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| THE BACKROOM BOYS TEAM FCS-ADE PART-I |
Part-1
(This is purely a tech piece. The human-interest story is in Part-II of World-Beaters)
ADE stepped into the LCA program with a major share of technical work -- the FCS, Avionics System and Flight Simulator. Being the only laboratory with prior expertise in flight control system of flying UAVs and expertise in building flight simulators, ADE was readily given this major responsibility. Feasibility study was carried out by Joint team of ADE, ADA, HAL and NAL on development, technical trade off and state-of-the-art Fly-By-Wire Flight Control System.
Joint development with American industry partner who had the expertise in designing and developing flight control systems with clear work share plan and SOW was worked out and thus ADE entered into contract with GE Aircraft, USA (BAE Systems, US during 1993). Data capture phase was carried out with the partner. Though BAE Systems, USA offered legacy and proven FCS for LCA program, well planned calculated risks were taken and preference was given to joint custom design & development of the FCS suite comprising of the sensors, actuators, flight control computer hardware, software with associated rigs and test systems for clearance of these integrated systems for LCA flights. ADE had a major role in the design & development of flight control computers Hardware with embedded flight critical software and test systems.
At ADE the team acknowledges the benefits of joint design & development with BAE Systems, USA, in absorbing the process and methodology as well as project and configuration management. The design was jointly done with the team from ADE deputed to USA. The choice of the processor was made by ADE and wanted to lead the design of the CPU board. Accordingly BAE agreed to partition the digital module in to two sides with CPU – A1 and CPU – A2. The A1 side contained the I/O handling functions including the BAE specific digital ASIC. The A2 side responsibility was given to ADE where in the CPU and its interface to all the components on the board viz., the CPU interface to all memories, timers, interrupt controller, parity for SRAM. The A2 side interface also encompasses the vital Transputer (T805).
Preliminary and critical design reviews were held to deliberate on the adequacy of the performance and reliability, environmental compliance, testability, safety and quality control provisions incorporated in the design. The first Brass Board computer was built by BAE at their facility and integration of the hardware/software with indigenously built ETS started during 1995.
There was initial apprehension expressed in manufacturing this class of equipment in India due to special to type infrastructure and process required for the same. ADE worked closely with BEL in jointly establishing all critical technologies and processes, test equipment including the rigs, fixtures and tools required for indigenous manufacturing of DFCC in India. BAE Systems (USA) denied these process related information to India due to technology denial by US.
As per the workshare, Engineering Test Station, a complex real-time test system was designed and developed by ADE. Two of these systems were installed by ADE in M/s GE A/c, for use by ADE & GE engineers. The GEAC management was impressed with the systems given by ADE and invited ADE to bid for developing such systems for their own projects – a first for DRDO. A total of 5 such ETS have been built and are the workhorse for ATP, HSI, V&V, PIL Open loop/ closed loop, fault free tests at HAL Iron Birds. These systems are operational since 1995 and have been used for all DFCCs & software operational in all the LCAs flying so far.
ADE also designed and developed automatic test systems for actuators and sensors which form a vital part in the testing of the FCS system to gain confidence before putting it on the aircraft. In additions there are onboard test panels required for Flight test for tests like flutter test. ADE has developed Flight Control Panel, Flight Test Panel for this.
ADE and BEL jointly completed building 3 Brass Board units, 6 flight worthy units. Concurrently the teams also build the necessary test equipment along with the necessary test software for SRU and LRU level testing of the DFCC. The LRU level ATP is written using the Laboratory Test Monitor (LTM) software exclusively developed by ADE and runs on the indigenously built Engineering Test Station (ETS) built by ADE. Variants of Group I ATP with sufficient coverage were also configured to clear the functionality of the DFCC during the ESS tests. As per the work share plan, all activities of fabrication, assembly, testing, integrating the DFCC, functional evaluation, Environmental Stress Screening tests & Qualification of the DFCC was total responsibility of ADE. All these activities were completed.
The DFCC incorporates state-of-the-art technology for chassis, printed wiring boards, board assembly and front panel inter-connection with the motherboard through flex circuitry. The construction of the chassis is dip-brazed double walled construction with provision for forced air-cooling. Front panel is fitted with filter pin connectors incorporating polarization for different channels. The chassis design, grounding scheme, routing of the interconnections have been carefully designed to meet the stringent EMI/EMC requirements as per MIL-STD-461C. The DFCC is designed to operate up to 1 hour after failure in supply of cooling air. The Printed boards are 10 to 22 layer type with heat sink bonding for thermal management. The average power dissipation is around 300 watts and the unit weighs 27.8 kgs. The unit has been built with highest reliability to meet the PLOC requirements of 1 x 10-7 per hour and MTBF of > 1200 hours. The CPU is Intel 80960 32 bit RISC microprocessor. Each of the four identical channels consists of one digital module, 3 Nos. of analog modules and one power supply module. They are housed in a single box of 1 ATR (long).
