NOTES ON MISSION AND WEAPON SYSTEMS OF ARMY/AIR FORCE WSI AND NAVAL WSI

Integration of military mission role equipment is an involved task which requires close co-ordination with Vendors of role equipment and Users of the helicopter.

The state-of-the-art, multi role, multi mission Advanced Light Helicopter is armed with sophisticated Mission Sensors, Electronic Warfare Suite and the Weapon Systems to meet the requirements of Armed Forces. MISSION SENSORS AND WEAPON SUITE ON ALH

To accomplish variety of mission roles in day and night, ALH is equipped with Electro Optical Day and Night observation and targeting system consisting of Infra Red camera, TV Colour camera, Laser range finder and Laser designator. ALH is also equipped with Helmet Pointing System provided for both the pilot and the co-pilot.

The ALH is equipped with ‘fire and forget’ Air to Air Missiles, would also be equipped Anti Tank Guided Missiles, the Rockets (that can be fired both in direct and indirect mode), the Turret Gun that can be slaved not only to the Electro Optical pod but also to the Helmet Pointing System. The pilot needs to merely look at the target for the gun to aim at it.

ALH-INTEGRATION ARCHITECTURE

Basic cockpit configuration of ALH consists of IADS (Integrated Architecture and Display System) made up of four Multi Function Colour Displays driven by dual redundant ‘Display and Mission Computers’ (DMC) (which generate the necessary flight symbology, carry out the navigation computations) act as the Mission Computers carrying out variety of mission calculations related to mission sensors and weapon systems. Two numbers of integrated Control Display Units (CDU) and Data Interface Units (DIU) form part of this configuration.

The basic Avionics, the Mission Sensors, Electronic Warfare systems and the Weapon Systems are configured around two numbers of multiplexed dual redundant MIL STD 1553 B digital data bus in a centralized processing environment, with flexibility in configuration and future expandability.

ALH- ARMY/AIR FORCE WSI:

WEAPON SYSTEMS

20 mm Turret Gun70 mm Rocket Air to Air Missile (ATAM)Air to Ground Missile (ATGM)

MISSION SYSTEMS

Electronic Warfare Systems (RWR, LWR, MWR)Counter Measure Systems (Flare and Chaff Dispenser, DIRCM)Helmet Pointing System (HPS)Electro Optical System (FLIR, TV Camera, LRF, LD)Data linkIR Jammer

LCH – AIRFORCE WSI

WEAPONS SYSTEMS

20 mm Gun with 400 rounds(Ballistic Computer System)68/70 mm Rocket - 36/40 nosAir to Air Missile (ATAM) – 4 nosAir to Surface Missile (ASM) – 16 nos.BombsAnti Radiation Missile (ARM) (used in DEAD role)Non Lethal Weapons (NLW)

MISSION SYSTEMS

EW suite (RWR, LWR and MWR)Counter Measure Dispensing System (CMDS – this is same as FCD)Electro Optical System (EO)IRSTHelmet Pointing System (HPS)Data linkDigital Video Recorder (DVR)DIRCM/Laser Transmitter

On ALH, we have evolved a twin MIL STD 1553 bus concept, a ‘Basic Avionics Bus’ and a ‘Mission Bus’ as shown in Fig. 1.

Fig. 1 MFD1 MFD2@

MFD3 MFD4

CDU2 CDU1 DMC1 DMC2 DIU1 DIU2

Counter-Measure

EW Suite

Basic Avionics

Basic 1553 Bus

Mission 1553 Bus

MissionSensors

WeaponSystems

IADS

The Mission role equipment Integration on ALH involves the task of integrating complex weapons and mission sensors from diverse origin on MIL STD 1553 bus.

For example on ALH, the Air to Air Missiles and Turret Gun are from France, Rockets are from Belgium, like Electro Optical System and Helmet Pointing System are from Israel, the Electronic Warfare Suite is from South Africa and Flare and Chaff dispensers are of indigenous source.

These weapon systems and mission sensors are not specifically developed for ALH, whereas the IADS is developed for ALH. Present day mission sensors and weapon systems come as ‘off the shelf’ items and have their own software. Respective vendors would only be adopting their basic software for specific MMI requirements as defined by the helicopter integrator.

Though weapon and mission systems are not developed for specific platform, the Integrated Display and Mission System is specifically developed for the platform. It is the Display and Mission Computer (DMC), which needs to take care of integration of all the weapons and mission sensors, including the EW suite. Hence, it was required to define the detailed software requirements of what DMC should do. This is done through the MMI, FRD and ICD documents which were evolved in co-ordination with Users, IADS vendor and vendors of mission and weapon systems.

