementThis role is usually conducted by two crew members, a pilot and a crew member to

operate the sensors and weapons systems. The advent of smart weapons or cooperative targetdesignation means that the mission can be conducted by a single crew, often a roledesignated to a fighter aircraft as a secondary role.Ground Attack - Aircraft Types

The various types of ground attack aircraft are as followsSepecat Jaguar;


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Panavia Tornado GR4;Fairchild A-IO Thunderbolt;Apache;Sukhoi Su-24 Fencer.

Strategic BomberRole Description

The role of the strategic bomber is to penetrate deep into enemy territory and to carry outstrikes that will weaken defenses and undermine the morale of the troops. The strategic bomberwas usually a very high-flying aircraft capable of carrying a large load of bombs which werereleased in a 'carpet bombing' pattern. The modem aircraft may choose to fly low and fast andrely on stealth to evade enemy radar defenses. Different weapons may also be employed such asCruise missiles and joint direct attack munitions (JDAM).

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Str .al1egl! i ;oomb1;;r mUl s s io n p o o fl .i e .Key Performance CharacteristicsStrategic bomber aircraft attributes include high altitude cnnse, long range and high

payload capacity.Crew Complement

The crew includes pilots, a navigator, an engineer and specialist mission crew. For verylong missions a relief crew may be provided.Systems Architecture

Typical strategic bomber platform architecture is shown in Figure


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Strategic Bomber - Aircraft Types

The various types of strategic bomber aircraft are as follows (Figure 1.10):Boeing B-52;AVRO Vulcan;Northrop B-2;Tupolev Tu-22M Backfire;Tupolev TU-160 Blackjack;General Dynamics F-111.

Battlefield SurveillanceDetailed knowledge of the tactical scenario on the battlefield is of importance to military

commanders and planners who need real-time intelligence of enemy and friendly forcedisposition, size and movement. Many commercial aircraft types have been converted to performthis role to complement specifically designed military types. The aircraft are equipped witha radar located on the upper or lower surface of the airframe that is designed to look obliquely atthe ground. The aircraft flies a fixed pattern at a distance outside the range of enemy defensesand detects fixed and moving contacts. These contacts are confirmed by using intelligencefrom other sensors or from remote intelligence databases to build up a picture of the battlefieldand the disposition of enemy and friendly forces. The mission crew operate as a team to build upa surface picture, and can operate as an airborne command centre to direct operations such as airor ground strikes.

Role DescriptionA battlefield surveillance mission profile is shown in Figure


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Key Performance CharacteristicsThe key performance characteristics are high altitude, long range and a stable platform

often based on a commercial airliner airframe.

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Crew ComplementThe flight deck crew consists of two pilots who may alternate the roles of flying pilot and

second officer throughout a long-duration mission in order to maintain vigilance. Some typesmay carry an engineer who will operate the general systems and usually acts as a monitor forheight. On types expected to perform very long-duration missions, for example, with air-to-airrefueling this may be in excess of 20 h, a supernumerary pilot may be carried. The mission crewwill be sized to operate the sensors and conduct the tactical mission. Crew sizes for a long-range,long-duration mission may exceed 10.

Systems ArchitectureTypical battlefield surveillance platform architecture is shown in Figure

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Airborne Early Warning:Role Description

Early detection and warning of airborne attack is important to give air superiority anddefensive forces sufficient time to prepare a sound defense. It is also important to alert groundand naval forces of impending attack to allow for suitable defense, evasion or countermeasuresaction.

Operating from high altitude gives the airborne early warning (AEW) aircraft anadvantage of detecting hostile aircraft at longer range than surface radar, which gives vitalseconds for ground defenses forces.Key Performance Characteristics

A long-range, long-endurance aircraft enables a patrol pattern to be set up to cover a widesector area from which attack is most likely. Radar with a 360 scan, and a capability to lookdown and look up, provides detection of incoming low-level and high-altitude attack. The radarwill usually be integrated with an interrogator to enable friendly aircraft to be positivelyidentified. The aircraft will also act as an airborne command post, controlling all airbornemovements in the tactical area, compiling intelligence and providing near real-time displays ofthe tactical situation to both local forces and remote headquarters.Crew Complement

The flight deck crew consists of two pilots who may alternate the roles of flying pilot andsecond officer throughout a long-duration mission in order to maintain vigilance. Sometypes may carry an engineer who will operate the general systems and usually acts as a monitorfor height. On types expected to perform very long-duration missions, for example, with air-to-air refueling this may be in excess of 20 h, a supernumerary pilot may be carried.

The mission crew will be sized to operate the sensors and conduct the tactical mission.Crew sizes for a long-range, long-duration mission may exceed 10.


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Systems ArchitectureTypical airborne early warning platform architecture is shown in Figure

AEW Aircraft TypesThe various types of AEW aircraft are as follows:

Grumman E-2 Hawkeye;Boeing E-3 Sentry;Lockheed P-3 AEW;Tupolev Tu-126 AEW;Westland Sea King

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