A Technical Study and Industrial Report on the various Electrical and Communication Systems used in choppers manufactured and Overhauled by Hindustan Aeronautics Limited.

1. 2018
Suhan Roy
3 RD YEAR, B. TECH
Electronics and Communications Engineering
Purulia Government Engineering College
Village – Agharpur, P.O.- Ramamoti,
Block – Joypur, Purulia - 723103
A Study Report on Electrical, Instrument &
Communication System of Cheetah and
Chetak Helicopters

2. ii
A Study Report on Electrical, Instrument & Communication System
of Cheetah & Chetak Helicopters
A report submitted in fulfillment of requirements of Industrial Training
at Hindustan Aeronautics Limited, Barrackpore Division.
Hindustan Aeronautics Ltd.,
Barrackpore Division,
9, Topkhana Road,
24 North Paraganas,
Barrackpore, Kolkata- 700120, West Bengal

3. iii
Certificate
This is to certify that “Study Report on Electrical, Instrument &
Communication system of Cheetah and Chetak Helicopters” is a
document of work done by Suhan Roy fulfill the requirements of
Industrial training program at Hindustan Aeronautics Limited,
Barrackpore division, under our supervision and guidance, during the
period 24thJuly , 2018 to 6th August, 2018.
Guided By: Certified By:
Mr. Goutam Adak Mr. Ram Raj Prabhakar
Manager (Shop) ChiefManager (Accys)
HAL Barrackpore HAL Barrackpore

4. iv
Statement by the Candidate
I hereby state that the report titled “Study Report on Electrical,
Instrument & Communication system of Cheetah and Chetak
Helicopters” has been prepared by me to fulfill the requirements of
Industrial Training and project work done at Hindustan Aeronautics
Limited, Barrackpore division from 1st August, 2016 to 16th August,
2016.
Suhan Roy
B.Tech , 5th Semester
Electronics and Communications Engineering
Purulia Government Engineering College
.Village – Agharpur, P.O.- Ramamoti, Block - Joypur
Distt- Purulia, Pin - 723103

5. v
Acknowledgements
I would like to express my sincere gratitude to Shri S
Anbuvelan, GM (BKP), Shri Pranab Kumar Sharma,
AGM (MFG&OH)and ShriRam Raj Prabhakar,
CM(ACCYS) for makingit possiblefor me to obtain some
knowledge on Cheetah and Chetak helicopters at
HindustanAeronautics Limited, Barrackpore Division. A
special thanks to Shri Gautam Adak, M (Shop) for
providing me their valuablesupportand guidance in this
project.
I wish to express my deep sense of gratitudeto Dr. Tirtha
Sankar Das, HoD Dept. of ECE, PGEC, who was my
mentor for providing me this opportunity. It has been a
wonderful experience to work in the esteemed
Organisationand with peopleof amazingcaliber. I would
also liketo thank all the employees of HAL Barrackpore
for helping me during the tenure of my stay in here.

6. vi
Contents :
Serial
No.
Topic Page Number
1) History of HAL 1
2) Products of HAL 1 - 2
3) Barrackpore Division (HAL) 3
4) Facilities of HAL, Barrackpore Div 4
5) Cheetah Helicopters (a brief
Introduction)
4
6) Chetak Helicopters (intro) 5
7) Services of HAL,Barrackpore 6
8) The Helicopter ( a brief overview) 7
9) Uses of Helicopter 7
10) Anatomy of the Helicopter 8 - 9
11) Flight Control 10 - 11
12) Transmission 12
13) Hydraulic System 13
14) Instrument Monitoring System 14 - 15
15) Communication System in Chetak
and Cheetah Helicopters
16 - 28
16) Electrical System of Cheetah and
Chetak Helicopters
29 - 41
17) Chetak and Cheetah Lighting
Sytem
42 - 44
18) Instruments used in Cheetah and
Cheetak Helicopters
44 - 45
19) Conclusion 46
20) References 47

7. vii
HAL (Hindustan Aeronautics Limited ) :
Hindustan Aeronautics Limited (HAL) based in Bangalore,
India, is one of Asia's largest aerospace companies. Under
the management of the Indian Ministry of Defence, this
state-owned company is mainly involved in aerospace industry, which includes manufacturing
and assembling aircraft, navigation and related communication equipment.
HAL built the first military aircraft in South Asia and is currently involved in the design,
fabrication and assembly of aircraft, jet engines, and helicopters, as well as their components
and spares. It has several facilities spread across several states in India including Nasik, Korwa,
Kanpur, Koraput, Lucknow, Bangalore and Hyderabad. The German engineer Kurt Tank
designed the HF-24 Marut fighter-bomber, the first fighter aircraft made in India.
Hindustan Aeronautics has a long history of collaboration with several other international and
domestic aerospace agencies such as Airbus, Boeing, Sukhoi Aviation Corporation etc.
History of HAL :
Hindustan Aeronautics Limited (HAL) came into existence on 1st
October 1964. The Company was formed by the merger of
Hindustan Aircraft Limited with Aeronautics India Limited and
Aircraft Manufacturing Depot, Kanpur.
The Company traces its roots to the pioneering efforts of an
industrialist with extraordinary vision, the late Seth Walchand
Hirachand, who set up Hindustan Aircraft Limited
at Bangalore in association with the erstwhile princely State of
Mysore in December 1940. The Government of India became
a shareholder in March 1941 and took over the Management
in 1942.
Today, HAL has 20 ProductionDivisionand10 Research & Design Centres in 8 locations in India. The
Company has an impressive product track record - 15 types of Aircraft/Helicopters
manufactured with in-house R & D and 14 types produced under license. HAL has manufactured
over 3658 Aircraft/Helicopters, 4178 Engines, and Upgraded 272 Aircraft and overhauled
over 9643Aircraft and 29775 Engines.

8. viii
HAL has been successful in numerous R & D programs developed for both Defence and Civil
Aviation sectors. HAL has made substantial progress in its current projects:
 Advanced Light Helicopter – Weapon System
Integration (ALH-WSI)
 Tejas - Light Combat Aircraft (LCA)
 Light Utility Helicopter (LUH)
 Light Combat Helicopter (LCH)
 Various military and civil upgrades.
Dhruv was delivered to the Indian Army, Navy, Air Force and the Coast Guard in March 2002,
in the very first year of its production, a unique
achievement.
HAL has played a significant role for India's space
programs by participating in the manufacture of
structures for Satellite Launch Vehicles like
 PSLV (Polar Satellite Launch Vehicle)
 GSLV (Geo-synchronous Satellite Launch
Vehicle)
 IRS (Indian Remote Satellite)
 INSAT (Indian National Satellite)
Apart from these, other major diversification projects
are manufacture & overhaul of Industrial Marine Gas
Turbine and manufacture of Composites.
HAL has formed the following Joint Ventures (JVs):
 BAEHAL Software Limited
 Indo-Russian Aviation Limited (IRAL)
 Snecma-HAL Aerospace Pvt. Ltd
 SAMTEL-HAL Display System Limited
 HALBIT Avionics Pvt. Ltd
 HAL-Edgewood Technologies Pvt. Ltd

9. ix
 INFOTECH-HAL Ltd
 TATA-HAL Technologies Ltd
 HATSOFF Helicopter Training Pvt. Ltd
 International Aerospace Manufacturing Pvt. Ltd
 Multi Role Transport Aircraft Ltd
Several Co-production and Joint Ventures with international participation are under
consideration.
HAL's supplies / services are mainly to Indian Defence Services, Coast Guard and Border
Security Force. Transport Aircraft and Helicopters have also been supplied to Airlines as well as
State Governments of India. The Company has also achieved a foothold in export in more than
30 countries, having demonstrated its quality and price competitiveness.
HAL, Barrackpore Division :
Barrackpore Division was established as a Repair Base in 1940 during Second World War under
the name of Tata Aviation. In 1951, Barrackpore Factory became a part of Hindustan Aircraft
Pvt. Ltd, Bangalore. Subsequently in 1957, it started functioning as an Outstation Base of HAL,
Overhaul Division. In 1957, Repair and Overhaul of Dakota Aircraft was undertaken and 1020
aircraft were overhauled till 1984. In 1973, Major Servicing of Caribou aircraft was established
and 108 aircraft were serviced till 1984. In 1980, Major Servicing line of single engine Otter

10. x
aircraft was setup and 81 aircraft were serviced till 1985.
During 1982-83, Major Servicing of Chetak / Cheetah helicopters of IAF was started and
subsequently Army, Navy and Coast Guard helicopters were also added. Servicing of AN-32
aircraft was also started from 1988-89 and continued up to 99-2000.
Facilities of HAL, Barrackpore :
Man Power:
Barrackpore Division employs around 200 highly skilled personnel for disassembly, repair and
overhaul, assembly, flight preparation and flight testing of Cheetah and Chetak Helicopters and
Rotables.
Infrastructure:
The main work area in the Division comprises of Two Assembly Hangars having an area of
approx. 6000 sq.mt each for Dismantling, Re-assembly, Equipping and Flight Preparation
activities and Accessories Overhaul Centre for repair and overhaul of Rotables.
Products of HAL, Barrackpore :
HAL Barrackpore Complex isdesignedforthe Maintenance,Repair, Overhaul ,FlightPreparationand
FlightTesting of CheetahandCheetakHelicopters.
CHEETAH Helicopters :
General Description :
Description Cheetah
Emptyweight 1130
Passenger(Incl.Pilot) 3+2
Payload(Kg) at6000mt 50
Fuel consumption (Kg/KW-hr) 0.47