DESCRIPTION OF ARMY/AIR FORCE –WSI EQUIPMENT

EW Suite :The ALH can be equipped with a light weight Electronic Warfare (EW) Suite which consists of the following warning systems integrated into a single processor.

Radar Warning Receiver (RWR) Missile Warning Reciever ( MWR) Laser Warning Reciever (LWR)

Radar Warning Receiver is able to detect emissions from various types of radars like the search, tracking, fire control, interrogator and guidance radars. RWR measures the detected radar’s frequency, pulse width, Direction of Arrival, PRF and identifies the threatening radar emitters based on preprogrammed library information and assigns threat priority. Four numbers of RWR antennas are used to provide spatial coverage of 360 degrees in azimuth and approximately 90 degrees in elevation. The frequency coverage is 1 to 40 GHz. DF accuracy of 10-15 degrees is expected. The system is capable of simultaneous detection and processing of 50 thrats and would display 15 threats in prioritywise colour scheme.

Laser Warning Receiver is able to detect emissions from a range of beamrider, designator and laser range finders. LWR detects laser emissions in the 0.53 to 1.8 micro meter wavelength range. Four LWR sensors are used for azimuth coverage of 360 degrees and elevation coverage of 60 degrees. Direction Finding (DF) is with an accuracy of 15 deg. Rms.

Lasers are monochromatic, by this it means ‘single frequency’.

Missile Warning Receiver Passive Ultra Violet Missile Approach Warning System working in the solar blind region would be provided. The system provides the detection and direction of Ultra violet emissions from an approaching missile’s burning solid fuel motor plume. Each of the MAWS sensor would cover conical FOV of approximately 90 deg. The Direction Finding (DF) accuracy in azimuth and elevation would be about 5 degrees rms.

In solar blind UV region, there are no natural clutter sources. MWR specifically helps to counter MANPADS. The system has fast react ion time and is able to discriminate between threatening and non-threatening missiles.

The integrated EW suite provides cue to Counter Measure Dispensing System ( CMDS) for dispensing of chaffs and Flares. The EW suite also is able to provide cue to the IR Jammer on-board, for jamming the in coming IR Missiles.

The system interfaces with the IADS for its control and display function via the MIL STD 1553 basic bus.

Counter Measure Dispensing System ( CMDS) . The CMDS is an airborne defensive system providing self protection by passive Electronic Counter Measure (ECM) against radar guided and IR seeking anti-aircraft missiles. Protection is achieved by dispersing the flares and by misguiding the missile with Flares.

Two numbers of flare and chaff dispensers would be fitted, one on each side of the helicopter. The dispenser can accommodate 30 cartridges which would be of NATO standard. The FCD will activate the specific programme for dispensing the flares and chaffs based on the trigger received from EW suite.

ELECTRO-OPTIC SYSTEM

The Electro-Optical System would consist of a FLIR, CCD Camera, Laser Range Finder and Laser Designator and associated mission grips.

FLIR of 3-5 micron and 8-12 micron are available.

Either a common Laser designator and Laser Range Finder would be available, or a Laser designator and an eye-safe Laser Range Finder would be separately made available. The crew will have facility to select either FLIR or CCD Camera.

The system facilitates area search/tank target detection, target recognition, target identification and target designation to weapon systems.

The output of the FLIR and CCD Camera would be available for display on the Multifunction Colour Displays which are part of the IADS. The Electro-optical pod will have freedom of movement in azimuth and elevation. Slaving signals would be available

from the Electro-Optical system for slaving the turret gun or slaving the seeker of missiles. The Electro-Optic Sighting System would have provision for accepting Ballistic Computer output (which would be part of IADS).

MRTD of FLIR is Minimum Resolvable Temperature Difference. NETD is Noise Equivalent Temperature Difference.

Laser Range Finder provides range of the target. LRF would be capable of resolving range ambiguity in case of multiple reflections.

Laser designator would have suitable range and accuracy to designate a target. The LD can designate targets for guiding the laser guided missiles towards the target.

The Electro-Optic pod would be installed in the nose region, in vertical upright position. The related electronic boxes would be housed in an equipment rack that would be located in the cabin area. The mission grips would be provided for the co-pilot who would be acting also as the weapon system operator.

HELMET MOUNTED DISPLAY

The HMD provides day and night flight symbology and crew Line of Sight information. It enables the crew to fly the helicopter using flight symbology, to steer the on-board sensors Electro-Optical pod in coupled mode and to fire weapons like Turret Gun, Rockets and Air to Air Missiles.

