|Vol. 6 No. 6 December 1998||ISSN: 0971-4413|
The high agility and manoeuvrability requirement of a modern fighter leads to the choice of a fly-by-wire design for the flight control system in which the on-board computer performs the central function. Integrated avionics is the key to its mission effectiveness and reliability. The advent of powerful digital processors, data buses, synthetic displays and artificial intelligence in the cockpit promises to revolutionise the way military aviation will develop in future. Dramatic advances in airborne radar and electronic warfare systems and electro-optic sensors have made them key elements of modern fighter aircraft, even more than the speed and agility features of these machines. The development of unmanned air vehicles makes special demands on technologies related to telemetry, telecommand, secure data link, navigation and mission sensors. Major DRDO accomplishments in this critical field of avionics technology are reviewed.
Avionics System of LCA
Fighter Avionics Upgrades
Software & Integration
Airborne Electronic Warfare
Airborne Surveillance Platform
Systems for Unmanned Vehicles
Electronic Components & Packaging
System of LCA
The avionics system enhances the role of Light Combat Aircraft (LCA) as an effective weapon platform. The glass cockpit and hands on throttle and stick (HOTAS) controls reduce pilot workload. Accurate navigation and weapon aiming information on the head up display helps the pilot achieve his mission effectively. The multifunction displays provide information on engine, hydraulics, electrical, flight control and environmental control system on a need-to-know basis along with basic flight and tactical information. Dual redundant display processors (DP) generate computer-generated imagery on these displays. The pilot interacts with the complex avionics systems through a simple multifunction keyboard, and function and sensor selection panels. A state-of-the-art multi-mode radar (MMR), laser designator pod (LDP), forward looking infra-red (FLIR) and other opto-electronic sensors provide accurate target information
to enhance kill probabilities. A ring laser gyro (RLG)-based inertial navigation system (INS), provides accurate navigation guidance to the pilot. An advanced electronic warfare (EW) suite enhances the aircraft survivability during deep penetration and combat. Secure and jam-resistant communication systems, such as IFF, VHF/UHF and air-to-air/air-to-ground data link are provided as a part of the avionics suite. All these systems are integrated on three 1553B buses by a centralised 32-bit mission computer (MC) with high throughput which performs weapon computations and flight management, and reconfiguration/redundancy management. Reversionary mission functions are provided by a control and coding unit (CCU). Most of these subsystems have been developed indigenously.
Flight & Propulsion Controls
The digital FBW system of the LCA is built around a quadruplex redundant architecture to give it a fail op-fail op-fail safe capability. It employs a powerful digital flight control computer (DFCC) comprising four computing channels, each powered by an independent power supply and all housed in a single line replaceable unit (LRU). The system is designed to meet a probability of loss of control of better than 1x10-7 per flight hour. The DFCC channels are built around 32-bit microprocessors and use a safe subset of Ada language for the implementation of software. The DFCC receives signals from quad rate, acceleration sensors, pilot control stick, rudder pedal, triplex air data system, dual air flow angle sensors, etc. The DFCC channels excite and control the elevon, rudder and leading edge slat hydraulic actuators. The computer interfaces with pilot display elements like multifunction displays through MIL-STD-1553B avionics bus and RS 422 serial link.The digital FBW system of the LCA is built around a quadruplex redundant architecture to give it a fail op-fail op-fail safe capability. It employs a powerful digital flight control computer (DFCC) comprising four computing channels, each powered by an independent power supply and all housed in a single line replaceable unit (LRU). The system is designed to meet a probability of loss of control of better than 1x10-7 per flight hour. The DFCC channels are built around 32-bit microprocessors and use a safe subset of Ada language for the implementation of software. The DFCC receives signals from quad rate, acceleration sensors, pilot control stick, rudder pedal, triplex air data system, dual air flow angle sensors, etc. The DFCC channels excite and control the elevon, rudder and leading edge slat hydraulic actuators. The computer interfaces with pilot display elements like multifunction displays through MIL-STD-1553B avionics bus and RS 422 serial link.