11. xi
IdeallySuitedFor :
Observation Logisticssupport
Surveillance Rescue operations
Earth resource survey HighAltitude operations
CHETAK Helicopters :
Fuel Capacity 575
Cruise speed,km/hr 192
Engine Model
1 × TurbomecaArtouste IIIB
Turboshaft Engine
Description Chetak
Passenger(incl.Pilot) 5+2
Emptyweight 1200
Payload(Kg) at6000mt Nil
Fuel consumption(Kg/Kwhr) 0.47
Fuel Capacity(Ltr) 575
Cruise speed,km/hr 209
Max. Range,km 500
Endurance,hrs. 3
Engine Model 1 × TurbomecaArtouste

12. xii
IdeallySuitedFor :
Passenger/VIPtransport Causalityevacuation
Troop transport Anti-tankwarfare
Airobservation Anti-submarine warfare
Services of HAL, Barrackpore :
Barrackpore Division offers service to customers on :
 Major Servicing (3200 hrs.) of Cheetah, Chetak and Lancer Helicopter of Indian Air Force,
Indian Army, Indian Navy and Indian Coast Guard.
 T1SI (400 hrs.) & T2SI (800 hrs.) Servicing of Chetak Helicopters of Indian Navy and Indian
Coast Guard.
 Repair,ServicingandOverhaul of Rotables
- Directly from customers.
- Other HAL Divisions.
 Assembly of new Cheetah helicopters and new Chetak helicopters.
IIIBTurboshaftEngine

13. xiii
 Repair,ServicingandOverhaul of :
- Propellers.
- Constant speed governor.
 In-situ repairs of helicopters.
 Scheduled and unscheduled servicing of helicopters.
 Supply of spares against AOG demands.
 Supply of Ground Handling and Ground Service Equipment.
 Assistance in Investigations of Accidents/Incidents and Defects.
Type of
Inspection
Time limit in operating
hours
Time
limit
absolute
Tolerance Definitionof Inspection
T1 400 1200
12
month
+20
+1
month
Elementaryroutine
Inspection
T2 800 +30
Intermediateinspection
(T1+additional
operations)
Overhaul 3600 +30
Extensive inspection:
Major
Maintenance
The Helicopter (
a Brief Overview
) :
A helicopterisa type of
rotorcraft inwhichliftand
thrustare suppliedby

14. xiv
rotors.This allowsthe helicoptertotake off andlandvertically,tohover,andtoflyforwards,
backwards,andlaterally.These attributesallowhelicopterstobe usedincongestedorisolatedareas
where fixed-wingaircraftwouldusuallynotbe able totake off or land.The capabilitytohover efficiently
for extendedperiodsof time allowsahelicoptertoaccomplishtasksthatfixed-wingaircraftandother
formsof vertical takeoff andlandingaircraftcannotperform.
Uses of Helicopter :
Due to the operatingcharacteristics
of the helicopter—itsabilitytotake
off and landvertically,andtohover
for extendedperiodsof time,aswell
as the aircraft's handlingproperties
underlowairspeedconditions—it
has beenchosentoconducttasks
that were previouslynotpossible
withotheraircraft, or were time- or
work-intensive toaccomplishonthe
ground.Today,helicopteruses
include transportationof people and
cargo, militaryuses,construction,
firefighting,searchandrescue,tourism,medicaltransport,law enforcement,agriculture,newsand
media,andaerial observation,amongothers.
Anatomy of the helicopter :
The following are the major components of a helicopter are discussed here in brief:
a) Main rotor blade -: The main rotor blade performsthe same functionasanairplane's
wings, providingliftasthe bladesrotate,liftbeingone of the critical aerodynamicforcesthat
keepaircraftaloft.A pilotcan affectliftbychangingthe rotor's revolutionsperminute (rpm) or
itsangle of attack,whichreferstothe angle of the rotary winginrelationtothe oncomingwind.

15. xv
b) Stabilizer-: The stabilizerbarsitsabove andacross the mainrotor blade.Itsweightand
rotationdampenunwantedvibrationsinthe mainrotor,helpingtostabilize the craftinall flight
conditions.
c) Transmission -:Just as itdoesin a motor vehicle,ahelicopter'stransmissiontransmits
powerfromthe engine tothe mainand tail rotors.The transmission'smaingearbox stepsdown
the speedof the mainrotor so it doesn'trotate as rapidlyasthe engine shaft.A secondgearbox
doesthe same for the tail rotor, althoughthe tail rotor,beingmuchsmaller,canrotate faster
than the mainrotor.
d) Engine - The engine generatespowerforthe aircraft.Earlyhelicoptersreliedonreciprocating
gasoline engines,butmodernhelicoptersuse gasturbine engineslikethose foundin
commercial airliners.
e) Fuselage- The mainbodyof the helicopterisknownasthe fuselage.Inmanymodels,a
framelessplasticcanopysurroundsthe pilotandconnectsinthe rearto a flush-riveted
Aluminiumframe.Aluminiumwasn'twidelyusedinaeronautical applicationsuntil the early
1920s, but itsappearance helpedengineersmake theirhelicopterslighterand,asa result,easier
to fly.
f) Tail boom - The tail boomextendsoutfromthe rear of the fuselage andholdsthe tail rotor
assemblies.Insome models,the tail boomisnothingmore thananaluminiumframe.Inothers,
it's a hollowcarbon-fibre oraluminiumtube.
g) Anti-torque tail rotor - Withouta tail rotor,the main rotor of a helicoptersimply spins
the fuselage inthe opposite direction.IgorSikorskyhadthe ideatoinstall atail rotor to counter
thistorque reactionandprovide directionalcontrol.Intwin-rotorhelicopters,the torque
producedbythe rotationof the frontrotor is offsetby the torque producedbya counter
rotatingrear rotor.
h) Landing skids- Some helicoptershave wheels,butmosthave skids,whichare hollow tubes
withno wheelsorbrakes.A fewmodelshave skidswithtwoground-handlingwheels.

16. xvi
Flight control
There are fourbasiccontrolsusedduringflight.Theyare the collectivepitchcontrol,the throttle,the
cyclicpitch control,andthe anti torque pedals.
a) Cyclic Pitch Control :
The cyclicpitchcontrol is usuallyprojectedupwardfromthe cockpitfloor,betweenthe pilot’s
legsor betweenthe twopilotseatsinsome models.Thisprimaryflight control allowsthe pilottoflythe
helicopterinanydirectionof travel:forward,rearward,left,andright.As we know,the total liftforce is
alwaysperpendiculartothe tip-pathplane of the mainrotor.The purpose of the cyclic pitchcontrol isto
tiltthe tip-pathplane inthe directionof the desiredhorizontaldirection.The cycliccontrolsthe rotor
disktiltversusthe horizon,whichdirectsthe rotordiskthrusttoenable the pilottocontrol the direction
of travel of the helicopter.
The rotordisktiltsinthesamedirectionthecyclicpitchcontrolismoved.If the cyclicismoved
forward,the rotor disk tiltsforward;ifthecyclicismovedaft, the disktiltsaft,andsoon.
b) Collective Pitch Control :
The collectivepitchcontrol (orsimply“collective”or“thrustlever”) islocatedonthe leftside of
the pilot’sseatandis operatedwiththe lefthand.The collectiveisusedtomake changesto the pitch
angle of the main rotorbladesanddoesthissimultaneously,orcollectively,asthe name implies.Asthe
collective pitchcontrol israised,thereisasimultaneousandequal increase inpitchangle of all main
rotor blades;asit islowered,there isasimultaneousandequal decreaseinpitchangle. Thisisdone
througha seriesof mechanical linkagesandthe amountof movementinthe collective leverdetermines
the amountof blade pitchchange.Anadjustable frictioncontrol helpspreventinadvertentcollective
pitchmovement.
Changingthe pitchangle onthe bladeschangesthe angle of incidence oneachblade.With
a change inangle of incidence comesachange indrag, whichaffectsthe speedorrevolutionsper
minute (rpm) of the mainrotor.As the pitchangle increases,angle of incidence increases,drag
increases,androtorrpm decreases.Decreasingpitchangle decreasesbothangle of incidence anddrag,
while rotorrpmincreases.Inorderto maintainaconstant rotor rpm, whichisessential inhelicopter
operations,aproportionate change inpowerisrequiredtocompensate forthe change indrag.This is
accomplishedwiththe throttlecontrol orgovernor,whichautomaticallyadjustsenginepower.