The HMD would include Helmet (with microphone and earphones), Day display module, Night Display module (ie the NVGs), Oxygen masks, Electronic units, Head tracking unit.

The Head tracking unit enables the tracking of the head movement of both pilot and co-pilot and generates the Line of Sight of crew. The pointing accuracy would be better than 8 mrad.

The HMD Electronics units interfaces with on-board systems and drives the two displays of pilot and co-pilot. The display includes flight symbology, warnings, HMD cues, cues from other systems like Electro Optic pod etc.

The Head Tracking unit enables the tracking of head movement (both Pilot’s & Weapon system Operator ) vis-à-vis the bore-sighting position thus generating the Line of Sight of crew .

Gun could be slaved to the HPS of the pilot or the co-pilot. HPS provides LOS (which is azimuth and elevation angle).

DATA LINK

The Data link enables down linking of on-board video and audio information to a ground station, in an encrypted format with anti-jamming features. Expected range is ~ 50Kms at 1000ft AGL . A ground station enables processing of received data from 3 helicopters simultaneously.

The system includes an airborne segment consisting of Antenna, Transmitter/ Receiver/ Integrated Encryption-Decryption/ Anti-jamming unit & Control unit and Ground Segment consisting of Antenna, Transmitter/ Receiver/ Integrated Encryption-Decryption/ Anti-jamming unit and Control & Monitoring units.

IR JAMMER

As there is a limit to the number of flare or chaffs that could be carried onboard the helicopter, IR Jammers could be used. IR Jammers provide continuous protection since they do not involve any dispensables. Also, new generation missiles have flare-rejection capability. Flares have no effect when fired from Short Range, as they go out of missiles FOV in short range.

The IR jammer is a high energy optical counter-measure used to protect the helicopter against a heat seeking missile.

IR Jammers can be Omni-directional or Directional Counter Measures (DIRCM). Omni-directional IRCM are less effective than DIRCM.

Missile Approach Warning System upon detection of the threat and after deciding it as ‘threatening’, gives the Direction Of Arrival information to the DIRCM. The DIRCM turret is swiftly directed towards the threat. The DIRCM turret is then slaved to the MAWS, which constantly tracks the missile trajectory. DIRCM then jams the threatening missile.

Inputs from the MWS includes threat direction , time to impact and threat type.

The system uses jamming techniques that enables it to defeat a range of IR threats like MANPADS , Ground to Air etc.

The DIRCM with Laser Transmitter are the most efficient way of defeating the threatening missiles. However DIRCM with Laser Transmitter are not easily available for the developing countries and their weight could be too high for light and medium weight helicopters.

TURRET GUN

The ALH would be equipped with a 20 mm Turret Gun with 300 rounds of ammunition. The turret gun will have azimuth and elevation freedom and will be slaved to the Electro-Optical system. The turret gun can also be slaved to the Helmet Mounted Display. The turret gun could be fired by both pilot and the co-pilot. The Common Control Display Unit (which is part of the IADS) would be provided in the center console with firing buttons on cyclic stick of the pilot and co-pilot.

The optimum location for turret gun installation would be in the nose. The feeder chute, flexible and rigid would be installed in the nose area. The armament boxes which would be able to accommodate 300 rounds of ammunition, would be installed in the cabin area.

The turret gun provides the following capabilities:

- Air to ground anti personnel and anti vehicle combat - Anti helicopter combat.- Close air support to ground troops

The rate of fire would be about 800 rounds/minute and is compatible to following NATO types of ammunition

- High explosive incendiary (HEI)- Armour piercing Tracer (APT)- Target practice tracer (TPT)

The following firing modes would be feasible : Single shot Programmed burst limited to 15 round / 50 rounds / 100 round Continuous fire

The effective range is about 2 kms

The total weight of the system including ammunition box, chutes and electronic control units is 190. Kgs. The weight of 300 linked ammunition is 100kgs.

ROCKET SYSTEM

70 mm rocket system with 12 tube rockets are expected to be integrated. The rocket system would be able to fire conventional and cargo warheads in both direct and indirect modes.

The Launcher Interface Unit generates the fuse and firing signals and transfer these data to the selected firing tubes upon triggering.

The launcher tubes are divided into zones for mixes of different warheads. The firing sequence is under software control with hardware interlocks on safety critical functions.

The Dhruv helicopter is capable of being fitted with 4 nos of 70mm Rocket launchers on the NATO flange suspension system with 2 attachment station on either side of the helicopter. These can be launched against armoured vehicles / bunkers using a range of warheads like :

- Programmable warheads ( flechette , multi-dart , submunitions)- Conventional warheads ( explosives) - Practice warheads ( impact markers)

Each launcher is capable of carrying 12 nos. of rockets .