While the sensors were off the shelf, actuators were built specifically for the LCA which are of DDV class. Proving the Built in test which is robust and which can cover each of the component failure either on the servo electronics or the actuator was challenging. This forces another challenge of not to declare nuisance failures.
For a safety critical system of this class of aircraft, development of zero defect software was a major challenge. Work share was drafted to ensure that the OFP would be developed fully by ADE and the backup software will be done jointly. The backup was developed with the work partition as Software Specification to be done by M/s BAE Systems while Design, Code and Testing will be by ADE and the system integration jointly. This partition ensured that ADE has the full ownership on the software and can adapt to the changes and complete technology know how is available in India. This software is first of its kind in India being developed for the Class I safety critical embedded application.
The process and methodologies to develop the software as per the standards (DoD std 2197) in 1990 was something challenging which has made ADE’s contributions to the fault control software development unforgettable. The formal process was followed by the Reviews as per MIL-STD 1521.
This class of software is not available to India from any of the foreign sources even today. In today’s world of patents it is impossible to get this kind of software along with source code. But for the LCA, As each byte of code is under our control, software can be reused, modified and adopted for the different variants of LCA as well as for the other future fighters.
In DRDO it was a new era to shift from Assembly to high-level programming (Ada – safe subset), following a strict software development process and methodology, recognition to the software engineering practices. BAE added to the confidence for paradigm shift and were critical since they were the certifying partners. This made ADE to put in enormous effort with handful of young people and limited resources. This made the team work for more than 15 hours/day which became worse due to the time difference between the two continents. It was 24X7 for the team with half working in India other half at USA.
Some of the highlights of the Onboard Software are Kernel working in real time, synchronization of the 4 identical computers, managing the redundancy to ensure accurate inputs for the Control Laws and the right drive to the actuators, software-controlled Built-In-Test for ensuring the health of the system before each flight.
When Sanctions were imposed during 1998 by USA, a major part of the work of hardware software integration, system integration activities were not completed. ADE had to take the challenge forward to successfully complete these activities with no support from M/s BAE systems. Two of the ETS systems were locked up for 4 years by GE A/c, as a consequence of the ‘Sanctions’ imposed by the US from 1998. The LCA-FCS community in India had to make to work with 3 systems round the clock to ensure maintenance of the pace of work.
Amongst the numerous pending technical issues the team had to resolve, the ones associated with the BAE specific ASICs used in then program for which complete information on use of these parts was very challenging. Among number of changes that were incorporated in the DFCC after sanctions, one important change was to remove the functionality of the DBU switchover and reconfigure the logic to work. That means only one software, for the flight controls with no backup. This resulted in the removal of the backup logic from the software. This could be achieved because the software is written as maintainable software. Hence there was enhanced need of the quality and confidence in the only software responsible for the flight and assurance that there will not be any generic failures in the software.
The long term dependency on the BAE specific components used in the design of DFCC was a specific concern for future DFCC production. ADE was accorded a separate project sanction to indigenize all the BAE specific parts used in the program. Technical solutions were found for almost all of these BAE specific parts and proto types were realized functionally tested and qualified.
Integrated Cockpit Display system for LCA: This consists of one monochrome Head Up Display, two colour Multi-Function Displays (LMFD and RMFD) and two Display Processors (DP) (dual redundant configuration). DP receives data on the MIL-STD-1553B avionics bus from Mission Computer and other LRUs, processes it and computes the relative positions of the symbols, generates the display symbology and updates them as display pages with flight information and status of various systems on-board, on the 3 displays, in real time. It monitors and conveys health status of the Cockpit Display System and pushbuttons/switches on the display surfaces to the Mission Computer. It also monitors and handles the Multi Function Rotractor (MFR) data selection. A Test Facility has been developed in-house to carry out Software Validation and Hardware Software Integration (HSI) and clearance of the entire Cockpit Display System. It simulates many functions of avionics to test the I/O interfacing in terms of data transfer and scheduling of messages with DP.
The Display software is the Second largest software component in the avionics suite of Tejas, display software (~80 Kilo Lines of 'C' code). It is responsible for processing the data received from various LRUs and updating all the display surfaces simultaneously in real-time. The entire Cockpit Display System along with other Avionics LRUs was integrated in a Dynamic Avionics Integration Rig which was also designed and developed by ADE.
A total of 17 Display Processor Units ported with the latest upgraded software version and 3 Head Up Display Units have been delivered to ADA, which have successfully completed more than 800 flights in TD1, TD2 and PV1 aircraft.