17. xvii
c)The Antitorque Pedals :
The antitorque pedals,locatedon the cabinfloorbythe pilot’sfeet,control the pitchand
therefore the thrustof the tail rotor bladesorotherantitorque system. Accordingto Newton’sThird
Law we know that for everyactionthere isanequal andopposite reaction.Thislaw appliesto the
helicopterfuselageanditsrotationinthe opposite directionof the mainrotorbladesunless
counteractedandcontrolled.Tomake flightpossibleand tocompensate forthistorque,most
helicopterdesignsincorporate anantitorque rotorortail rotor. The antitorque pedalsallow the pilotto
control the pitch angle of the tail rotor blades,whichinforwardflightputsthe helicopterinlongitudinal
trimand, while ata hover,enablesthe pilottoturnthe helicopter360°. The antitorque pedalsare
connectedtothe pitch change mechanismonthe tail rotorgearbox and allow the pitchangle onthe tail
rotor bladestobe increasedordecreased.
d) Throttle Control :
The functionof the throttle istoregulate engine rpm. If the correlator or governor system does
not maintain the desired rpm when the collective is raised or lowered, or if those systems are not
installed,the throttle mustbe movedmanuallywiththe twistgripinordertomaintainrpm.The throttle
control is muchlike amotorcycle throttle, andworks in virtually the same way. Twisting the throttle to
the left increases rpm; twisting the throttle to the right decreases rpm .
(Flight Controls of Cheetah Helicopter)
Transmission :
The transmission system includes all components necessary to transmit the engine drive and
powerto the mainand tail rotors.
It consistsof:
a) The main rotor drive assembly,whichisthe linkbetweenthe engine andthe mainrotor.
b) The tail rotor drive assembly,whichisthe linkbetweenthe MainGearBox (MGB) andthe tail
rotor.

18. xviii
Hydraulic system:-
These helicopters,incorporatethe use of hydraulicactuatorsto overcome highcontrol forces.The
hydraulicsystemconsistsof actuators,alsocalledservos, oneachflightcontrol,apumpwhichisusually
drivenby the mainrotor transmissionandareservoirtostore the hydraulicfluid.Some helicoptershave
accumulatorslocated onthe pressure side of the hydraulicsystem.Thisallowsfor acontinuousfluid
pressure intothe system.A switchinthe cockpitcan turn the system off,althoughitislefton
undernormal conditions.Whenthe pilotplacesthe hydraulic switch/circuitbreakerintothe onposition,
the electrical powerisbeingremovedfromthe solenoidvalve allowing hydraulicfluidtoenterthe
system.Whenthe switch/circuitbreakerisputinthe off position,the solenoidvalve isnow de-
energizedandcloses,whichthenallowsthe pilotto maintaincontrol of the helicopterwiththe hydraulic

19. xix
fluidinthe actuators.Thisis knownasa fail safe system.If helicopterelectrical powerislostinflight,the
pilotisstill able to maintaincontrol of the hydraulicsystem.A pressure indicator inthe cockpitmayalso
be installedtomonitorthe system.
Whenmakinga control input,the servoisactivatedand providesanassistingforce tomove the
respective flight control,thusreducingthe force the pilotmustprovide.These boostedflightcontrols
ease pilotworkloadandfatigue.In the eventof hydraulicsystemfailure,apilotisstill able to control the
helicopter,butthe control forcesare veryheavy.
Thus these helicoptersinwhichthe control forcesare sohigh that theycannotbe movedwithout
hydraulicassistance,two ormore independenthydraulicsystemsmaybe installed. Hydraulic
accumulators may alsobe includedtostore pressure,whichcanbe usedfora short periodof time in
an emergencyif the hydraulicpumpfails.Thisgivesyouenough timetolandthe helicopterwithnormal
control.
( Flightcontrol )
Instrument Monitoring System – Operation :
The various operational installations are monitored by:
 Indicators, which shows the variations of the parameters to be monitored (for instance -
pressure, temperature etc)

20. xx
 Warning light, this indicates that the characteristic condition of a parameter has actually been
reached. (for instance - minimum pressure , maximum temperature etc.)
INSTALLATION MONITORED PARAMETER MONITORING MEANS USED
Power plant (engine) Oil pressure/Oil temperature
Rotational speed
T.G.T temperature
Torque & Engine Limit (ΔNg)
Starting sequence
Engine Chip
Engine Oil FLTR Indication
Fuel FLTR Indication
Engine Oil Temp & Pressure
Indicator
NF/NR/NG indicator
TGT Indicator
Engine Torque/Limit Indicator
Warning light
Warning light
Warning light
Warning light
Fuel system Fuel level in the tank
Low fuel level
Booster pump pressure drop
Fuel Content Gauge
Warning light on gauge
Warning light
Transmission system M.G.B oil pressure
M.G.B oil temperature
MGB Chip
IGB Temperature
IGB Pressure
IGB Chip
Warning lights
Flying controls Collective pitch Pitch indicator
Electrical power Voltage
Generator output
Voltmeter
Warning light
Flight control instruments Pitot tube heating
Gyroscopic instruments
Pitot heat warning light
AH indicator,
DG indicator

21. xxi
Instrument Monitoring System - ( Chetak Helicopter ) :

22. xxii
Different Types of Communication System in CHEETAH AND
CHETAK Helicopters :
a) InterCommunication System
b) VHF/UHF Communication System(VUC201A)
c) COM 105A System(CO105A)
d) ADF Communication System(ARC-610A)
e) CockpitVoice Recorder(CVR)
Inter Communication System :
DescriptionandOperation:
The IntercommunicationSystem(ICS) installationprovidesthe communicationslinkbetween
helicoptercrewmembers(pilot,copilot,andobserver).Inaddition,the crew maymonitorsignalsfrom
communicationandnavigationradios,andmayselectaCOMM transceiverforvoice transmissionto
otheraircraft or groundstations.
The ICS installation consists of one ICS control panel and one microphone-earphone
headset for each crew member, and wiring harnesses. The ICS control panel contains amplifiers
for micro- phone and headset signals, and contains the necessary switching circuits to provide
for intercommunication (with or without hot mike) and modulation, monitoring,andcontrol of up
to five transceivers.
The ICS control panel hastwo basicoperatingcontrols:
(1). A rotary switch to select intercom operationor a particular transmitter,
and
(2). Toggle switches to select any or all of the various receivers.

23. xxiii
Signals from all ICS control panels are transmitted outside the helicopter. A warning signal
(engine out, low rpm rotor speed) which cannot be disconnected or varied in volume is
permanently connected to the audio circuit.
A RADIO-ICSrockerswitchislocatedonthe pilot'sandcopilot'scyclicsticks. Whenthe switchispressed
to the
RADIOposition,radiotransmissionisenabled;whenpressedtothe ICSposition,intercomoperationis
enabled.The middle(released) positionselectsVHFreceiveraudio,andisthe listeningpositionfor
interphone andmonitoringof the COMMand ADFreceivers.
AIRCRAFT INTERCOM SYSTEM TF-AP-6F :
General information:-it is fully transistorized ,submature intercom systemequipment and is
common to both the versionsof Helicopters.The purpose of ICS is to:-
a) Have intercommunication between membersof the crew
b) Transmitand receive in conjunction with different radio installations on board the aircraft

24. xxiv
TECHNICALSPECIFICATIONS:-
 Power supply 27.5( nominal)
 Power consumption :-Not more than 1.5A
 Outputimpedance :Approx 600 ohm perstation
 Headset:- Electromagnet microphone of impedance 75 ohm
 Temperature :- -40 degree Celsius to 55 degree Celsius
 Altitude :-30000 feet
 Humidity :-not less than95% at 40 degree Celsius
 Output power:-Greaterthan 20 mw
 Distortion :-lessthan 100% for output power of 200mw at 1 kHz
 Response curve :-Within (+3db /-3db) between 300-3000 Hz withrespect to 1 kHz
Sub Assemblies :-
Equipment consists of the following subassemblies:-
1. IC Control Unit
2. IC Junction Box
3. Filter power supply
IC CONTROL UNIT:-
The main purpose is to establish the intercommunication between the members of the crew. A
relay assures the two way ‘intercom-radio’ circuit .When the relay in the closed position ,the
microphone is coupled to the selected transmitted channel. It contains the Change over switch
[KR-42A] which comprises of:
 An amplifier AM -55A
 An audio channel mixing circuit
 Three rectifying cells
 A relay inverting microphone to the intercom or radio circuits
 A transmitter channel selector for ‘normal’ or ‘emergency’ positions
Junction box :-
It is mainly composed of four amplifiers connected together. Out of these two are preamplifiers
[AM -54A] and the rest are amplifiers [AM -55A] .the junction box BJ -88A serves three main
purposes:-
 It makes the inter connection between different change over switches[KR-42A]