The rocket system can be fired using the helmet pointing system , Day night Sighting system or fixed sight in the fixed forward mode. It can be fired in both direct and indirect mode in co-ordination with on-board navigation system.

The following modes of firing is possible.

- Single rocket- Selective ripple /salvo (1,2,4,6 or all rockets)

These modes are selectable and the system also allows selection of above modes for LH, RH or both LH & RH stations.

AIR TO AIR MISSILE SYSTEM

The Dhruv helicopter is capable of carrying the Air to Air Missile (ATAM) on 2 missile launcher fitted on the armament boom with NATO flange (Ref fig1). Each of these launchers are capable of carrying 2 nos. of ATAM each and is equipped with cooling bottles.

The Dhruv helicopter equipped with the ATAM is capable of engaging in Air to Air combat.

The ATAM is a 92.5mm caliber fire and forget missile with a solid state propellant .The missile has a passive infrared homing guidance system, an laser proximity fuse along with the warhead. The war head is a fragmentation type with powerful piercing effect. The missiles use argon cooling bottles.

The total weight of the system including 2 launchers, 4 missiles and electronics units is ~ 205kg. The weight of each missile is 19kgs.

ANTI TANK GUIDED MISSILE SYSTEM

The Dhruv helicopter is capable of being fitted with a “ fire & forget “ Anti Tank Missile. In this configuration the helicopter is capable of engaging ground targets like armoured vehicles and tanks

NAVAL MISSION SENSORS & WEAPONS

SONAR/SONICS SYSTEMS

The sonar /sonic system provides capability to detect, localize, track, classify and fix submerged targets by processing signals received from the dipping sonar and sonobuoys. An indigenous integrated Sonar / sonics system (MIHIR) from NPOL, Kochi , is installed on the Naval Dhruv. Typical frequency of operation 12-15kHz. Typical mazimum operating depth is 250 to 300 m.  

In sonar mode, the system can be operated as either active or passive sonar and in bathy mode, the system acquires and stores bathy thermogram using environmental sensors in

the sonar dome and displays the sonar performance plot,along with the sea- temperature profile.

In sonobuoy mode, LOFAR( low frequency analysis and recording), CODAR (correlation detection analysis and recording) and DEMON ( demodulation of noise) processing of 4 nos: of passive sonobuoy signals are possible.

The most challenging task of integrating sonar system onboard is, linking it with the AFCS for sonar related autopilto modes like the ‘cable height hold’ and ‘cable angle hold’. Integrating Navigation system with AFCS (Automatic Flight Control System) is also a challenging task. The doppler navigation system needs to guide the autopilot to make the helicopter to smoothly ‘transit down to hover’ for sonar dunk operation. As doppler performance over water depends on the sea condition, the overall integration of ASW role equipment like the sonar system takes significant amount of flight testing.

SURVEILLANCE RADAR

The surveillance radar provides long range detection of surface ships and land.,medium and short range detection of submarine snorkels and periscopes and medium range detection of airborne targets. The system is capable of automatic track while scan of designated multiple targets. The system also has a weather avoidance and ground mapping mode.

As 360 deg. radar coverage in azimuth is important, it is a difficult task install the antenna on small helicopters where space is a constraint. For the antenna to provide full 360 deg. coverage, care should be taken to see that protrusions on the helicopter or the body of the helicopter itself is not coming in the way of radar signals, otherwise this would create blanking zones. In a small helicopter, shorter ground clearance poses added difficulty in locating the radar antenna.

The radome design and testing is another important aspect to be taken care while integrating surveillance radars on any platform. Ideally the radome should pass the radar signals with minimum attenuation and least beam distortion.

The indigenous surveillance radar from LRDE, B’lore provide a 360 deg panoramic view. The radar operates in the X band and provides ~ 100 nm in surveillance mode and ~ 160 nm in the weather mode. The RF power output is ~ 3.5 KW. The total weight of the system is ~ 102 kg.

ELECTRONIC SUPPORT MEASURES (ESM)

The ESM system provides reconnaissance of ground based enemy radars, ship borne, and airborne radars. The system intercepts, detects & identifies radar signals and displays their parameters. It also provides threat warning from a programmable threat library for threat prioritisation. ESM is a passive system that provides Direction of Arrival only not range. (ie. Bearing information only not distance).