The Kaveri engine is controlled by two digital engine control units (KADECU) in a redundant fashion. The units are mounted on the engine and thus face a demanding environment in terms of temperature (135 0C) and vibration. A variety of analog electronics interface various sensors and actuators on the engine to the high performance Intel i960 CPU. Time critical (30 ms inner loop) software, programmed in Ada, implements complex engine control algorithms to effectively control the propulsion system. Since the full authority engine control is a safety-critical function, an independent mechanism is provided to monitor critical parameters and perform corrective action independent of the main controller (independent limiter).
Multi-mode radar (MMR), the primary mission sensor of the LCA in its air defence role, will be a key determinant of the operational effectiveness of the fighter. This is an X-band, pulse Doppler radar with air-to-air, air-to-ground and air-to-sea modes. Its track-while-scan capability caters to radar functions under multiple target environment. The antenna is a light weight (<5 kg), low profile slotted waveguide array with a multilayer feed network for broad band operation. The salient technical features are: two plane monopulse signals, low side lobe levels and integrated IFF, and GUARD and BITE channels. The heart of MMR is the signal processor, which is built around VLSI-ASICs and i960 processors to meet the functional needs of MMR in different modes of its operation. Its role is to process the radar receiver output, detect and locate targets, create ground map, and provide contour map when selected. Post-detection processor resolves range and Doppler ambiguities and forms plots for subsequent data processor. The special feature of signal processor is its real-time configurability to adapt to requirements depending on selected mode of operation.
Fighter Avionics Upgrades
With the ever-growing cost of acquisition of modern combat aircraft and the long gestation periods associated with their development and induction, it has become imperative to extend the operational life of existing fleet through improved performance and mission effectiveness. The most common route is by upgrading the avionics and weapons system. Major avionics development and integration programmes have been taken up. A key feature of these programmes is the use of common core modules.
Core Avionics Computer
This core avionics computer combines the functions of mission computer, display processor, data logger and interface unit. New concepts in modularity and integration at the box level have been evolved to ensure that this avionics computer will meet varying requirements associated with different aircraft, cost-effectively. Some of the function-oriented modules designed to meet current needs and futuristic demands are:
High level of functional integration of digital avionics has made software the long pole in the tent. Avionics systems are hard real-time systems with basic computational time frames in the range of milliseconds. Software has to run efficiently and robustly. Realising this, major efforts have been launched to establish effective software development practices. Strict discipline is enforced to develop flight critical software. Extensive use of tools right from the requirements phase, such as the requirement-driven development RDD100 tool, has resulted in high productivity with minimal errors.
Not withstanding extensive testing at all phases of software development, the final product has to be evaluated in an integrated manner. Experience has shown that static testing on the ground leads to costly fix-fly-fix situation during the flight test phase. DRDO has therefore established various integration facilities wherein the dynamic behaviour of aircraft and its systems are simulated and the resulting outputs provide stimuli to the system under test, leading to the flight testing in the laboratory concept.
The dynamic avionics integration rig (DAIR) is a ground-based facility for integrated testing of LCA avionics. The aircraft and its sensors (INS, radio altimeter, air data sensors etc.) are simulated in a host computer system. A joystick interface enables the pilot/operator to 'fly' the aircraft. The cockpit environment is created using the actual displays and controls which are interfaced to the display processors and mission computers running the operational flight programme software. Aircraft systems such as fuel, hydraulics, and engine are simulated and interfaced with the host system. These generate dynamic stimuli for the USMS systems. A powerful data acquisition, reduction and analysis system (DARAS) monitors and logs all data exchanges in the avionics system. It provides test engineers with real-time displays of selected parameters. This system also supports post-flight analysis.