25. xxv
 It makes the inter–connection betweenthe various radio equipmentsand the change over
switches
 It supplies 27DC battery supply to the change over switch besides making inter connection
FILTER unit:-
The filter unit F1-15A performs the operation of filtering any ripple in the DC Supply for a
smooth 27.5V Dc to IC system.The filter is contained in a small box whichisfixed to the base SK-
34A .The filter is composed of a condenser C-201 and an iron cored choke L-201.These elements
are connected to a miniature ‘SOPOS’ 5 branch socket FF -201.The filter is connected between
the aircraft battery supply and junction box BJ-88A.
INTER COMMUNICATION SYSTEM -CH IC :
General Information:
This is indigenous ICS and is installed in Cheetah helicopter only. Methods of
operation and front panel controls are similar to TF-AP-AF system, however electrical
and mechanical design is different .
The system comprises of three identical station boxes(CHIC-1) and one junction box
(CHIC-2) which also houses the power supply filter circuit , one jack box(CHIC -3)
for pilot/copilot and other jack box (CHIC-4) for passenger.
The control box unit comprises of:-
 Amplifier with anti crosstalk networks
 Channel selection rotary switch
 Panel lamp
 Relay lamp
 Volume control parameter
VHF/UHF COMMUNICATION SYSTEMS:

26. xxvi
General Information:
VUC 201A is an airborne V/UHF transceiver. It belongs to new generation state of art
with complete solid state technology. It employs modular construction for ease in
maintenance. It provides RF reception and transmission of amplitude modulated signals.
Its main function is to provide simplex two way communication of AM, radio telephony.
Using this communication is carried out between aircraft to aircraft and aircraft to
tower.
Technical Specifications :
 Frequency range: 100 MHz-399.975 MHz
 VHF range : 100 MHz-155.975 MHz(2240 channels)
 UHF range : 225 MHz-399.975 MHz(7000 channels)
 Channel capacity: 25KHz
 Number of preset channels : 19+1 manual, this is also a preset channel.
 Power Supply: 27.5 V DC(nominal)
Power output:
*VHF-10 W
*UHF-20 W
 Power Consumption:
*Receiving Mode-100 W
*Transmitting mode-550 W
 Range: Air to Air and Air to Ground communication over radio horizontal ranges of 350 Kms.
 Frequency Stability: ± 5ppm(maximum)
 Main receiver sensitivity: 2 μV
 Duty cycle: 1 minute transmit, 5 minutes receive for 12 hrs.
 Main receiver selectivity:
*Not less than 20 KHz at 60 dB
*Not more than 70 KHz at 60 dB
 Antenna used: VHF and UHF combined.
 Antenna impedance: 50 Ω
Additional Functionality:

27. xxvii
 Continuous monitoring of UHF AM in guard band fixed tuned guard receiver is used in the
guard channel between 238. MHz-248 MHz.
 Reception of V/UHF ADF signal.
 Automatic relaying in V/UHF band.
 Remote display of ratio set operating frequency and preset channel number.
 Preselection of any 20 channel in any combination among the 9240 available channels along
with in-flight programming.
 BITE facility
1. Synthesizer lock-on.
2. Receiver and Transmitter serviceability.
Functional Description:
 TRANSMIT FUNCTION IN VHF:
Injection signal from the synthesizer mixed with 50MHz from the VCO of PLL in VHF tuned amplifier
(VTA) transmit mixer. The microphone output is fed to the Voice Operated Gain Adjustable
Device(VOGAD),whichensuresthe constant output level. The output is superimposed on modulating
DC voltage inthe keyingandAutomaticLevel Control(ALC)module.ThismodulatedDCisboostedbythe
driver amplifier whose output is fed to power amplifier. The output of VTA is fed to the antenna
throughthe directional couplerreceive transmitrelayandLPF.The directional couplercouplesaportion
of RF power output to the ALC circuit. The detector RF from the directional coupler is also fed to the
audio and squelch card as side-tone for further amplification.
 TRANSMIT FUNCTION IN UHF:
The injection signal from the synthesizer is mixed with 50MHz from VCO of PLL in UHF Tuned
amplifier (UTA) transmit mixer. The microphone output is fed to the Voice Operated Gain
Adjustable Device (VOGAD), which ensures the constant output level. The output is
superimposed on modulating DC Voltage in the keying and Automatic Level Control
(ALC)module.Thismodulated DC is boosted by the driver amplifier whose output is fed to the
poweramplifier.The outputof UTA isfed to the antennathroughthe directional couplerreceive
transmitrelayandLPF. The directional couplercouplesa portion of RF power output to the ALC
circuit.The detectorRF fromthe directional couplerisalso fed to the audio and squelch card as
side tone for further amplification.
 RECEIVE FUNCTION IN VHF:
In the receive mode, RF signal received through VHF low pass filter(LPF) and VHF receiver
transmittercoaxial relayisfedtoVHFfront-endamplifier.The DACprovidesthe control voltage

28. xxviii
for tuningthe front-endvaractorsandfilters.The synthesizer(LO) provides the injection signal.
Intermediate frequency signal is fed through a crystal filter and an amplifier.
After demodulation it is applied to audio amplifier in audio and squelch mode.
Automatic gain control(AGC) voltages are also available.
In audio and squelch module the audio signal is boosted to the required level to drive the
headset.Additionalinputslike side-tone intercom, auxiliary audio and guard receiver audio are
also amplified and fed to the headset. The coming signal is taken from this stage for further
processing.
 RECEIVE FUNCTION IN UHF:
RF signal received by wide band UHF antenna is routed through the UHF, LPF and UHF receive
transmitrelaycontact to a 'T' junction.The DACamplifierprovidescontrol voltage fortuningthe
front-endvaractorsandfilters.Synthesizerprovidesthe injection signal. The received RF signal
is mixed with synthesizer frequency to generate an intermediate frequency(IF) signal. After
several processesthissignal is converted to a second IF signal which is amplified and detected
by an IC detector.The demodulatedsignalisappliedtothe audioamplifierinaudio and squelch
mode. Automatic gain control(AGC) voltages are also available.
In an audio and squelch module, the audio signal is boosted to the required level to drive the
headset.Additionalinputslike side-tone intercom, auxiliary audio and guard receiver audio are
also amplified and fed to the headset. The homing signal is taken from this stage for further
processing.
COMUNICATION ( COM 105A) SYSTEMS:
GENERAL INFORMATION :
The COM 105A isa remotelymountedairborne VHF communication set and was developed by
HAL- Hyderabad mainly for use by coast-guard and navy. This transceiver provides amplitude
wireless communication in the frequency range 118MHz to 135.975 MHz with channel spacing
of 25 KHz. This transceiver is provided with 4 present channels of the 720 available channels.
Any one channel out of 4 present channels can be selected by an external control box. It can
alsobe usedassignal channel setforstand-byapplications,withoutthe control box, by suitable
aircraft wiring. The main function of the equipment is to provide simplex two-way
communicationof AMradio telephony.Additionallythe equipmentshallprovidethe capabilities
for inter- communicationamongcrew members.Some of the specialfeaturesof the equipment
are:-
. Full solid state with integrated circuits adopting latest technology for good operational
Performance & reliability.

29. xxix
. Small size, light less power consumption.
. Modular construction makes the maintenance and service very easy. Modules are easily
Interchangeable.
. Intercom, squelch and muting control facilitates are provided.
TECHNICAL SPECIFICTION:
¥ Frequency range: 118MHz to 135.975MHz
¥ Stabilization time: 10 minutes for climatic condition and 1 minutes at ambient.
¥ Humidity: Room (ambient) up to 90% maximum relative humidity.
¥ Frequency Stability: ±25ppm (max)
¥ Numberof channels: 720 channels out of which 10 channels will be allowed to be degraded
in receiver sensitivity.
¥ No. of present channel: 4 out of 720 channels.
¥ Supply voltage: 27.5V DC(nominal), permissible variation of 22V to 31V DC.
¥ Temperature: -40°C to 80°C (storage).
¥ Dimensions: The equipment is fabricated in the shape of a rectangular box having the
following overall dimensions:
- Width-- 135mm
- Height-- 140mm
- Length/depth-- 265mm
- Weight: 4.3 Kg
- Input power: 200mV (max) in the frequency range of 118 to 135.975MHz.
- Receiver to transmitter time interval : 100ms (max).
- Channel selection time: Is maximum.
- Range:Airto groundtwo waycommunicationscanbe had for a distance of 220Km overradio
horizon ranges.
CONSTRUCTIONAL DETAILS:
Modular constructional style had been adopted in COM 105A. The equipment consists of 11modules
comprisingthe entire assembliesandsub-assemblieswhichare mountedon a chassis frame connecting
the front panel andback panel. Eachpanel ismade of a single piece casting that forms a fixed heat sink
for the widebandpoweramplifierandthe powersupplyunit.The entire equipment is closed by a plate
at the bottom and a cover at the top.
ELECTRICAL DESCRIPTION:

30. xxx
Electrical connections to the transceiver are made through the connector located on the front panel.
The
COM 105A is a completely solid state VHF communication transceiver. Internal R.F. signals are
generatedbya VHFfrequencysynthesizer.Duringtransmitthe R.F.output of the synthesizer amplified
by several stages of wideband amplifier where last stage is collector modulated.
The equipmentcoveredbythisspecificationshallprovideradiofrequencyreceptionandtransmissionof
amplitude modulated signals of any of 720 channels in the 118 to 135.975 MHz of VHF band in the 25
KHz increment.
FUNCTIONAL DESCRIPTION:
The transceiver basically consists of three functional sections: transmitter, receiver and frequency
synthesizer.
The synthesizerinterprets the paralleldatainputfromthe channel presentwhen the particular channel
is selected by external control and provides an internal RF signals required by the receiver and
transmitter sections.
In the receive mode the RF signal from the antenna is applied through the low pass filter and coaxial
relay to the RF Front end.
In the transmitter mode the synthesizer removes the receiver injection and provides transmitter
excitation at the present frequency.
¥ RECEIVE MODE:
RF signal fromthe antennapassesthroughthe low passfilterwhose cut-off frequency is sufficiently
high enough to pass the band of frequencies lying in the range 118 MHz to 136 MHz. Signal after
detection is divided into two paths.
¥ TRANSMIT MODE:
Transmitter is energized by grounding the PTT control line.
COCKPIT VOICE RECORDER:
GENERAL INFORMATION:
The cockpit voice recorder(CVR) isdesignedasahighqualityaudio-frequencyrecorderwithalow inter-
modulationdistortionandhighsignal tonoise ratio.Itrecordswhateverishard in headset of i) pilot ii)

31. xxxi
Co-pilotiii)passengeriv) cockpitareaconversation.Highqualitycomponentsandsolidstate devices are
used throughout to ensure maximum reliability and trouble free operation.
TECHNICAL SPECIFICATION:
- Recording medium: 6.35mm wide magnetic tape.
- Tape speed: 47.5 mm per second
- Recording duration: last 30 minutes.
- Tape length:one spool,endlessloopof 95m length.
- Temperature: tape assembly can withstand
temperature of 1100°C for 30 minutes.
- Bulk erase time: it takes 0.8 to 1 second to active
bulk erase coil and within 5 to 12 second erases the
whole tape on pressing 'Erase' switch in control unit.
SUB-ASSEMBLIES:
The CVR is comprised of two major units:
- Main Recorder Unit (MRU-101)
- Remote Control Unit (CU-101).
SYSTEM DESCRIPTION:
The recorderis an endlessmagnetictape functionrecorderwhichautomaticallyerasesrecordedvoice
signal afterhalf an hour of continuous operation. Earlier, CVRs were magnetic tape. Modern day CVRs
are of solid state type and can record pilot communication up to 90 minutes. The black box is of
international orange colour and usually made of Titanium because of its high melting point of 4500°C.
The control unitcontains the areamicrophone ,preamplifier,bulk erase switch, indicating meter, head
phone jackand a test switchformonitoringrecordedsignals. They are remotely located from the Main
Recorder Unit. Engine, turbine and other mechanical noises are suppressed electronically.
Automatic Direction Finder (ADF) :
General Information :

32. xxxii
ADF (Automatic Direction Finder) is the radio signals in the low to medium frequency band of
190 Khz. to 1750 Khz. It was widely used today. It has the major advantage over VOR navigation
in the reception is not limited to line of sight distance. The ADF signals follow the curvature of
the earth. The maximum of distance is depend on the power of the beacon. The ADF can
receives on both AM radio station and NDB (Non-Directional Beacon). Commercial AM radio
stations broadcast on 540 to 1620 Khz. Non-Directional Beacon operate in the frequency band
of 190 to 535 Khz.
Airborne installation consists of the following line replaceable unit (LRU) /rotable:-
 ADF RECIEVER
 CONTROL UNIT
 LOOPANTENNA
 SENSE ANTENN
 QUADRANTAL ERROR CORRECTOR(QEC)
 SUSCEPTIFORMER
 SENSE ANTENNA CABLE EQUALISER
 RADIO MAGNETICINDICATOR(RMI)
 INTERFACEUNIT FOR INSTALLATIONS HAVING TWO CONTROL UNIT OPERATIONS
TECHNICAL SPECIFICATIONS:-
 FREQUENCY RANGE :190 KHZ -1700 KHZ
 CHANNEL SPACING:0.5 KHZ
 PRESET CHANNEL: 10
 POWER SUPPLY :27.5 DC(NOMINAL)
 POWER CONSUMPTION: NOT MORE THAN 60 WATT
 MODE OF OPERATION :ANT & ADF
 AGC RANGE : ANT MODE(25 MICROVOLT /METER -100 MICROVOLT/METER)
ADF MODE (50 MICROVOLT /METER -100 MICROVOLT /METER)
 SELECTIVITY: NOT LESS THAN 19 KHZ FOR 6 DB BANDWIDTH
NOT LESS THAN 10 KHZ FOR 60 DB BANDWIDTH
Operation :

33. xxxiii
ADF operate in the low and medium frequency
bands. By tuning to NDB station or commercial AM
radio stations. NDB frequency and
identification information may be obtained
from aeronautical charts and Airport Facility
Directory. The ADF has automatic direction
seeking qualities which result in the bearing
indicator always pointing to the station to
which it is tuned. The easiest and perhaps the
most common method of using ADF , is to " home " to the station . Since the ADF pointer
always points to the station , the pilot can simply head the airplane so that the pointer is on the
0 (zero) degree or nose position when using a fixed card ADF . The station will be directly ahead
of the airplane. Since there is almost always some wind at altitude and you will be allowing for
drif, meaning that your heading will be different from your track. Off track , if the aircraft is left
of track, the head of the needle will point right of the nose. If the aircraft is right of track , the
head of the needle will point left of the nose.
UNITS OF ARC610A :
 ADF RECERIVER- It is a completelysolid state signal conversion super heterodyne receiver
with ICS adopting latest technology .frequency generation is by the frequency synthesizer
with high stability. It covers a frequency range from 190 kHz to 1700 kHz with increment of
0.5 kHz
 CONTROL UNIT-Thisunit is situated inthe cockpit forthe operation bypilotand providesthe
following controls and facilities
1. ON/OFF CONTROL
2. VOLUME INTENSITY CONTROL
3. MODE SELECTION SWITCH
4. CHANNEL SELECTION SWITCH
5. FREQUENCY SELECTION SWITCH
6. PROGRAM STORE SWITCH
7. TEST SWITCH

34. xxxiv
 LOOP ANTENNA :-Electromagnetic field is sampled by a device known as the fixed loop
aerial. It consists of two small coils of wire wound on ferrite cores of high magnetic
permeability
 SENSE ANTENNA: this is a capacitive antenna intended to couple only the electric field
component at the vertically polarized electromagnetic field.
 QEC( loop equalizer):It provides a quadrantal error connection and required
compensation for various lengths of loop antenna feeder cable
 SUSCEPTIONER- This is an auto transformer which increases the apparent capacitance of
the sense antenna and lead in to 1750 pF
 SACE:-It provides the lump capacitance and inductance to compensate for the reduction
of capacitance and inductance in sense antenna cables
 RMI :- It provides indication of aircraft heading and relative bearing of a transmitting
radio station with respect to magnetic north
 INTERFACE UNIT: It facilitates control of the ADF receiver ARC 610A through two control
units designated ‘MASTER’ and ‘SLAVE

35. xxxv
Electrical System of CHEETAH and CHETAK Helicopters :
The electrical systems, in these helicopters, reflect the increased use of sophisticated avionics
and other electrical accessories. More and more operations in today’s flight environment
are dependent on the aircraft’s electrical system; however, all helicopters can be safely flown
without any electrical power in the event of an electrical malfunction or emergency.
These turbine powered helicopters use a starter/generator system. The starter/generator is
permanently coupled to the accessory gearbox. When starting the engine, electrical power from
the battery is supplied to the starter/generator, which turns the engine over. Once the engine is
running, the starter/generator is driven by the engine and is then used as a generator.
Current from the alternator or generator is delivered through a voltage regulator to a bus bar. The
voltage regulator maintains the constant voltage required by the electrical system by regulating
the output of the alternator or generator. An overvoltage control may be incorporated to prevent
excessive voltage, which may damage the electrical components. The bus bar serves to distribute
the current to the various electrical components of the helicopter.
A battery is used mainly for starting the engine. In addition, it permits limited operation of
electrical components, such as radios and lights, without the engine running. The battery is also a
valuable source of standby or emergency electrical power in the event of alternator or generator
failure.
An ammeter or load meter is used to monitor the electrical current within the system. The
ammeter reflects current flowing to and from the battery. A charging ammeter indicates that the
battery is being charged. This is normal after an engine start since the battery power used in
starting is being replaced. After the battery is charged, the ammeter should stabilize near zero
since the alternator or generator is supplying the electrical needs of the system.
A discharging ammeter means the electrical load is exceeding the output of the alternator or
generator, and the battery is helping to supply electrical power. This may mean the alternator or
generator is malfunctioning, or the electrical load is excessive. A load meter displays the load
placed on the alternator or generator by the electrical equipment. The RFM for a particular
helicopter shows the normal load to expect. Loss of the alternator or generator causes the
load meter to indicate zero.
Electrical switches are used to select electrical components. Power may be supplied directly to
the component or to a relay, which in turn provides power to the component. Relays are used
when high current and/or heavy electrical cables are required for a particular component, which
may exceed the capacity of the switch.
Circuit breakers or fuses are used to protect various electrical components from overload. A
circuit breaker pops out when its respective component is overloaded. The circuit breaker may be
reset by pushing it back in, unless a short or the overload still exists. In this case, the circuit
breaker continues to pop, indicating an electrical malfunction. A fuse simply burns out when it is