An indigenous ESM system (EAGLE) from BEL , Hyderbad. Is integrated on the Naval Dhruv . The system operates in the frequency range of 1-18 Ghz . The system consists of six spiral antennas, six front end recievers , an RF unit and an ESM processor. The control and display of the processed information of the enemy radars is on the 14” display unit in the Tactical operator’s console rack in the rear cabin.

The system provides 360 deg azimuth coverage and an elevation coverage ranging from -20 to +15 deg. DOA ( Directional of Arrival) measurement accuracy : 5 deg. rmsSensitivity : -50 dbm

DATA LINK

The data-link is under development at WESSE , New Delhi . The data-link establishes RF links among the fleet units ( ships / aircrafts / submarines & shore stations) . It provides facility to exchange tactical data among these fleet units. The system interfaces with the on-board mission systems like surveillance radar , ESM system, sonar/sonics systems etc for obtaining tactical information, in stand alone configuration. In TMS configuration, the Data Link is a module inside TMS.

TORPEDOE/ELECTRONICS

Torpedoes are weapons used against ships & under-water targets ( submarines) The Dhruv helicoper is capable of carrying and releasing 2 No: torpedoes of type A244S (one on either sides of the helicopter) in the Anti-submarine Warfare (ASW) role .

The Torpedo is available in three configurations:- Warhead configuration (Operational version) and weighs ~ 220kgs each - Exercise Configuration (used for exercise and evaluation purpose )

- Drill configuration (used for training )

The Torpedoes would be released by the operators / pilots using a Torpedoe presetter unit which is used to set the various parameters like depth , search pattern , range and bearing of the under-water Target. The torpedo presettings include, initial turn angle, at what range Acoustic enabling should take place etc.

DEPTH CHARGES

Depth charges are weapons used against under-water targets ( submarines) and can be dropped from a height ~ 750 ft (max) . The Dhruv helicoper is capable of carrying and releasing 2 No: Depth charges ( one on either side of the helicopter) in the Anti-submarine Warfare (ASW) role . Depth charges explode at pre determined depths.

ANTI SHIP MISSILE SYSTEM

Yet be identified by user. Anti ship missiles are very similar to Air to Air Missiles in operation and function, except that the ASM is used against surface vehicles like ships.

ASMs are also fire and forget missiles. However, they have radar seekers and get their target information from surveillance radar.

Semiconductors

A semiconductor is a solid material that is neither a ‘conductor’ nor an ‘insulator’. Semiconductor has ‘electrical conductivity’ in between a conductor and an insulator; it can vary over that wide range either permanently or dynamically.

Semiconductors are important in electronic technology. Semiconductor devices (electronic components made of semiconductor materials), are used in almost every modern electronic device like the computers, mobile phones, digital cameras.

Silicon is used to create most semiconductors commercially, but dozens of other materials are used as well.

GENERAL READING

Semiconductor Devices

Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials (like the silicon, germanium, and gallium arsenide). Semiconductor devices have replaced ‘vacuum tubes’ in most applications. They use electronic conduction in the ‘solid state’ as opposed to the ‘gaseous state’ (ie thermionic emission in high vacuum) in vacuum tubes.

Semiconductor devices are manufactured both as single discrete devices and as ‘Integrated Circuits’ (ICs), which consist of a number—from a few to millions—of devices manufactured and interconnected on a single semiconductor substrate.

Semiconductor Sensors

The main reason why semiconductor materials are so useful is that the behaviour of a semiconductor can be easily manipulated by the addition of impurities, known as ‘doping’. Semiconductor’s ‘conductivity’ can be controlled by introduction of an electric field, by exposure to light, heat or even pressure. This is the reason, why semiconductors make excellent sensors.

Infra Red (IR) and 3 to 5 micron Devices

Electromagnetic Radiation in the wavelengths that the human eye can see is very limited. The radiation that we can see is called ‘visible light’. There are, however, a number of ‘electronic

detectors’ that can detect wavelengths much longer and much shorter than is visible to our eye. In the visible range, ‘red’ is the longest visible wavelength and therefore light just beyond this is called ‘infrared’. Hence, the wavelength of Infra Red is longer than that of visible light, but shorter than that of microwaves. In simple terms, Infra red means "below red" (from the Latin ‘infra’ meaning "below").

The wavelength of IR radiation is measured in micrometers (microns or µm).

The atmosphere absorbs IR radiation, however there are two windows, one at ‘3 to 5 micron’ bandwidth and another at ‘8 to 12 micron’. The IR of these wavelengths is not much attenuated in the atmosphere. This is the reason FLIR (Forward Looking Infra Red) electro optical devices use these frequencies for detecting the target.