For the test and evaluation of the LCA flight control system, two independent test platforms, viz., mini bird and iron bird rigs are used. Both these rigs are built around an engineering test station (ETS) which caters to all interfacing needs for testing of DFCC. It simulates inputs, injects faults and gathers frame-wise outputs so that software verification and validation tests can be done automatically. The ETS has the capability to interface with the actual hardware (actuators, sensors, pilot stick etc.) or to emulate these inputs/outputs. The iron bird rig used for complete validation of IFCS with the aircraft dynamics in the loop has the capability to interface with the actuators and pilot stick etc., thus enabling validation of IFCS at a higher level. The mini bird rig, on the other hand, interfaces with one of each type of hardware actuators, the rest being simulated by software models. The mini bird rig is used for hardware-software integration of DFCC and system integration tests. The LCA IFCS is undergoing validation tests simultaneously in several test platforms including the pilot-in-the-loop real-time simulator (RTS) in which the flight control laws are evaluated for correctness and adequacy.
The survivability of a combat aircraft against sophisticated radar guided weapon systems can be enhanced only by equipping the aircraft with advanced electronic support measure (ESM) and electronic countermeasure (ECM) systems. The integrated EW suite performs the basic functions of threat identification and effective electronic countermeasure action besides providing the pilot with a cue to initiate additional evasive measures. Both ECM and ESM systems developed have already been flight-evaluated and production is in progress. DRDO is actively pursuing the development of advanced component, subsystem, software and integration technologies of importance to futuristic EW systems.
Integration of EW Systems in Fighter Aircraft
This technology includes resolution of EMI/EMC problems, modification kit development, aircraft modification, system integration and flight evaluation. Several types of fighter aircraft platforms have been upgraded with modern EW equipment
EW Test & Evaluation Capabilities
Range-on-Wheels is a unique facility conceived for the evaluation of airborne EW systems during development, user acceptance and system enhancement phases. It comprises six mobile ground stations, viz., reference radar for reference target data, threat radar, data acquisition centre, mission control centre, slaved Tx/Rx pedestal, and electrical generator. Range-on-Wheels is a unique facility conceived for the evaluation of airborne EW systems during development, user acceptance and system enhancement phases. It comprises six mobile ground stations, viz., reference radar for reference target data, threat radar, data acquisition centre, mission control centre, slaved Tx/Rx pedestal, and electrical generator.
Airborne surveillance platform (ASP) is one of the key force multipliers in the modern war scenario. DRDO is developing an advanced surveillance platform based on an HS 748 aircraft to detect targets at extended ranges with all round azimuth coverage. It is designed to handle 50 targets. It features a hybrid navigation system and the secure communication and data links.
ASP Antenna & Rotodome
The antenna used in the rotodome of ASP is a low side lobe slotted wave guide planar array. The antenna features very low side lobe levels and a narrow beam width in azimuth. It handles high power (better than 3.3 KW average) and weighs 160 kg. For housing the primary and the secondary (IFF) antennas, an ellipsoidal structure (7.315 m x 1.524 m) rotodome has been indigenously fabricated. It largely comprises composites and aluminium alloy parts. The indigenous rotodome has since been successfully fabricated and flight tested on the ASP system. The rotodome is driven by a hydraulic servo system using aircraft hydraulic power.
Airborne Data Processor
The airborne radar data processor (ARDP), supporting track-while-scan, is required to form target tracks after receiving data from the various sensors of ASP, such as the primary radar (PR) and the secondary surveillance radar (SSR), which operate in TWS mode. The ARDP correlates the target plots from scan to scan to maintain the target tracks. It also performs the correlation of target information obtained from SSR and endorsement with the PR track information.