36. xxxvi
overloaded and needs to be replaced. Manufacturers usually provide a holder for spare fuses in
the event one has to be replaced in flight. Caution lights on the instrument panel may be installed
to show the malfunction of an electrical component.
DC Power Supply System :
1. DC power sources : Both Chetak and Cheetah helicopters have a 24 volts dc supply system.
Variouselectrical equipmentare providedpowersupply from the bus bar. Aircraft generator as
well as the internal battery is connected to the bus bar through reverse current relay and
batteryrelayrespectively.All the electrical equipmentlocatedremotely,are operatedfromthe
cockpit . The different power sources are:
a) Nickel cadmium alkaline battery :
i) Purpose and description : A 24 volts 40AH alkaline battery type 4000A or
4000 A1 forms the source of dc power supply for starting the a/c as well as a
stand by source . There are 20 cells (each 1.2 volt) connected in series . The
total weight of the battery is 35.5 kg.
ii) Like all other batteries, nickel cadmium batteries are also rated by nominal
discharge voltage and nominal capacity.
 Nominal discharge voltage - 24 volts.
 Nominal capacity - 40 AH
 Nickel cadmium cells have a nominal voltage of 1.2 volts.
Therefore the nominal batteryvoltage is1.2timesthe number of cells (
1.2×20 =24 volts).
b) Starter generator –type Labinal 2678A1/2687A2:
i) Purpose : This functions as a starter to crank the engine while starting ,up to
an engine speed of app. 14,000 rpm. After this it works as a generator ,taking
drive from the engine gear box.
c) External starting trolley : External starting trolley batteries are lead acid type with four 6
volt batteries connected in series . Capacity of each battery is 180 or 230AH.
i) Ground powerreceptacle : Ground powersupplysocketislocatedatthe bottompart side
of center section in Chetak helicopter .In cheetah helicopter , it is located on 1P junction
box.

37. xxxvii
Purpose : For connecting external power supply to the a/c.
2. DC power components:
a) 1P junction box:
i) Location : It is located behind fuel tank at the port top side of center structure .
ii) Purpose : it houses various dc power components of the a/c .
b) Battery relays (2P and 4P) – type SPST-2520:
i) Location : two similar relays are mounted inside 1P junction box.
ii) Purpose : one of the relays (named 2P relay) connects internal battery supply to
busbar,throughbattery master switch .whereas the other relay (named 4P relay )
,connects external trolley supply to the busbar, through “ground /flight switch “
mounted on the external trolley .
c) Voltage regulation (14P) :
i) Location : location regulation is located inside 1P junction box.
ii) Purpose : a carbon pile voltage regulation is fitted in Chetak and an electronic
voltage regulation(GCPU) isfitted in Cheetah helicopters .Its purpose is to keep
the generator voltage constant under varying electrical load conditions .
d) Reverse current relay (10P)- type EC 2200:
i) Location : reverse current relay is located below voltage regulation in 1P
junction box.
ii) Purpose : Asthe generatorvoltage rises above the battery voltage by 0.5 ± 0.15
volts,RCrelayconnects the generator supply to the busbar and generator stars
charging the battery and feeding various electrical
loads.Another purpose of RC relay is to disconnect the generator supply from
the busbar whenever a reverse current of 9 to 22 amps flows from battery to
generator .
e) Generator switch type ECE 60:
i) Location : It is also located on the middle control panel by the side of
generatorswitch andon overheadpanel incase of cheetah /modified chetak.

38. xxxviii
ii) Purpose : The switch is for remote control of the 2P relay (internal battery
relay ) to connect the internal battery to busbar.
3. Indicating devices:
a) Voltmeter:A voltmetertype 511-1 witha range of 0 to 35 volts is located in middle control
panel . It indicates the voltage of power source connected to the busbar.
b) GPFWL: Generator power failure warning light indicates disconnection of generator from
busbar.
4. Protective device : Circuit breakers of 5 amp and 10 amp rating are in the system as protective
devices.However there are three fuses of 10 amp rating in 1P junction box .They are coded as
3P,11P,15P and 6P.

39. xxxix
3P FUSE: It is in battery master switch circuit . If blown ‘OFF’ , battery supply will not be
connected to busbar.
11P FUSE: It isin generatorcircuit . If it is blown off, generator supply will not be connected to
bus bar and generator failure warning light will come ‘ON’.
15P FUSE: It isin the voltmeterandgenerator power supply failure warning light circuit . If it is
blown off, the voltmeter will not indicate any voltage ang generator warning light will remain
‘OFF’.
POWER FUSES : Power fuses are numbered as 21P and 22P.
5. Safety relay (23P):
a) Location : safety relay is located inside 1P junction box,just below 10 amp fuses .
b) Purpose : The purpose of this relay is to automatically disconnect internal battery ,
wheneverexternalpowersupplyisswitchedon.It alsopreventsthe generator supply from
being connected to busbar in case of external power supply is on. Even though the
generator voltage may be higher than busbar voltage .It consists of following circuits:
i) Battery relay circuit (2P relay )
ii) External battery circuit (4P relay )
iii) Generator circuit (RC relay )
6. Additional components fitted on cheetah helicopter :
Following additional components are fitted on cheetah helicopter :
a) 31P fuse:
i) Location : This fuse is located behind the control pedestal .
ii) Purpose : itis an 16 amp rating.If it isblownoff ,the voltmeter wll not indicate any
voltage and generator warning light will remain off.
b) 12P (4 amp) and 13P (10 amp) fuses :
i) Location : These fuses are located inside the 1P junction box.
ii) Purpose : If blown off, the voltage regulator will not function .
c) Diodes (26P, 27P,28P, and 29P):
i) Location : These four diodes are located inside the 1P junction box.
ii) Purpose : 26P diode is connected in series with safety relay coil and its prevents
safetyrelayenergisation, in case of reverse polarity . 27P, 28P, and 29P diodes are
connectedinparallel withsafetyrelaycoil,internal battery relay coil, and external
batteryrelaycoil respectively.Since electronicvoltage regulator is used in cheetah
h/c, these diodes ground any trapped voltage in the system and also prevent
respective circuit from reverse polarity .
d) 30P relay :
i) Location : These relayismountedbehindcontrol pedestal .When internal battery is
switchedON,these relaygetsenergizedandthroughitsenergizedcontactsthe supply
is fed to starter circuit breaker ,voltmeter and generator failure warning light

40. xl
.Howeverwhenthe external startingtrolleyis on,this relay remains in de energized
condition but still through its normally closed contacts ,supply is fed to voltmeter,
starter circuit breaker and generator warning light
Details of Some Important DC Power Components :
1. Starter generator labinal type 2687 A1 or 2687 A2:
This machine works as starting condition and then works as generator, taking drive
fromthe engine.Generatorismountedonforwardrow of the engine accessory gear box and it
is driven by the upper trainof gears at a speed of N:5,108, where N is engine speed. A
detachable drive connects the starter drive with the engine drive. At the commutator end, a
nozzle isprovidedforadmitting cool airintothe generator. A shield having a hinged bracket is
mating over the body of the generator to remain fully in enclosed position.
a) Leading particulars:
Output - 4kw at 30 volts
Brush used - KCEG 11 or PEG 11
Cutting in speed - 3700 rpm (generator ) at 21000-22000 engine rpm
New brush length - 27 mm
Minimum brush length - 12-15 mm
Minimum insulation resistance - 500000 ohms or 0.5 meg ohms
(with 45 volts dc insulation tester)
At rated engine speed ( 3350 ± 200 rpm) generator speed is 6500 rpm
approximately. As a starter it consumes 700 to 750 amps current for a second or two and
then current gradually falls to 250 to 300 amps, towards the end of starting cycle. At 20
voltssupplyand400 amps currentflowing, the starter develops 22 ft lbs. Torque and sets
up a rpm of 1400.
2. Voltage regulator (14P) type 85141 (fitted on chetak) :
A carbon pile type voltage regulatorismounted on a base, fixed inside 1P junction
box.It isdesignedtoproperlyregulatethe voltage of the generator. The rated capacity ranges
from 1200 watts to 12000 watts at the rated speed from 2500 to 7500 rpm.
a) Leading particulars:
Rated regulated voltage - 28 ± 0.5 volts .
Regulating capacity with trimmer - 27-31 volts .
Static resistance of the carbon piles - 0.2 ohms (max)