Humidity in the atmosphere is often a major interference with infrared systems. However, 3 to 5 micron has further advantage because, water vapor is transparent to infrared from 3 to 4.6 micron but shows significant absorption outside this band in the mid-infrared range.

(NOTE: During the testing of FLIRs before the vendor for EO system was identified for ALH, we had obtained 3 to 5 micron FLIR and 8 to 12 micron FLIR from the shortlisted vendors. On the night of these FLIR testing, there was heavy rain, with MET department reporting 100% humidity. Despite the rain, we could see the objects in the pitch dark clearly in the 3 to 5 micron FLIR whereas the picture was a ‘washout’ in the 8 to 12 micron FLIR).

Apart from FLIRs, in guided missile technology the 3-5 µm ‘seekers’ are used. The seeker’s homing head of IR 'heat seeking' missiles are designed to work to ‘home onto’ the IR signature of the target aircraft (which is typically the jet engine exhaust plume).

Most of the Modern weapons systems use infrared imaging for acquisition and tracking of targets.

Charge Coupled Device (CCD)

Charged Coupled Device (CCD) is an ‘image sensor’ which senses an image.

An image sensor is a device that converts an optical image to an electric signal. It is used mostly in digital cameras and other imaging devices. Complementary metal–oxide–semiconductor (CMOS) are also ‘image sensors’.

Today, most digital still cameras use either a CCD image sensor or a CMOS sensor. Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.

A CCD is an analog device. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information.

CCD is typically referred to as ‘passive-pixel sensors’- that is, pixel sensors without their own amplifiers. CMOS is typically referred to as ‘active-pixel sensor’. It consists of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. CMOS is used most commonly in cell phone cameras and web cameras.

Neither technology has a clear advantage in image quality. CMOS can potentially be implemented with fewer components, use less power and provide data faster than CCDs. However CCD is a more mature technology and is in most respects the equal of CMOS.

(NOTE: On ALH, the EO system consists of a CCD Colour Camera, which is like a ‘digital TV camera’ producing an ‘image’ when there is enough ambient visible light.)

Night vision Devices

Night vision is the ability to see in a dark environment. Humans have poor night vision compared to many animals.

Night vision devices make the viewer sensitive to types of light that would be invisible to a human observer. Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-infrared or ultraviolet radiation). Some animals can see well into the infrared and/or ultraviolet compared to humans, enough to help them see in conditions humans cannot.

Night vision devices gather existing ambient light (starlight, moonlight or infra-red light) through the front lens. They operate through a process involving the conversion of ambient light photons into electrons, which are then amplified by a chemical and electrical process and then converted back into visible light. A night vision device (NVD) is basically an optical instrument that allows images to be produced in levels of light approaching total darkness. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system.

NVDs are typically mounted on the user's head for handsfree use with a helmet attachment, either as a monocular device, or in aligned pairs for binocular "night vision goggles" which provide a degree of depth perception as do optical binoculars.

Night vision devices (NVD) work in the near-infrared band at a wavelength of about 1 micrometer. For comparison, the human visual system is sensitive to light wavelengths in the range of about 0.4 to 0.7 micrometers. Unlike thermal imaging systems, which operate in complete darkness by detecting heat radiation signatures in infrared wavelengths beyond 3 micrometers, NVDs work in near darkness by detecting ordinary ambient light, usually from the moon and stars, that is reflected by objects in the scene being viewed. NVDs contain an image intensifier tube that uses the photoelectric effect to amplify very weak light. As each photon of incoming light collides with a detector plate inside the intensifier tube, the plate ejects several electrons that are further amplified into a cascade of electrons. These electrons are accelerated by a strong electric field towards a phosphor screen which emits light at the point of impact of the electrons. A bright image is thus formed on the phosphor screen. Outdoor environments that are illuminated only by star light can be easily viewed using night vision devices.

Most night vision devices do not detect color information, and hence a monochromatic phosphor screen is sufficient. A green phosphor display is generally used because the human eye is most sensitive to the color green, which falls in the middle of the visible light spectrum.

Night vision devices were originally developed for military use, but have since spread into other areas, such as security and police work, rescue outfits and various amateur uses (for example animal watching or hunting).

Missile Seeker Devices

Missile seekers could be of many varieties. An Anti ship missile, typically has a ‘radar’ in its nose as a ‘seeker’. A torpedo (which is an underwater weapon) has a ‘sonar’ in the nose as a ‘seeker’. However, the Air to Air Missile seekers, the ATGM seekers, MANPADS (shoulder launched missiles) typically use ‘IR seekers’. These missiles are ‘heat seeking’ missiles.