Integrated Navigation System
The ASP is guided by a high accuracy navigation system, which consists of an inertial navigation system (INS) and a Doppler navigation system. The velocity drifts of INS are contained by Doppler velocities using a Kalman filter, resulting in good navigation accuracy required for long duration flight of ASP. Work is in hand to integrate GPS receiver with INS to enhance performance, reliability and robustness.
for Unmanned Vehicles
Comprehensive capabilities have been established in all aspects of flight control design and engineering for unmanned air vehicles (UAVs) which include design of control laws, flight control electronics, sensors and actuators. Digital processors, software and analog flight control electronics and electromechanical actuators have been developed. The flight control electronics (FCE) for Lakshya aircraft employs an analog electronic design backed by an ASIC to perform flight control and recovery functions of the aircraft. In addition to altitude stabilisation and other flight control functions, the FCE also provides command and autopilot modes.
A single LRU integrated avionics package (IAP) has been developed to perform flight control, navigation and mission functions of Nishant aircraft. It consists of onboard encoder/decoder, GPS, flight control, mission and navigation modules. The digital flight control function is backed up by an analog stand-by module. IAP also manages automated safe launch, in-flight programmable way point navigation, and operation of payloads. It has been proven in more than 20 test flights of Nishant.
Ground Station for UAVs
Several configurations of ground stations have been developed for UAV programmes to meet diverse needs of aerial targets and reconnaissance missions. Integrated telemetry, telecommand and tracking system designs have been realised. The mobile ground control station (GCS) incorporates a microprocessor-based encoder/decoder unit which interfaces with the jam-resistant data link to exchange command and data from Nishant. The air vehicle controller and the payload operator are provided with cues in the form of synthetic electronic displays which provide flight and trajectory data. A digital map display using GIS technology aids the controller to fly the UAV.
Mission Payloads for UAVs
Several indigenously developed payloads are now available for UAV applications, such as electro-optic imaging, laser ranging and designation system, airborne laser ranger and marker (ALARM), and airborne infra-red target sensor. The gimballed payload assembly (GPA), a two-axes stabilised platform for CCD camera and laser range finder payloads, has been developed to provide azimuth and elevation stabilisation of the sight line against aircraft motion and jitter. An advanced correlation technique-based video tracker has been integrated with this platform for automatic target tracking. The entire system can be installed on manned or unmanned aircraft. The system can also be configured to carry different electro-optic payload combinations.
Two types of scoring systems have been developed as a part of Lakshya aerial target tow body electronics for estimation of the miss distance. The acoustic miss distance indicator (AMDI), which utilises the over pressure produced by the supersonic projectile to estimate the miss distance, provides both distance and sector information. The other system is based on Doppler FM-CW radar principle.
Components & Packaging
The revolution in avionics has been brought out by the developments in the electronics industry which has reached on chip packing densities of 15,000 transistors per square millimetre. Frequencies, normally encountered in RF circuits, are now driving digital circuits in the range of hundreds of MHz. Hence, heat dissipation and EMI/EMC problems have come to the fore. Also, the avionics equipment have to work at very high temperatures, acceleration and vibration environment. For example, KADECU has been designed to be cooled by the aircraft fuel circulating through its chassis to enable it to work at 130o ambient. DRDO has established state-of-the-art tools and facilities in the area of RF circuit design, analog and digital circuit design, and thermal design. Detailed design and analysis are performed using logic circuit simulation and VHDL-based complex circuit design tools. Facilities for hybrid microwave circuit development and fabrication have been established. Some of the special components that need mention here are:
High Power Pulse TWTs
Broad band high power gridded, helix travelling wave tubes (TWTs) have been designed and developed in association with BEL.
High Voltage Power Supplies & Modulators (HVPS/M)
These modulators, suitable for pulse and CW high power TWTs, are capable of generating up to 12 KV.
Broad Band Microwave Integrated Circuits (MIC) & Super Components for Channelised EW Receivers
Specifically, an MIC version of high speed microwave antenna select switch (MASS) as a front-end of digital instantaneous frequency measurement unit (DIFM) realised within 5.5" x 4.5" x 0.35" and operating with a switching speed of 35 ns has been designed and developed. Miniaturisation of complex circuits has been accomplished through hybrid microcircuit design and fabrication. Sync generators for the LCA display processor, filters for the MDI system, and signal conditioners for Nishant are some important examples.