41. xli
b) Servicing: checkthe regulatorcontact pinsforpitting, cleanif necessary.Adjust
the voltage if required, as follows:
i) Allow the regulator to warm up ( app 30 minutes ground run)
ii) Checkthe voltage with a precision voltmeter between B+ve terminal of
RC relay and the negative terminal of the battery. Carry out several
checks at different rpm and take the average as result. If necessary,
adjust the voltage to 27.5 volts in summer and 28.5 volts in winter with
trimmer.
3. Voltage regulator (14P) – type D 091 (fitted on cheetah ):
The voltage regulator is rectangular case secured in side the 1P junction box, by
screws. It is a transistorised regulator and therefore no servicing is recommended. Two fuses
12P (4 amp) and 13P (10 amp) have been additionally installed. Which are also located inside
the 1P junction box.
4. Voltage regulator (14P) – type GCPU (fitted on Cheetah /Chetak):
GCPU is the abbreviated form of Generator Control and Protection Unit. It’s a kind of solid
state electronic unit placed inside the 1P box. This unit not only offers control but also offers
protection to the generator. By this unit 28V regulated DC Supply is supplied to the electrical
systemof the helicopter. This unit controls the generator voltage by controlling the magnetic
flux of the generator.
5. Reverse current relay (10P) – type ECE 2200:
This cut-out operates on the principle of difference of potential between the
generatorandbattery.Asthe generatorvoltage rises above that of the battery voltage by 0.35
volt to 0.65 volt, the differential coil acts to close a pair of contacts (INT-GMG) and the
generatorsupplycomingthroughthese contactsis connected to the main contractor coil of RC
relay. The main contractor coil closes the main contacts. The generator supply is directly
connectedtothe busbar througha series windingof the differential relay.The main contractor
while operatingbreakstwopairof auxiliarycontacts,whichwere normallyclosed.Onbreaking,
one pair of contacts disconnectsthe negativesupplyline tothe generatorwarninglightand the
otherpair of contacts introducesaresistive coilwiththe maincoil toreduce the current drain in
the coil. As the generator speed is reduced , battery potential becomes greater a reverse
current through the coil. With reverse current of app 9 to 22 amp flowing from battery to
generator,the relay action breaks INT-GMC contacts. Thus the main contactor is de-energised
and generator gets disconnected from bus bar.
a) Leading particulars:
Differential relay pick up voltage - 0.35-0.65 volts
Reverse current drop out - 9-22 amps
Relay current range - 220 amps continuous
Relay overload capacity - 440 amps for 10 minutes
Temperature range - 40 °𝑐 to 70 °𝑐

42. xlii
Altitude operation satisfactory - sea level to 20000 ft
Differential coil resistance - 25-29 ohms
( between BAT+ve and GEN+ve )
Main contactor pick up voltage - 18 volts
Insulation resistance - 75 Meg ohms (Min)
Mili volt drop across main contacts - 100 mV
(with 220 amps flowing )
6. External and internal battery contractors (2P & 4P)- type SPST 2520:
These relay are located inside the 1P junction box for connecting internal and
external power to the busbar. These relay are arranged to work in conjuction with a safety
relay. The insulation resistance is minimum 75 meg ohms. Main contacts current rating is 200
amps. Maximum mili volt drop allowed with 200 amps current flowing is 110 mili volts.
7. Safety relay (23P):
It islocatedinside the 1Pjunctionbox andhas three pairsof contacts which control
the following circuits:
a) Internal battery relay circuit.
b) External battery relay circuit.
c) Reverse current relay circuit.
A study of power circuit will indicate that this relay ensures either internal battery
supply or external power supply will only be connected to the busbar. It also
prevents the generator supply from being connected to the bus bar, in case
external power is switched ON, even though the generator voltage may be
higher than the busbar voltage.
8. Fuses :
There are three 10 amp fuses and four 50 amp fuse ( 2 dummy ) or one 100 amp
fuse, which provide safety for thr power circuit.
a) 3P - battery master switch circuit .
b) 11P - generator switch circuit.
c) 15P - voltmeter,generator and engine fuel oil level warning light circuit .
d) 6P - dummy or spare.
These fuses are of 10 amp each. The 50 amp fuses are coded as 18P, 19P, 21P
and 22P on chetak helicopter and 21P and 22P are coded as 16P and 17P respectively on
cheetah helicopter.
9. DC voltmeter – type 511-1:
A movingcoil type dcvoltmeterismountedonthe control pedestal.Itsrange is 0 to
35 volts.Thisvoltmeteris calibratedbymakingthe permanent magnet stronger or weaker and
not by connecting the resistance in series with the coil as in the case of other voltmeters.

43. xliii
10. Generator power failure warning light (GPFWL):
A power failure warning lamp is mounted on the warning light panel. It provides
indication for the failure of generator supply. The particular light is provided with a screen to
viewdimmingeffect.One pairof auxiliary contacts in the RC relay controls the negative of the
light.The serviceabilityof lamp can be checked during engine running by pressing the holder.
11. Suppressors:
There are three suppressors in
chetak and cheetah. One suppressor type
8501 is fitted inside the shield of the
generator.Anothersuppressortype 7502 is
fitted behind the 1P junction box. Third
suppressortype 8301 is mounted near fuel
booster pump.
Purpose : These are meant to reduce radio
interference.
12. Internal and external power receptacles :
a) A two-pinpowerreceptacle ismountedonthe centerstructure nearthe battery on chetak
and at the front , behind the control pedestal on cheetah. These provide the pick up of
internal battery.
b) A three pinexternal powerreceptacleismountedonthe portbottomside of centersection
in chetak and on 1P junction box in cheetah. This provides of the external power.

44. xliv
DC Power Circuit ( CHETAK ) :
INTRODUCTION :
Chetak and cheetah helicopters are provided with 24 volt dc power supply. The system
supplies electrical power to various electrical equipment mounted on the aircraft. The
devices mounted on the front instrument control pedestal remotely control them. This
systemisknownas “ powersystem “. Three differentsourcesof powerare available to the
aircraft busbar. They are:
a) From internal battery.
b) From external starter trolley.
c) From aircraft generator.
1. Power from internal battery :
When aircraft battery switch is selected to ON position, supply from the battery
positive istakenthrough3Pfuse (10 amps),centerpairof safetyrelay contact, battery switch
( selecttoON) and connectedtooperatingcoil of internal battery relay (2P). Internal battery
relaygetsenergizedandattractsthe plunger, which makes a pair of heavy-duty contacts and
opens other pair of auxiliary contacts. When the auxiliary contacts are opened the supply
flowsthroughthe parallel pathof holdingcoil,which assists to hold the plunger in energized
position and also limits the current drains through the relay. Simultaneously the battery
positive is connected to reverse current relay ‘s “battery terminal “, which is connected to
busbar. Hence the supply is now made available at the busbar. This is indicated by the
voltmeter which registers the exact voltage of the battery and also by the power failure
warning light (comes ON) which indicates the battery is connected to the busbar and the
generatorisnot runningorif generatorisrunningitis not buildingup the required voltage to
operate reverse current relay.

45. xlv
2. Power from external starter trolley :
When 24 volts external starter trolley is connected to the external receptacle and ground
flight switch selected to flight operation, supply from small positive pin flows through the
safetyrelaycoil (23P).These safetyrelaygetsenergizedclosingapair of contacts, which were
normallyopened.The closedpairof contactsprovide supplytoexternal batteryrelaycoil (4P),
whichcloses a pair of heavy-duty contacts through which supply from the external trolley is
connectedtobusbar.Voltmeterregistersexternaltrolleyvoltageandgeneratorpowerfailure
warning light comes ON. Simultaneously the center and bottom pairs of contacts of safety
relaygetsopened(the contactsare normallyclosed). Thus the battery supply to the internal
battery relay coil (2P) and continuity in the main contactor of RC relay are disconnected. 2P
relaygetsde-energisedand disconnects the internal battery from the busbar. If generator is
running the generator supply will not be connected to external starter trolley due to the
bottom pair of contacts of safety relay, which are now opened.
3. Power from aircraft generator :
When aircraft generator builds up 0.35V to 0.65V more than the battery voltage, a
differential circuit flows from generator to battery through the differential coil of RC relay,
which energises and makes a pair of differential contact (opend normally ). The generator
supply is now connected to main operating coil of RC relay through 11P fuse (10 amps), one
pair of safety relay contacts, generator s/w (selected to ON at 19000 rpm) and differential
contacts. The main operating coil gets energized and closes a pair of heavy duty contacts
throughwhichgeneratorsupplyisconnectedtobusbar(whichisregisteredbythe voltmeter)
and openstwopairsof auxiliarycontacts.A secondcoil knownas holdingcoil (resistive coil)is
inserted in series with the main coil through opening of one pair of auxiliary contacts to
minimize the current drain. Power failure warning light goes OFF due to the opening of
second pair of auxiliary contacts, which disconnects the return path of GPFW light.