Basically the missile ‘seeker’ is the one that ‘seeks out the target’. It looks for and tracks the target.

There are ‘active’ seekers and ‘passive’ seekers. (The term ‘Active guidance’ and ‘Passive guidance’ are also used). Active seekers are those, which emit certain radiation to ‘seek’ the target. For example, radar seeker is an active seeker. It emits radar waves (electromagnetic waves) to see the target. IR seeker is a passive seeker, it does not emit any radiation. It is a heat seeking missile. It seeks the hot spots of the target ie. the heat emitted by the target.

BASIC AVIONICS

Communication Systems:

V/UHF main and stand byHF(SSB)Intercom

Navigation Systems:

Doppler/GPSADFRadio AltimeterWeather Radar

Identification Systems

IFF

Others:

ELTFDR/CVRULB

It is important to know the frequency band of each of the systems. For eg: PLB – emits 121.5 MHz and 243 MHz.

Also important to know the TSO, ED standards that the systems are certified. For eg. ED 55 related to FDR. How the system work, simple explanation should be understood. Arinc 717 used in FDR.

Different Arinc standards: What is Weather Radar video output standard etc. What is Doppler nav out, ISU output standards etc. For eg: Output of RAM 703 is in Arinc 552.

CIVIL SYSTEMS

VOR/ILS/DME etc.

Know briefly how these work. For eg: Localiser (in ILS) provides azimuth guidance. TACAN gives distance and bearing.

BRIEF NOTES ON SOME OF THE AVIONICS SYSTEMS

DOPPLER/GPS

The Doppler/GPS Navigation System which is part of SOP of ALH provides the navigational information by use of following sensors:

Doppler Velocity Sensor (DVS) Global Positioning Sensor (GPS)

The Doppler/GPS Navigation System has following modes of operation:

Doppler/GPS integrated Mode (in which case it takes velocity update from DVS and position update from GPS)

GPS mode (used when DVS is not available) Doppler Alone mode (used when GPS data is not available) Backup Mode (used when both GPS and DVS is not available. Navigation is

carried out through TAS data received from ADU through AHRS)

Know how doppler works and the various navigational parameters that the system calculates. For eg. doppler calculates wind speed and direction using TAS. Doppler: track angle error is angle between actual tract and desired track. We have struggled on ALH to achieve 1% accuracy in Doppler alone mode. This is practically difficult to achieve because Doppler accuracy depends on various factors. Know those factors. Doppler navigation accuracy depends on ‘all of these’ – antenna alignment, magnetic variation, heading etc. Many of Avionic systems are linked to AFCS. Basic knowledge. For eg: Guided transition down to hover mode relates to Doppler-AFCS

GPS: Know about Gelileo, GLONAS etc. (Gelileo is Global Nav. of European union). Approx height of geostationary satellite is 40,000 km.

For LUH we are going for INS/GPS. INS is a non-radio navigational aid. Inertial Nav. systems use accelerometers.

IFF

The IFF transponder enables identification of friendly aircraft. The airborne transponder transmits coded replies in response to the ground or airborne station interrogations.

The transponder consists of a transmitter and a receiver, operating at 1090 ± 3 MHz and 1030 ± 3 MHz respectively. It has the following modes:

(a) Mode 1 (Military Mode)

(b) Mode 2 (Military Mode)

(c) Mode 3 (Civil Mode A)

(d) Mode C (Altitude Information)

(e) Mode S (Selective Addressing)

There are two antennas provided in the system. One antenna is located aft of the radome and the other under the tailboom. The locations enable full coverage. The two antennas are alternately switched, at a frequency of 42 ± 3MHz by the antenna switching unit. The control unit is the interface between the transponder and the pilot.

WEATHER RADAR

How the system works. The colour coding used. Weather Radar detects ‘precipitation’ associated with dangerous thunderstorm. Rain has high reflective levels. Heavy rain fall shown in red colour.

RADIO ALTIMETER

Basic principles of working. Type of antenna used. AID means Aircraft Installation delay.

BASICS:EMI/EMC

Previously, the standard that was put in the specification was MIL STD 461B. However, though MIL STD 461F is released, we are following now MIL STD 461E. Any new system’s specification, if we are writing today, EMI/EMC standard should be MIL STD 461E.

Need to know, the basic tests under following category:

Conducted emissions tests Conducted susceptibility tests Radiated emission tests Radiated susceptibility tests

MIL STD 1553

Basic knowledge. What is ‘half duplex’ etc. The transmission rate on ALH- basic bus is 20 Hz, whereas the transmission rate on mission bus is 50 Hz. Version of MIL 1553 where optical cables used is called MIL STD 1773.