46. xlvi
4. Power systemfaults (chetak): probable causes of few power system faults are enumerated
below:
a) Probable causes if internal battery supply is not getting connected to busbar:
i) 3P switch blown OFF.
ii) 2P relay fault.
iii) Battery s/w fault.
iv) Safety relay fault.
v) External battery is connected and switched ON.
b) Probable causes if external battery supply is not getting connected to busbar:
i) 4P relay fault.
ii) Safety relay fault.
iii) Ground /flight switch on external trolley is faulty.
c) Probable causes if generator supply is not getting connected to busbar:
i) 11P fuse blown OFF.
ii) Generator s/w faulty.
iii) Safety relay faulty.
iv) RC relay faulty.
v) External battery is connected and switched ON.

47. xlvii
Chetak and Cheetah Lighting System :
Cheetah and Chetak Helicopter’s lighting system can be classified as follows :
a) Position (navigation) and anti-collision lights.
b) Cabin lights.
c) Panel lights.
d) Landing light.
1. Position and anti-collision lights:
i. Location: Position lights are located at port side (red) and starboard (green) side of
cockpit and at the tip of tail boom (clear).
ii. Specification:
I. Port navigation light: This light is SGE-31.01 type and wattage of lamp is 21
watts.
II. Starboardnavigationlight: ThislightisSGE-31.03 type and wattage of lamp is 21
watts.
III. Tail navigation light: This light is SGE-31.75 type and wattage of lamp is 18
watts.
iii. Anti- light collision: Both chetak and cheetah helicopters are equipped with two anti-
collision light each.
i) Location: Top anti-collision light is fitted at the top of cabin and bottom anti-
collision light is fitted below centre structure.
ii) Description: Each anti-collision light has two 40 watt bulbs, mounted
diametricallyopposite onadiscrotatingay app. 45 rpm. Therefore there will be
app. 90 flashes observed from light. Upper anti-collision light assembly is
interchangeable with bottomlight,but the red glass dome of upper lightt has a
plug to blank hole in glass dome. This prevents entering of water in top light.
Glassdome hole iskeptopenincase of bottom light , to allow escape to any oil
or water entering bottom light. There are two types of connectors for anti-
collision light; lndian type and French type. Therefore before proceeding with
replacement of light, type of connector should be confirmed.
iv. Navigation light circuit operation:
Whenpilotputsanti-collisions/w to ‘POS’position,afterputtinganti-collisionlight
CB ‘IN’,supplywill goto all the three navigation lights and all the lights will come ‘ON’
simultaneously.
If pilot selects s/w to ‘EXT’ position, 70L relay will energise and both the anti-
collision light will come on along with three navigation lights.
Since there isa parallel supplytoboththe anti-collisionlights,if one of these light is
unserviceable, other light will operate normally along with all the navigation lights.

48. xlviii
2. Panel lights: Both chetak and cheetah helicopters are provided with panel lights to
illuminate different panels in a/c.
i) Description: Panel lightbulbs (chetak) are of 1.1 watt each. Panel light brilliancy is
ontrolled by variable rheostats. There are three rheostats on lower control penal,
incase of unmodified chetak and two rheostats on overhead penal, in case of
cheetah and modified chetak.
3. Cabin light:There are two cabin lights, mounted inside of the root of a/c, in case of chetak
and there is only one cabin light in case of cheetah.
i) Description: Wattage of cabin light lamp is 4.8 watt.
4. Landing light: Landing light SYNERVA type PE-250 is used on both chetak and cheetah h/c.
i) Location:
I. Landing light: Landing light is located in the front bottom side panel of cockpit
and at bottom of cabin in case of chetah.
II. LandinglightON/OFFswitch: Incase of chetak,there are twoswitchsforlanding
light’s‘ON/OFF’operation,one eachonpilotandco-pilotcollectivestick.Incase
of cheetah, there is only one s/w on pilot’ collective stick.
III. Landing light extension/retraction: In case of chetak, two extnsion/retraction
switchsknownastriggers/w,are mountedontopof boththe collectivestick.In
case of cheetah, there is only one s/w on pilot’s collective stick.
ii) Description: Wattage of landing lamp is 250 watts.in chetak dual operation is
available for pilot and co-pilot, but pilot has an over-riding facility for
extension/retraction of landing light i.e pilot can over-ride extension/retraction
operationof co-pilot.Incheetah,since there isonlyone s/w,pilothasfull control on
landing light operation. Landing light is inter-changeable from chetak to cheetah.
iii) Landing lightcircuit operation: Whenthe operator presses landing light CB, supply
is availableto both pilot and co-pilot’ON/OFF’ s/w as well as ‘EXT/RET’s/w. The
supply for co-pilot ‘EXT/RET’ s/w is passing through pilot’s ‘EXT/RET’ s/w.
Thus landinglight‘ON/OFF’operationcanbe done independently,bypilotas well as
co-pilot.Butfor‘EXT/RET’ operationof light,pilotcanover-rideco-pilot’s operation
by operating ‘EXT/RET’ s/w on pilot’s collective stick.

49. xlix
Instruments Used in CHEETAH and CHETAK Helicopters :-
In CHEETAH AND CHETAK HELICOPTERS the instruments are very simple in design and
are few in number .According to their characteristics these instruments are classified in
six groups :-
Flight Instruments:-
 ALTIMETER (TYPE -55 JEAGER )
 AIRSPEED INDICATOR
 RATE OF CLIMB INDICATOR

ENGINE INSTRUMENTS:-
 FUEL CONTENTGAUGE
 TACHOMETER INDICATOR
 TACHO GENERATOR
 ENGINE OIL TEMPERATURE AND PRESSURE INDICATOR
 TAIL PIPE TEMPERATURE GAUGE
Navigation Instruments:-
 MAGNETIC COMPASS -VION TYPE 143
 MAGNETIC COMPASS -E2B
 GYRO MAGNETIC COMPASS -CG-512
Gyroscopic Instruments:-
 DIRECTIONAL GYRO -BADIN TYPE 830
 GYRO HORIZON INDICATOR -BADIN TYPE 850
 SUCTION RELEIF VALVE
Oxygen Instruments:-
CHEETAH :-GLF 313
CHETAK :-GLF 333

50. l
General Instruments:-
 OUTSIDE AIR TEMPERATURE GAUGE
 BANKINDICATOR
 CLOCKTYPE II
 DIGITAL CLCK TYPE SE 1010
 COLLECTIVE PITCH INDICATOR
 TRANSMITTER –POTENTIOMETER TYPE
 COLLECTIVE PITCH COMPUTER
 WARNING LIGHTS

51. li
Conclusion:
I AM USING THIS OPPORTUNITY TO EXPRESS MY GRATITUDE TO
EVERYONE FOR WHOM I HAD THE PRIVILEGE TO JOIN THE
INTERNSHIP PROGRAMME CONDUCTED BY HINDUSTAN
AERONAUTICS LIMITED THE ESTEEMED ORGANIZATION OF MY
NATION . I HAVE BEEN DOING MY B.TECH IN AERONAUTICS
THEREFORE THIS 14 DAYED TRAINING PROGRAMME WAS OF
IMMENSE PROMINENCE ATLEAST FOR ME SINCE I GOT THE
OPPORTUNITY TO LEARN AND EXPLORE ALMOST EVERY FIELDS
OF AERONAUTICAL ENGINEERING ASSOCIATED TO
HELICOPTER TECHNOLOGIES THAT INCLUDES STRUCURE,
PROPULSION , INSTRUMENTS,HYDRAULICS,ECS,PNEUMATICS
AND LAST BUT NOT THE LEAST THE TRANSMISSION SYSTEM
INVOLVED IN THE APPOSITE FUNCTIONING OF A HELICOPTER .
LASTLY I AM UNDOUBTEDLY GRATIFIED TO THOSE
INDIVIDUALS WHOSE ASPIRING GUIDANCE AND INVALUABLY
CONSTRUCTIVE CRITICISM HAS PROVIDED ME WITH THE
FACILITIES BEING REQUIRED & THE CONDUCTIVE
CONDITIONS FOR MY AERONATICS PROJECT.

52. lii
References :
Web Links :
a) http://www.hal-india.com/
b) https://en.wikipedia.org/
c) http://www.faa.gov/
d) http://www.copybook.com/military/news/upgraded-hal-cheetal-
helicopters-for-indian-army
e) https://www.flightglobal.com/pdfarchive/view/1975/1975%20-
%201262.html
PDF Docs :
a) Airplane Magazine". 1 (5). London: OrbisPublishing Ltd.
b) Chant, Chris. "A Compendium of Armamentsand Military Hardware."
Routledge, 2014.
c) Chris. "HAL spools up" Flight International, 18 December 1982.
d) Taylor, John W. R.(1982). Jane'sAllThe World'sAircraft1982–83