ARINC 429

Basic knowledge, speed of the high and low Arinc 429. Various bits of Arinc standard. Arinc 429 SSM bits etc.

ANTENNAS:

Antennas how they work basics: Eg: a dipole antenna radiation intensity is maximum along the normal to the dipole axis. Antenna radiation pattern: transmitting or receiving is same. Grounded antenna near the ground acts as a single antenna of twice the height. Dipole antenna , each section of dipole is approximately equivalent to half wavelength.

Know about the type of antennas used. Their typical polar patterns. For eg: loop antenna is used in ADF.. Standard reference antenna for directive gain is isotropic antenna.

WAVE PROPAGATION

How the electromagnetic waves propagate. For eg: Microwave signals follow the curvature of the earth – this is known as ducting. Critical frequency of a given layer in ionosphere is what?Electromagnetic wave propation in waveguide – they are reflected from walls but do not travel along them. Depth of penetration of a wave in a lossy dielectric increases with increasing wavelength. Different types of wave propagartion. For eg: 3 to 30 MHz propagation is sky waves.What is skip distance is the distance from a transmitter to the point where the refelceted sky wave first reached, in sky wave.

COMMUNICATION BASICS

Types of modulation: AM, FM etc., how many side bands it produces. For example, an AM signal at frequency fm (carrier frequency fc) produces two side bands at (fc+fm) and (fc-fm).

Conversion of frequency to wavelength and vice versa. Aircraft altitude and the LOS range relation. Eg: 10,000 mAGL, 213nm.

ECUADOR SYSTEMS

SATPHONE

Satphone provides the facility to communicate with land lines directly from air with the use of Low Earth Orbiting satellites.Provides high quality voice connection (air to ground, ground to air and air to air) EADS has integrated following Satphone on their helicopters:Aircell ST 3100 through Iridium Satellite NetworkDetails were obtained from AircellIt consists of a Transmitter/Receiver unit, an antenna and a handset. Technically, the system was simple and integration on ALH was feasible.However, it was understood that there are some issues with DGCA on the sale and installation of Satphones into aircrafts in India that relates to a dispute between the Indian Government and Iridium that has precluded selling direct to India. Commissioning of Satphone was not allowed in India. For commissioning the system, the end user will have to activate an account with Aircell for the airtime contract to allow access.It was also understood that ‘Satphones’ marketed in India must obtain proper license by the Department of Telecommunications. It was also understood that no license has been issued for satphones to operate in India. However all the problems were overcome and Satphone was certified on Ecuador ALH, before the first helicopter was devlivered.

TCAS II

TCAS is installed on Commercial Aviation Aircrafts. TCAS was considered to be unsuitable for helicopters, as helicopters are slow, do not have good climb rates, difficult to install many antennas and antennas would suffer from rotor interference

However, Eurocopter AS 332 Super Puma, on April 9, 2008 became the first helicopter to be fitted with a second-generation Traffic Alert and Collision Avoidance System (TCAS II).

It would be a challenging experience to integrate and certify TCAS II on ALH.

TCAS - Traffic Alert and Collision Avoidance System is an aid to the pilot in detecting the presence of nearby aircrafts and determining their potential as an airspace threat.

TYPES OF TCASTCAS I TCAS II

TCAS I

TCAS I systems are able to monitor the traffic situation around a plane (to a range of about 40 miles) and offer information on the approximate bearing and altitude of other aircraft. It generates collision warnings in the form of a "Traffic Advisory" (TA). The TA warns the pilot that another aircraft is in near vicinity, announcing "traffic, traffic", but does not offer any suggested remedy; it is up to the pilot to decide what to do, usually with the assistance of Air Traffic Control. When a threat has passed, the system announces "clear of conflict".TCAS IITCAS II is the second and current generation of TCAS, used in majority of commercial aviation aircraft. It offers all the benefits of TCAS I, but will also offer the pilot direct, aural instructions to avoid danger, known as a "Resolution Advisory" (RA). The suggestive action may be "corrective", suggesting the pilot change vertical speed by announcing, "descend, descend", "climb, climb" or "Adjust Vertical Speed Adjust" (meaning reduce or increase vertical speed). By contrast a "preventive" RA may be issued which simply warns the pilots not to deviate from their present vertical speed, announcing, "monitor vertical speed" or "maintain vertical speed". TCAS II systems coordinate their resolution advisories before issuing commands to the pilots, so that if one aircraft is instructed to descend, the other will typically be told to climb — maximising the separation between the two craft.